Metsähovi Reports HUT-KURP-13

Metsähovi Radio Observatory
Helsinki University of Technology

Metsähovin radiotutkimusasema
Teknillinen korkeakoulu

Espoo 1998

Director (on leave of absence):
Prof. Seppo Urpo

Acting director:
Dr. Silja Pohjolainen
Tel. +358-9-2564 424
Email: Silja.Pohjolainen@hut.fi

Secretary:
Ms. Solveig Hurtta
Tel. +358-9-2564 831
Email: Solveig.Hurtta@hut.fi

Metsähovi Radio Observatory
Helsinki University of Technology
P.O. Box 3000
FIN-02015 HUT
Finland

Metsähovin radiotutkimusasema
Teknillinen korkeakoulu
Metsähovintie 114
02540 KYLMÄLÄ

Tel. +358-9-2564 831
Fax. +358-9-2564 531
Email: Firstname.Lastname@hut.fi

ISSN 1455-9579

Tummavuoren kirjapaino Oy
Vantaa 1998

Contents

• Introduction
• Research Activities
  • Radio Astronomical Instrumentation
    • 43 GHz VLBI Receiver
    • A Correlation Receiver for Solar Research at 37 GHz
    • Maintenance and Upgrade of Receivers
    • Survey of Harmful Radio Frequencies
    • Data Handling and Processing
    • EVN and JPL Mark IV R/W Upgrades
    • Antenna Control System Upgrade
  • Quasar Research
    • Monitoring of Quasars at Metsähovi
    • SEST Observations
    • AGN Science
    • Extragalactic Radio Sources
    • List of Observations with other Facilities
  • VLBI Research
    • EVN
    • CMVA, Coordinated Millimetre VLBI Array
    • Space-VLBI
    • Astronomical Masers
    • FS Support
  • Solar Research
    • Solar Observing Campaigns
    • Solar Data Analysis
    • High Latitude Active Regions and Solar Rotation
    • INTAS
  • HRDL for Alpha Magnetic Spectrometer (AMS)
  • Radio Spectroscopy
• Publications
  • International Journals
  • International Conferences
  • Laboratory Reports
  • Other Publications
• Visits to Foreign Institutes
• Visiting Scientists
• Theses
• Teaching
• Other Activities
  • Participation in Boards and Committees
  • International Meetings and Talks
  • National Meetings and Talks
  • Public Relations
• Personnel in 1997
• About this document ...

Foreword

You are now reading the first issue of the new Metsähovi series of publications, called Metsähovi Reports (HUT-KURP-). This series is a sequel to the 'Metsähovi Radio Research Station, Helsinki University of Technology, Series B, Report', which came to its end when the institute was renamed Metsähovi Radio Observatory, on March 20, 1998. The series includes, e.g., annual reports and internal technical reports. Our second new series of publications, Metsähovi Publications on Radio Science (HUT-MET-), is similarly a follow-up to the series 'Metsähovi Radio Research Station, Helsinki University of Technology, Series A, Report', which is for publishing scientific papers and reports.

The year 1997 was a very busy one at Metsähovi. The antenna was still mainly used by the 'old' projects, i.e. monitoring of quasars and solar observations, but this year brought along regular EVN- and millimeter-VLBI observing sessions. Being technically very challenging - and sometimes even despairing - VLBI also introduced the need for allocating antenna and receiver maintenance time. The proposed small reduction in active observing time was felt to be a serious setback by some of the staff.

The construction of the 43 GHz VLBI-receiver was completed successfully at the end of the year, and two theses related to it are now in preparation. The members of the project team for AMS started their frequent travels to the U.S., to Houston and Kennedy Space Centers, to test the equipment for the June 1998 shuttle test flight. This has proved to be a very exciting project, not to mention the fabulous sun-tans that come with it!

At Metsähovi, preparations for the upcoming solar radio astronomy meeting were started. The meeting will be held in Espoo, in June 1998, and some 80 solar scientists from around the world are expected to attend.

In August 1997 the director of the institute, Prof. Seppo Urpo, started his one-year assignment as a senior research scientist for the Academy of Finland, to study the secrets of the Sun. Dr. Silja Pohjolainen was named as the acting director during his leave of absence. A summer trainee, Mr. Juho Heikkilä, was allured by the solar project to continue to work at Metsähovi during the winter, too. The main product of his work is visible as the new Metsähovi Web pages, at http://kurp-www.hut.fi/.

This annual report was edited using the Latex files submitted by the Metsähovi personnel. Ms Solveig Hurtta did all the hard work by gathering up the pieces and by solving quite a few Latex error messages, of which we are most thankful. Silja Pohjolainen
Metsähovi Radio Observatory, April 1998

Introduction

The Metsähovi Radio Observatory, a separate research institute at the Helsinki University of Technology since May 1988, operates a 14-m diameter radio telescope at Metsähovi, Kylmälä, about 35 km west from the university campus. The institute also has premises in the Electrical Engineering Faculty building, Otakaari 5, Espoo. The main users of the station are the Helsinki University of Technology, the University of Helsinki, and the University of Turku. In the same area, near Metsähovi Radio Observatory, there are also the buildings of the Metsähovi Observatory (University of Helsinki; optical astronomy) and the Metsähovi Space Geodetic Station (Geodetic Institute; geodesy).

The Metsähovi Radio Observatory has been operational since 1974. The upgrading of the telescope was done during 1992-1994. The radome was replaced with a new one and new surface panels were installed. The surface accuracy of the present telescope is 0.1 mm (rms).

The Metsähovi Radio Observatory is active in the following fields:

- research in radio astronomy
- development of instruments needed in radio astronomy
- development of methods for radio astronomical measurements
- propagation studies of radio waves for satellite communication applications
- space research and
- education.

The activities at Metsähovi are concentrated on millimeter waves and microwaves. The used frequencies are 5 120 GHz, and the corresponding wavelengths 60 2.5 mm. The research in technology includes development of microwave receivers, development of receiving methods, development of data processing and development of antenna technology. The objects of radio astronomical research are: solar millimeter and microwave radiation, variable quasars, active galaxies, molecular line radiation, and very long baseline interferometry (VLBI). Metsähovi participates in the education at the Helsinki University of Technology by organizing courses and exercises for students, and graduate students can study for a licentiate's or doctor's degree at Metsähovi.

Around 15 scientists, engineers, or research assistants, and support personnel from the Helsinki University of Technology work at the institute. In addition about 10 students did radio astronomical observations under the guidance of Metsähovi staff. Five of the employees are paid by the Helsinki University of Technology, and the others are employed by research projects financed mainly by the Academy of Finland. The other users of the institute are the propagation study group at the Radio Laboratory of the Helsinki University of Technology, the radio astronomy group at the University of Helsinki, and the radio astronomy group at the University of Turku.

In 1997 the total expenditure of the Metsähovi Radio Observatory was about 4.7 million FIM, including salaries. This was financed by:

Helsinki University of Technology 57 %
Academy of Finland 39 %
Others 4 %

Research Activities

In this chapter the main research activities at Metsähovi are introduced. Some of the project teams include also scientists working at other institutes. The contact person at Metsähovi is underlined in each project team list.

Radio Astronomical Instrumentation

Research Group at Metsähovi: Urpo, Engelberg, Karlamaa, Koistinen, Mujunen, Oinaskallio, Peltonen, Ritakari, Rönnberg, Tornikoski, Wiik

43 GHz VLBI Receiver

Project Team: Koistinen, Karlamaa, Peltonen, Rönnberg

The design and development of the 43 GHz receiver for VLBI was completed in 1997. The integration of the receiver was completed and the first test measurements with the telescope showed 80/100 K receiver noise temperature for LCP/RCP channels. The problems with the phase locked YIG local oscillators were solved by introducing new digital PLL's. Phase performance tests showed better than 2 degrees oscillator phase stability over a 300 s measuring period. Fringe tests for the receiver are to be made in February 1998.

A Correlation Receiver for Solar Research at 37 GHz

Project team: Koistinen, Urpo, Rönnberg

All subsections of the 37 GHz solar receiver were measured and found to function properly during 1997. The integration of the receiver was started and is expected to be completed in 1998.

The measured receiver noise temperature was 420/425 K for left/right polarization channels. The analogue correlator unit was tested to have 2 dB amplitude flatness and 5 degrees phase jitter over the 750 MHz measurement band.

A fast A/D converter is used for data acquisition. The sample rate is 10 kHz for each channel which facilitates better than 1 ms time resolution in the measurements.

Maintenance and Upgrade of Receivers

Project team: Peltonen, Oinaskallio, Rönnberg

The following old receivers have been operational during the year 1997: 22 GHz and 37 GHz receivers (operating at room temperature) for continuum and solar observations, 22 GHz cryogenic VLBI receiver and 80-115 GHz cryogenic spectral line receiver.

The 22 GHz Dicke-switched receiver has proved to be very reliable and stable in use mainly due to the accurate temperature stabilization of microwave and IF-components, and careful mechanical construction. The noise temperature of this receiver is around 300 K. The 37 GHz receiver has been upgraded by installing a remote controllable, low loss waveguide switch in the second signal branch before observable Dicke-switch. Thus the operation mode of the receiver between continuum and solar observations can be easily selected from the control room. In order to improve the sensitivity of the receiver a low noise preamplifier was purchased and will be installed during 1998. Also a logarithmic IF-amplifier will expand the dynamic range of the receiver for solar observations.

The cryogenic 22 GHz VLBI receiver has also been operational during this year without failure, with noise temperature of 60 K for both polarizations. However, a modern low noise YIG-oscillator combined with digital phase lock circuitry as a LO source would give better phase stability for VLBI observations.

The phase locking of the 80-115 GHz spectral line receiver is quite critical due to the high harmonic number (17-22) used in the locking scheme. A new harmonic mixer was designed and constructed with lower conversion loss for the signal and better rejection for the LO-power (at $$ 5 GHz) to the IF-port. Also tuning procedure of the receiver was made easier by inserting a broadband isolator after the Gunn-oscillator thus preventing the pulling of the LO-frequency during tuning of the narrowband ringfilter which feeds the LO-power to the cryogenic mixer. Once the beam-lead Schottky diode mixer was installed for the first time into the dewar, some degradation of the sensitivity of the receiver was noticed during the first year (1992) after consecutive coolings. Now such phenomenon is not visible anymore and the average noise temperature over the signal band is 150 K.

Survey of Harmful Radio Frequencies

Project Team: Engelberg, Oinaskallio

The band 200 MHz - 2 GHz is monitored on daily basis. The system consists of two log-periodic vertically mounted receiver antennas. The antennae are on a mast which is located on the roof of the laboratory building. The direction of the antennae is selected with remotely controlled antenna rotator system (YAESU G-800SDX). RF signals are amplified nearby both antennae due to cable attenuation. Total length of each interconnecting cable (RG214) is 45 meters. The signal under measurement is selected with a pin switch. The signals are measured and corresponding data temporarily stored in IFR 920 Spectrum Analyzer. Data is finally analyzed with a PC.

 
Figure: Block diagram of the interference measurement system.

A test to measure interference, caused by Fixed System radio links on the 22 GHz Radio Astronomical band, was tried. The receiver used was the 22 GHz VLBI receiver. No interference was observed during the short test period. The tests will continue in the future on Radio Astronomical bands near 22 GHz and 37 GHz.

Heavy administrative work had an important role, too. Jan Engelberg's nomination as the Finnish representative on the Committee on Radio Astronomical Frequencies (CRAF) was acknowledged by the European Science Foundation (ESF) Board. CRAF coordinates European efforts for the protection of radio spectrum bands used by the Radio Astronomy Service and other passive applications, such as the Remote Sensing Service. Good relations with national Telecommunication Administration Centre are daily practice. The so called Kyoto declaration was signed by Seppo Urpo together with 35 directors of observatories around the world.

The Kyoto declaration formulated by Roy Booth (Onsala, Sweden), reads as follows:

'As directors of the world's radio observatories, we note the increasing use of radio spectrum by commercial and other interests. While recognizing the economic importance of such use, we are concerned that it should not harm radio astronomy, a uniquely powerful means for the study of the Universe. To protect the benefits of radio astronomy to human kind, we resolve to undertake the following initiatives. We will conduct a programme of activities to educate our fellow scientists, the telecommunications industry, and the general public to the necessity of protecting radio astronomy's spectrum requirements. Further, we will study technical means to mitigate the problem of interference.

We endorse the information of the OECD Megascience Forum Working Group on Radio Astronomy and will support it in its efforts to inform science policy makers of radio astronomy's concerns in the area of spectrum management. Additionally, we will all intensify participation in regulatory process conducted through IUCAF (the Inter Union Committee on the Allocation of Frequencies) and by the International Telecommunications Union and its member nations' agencies by increasing the number of personnel and resources devoted to spectrum management.

In order to make our actions more effective we agree to increase the level of co-ordination between the world's radio observatories so that we can present a common position on issues of radio spectrum management. In North America and Europe co-ordination groups already exist (CORF, the Committee on Radio Frequencies, and CRAF, the Committee on Radio Astronomy Frequencies) and we endorse proposals to generate similar co-ordination groups in the Asia-Pacific region and in South America.

Kyoto, Japan, at the XXIIIrd General Assembly of the International Astronomical Union, August 1997.'

Data Handling and Processing

Project Team: Mujunen, Turtiainen (until 30-June-1997)

Metsähovi local area network used to be connected to the Internet wide area network via a 64 kbit/s synchronous HDLC serial line. Internet services have proved to be so useful to Metsähovi staff that even relatively short 1-2 hour connection problems are immediately perceived as a serious hardship. Sending and receiving electronic mail, remote ssh and telnet sessions to university computing centre machines, as well as FTP sessions to file archives both nationally and internationally, are among the most used networking services. Transparent Internet-wide information access, as provided World Wide Web servers, has proven to be a necessity. For example, the most up-to-date information of EVN VLBI network is kept on a WWW server which is most conveniently accessed by using Netscape or NCSA Mosaic. Currently we have several Linux machines available for this purpose.

Increased use of the Internet necessitated an upgrade of the line speed of our connection and in July 1997 a new 2 Mbit/s dedicated leased line replaced the old 64 kbit/s ``pre-ISDN'' semipermanent dial-up link. A NAT LANB/290 dedicated IP router routes the TCP/IP network traffic between Metsähovi LAN and Internet WAN--no upgrade to it was necessary as 2 Mbit/s is its maximum WAN connection speed. Four 28.8k modems provide dial-in facilities for observatory personnel.

In the spring of 1997 Metsähovi became a victim of an intruder (``hacker'') attack. An illegitimate user managed to resolve (guess, ``crack'') a weak password on our computers and thus gained normal user access privileges. The main motive of this hacker seems to have been to get hold on as many user accounts and passwords as possible. No direct damage was caused but certainly hundreds of man-hours were wasted in assessing the situation and repairing the damage. To make the system more manageable security-wise in the future, direct Internet access was limited to one single Linux computer, ``kurp.hut.fi''. Access to WWW and FTP is arranged by running a ``squid'' proxy server on ``kurp.hut.fi'' and ssh / telnet to the outside world is performed from ``kurp.hut.fi'' only.

Spring 1997 was also an active time range for upgrading our 12 (or so) Linux computers from a 1995-vintage Slackware distribution to a more up-to-date Linux version. Debian 1.3.1 (see http://www.debian.org) was chosen primarily because it promised continuous upgradability package-by-package. Other distributions such as Slackware seem to require periodic complete re-installations. The Debian ``dselect/dpkg'' mechanism seems to work surprisingly well, since we have had a couple of machines undergo a 1.1 $\to$ 1.2 $\to$ 1.3 $\to$ 1.3.1 chain of upgrades.

In September we finally acquired color printing capability. After carefully studying the capabilities of color laser printers we decided to rely on cheap ink-jet technology for at least a couple of years. We bought two Canon printers, BJC-610 and BJC-620 and installed them with Linux Ghostscript PostScript emulation. At one-tenth of the price of a color laser, these printers deliver surprisingly good-looking presentation transparencies which was deemed the primary use of a color printer. Two printers help when everybody wants to print slides at the same time, and the older model BJC-610 seems to produce slightly better-quality transparency output than the marginally faster BJC-620.

IDL 5.0 was purchased and installed on ``kurp.hut.fi'' (2 floating licenses) and on two Linux computers dedicated to solar research. The ``15APR97'' release of AIPS VLBI data and image processing system was installed in November at our university site, at the same time when its main server was upgraded to Debian 1.3.1 and all IP addresses were changed. Metsähovi main NFS server `` /home'' disk space was increased from 4 GB to 9 GB using Linux built-in RAID0 disk array mechanism.

The main system disk of ``kurp.hut.fi'' broke down in October and although the computer was supposed to be under three-year on-site warranty, the replacement took over a week.

 
Figure: NTP network topologies of the Metsähovi network.

Implementation of NTP (Network Time Protocol) was done early 1997. Most of the computers running Debian Linux in the Metsähovi network are using NTP for synchronization. No major problems occurred, fine tuning of the systems is an ongoing issue. Computers are using several different time standards indifferent locations as a reference clock and/or computer. Locally master time is produced with an HP58503A GPS Time and Frequency Reference Receiver connected to maser.kurp.hut.fi with serial-line. First tests with NTP have been done and the network seem to synchronize nicely, i.e., computers with NTP have their clocks within one second accuracy.

EVN and JPL Mark IV R/W Upgrades

Project Team: Mujunen, Engelberg, Oinaskallio, Ritakari

The year 1997 marked the completion of EVN and JPL Mark IV recorder read/write upgrade project. Both EVN and JPL successfully installed and certified the modules in 1996 - early 1997. The project continued, though, on other related areas. In February-March MIT Haystack Observatory (Westford, MA, USA) ordered several Read/Write upgrade modules and printed circuit boards for USD 12000. A further quotation for additional modules was presented in July to Haystack, JIVE, and Chinese EVN telescopes for consideration and it is pending while waiting for financing decisions.

The Mark IV upgrade module kit we supplied to the Ny-Ålesund geodetic observatory in Svalbarden, Norway, was completed in 1997 and we supported them in testing the modules in May 1997. Support commitments for EVN R/W continue, as was demonstrated by a warranty cable swap at NRAL (Jodrell Bank, UK) in November.

The EVN/JIVE-initiated VIV project (VLBA to Mark IV upgrade) needs some of the R/W upgrade modules; additional/new modules must be developed as well. A crate/enclosure for the JIVE-funded Mark IV formattter upgrade must be designed and in the VIV kick-off meeting in JIVE (Dwingeloo, the Netherlands) in October Metsähovi was listed as a probable contributor. In December we generated an outline of the upgrade process for EVN and distributed the document, but very limited response was received. It is likely that interest in VIV will resurface in 1998, when the new formatters have been received from industry and they are waiting for installation.

Antenna Control System Upgrade

Project Team: Mujunen, Engelberg, Oinaskallio

In the spring of 1997 our FET07R DC motor FET driver board was tested and developed to its second prototype stage. A third prototype stage is envisaged in 1998 to ensure robustness against motor and software failures and to have both plain PWM and locked anti-phase drive capability on the same board. Other projects, most notably AMS, seriously drained resources from the antenna upgrade, and only negligible advances in systems design were achieved.

Several rack-mounted Linux PCs (see Table 2) for antenna control were acquired and mounted in our control rack.

For analog data acquisition a Datel PCI-416M 4-channel 200 kHz simultaneous sampling 16-bit A/D converter board was purchased and installed in ``daqqer''. It has been tested using its own DOS-based software, but it will require a new time-synchronization board and corresponding Linux-based data acquisition software to become useful in astronomical measurements.

A pair of Davis GroWeather (see ``http://www.davisnet.com'') weather stations was acquired from a local systems integrator, Envia Oy. Both stations feature temperature, barometric pressure, and relative humidity sensors. The first station is located near the telescope and radome, and the second one is a bit farther away and about 10 meters lower in altitude. It acts both as a backup of the first station, as a ``second opinion'', and also hopefully as an ``early warning'' system, as mist and dew seem to appear first in the low-altitude ``valley'' area. At the moment the stations still run Davis Windows-based software, but the goal is to integrate them in the overall measurement system with logging and network-capable Linux software.

In May we completed the backbone of our ADAM/NuDAM monitor/control network. It is based on commercially available ADAM/NuDAM A/D, D/A, and digital I/O modules which are connected together using a multi-drop RS485 single twisted pair wiring. These modules allow centralized and coordinated monitoring and control of discrete adjust values spatially dispersed across the whole observatory site. A single Linux PC masters the RS485 bus while a TCP/IP server process running on it makes all ADAM/NuDAM modules equally accessible from any computer on the Metsähovi LAN using a simple, telnet-style protocol.

Quasar Research

Research Group at Metsähovi: Urpo, Karlamaa, Lähteenmäki, Teräsranta, Tornikoski

Monitoring of Quasars at Metsähovi

Project Team: Teräsranta, Heikkilä, Karlamaa, Lähteenmäki, Tornikoski

The monitoring of quasars continued in 1997 for the 17th year. The antenna time given for the project was considerably less than earlier, with long breaks between sessions. The old goal of getting monthly sampling of the most important sources can be forgotten, as the breaks were typically more than 4 weeks. The main sample consisted of about 85 sources, mostly highly polarized quasars and Bl Lac type objects. Additional 50 sources were observed at least a few times a year, mostly at 22 GHz. Due to the shortness of money in the first half of the year, automated observations were done more than earlier (around 20% of all the observations). The number of individual observations during 1997 was about 3880, a few more than during the year before. The total number of observations is over 37000. The observers and their share of the observations during 1997 is shown in Table 3. An example of our long term monitoring can be seen in Figure 3, the flux of the quasar 3C 454.3 at 22 and 37 GHz since 1980.

 
Figure: The flux density of 3C 454.3 from 1980 at 22 and 37 GHz.

Besides our own long term monitoring, we participated in several multi-frequency studies including astronomical space borne instruments like RXTE, ASCA and EGRET. Some sources were also shown to be the most likely identifications for previously observed gamma-ray sources. The radio properties, mainly flat spectrum to the high millimeter frequencies seem to be one of the most important for these gamma-ray sources, together with our earlier found correlation between the high stage at millimeter wavelengths and gamma-radiation. The X-ray satellite RXTE is doing weekly monitoring on a few AGN (3C 273, 3C 279 and 3C 454.3), which should give interesting results when compared to observations at lower frequencies. The slow data processing for the RXTE data unfortunately prevents the X-ray data to be used for ToO at other bands.

SEST Observations

Project Team: Tornikoski, Lainela (Turku), Lähteenmäki, Karlamaa, Pursimo (Turku), Teräsranta, Valtaoja (Turku)

High radio frequency observations (90 to 230 GHz) with the Swedish-ESO Submillimetre Telescope (SEST) in Chile were continued. We had observing time every even (=''Nordic'') month except in October, when there was a long maintenance period at SEST, and we were allocated observing time in November instead. In 1997 we had slightly less observing time in total than in 1996 or 1995, but the number of data points obtained - especially at 230 - GHz was dramatically less than, e.g., in 1995. This was partly due to very unfavourable weather conditions, during which clouds, humidity and high wind speeds prevented us from using the 230 GHz bolometer for many of the scheduled bolometer sessions. At least part of the blame can be put to the El Niño weather effects, which are reported to have ruined a considerable number of observing runs on La Silla during the past year or so.

The yearly observing statistics at SEST are presented in Figures 4 and 5.

In recent years the simultaneous availability of several satellites and a very active ground-based collaboration, that has access to telescopes operating across the electromagnetic spectrum, has prompted numerous projects related to the study of the multi-frequency behaviour of AGN. In many of them the SEST data is of great importance because of the southern hemisphere location and the mm-wavelengths.

In 1997 the Metsähovi quasar research group had the following two observing projects running at SEST:

1. High radio frequency ground support for VSOP observations of AGN. This project was started as a support for the VSOP project, where the new powerful tool of space-VLBI technology will be used for studying the structure and physics of AGN. Ground-based radio observations are essential for most of these projects, because:

• The monitoring data can be used to relate the observed VLBI features to the events observed in the flux curves, and thus help in understanding the shock formation and the structural changes in the shock component. SEST is one of the few telescopes capable of observing the southern VSOP sources, and its high frequency flux curves also for the more northern sources are very valuable.
• Radio monitoring data can be used to determine whether the source is in its flaring or quiescent state, or to select sources with currently observable interesting events (especially Targets-of-Opportunity).
• Flux density information gathered with ground based telescopes is important in constructing spectra for the observed sources.

   
  Figure: SEST observing time granted to the Metsähovi QSO-group, 1989-1997.
  

   
  Figure: AGN observations at SEST, 1987-1997.
  

• Long time series of monitoring data (as we already have for some of our sources observed with the SEST) can be used to determine the variability evolution of the source.
• High radio frequency observations can be used to predict outbursts at lower frequencies, because the outbursts often are time-delayed towards the lower radio frequencies.

Even though the 22 GHz receiver on board the HALCA satellite of the VSOP project turned out to be defective and the 22 GHz observing programs were sub-sequentially cancelled, the SEST support for the low frequency programs continues to be vital especially for the southern sources.

2. Long term monitoring of active galactic nuclei. This is an on-going project continued from the previous years. The objective of this project is to frequently monitor a relatively small sample of bright and variable sources in order to get well-sampled high frequency time series for the selected sources, as well as to get good multi-frequency coverage for some of the most interesting nearly-equatorial AGN.

AGN Science

Project Team: Tornikoski, Valtaoja (Turku)

Radio-optical correlations. We have continued to study the correlation of the radio and optical flux curves and especially the possible simultaneity of radio-optical outbursts in order to better understand the outburst mechanisms at both frequency domains. We have studied both the very long term behaviour of an individual source (some 15 years of continuous radio and optical data for OJ 287), as well as individual simultaneous radio-optical events (e.g., a flare in CTA 102 in the summer 1997).

Classification of AGN. One of the intriguing questions in the study of AGN has been whether the current division of AGN into several classes is somewhat arbitrary, based on some observationally biased property, or indeed a sign of some more fundamental difference between the various sources. We have studied a large sample of southern AGN, trying to find out how well justified the current classifications are. The methods involved in these studies have been both conventional as well as more advanced statistical methods, e.g., Principal Component Analysis and Cluster Analysis.

Spectra and variability of southern sources. During our SEST observing projects we have discovered that some of the rarely observed southern sources are indeed very interesting in their spectra or variability behaviour. We have studied some of these sources in more detail, together with our collaborators from the southern hemisphere. Examples of such sources, with results already published or in preparation to be published are the nearest GHz peaked - spectrum radio galaxy PKS 1718-649, and the highly variable and also at mm-wavelengths very strong source PKS 2255-282, see Figure 6.

 
Figure: SEST flux curves of PKS 2255-282.

New identifications of EGRET sources. The majority of the EGRET (the detector on board the Compton Gamma-Ray Observatory) gamma-ray detected sources remain either unidentified or questionably identified at other wavelengths. The Metsähovi and SEST telescopes have been successfully used in studies to try to identify some of these sources. One of the most interesting of such sources is PMNJ 0850-121, which was studied at radio frequencies in early 1997, and which has a flux of 1.5 Jy and a nearly flat spectrum up to 230 GHz, and is likely to be the correct identification for the EGRET source 2EG J0852-1237.

Radio behaviour of EGRET detected sources. One of the interesting questions related to the gamma-ray behaviour of AGN is, why some sources have been detected with EGRET, while others with similar radio properties have not been detected. With our collaborators we have compiled multi-frequency radio observations of a number of sources, in an effort to confirm previously reported correlations between activity at radio wavelengths and EGRET detections, and to investigate whether the non-EGRET-detected sources were in radio- and gamma-ray-quiet phases during this period.

Multi-frequency studies. Even though multi-frequency campaigns to study an individual interesting source across the electromagnetic spectrum usually take a considerable coordination effort and often bring only little merit to the numerous observers involved in the campaign, these campaigns continue to be very essential in understanding the physics of AGN. Also, the flexible scheduling of the Metsähovi telescope as well as our freedom to reorganize our SEST observing list on demand, enables us to participate in the campaigns relatively easily, and we willingly continue to collaborate in multi-frequency studies whenever possible. In 1997 the results of several multi-frequency campaigns were published (the sources AO 0235+164, PKS 2155-304, NRAO 190, 3C 273, 3C 279, and others).

Extragalactic Radio Sources

Project Team: Lähteenmäki, Valtaoja (Turku)

The pursuit of studying extragalactic radio sources at various frequencies continued with further analysis of Metsähovi quasar monitoring data. We modeled the total flux density variations in active galactic nuclei (AGN) with self-similar flares, the rise and the decay of a flare being exponential and the timescales $\tau$_decay = 1.3 τ_rise. These decompositions of radio flares may be used to find correlations between radio and other frequencies, to calibrate and study VLBI observations, as well as derive physical parameters of the shocks. We have used this method of estimating the associated brightness temperatures of the flares, together with VLBI observations, to obtain Doppler boosting factors, viewing angles, and Lorentz factors for individual sources.

 
Figure: The 22 GHz radio data of 3C 345 decomposed into self-similar flares. Top: data points and fitted curve middle: model peaks bottom: 22 GHz VLBI components compared to the total flux density variations.

A significant application of total flux density variation Doppler factors is to compare them with the traditional synchrotron self-Compton (SSC) Doppler factors, and thus obtain an estimate of the maximum intrinsic brightness temperature $T$_b,lim. Another independent estimate of $T$_b,lim is obtained by comparing the brightness temperatures derived from variability data with the values calculated from VLBI observations. Using several data sets, we find that both methods yield a value of $T$_b,lim ≤10¹¹ K, significantly less than the usually adopted value of $1012$ K.

The decompositions of radio flares were further exploited in studying the relationships between radio and gamma-ray properties in AGN. We compared the Metsähovi total flux density variations with EGRET Phase 1+2+3 gamma-ray data and found that there is a connection between the type of the source, the phase of the radio flare, the associated variability brightness temperature and the gamma-ray emission. It seems that the gamma emission originates within the same shocks which produce the synchrotron flares is radio --induced by the SSC mechanism.

An alternative exploration of extragalactic radio sources has been carried on with the Nordic Optical Telescope in La Palma, Spain. A second observing run of optical hot spots in classical double radio galaxies took place in July. So far we have been able to verify the existence of optical hot spots in four 3C sources. They are all highly polarized, thus confirming the synchrotron nature of the optical emission. The first ever optical double hot spot in the quasar 3C 351 was confirmed, and carefully re-observed in July 1997. The improved optical polarization observations together with sub-arcsecond resolution radio polarization maps, offer an unique opportunity to study the formation of multiple hot spots, their interactions with the intergalactic medium (IGM), and the details of the acceleration mechanisms.

List of Observations with other Facilities

Swedish-ESO Submillimetre Telescope (SEST), Chile. Observing time scheduled on: February 11th to 13th (34 hours), April 1st to 2nd (29 hours), April 29th to 30th (26 hours), June 27th to 30th (58 hours), August 1st to 2nd (16 hours), August 30th to 31st (34 hours), November 4th to 6th (40 hours), December 29th to 31st (28 hours). P.I. Tornikoski, Co-Is Valtaoja and Teräsranta, and P.I. Valtaoja, Co-Is Tornikoski and Teräsranta.

VLBA. Observing time from November 30th to December 1st, 6 + 3 hours, 0.7 & 2 cm: ``Very high brightness source 1921-293'', P.I. Edwards, Co-Is Tornikoski, Valtaoja et al.

EGRET. Observing time scheduled on: December 30th, 1996 to January 28th, 1997 (3C 279), February 18th to March 18th (0528+134), Co-Is Teräsranta, Tornikoski, Valtaoja.
April 9th to 15th (Mark 501), June 17th to 24th (3C 279), July 15th to 22th (BL Lac), August 8th to 26th (1622-297), November 3rd to 11th (0235+164), November 11th to 25th (2155-304), December 30th, 1997 to January 13th 1998 (2155-304), participation in the campaigns.

VLBI Research

Research Group at Metsähovi: Urpo, Karlamaa, Liljeström, Mujunen, Wiik

EVN

Project Team: Wiik, Engelberg, Karlamaa, Mujunen

Metsähovi participated to all four EVN 22 GHz sessions with nominal success.

Jan Engelberg, Juho Heikkilä, Kirsi Karlamaa, Ari Mujunen, Jouko Ritakari, Pasi Suvikunnas and Kaj Wiik participated in organizing TWG (Technical Working Group) meeting in Finland at Siikaranta, in June 1997.

A prototype of a GPS-H-maser clock difference measurement device was created. This simple device is based on programmable logic and it interfaces to a parallel port of a Linux PC. It can be straightforwardly expanded to handle multiple 1 pps sources simultaneously. Since the device can measure the differences on every second pulse it does not ``throw away'' any material for averaging.

In May thin tape upgrade was installed in our VLBA recorder with the help of Michael Wunderlich (MPIfR, Bonn) and Leslie Parry (NRAL, Jodrell Bank). The upgrade itself went smoothly, but it uncovered a latent problem in our idle roller alignment. After a laborious dismantling--reassembly procedure we managed to get reverse--forward tape offset below an acceptable limit, and we also attempted to help other EVN stations, most notably Noto and in November Medicina (both in Italy) which experienced similar problems. In July a thin verification test tape was recorded and sent to Socorro for quality checks--it passed alignment criteria, but another problem with jitter in tape speed was discovered. Capstan servo adjustments were made and we are waiting for correlator reports to certify that jitter problems have been indeed cured.

In December we finally decided to acquire a full-fledged tape degausser which would enable us to perform head stack calibrations in a proper way since a given single tape can be then reused in the calibration process. The unit ``V91M' was purchased from Verity Systems (UK, email ``eyecote@compuserve.com'') and it is a tabletop device on which tape reels must be rotated manually. It promises to effectively erase high-coercivity tapes (as thin tapes apparently are) and it is well-suited for erasing small batches of tape reels.

CMVA, Coordinated Millimetre VLBI Array

Project Team: Wiik, Engelberg, Karlamaa, Valtaoja (Turku)

In the April 1997 test experiment the first correlation fringes were detected to Metsähovi at 3 mm. The strength and coherence of the signal were so good that Metsähovi participated fully to the July 1997 global 3 mm VLBI experiment and afterwards routinely to the CMVA experiments.

 
Figure: The Coordinated Millimetre VLBI Array (CMVA). The telescopes that participate routinely to 3 mm VLBI observations are Kitt Peak, Pie Town, OVRO, Hat Creek, Quabbin and Haystack Observatory from the USA, SEST from Chile, Pico Veleta, Effelsberg, Onsala and Metsähovi from Europe

 
Figure: The upper panel shows results of pointing observations (elevation errors) after a focus change. In the lower panel error residuals (dots) and actual observations using the new fitted model (circles) are plotted. Note how e.g. the bump at Az = 200$o$ has been corrected.

 
Figure: First correlation fringes to Metsähovi at 3 mm were detected in the April 1997 mm-VLBI experiment. The strong fringes between Pico Veleta in Spain, Effelsberg in Germany, and Metsähovi are expressed as a contour map in residual rate and delay space.

During April CMVA session a problem with standard tape prepassing schedule was found--tapes can be destroyed if the recorder head stack is left in an extreme position. Correction for this was suggested to FS developers at GSFC.

One link in the chain of a successful VLBI experiment is of course the receiver. The problem with the old Metsähovi 3 mm receiver was the incompatible IF frequency with the VLBA standard. After some brainstorming with Dr. Peltonen, it was found that the IF amplifier was in fact useful (but of course not the best possible) below the specified frequency. The old receiver was also sensitive only to linear polarization, contrary to the standard of left-hand circular polarization used in mm-VLBI. Ms. Karlamaa designed and fabricated with the aid of the Metsähovi machine shop a quarter wave plate which was also tested before the first session. A very critical part of a VLBI receiver is the local oscillator system. With the aid of a frequency multiplier from CMVA/Haystack Observatory, the phase stability and spectrum of the local oscillator was improved to an acceptable level.

After some nights of observing continuum sources to find possible pointing offsets, it became evident that adequate accuracy will not be achieved. It was decided to use VLBI back-end with narrow filters and strong SiO maser sources instead, for better results. The standard VLBI observing software which is called 'Field System' (FS), from NASA Goddard, was used to gather the pointing data automatically. After some nights of observing, a bug in the pointing software (which ignored the parameter describing the receiver horizontal location in the focus cabin) was found. After Ari Mujunen successfully corrected the bug, pointing observations produced sensible and consistent data.

The original model was so far off that simple constant offsets would cause the source to wander occasionally about two half-power beam-widths from the center of the beam. A new pointing model fitting program was written using PDL (Perl Data Language). It uses a variant of a simulated annealing algorithm to cope with the local minima of our nonlinear pointing function. The model improved dramatically and all essential systematic errors were fitted, and now measured RMS pointing offsets are below one tenth of a half power beam-width, see Figure 9. Since then the fitting program has been applied to both 22 and 43 GHz VLBI pointing and results have been good in all cases.

 
Figure: Receiver temperature during the November 1997 CMVA experiment. The step at the start of the experiment is caused by a change in the observing frequency. The lower noise observations are performed at 86 GHz (Silicon Dioxide) and the higher at 92 GHz (Carbon Monoxide absorption observation).

 
Figure: Atmospheric opacity towards zenith during the November 1997 CMVA experiment. $\tau$₀ = 0.1 means that the atmosphere is absorbing about 10 % of the radiation coming through it from straight up.

The VLBI data acquisition program expects to be able to control a noise source to inject a calibrated amount of noise in the system. The program calculates the equivalent system noise temperature from this measurement, and it is used to correct the normalized correlation coefficient coming from the correlator to Janskys. Unfortunately, as our 3 mm receiver was not designed for VLBI, it has only support to hot and cold calibration loads. A PDL program was written to read the raw power values from the FS log and calculate system temperature values from that information. To improve calibration, sky dip observations are inserted about every half hour to the observation schedule. This information is used to estimate the sky zenith opacity and further to correct the system noise temperatures to be referenced above the atmosphere. PDL and Perl SLALIB module were used to calculate airmass values for the observed sources.

Full and accurate amplitude calibration requires also that the so called gain curve (antenna gain vs. elevation) is known. The spectral line sources have also been used for gain curve observations but the measurement method is still being developed.

Space-VLBI

Project Team: Wiik, Leppänen (Nokia), Liljeström, Lähteenmäki, Teräsranta, Tornikoski, Valtaoja (Turku)

Metsähovi participated in the calibration of the HALCA space radio telescope. Calibrated single dish spectra were taken of water maser source W49N (see Figure 13) and the HALCA gain could have been calculated. However, because of HALCA receiver and pointing problems, the HALCA part of the calibration was postponed to a future date.

Astronomical Masers

Project Team: Liljeström, Leppänen (Nokia), Wiik

The work on the 22 GHz linear polarization data of W51M, obtained with VLBA, was continued. High-resolution polarization observations of water masers provide a powerful tool for studying, e.g., Alfvenic turbulence and magnetic fields in dense star-forming regions. The principal difference of polarimetric VLBI from total intensity VLBI is the need to calibrate the instrumental polarization parameters, which have been solved by Leppänen (Dr. Tech. thesis, Helsinki Univ. of Technology, 1995) with a feed self-calibration algorithm. The uniformly weighted restoring (CLEAN) beam obtained was 0.71 $0.26$ milliarcseconds; the velocity resolution was 0.2 km/s.

 
Figure: The left spectra of W49N are observed with the narrow band and the right spectra are observed with the broad band acusto-optical spectrometer.

 
Figure: a) Velocities of the W51M maser spots. b) Spatial distribution of the W51 maser spots (See text for details.)

Figure 14a shows the spatial distribution of the maser spots. Superimposed on the spots are the linear polarization vectors with their lengths proportional to the degrees of polarization. The inset of Figure 14a is an enlargement of the compact maser concentration near the reference position (0,0) of W51M. With a distance of 7.0 kpc to W51M, the inner and outer radii of this maser concentration, hereafter called the protostellar cocoon, are 5 AU and 66 AU, respectively. Figure 14a reveals also a 1200 AU long linear maser structure oriented roughly NNE-SSW, which is aligned along the large-scale galactic magnetic field projection on the sky, and the polarization vectors of these masers. Figure 14b shows that these masers move longitudinally along this direction with a median velocity of 25 ($\pm 8.7$) km/s relative to the centroid of the cocoon. The proper motions exclude the interpretation of this streamer as a low-velocity bipolar outflow from W51M. Most likely this stream is produced by shocks caused by the nearby expanding HII region, W51 IRS-1, which interacts with the dense molecular core of W51M on its western side.

In contrast to the cocoon masers, which show a mean linear polarization of only 3$\%$ (maximum 13$\%$), the masers in the streamer exhibit higher degrees of linear polarization (mean 12$\%$, maximum 35$\%$). The level of distortion in the polarization directions of the streamer masers from the magnetic field direction, together with the observationally estimated non-thermal velocity dispersion of the streamer spots with respect to the mean velocity of the streamer, yield preshock magnetic field strengths (perpendicular to the shock velocity) of 0.91 - 1.2 ($\pm 0.32$) mG. The corresponding Alfven velocity is 0.86 - 1.1 ($\pm 0.23$) km/s.

Inside the masing regions the strength of the magnetic field is independent of the preshock field, since the magnetic pressure (which is determined by the ram pressure of the shock) dominates in the masing region. Assuming that the median space velocity of the maser stream, 25 km/s (with respect to the centroid of the cocoon), characterizes also the shock velocity, we obtain a typical total magnetic field strength around 38 mG inside the masing regions of the streamer.

Besides water masers we will in the coming years expand our observations also to other masers of astrophysical interest.

FS Support

Project Team: Mujunen

Since 1995 Metsähovi has participated in and contributed to the development of the Field System. In October 1997 Mujunen visited NASA GSFC (Goddard Space Flight Center) to suppport migration from Linux 1.2.12 to 2.0.30--this was required to support emerging new PC hardware and to enhance FS compatibility in networked Linux environments. A considerable level of Linux support via email was given to collaborators at NASA GSFC geodesy VLBI project, Ed Himwich and Nancy Vandenberg. This included about 100 emails in 1997. Additionally, specific FS support for Chinese EVN stations was given in July.

In November it was decided to move the European FS FTP archives to Metsähovi. This decision was mainly motivated by the increased availability of Internet bandwidth at Metsähovi.

Solar Research

Research Group at Metsähovi: Urpo, Heikkilä, Pohjolainen

Solar Observing Campaigns

Project Team: Pohjolainen, Heikkilä, Tornikoski, Urpo

The international Flare 22/Max'91 solar observation campaign has ended as the Solar Cycle 22 reached its minimum in 1996. However, data are still being analyzed and ad hoc experiments are done occasionally. The new Solar Cycle 23 is now in the rising phase, but flare frequency and flare intensities are still low. The mean rise time for solar cycles is around 4 years, and the next maximum solar activity is expected to occur around 1999-2002.

The ESA/NASA Solar and Heliospheric Observatory (SOHO) was successfully launched on December 2, 1995, and the spacecraft is now in its halo orbit around the Lagrangian point L1. The satellite carries 12 different instruments, and investigates the radiation from the solar corona and solar wind, as well as the solar interior by methods of helioseismology. One of the scientific instruments on board SOHO is the energetic particle instrument ERNE of the University of Turku. The energy eruptions in the solar atmosphere can lead to the acceleration of local gas particles to extremely high energies and their injection into the interplanetary space, and these fast moving streams of particles are recorded by ERNE. Another SOHO instrument, SWAN (Solar Wind Anisotropies), is a collaboration between the Finnish Meteorological Institute and the French Service d'Aeronomie. Ground-based observations are also very important for the correlation of space observations, and Metsähovi has tried to take part in many of the observing campaigns connected with SOHO.

In 1997 solar observations were carried out at Metsähovi during 57 days. Altogether 605 solar maps were measured, and selected active regions were observed for 47 hours.

  
Figure: Top: Metsähovi radio Sun at 8 mm wavelength on June 28, 1997, at 9:04-9:12 UT. Middle: Kitt Peak He I line (10830 Å) on June 28, 1997, at 20:32 UT. Bottom: SOHO EIT Fe IX/X line (171 Å) on June 28, 1997, at 19:00 UT.

 
Figure: Left: Solar maps measured at 3 mm wavelength (87 GHz) at Metsähovi, on August 16-19, 1997 (Image reduction by S. Pohjolainen with the new IDL program). Right: Solar maps observed by the Yohkoh satellite in soft X-rays, on the same days (Images from the Yohkoh Data Archive at Mullard).

At present four Metsähovi receivers can be used in solar observations: the 22 GHz VLBI receiver (with right and left hand circular polarization), the 37 GHz Dicke-switched radiometer, the 43 GHz VLBI receiver (with right and left hand circular polarization), and the 80...115 GHz spectral line receiver. The receivers are used as fixed frequency continuum receivers during solar observations, but at present only one frequency can be observed at the same time. Also the present software, for solar observations with the old MicroVAX computer, is able to record only one polarization with the maximum sampling speed of 20 samples per second. This will be improved in the future with the upgrading of the present antenna servo system. The construction of the 43 GHz receiver for VLBI was completed in the autumn of 1997, and solar observations were used to test it in March and October. The 22 GHz VLBI receiver has been used in solar observations previously, with good results.

The surface panels of the Metsähovi radio telescope were replaced with new ones in 1994, and at present the surface accuracy is 0.1 mm (rms). With this improvement the solar group has now concentrated on observing at high frequencies, i.e., at around 90 GHz (3 mm). The 22-day solar observing run in August 1997, at 86.2 GHz, has so far been the longest continuous observing campaign at this frequency after the telescope upgrade. Figure 17 shows the locations of radio telescopes capable of solar observing at mm-waves (BIMA, Itapetinga, Metsähovi, RT-7.5, and the Nobeyama 45-m telescope), as well as the main instruments used at cm-waves (OVRO, VLA, and the Nobeyama radioheliograph). BIMA, OVRO, VLA, and the Nobeyama radioheliograph are all interferometers that give good spatial and flux resolution, but are sensitive to source widths. The Itapetinga 14-m, Metsähovi 14-m, RT 7.5-m, and the Nobeyama 45-m telescopes are single dish telescopes, and their spatial resolution depends on the antenna diameter. Single dish antennas can easily be used for imaging the whole Sun, using different scanning techniques.

 
Figure: Radio telescopes and interferometers used for solar observations at millimeter waves (BIMA, Itapentinga, Metsähovi, RT-7.5, and the Nobeyama 45-m telescope), and centimeter waves (OVRO, VLA, and the Nobeyama radioheliograph).

Solar Data Analysis

Project Team: Pohjolainen, Heikkilä, Urpo, Wiik

The study of solar flares has continued in cooperation with several research groups and observatories, using the data recorded during the previous solar activity Cycle 22. The Metsähovi radio data have been studied, e.g., in comparison with soft X-ray data (GOES satellites) and hard X-ray data (Compton-GRO BATSE instrument). Besides flares and active regions, also coronal holes have been studied in microwaves and soft X-rays using the instruments on board the Japanese satellite Yohkoh. This is a common project with scientists from Metsähovi, National Astronomical Observatory in Japan, Hvar Observatory, and Kiepenheuer Institut für Sonnenphysik.

Until 1997 Metsähovi solar maps were analyzed with a program working under DOS, which created a real problem when practically all Metsähovi computers were upgraded into Linux. After a long consideration IDL was purchased in May 1997, and a new software written by S. Pohjolainen. Time series of active region tracking are still analyzed with a software written by K. Wiik in Matlab. There are plans to integrate these programs in the near future, so that all Metsähovi solar software will be in IDL, and also Solarsoft-compatible. Figure 15 shows a Metsähovi solar radio map at 37 GHz (8mm) from June 28, 1997, and the corresponding solar images in He I 10830 Å line (Kitt Peak) and in Fe IX/X line (SOHO EIT), from the same days. The active regions show as enhancement in radio, as strong absorption in the He I line, and as bright loops in the EUV Fe IX/X line. A dark H$$_α-filament near the south pole is seen as a depression in radio and as strong absorption in He I. Coronal holes that are clearly visible in EUV usually show weak absorption in He I, and local depression/enhancements in radio.

Long observing runs make it possible to follow the evolution of centers of activity and low temperature regions in radio. Examples of Metsähovi solar radio maps observed at 3 mm during August 16-19, 1997, and the corresponding solar images observed by Yohkoh in soft X-rays on the same days, are presented in Figure 16. The solar observing run in August lasted for a total of 22 days.

Solar active region development at millimeter wavelengths. Solar active regions observed at 3 mm wavelength have been analyzed and compared with SOHO and Yohkoh images. The first study was made from the solar maps observed between 12 and 23 April, 1996, when also a large number of partial maps were available of the active regions near the solar west limb, on April 20. This study will be continued with later data from 1996 and 1997.

Microwave emission from coronal heights: studies of non-thermal radio flares. Two small radio flares observed at 22 GHz, following the great gamma-ray burst on June 11, 1991, were studied. We analyzed the different association of emission features in microwaves, decimeter waves, and soft and hard X-rays for these events. The first flare had well defined emission features in microwaves and soft and hard X-rays, and the second event was otherwise very similar, except that soft X-ray emission was missing from the event. Two different explanations were proposed for the lack of soft X-ray emission, but because there were no radio or X-ray maps available from this event, we cannot be sure of the emission site geometry. No other similar events were found from the large Metsähovi data set from 1989-1993 (analyzed and published in Astron. Astrophys., 1996), and new observations will be necessary to verify these findings.

High Latitude Active Regions and Solar Rotation

Project Team: Urpo, Riehokainen (Turku), Valtaoja (Turku)

Full-disk solar maps at 36.8 GHz show localized regions of enhanced mm-wave emission at low, 0 - 45 degrees, and at high, 50 degrees or more, solar latitudes. Both spatial and temporal distribution of these active regions have been studied. The activity of the low latitude sources follows the 12 years cycle of sunspot activity. The high latitude radiation enhancements are yet of unknown origin. Typically in our measurements these sources are 100-400 K hotter than the quiet Sun. However, we have some evidence that these sources are much smaller than our telescope beam size so that the actual brightness of these sources is at least 1000 K or more. We have found that these mm-sources are statistically connected to polar faculae.

INTAS

Project Team: Urpo, Bogod (Pulkovo), Krüger (Potsdam), Pohjolainen, Stepanov (Pulkovo), Zaitsev (Nizniy Novgorod)

This research is based on INTAS grant INTAS-RFBR-95-316 "Coronal Physics from Observations at Centimeter and Millimeter Wavelenghts" where S. Urpo is the coordinator.

The main goal of this project is the study of the physical processes in the solar corona using observational data obtained by the unique radio telescopes of RATAN-600, Russia, and Metsähovi, Finland, at mm-cm wavelengths. Coronae of the Sun and active stars are places where remarkable energy transfer and energy release processes occur. They can be rapid flare-like and/or long-term events. Particle acceleration, plasma heating, mass ejections, and magnetic field changes in corona are reflected clearly in mm-wave radiation, which is a good tool for diagnostics of coronal plasma. Particular objectives of the project are:

• Origin of solar coronal mm-wave sources (CMMS) observed occasionally at heights up to 0.4 solar radii
• Diagnostics of solar and stellar coronal plasmas using data on radio, optical and X-ray emission
• Origin of peculiar sources on the Sun, which are regions of long-term energy release.

Diagnostics of electric parameters of current-carrying coronal loop. The model for a current-carrying coronal magnetic loop based on the equivalent LRC-circuit analog was proposed. It was suggested that the electric current, driven by the converging motions in the photosphere, flows through the coronal part of a loop from one foot-point to another and closes deep in the photosphere. In a self-consistent approach both the resistance and the capacitance of a LRC-circuit depend on the electric current along the loop. This opens new possibilities for the diagnostics of electric currents in coronal loops by using data on the modulation of the flare emission. In order to perform diagnostics of the electric parameters of the current-carrying coronal magnetic loops several flare-associated solar mm-wave bursts observed at the Metsähovi Radio Observatory at 22 and 37 GHz during 1989-1993 have been analyzed. 16 events with long-term pulsations were chosen after spectral analysis which revealed the pulsation periods of 0.7 - 17 sec. Using LRC-circuit model together with the Metsähovi data we obtained current 6$$$1010$ - 1.4$$$1012$ A and total circuit energy $1030$ - 5$$$1032$ ergs. Comparison of this energy with the flare energy gives quite unusual result that only 5-10 % of energy stored in the flaring loop were released. Moreover, in the studied events there were a tendency to decrease the energy release with the increase of the current. This tendency can be interpreted in terms of plasma beta, which is getting smaller as the current grows. Therefore the plasma instabilities responsible for the flare process manifestate themselves weakly with the increase of the current.

Thermal/nonthermal model for coronal microwave sources. A thermal/nonthermal (T/NT) multi-layer model for the coronal mm-wave source was proposed. The model considers the source as a coronal magnetic arch containing thermal background plasma and magnetically trapped >10 keV electrons. Spatial variations of the parameters of both the thermal plasma and the energetic particles along the line-of-sight were taken into account using multi-layer (up to 100 layers) approximation. Contributions of three emission mechanisms were considered simultaneously: Coulomb bremsstrahlung, gyroresonance absorption, and gyrosynchrotron radiation. Particular attention has been paid to the origin of the radiation of the coronal source on June 20, 1989, observed simultaneously at Metsähovi, VLA, RSTN, and Bern in the frequency range 1 - 37 GHz. An attempt to construct the observed spectra using single T/NT multi-layer source was unsuccessful because the conflict between Razin suppression and optically thin bremsstrahlung. T/NT two source model is more perspective for the diagnostics of plasma parameters in the coronal sources.

HRDL for Alpha Magnetic Spectrometer (AMS)

Research Group Heads: Urpo, Ting (Massachusetts), Torsti (Turku)

Project Team at Metsähovi: Ritakari, Engelberg, Karlamaa, Mujunen, Tornikoski, Wiik

Metsähovi participates in the Alpha Magnetic Spectrometer project initiated by professor Samuel Ting of Massachusetts Institute of Technology. The purpose of the AMS is to search for antimatter particles. Because antimatter particles are destroyed in the Earth atmosphere, it is necessary to send the spectrometer to orbit, the Earth. AMS will be tested on a space shuttle flight, STS-91, to be launched in June, 1998. When the International Space Station is built, AMS will be one of its four scientific instruments. Metsähovi is building the High Rate Data Link (HRDL) data acquisition system for the AMS project. The HRDL data link is a 2 Mbit/s link from the space shuttle to earth via the TDRSS satellites.

In January and February 1997 the basic X13 data capture concept was proven in a series of tests at both CERN and NASA ESTL (Electronics Systems Test Laboratory at Johnson Space Center, Houston). A DCU (Data Conversion Unit) simulator developed by AMS Chinese and Taiwanese collaborators was connected to our X13 data acquisition board and DOS-based software. A test report of this activity is available at `` ftp://kurp-ftp.hut.fi/pub/ams/estl1.ps''.

In late September we started assembling two copies of the data acquisition rack. The rack consists of two or three identically-equipped Pentium 200MMX PCs running Linux 2.0.32. The main PC keeps the on-line Ultra Wide SCSI hard disk array of eight 8GB disks fed with new data which can be simultaneously retrieved via a dedicated 100Mbit/s Ethernet FTP connection. The secondary backup PC runs a separate DOS-based acquisition program which stores a backup copy of raw HRDL data on a set of removable 6.4 GB IDE disks.

In December the second generation of X13 data acquisition boards, that is ten copies of the X13V2 board, was completed. This second-generation synchronous serial data capture ISA board is based on MACH211 programmable logic device technology. It offers the detection of inverted data stream and out of-phase data clock, and these two features are required in practice by NASA ground support equipment because both data polarity and clock phase will vary unpredictably during a given shuttle mission.

Radio Spectroscopy

Research Group/Project Team: Liljeström, Wiik

The Metsähovi radio telescope has been used to monitor water maser outbursts at 22 GHz in the most powerful maser source of our Galaxy, W49N. Combining the data of these long-term water maser outburst observations (Liljeström et al. 1989) with simultaneous VLBI observations of W49N (Gwinn 1994), it is possible to extract both the preshock and postshock magnetic field strength, the typical diameter of the masing regions, the postshock density, temperature plateau, water abundance, Alfvenic turbulence, and many other parameters of astrophysical interest. The observations strongly support the dissociative shock model of Hollenbach and McKee (1989) and the maser model of Elitzur, Hollenbach and McKee (1989). The observations reveal also the presence of coherent scattering of the maser emission in ambient dense plasma (most probably due to sound waves). The physics of the very strong shocks that scatter the maser radiation into water halos around massive protostars will be further studied with the space-VLBI satellite HALCA (Metsähovi Radio Observatory is involved in three water maser proposals).

Publications

International Journals

1. Brajša, R., Ruždjak, V., Vršnak, B., Pohjolainen, S., Urpo, S., Schroll, A., and Wöhl, H.: On the possible changes of the solar differential rotation during the activity cycle determined using microwave low brightness temperature regions and H$$_α filaments as tracers. Solar Physics, Vol. 171, 1997, p. 1-34.
2. Liljeström, T., Olofsson, G.: Evidence for infall toward Z Canis Majoris from radio and near-infrared spectroscopy. Astrophysical Journal, Vol. 478, 1997, p. 381-394.
3. Catanese, M., Akerlof, C.W., Biller, S., Boyle, P., Buckley, J.H., Carter-Lewis, D.A., Cawley, M.F., Connaughton, V., Dingus, B.L., Fegan, D.J., Fichtel, C.E., Finley, J.P., Gaidos, J., Gear, W.K., Hartman, R.C., Hillas, A.M., Lamb, R.C., Lin, Y.C., Krennrich, F., Lessard, R., McEnery, J.E., Marscher, A.P., Mohanty, G., Mukherjee, R., Quinn, J., Robson, E.I., Rodgers, A.J., Rose, H.J., Samuelson, F.W., Sembroski, G., Schubnell, M.S., Stevens, J.A., Teräsranta, H., Thompson, D.J., Weekes, T.C., Wilson, C., Zweerink, J.: Detection of Gamma Rays with E > 100 MeV from BL Lacertae. Astrophysical Journal, Vol. 480, 1997, p. 562-567.
4. McGlynn, T.A., Hartman, R.C., Bloom, S.D., Aller, M., Aller, H., Filippenko, A.V., Barth, A.J., Gear, W.K., Marscher, A.P., Mattox, J.R., Reich, W., Robson, E.I., Schramm, J., Stevens, J.A., Teräsranta, H., Tornikoski, M., Vestrand, T.W., Wagner, S., Heines, A.: A gamma-ray flare in NRAO 190. Astrophysical Journal, Vol. 481, 1997, p. 625-632.
5. von Montigny, C., Aller, H., Aller, M., Bruhweiler, F., Collmar, W., Courvoisier, T.J-L., Edwards, P.G., Fichtel, C.E., Fruscione, A., Ghisellini, G., Hartman, R.C., Johnson, W.N., Kafatos, M., Kii, T., Kniffen, D.A., Lichti, G.G., Makino, F., Mannheim, K., Marscher, A.P., McBreen, B., McHardy, I., Pesce, J. E., Pohl, M., Ramos, E., Reich, W., Robson, E.I., Sasaki, K., Teräsranta, H., Tornikoski, M., Urry, C.M., Valtaoja, E., Wagner, S., Weekes, T.: Multiwavelength Observations of 3C 273 in 1993-1995. Astrophysical Journal, Vol. 483, 1997, p. 161-177.
6. Tingay, S.J., Jauncey, D.L., Reynolds, J.E., Tzioumis, A.K., King, E.A., Preston, R.A., Lovell, J.E.J., McCulloch, P.M., Costa, M.E., Nicolson, G., Koekemoer, A., Tornikoski, M., Kedziora-Chudczer, L., Campbell-Wilson, D.: The nearest GHz peaked-spectrum radio galaxy, PKS 1718-649. Astronomical Journal, Vol. 113, 1997, p. 2025-2030.
7. Jetsu, L., Pohjolainen, S., Pelt, J., Tuominen I.: Is the longitudinal distribution of solar flares nonuniform? Astron. Astrophys., Vol. 318, 1997, p. 293-307.
8. Pohjolainen, S., Valtaoja, E., Urpo, S., Aurass H.: Microwave emission from coronal heights: study of a non-thermal radio flare. Solar Physics, Vol. 173, 1997, p. 131-149.
9. Zook, A.C., Giammona, W.J., Unwin, S.C., Wehrle, A.E., Teräsranta, H., Valtaoja, E., Kidger, M.R., Gonzales-Perez, J.N.: Radio counterparts of unidentified EGRET gamma-ray sources. Astronomical Journal, Vol. 114, 1997, p. 131-149.
10. Bloom, S., Hartman, R., Teräsranta, H., Tornikoski, M., Valtaoja, E.: Possible new identifications for EGRET sources. Astrophysical Journal, Vol. 488, 1997, p. L23-L26.
11. Pesce, J.E., Urry, C.M., Maraschi, L., Treves, A., Grandi, P., Kollgaard, R.I., Pian, E., Smith, P.S., Aller, H.D., Aller, M.F., Barth, A.J., Buckley, D.A.H., Covino, E., Filippenko, A.V., Hooper, E.J., Joner, M.D., Kedziora-Chudczer, L., Kilkenny, D., Knee, L.B.G., Kunkel, M., Layden, A.C., Magalhaes, A.M., Marang, F., Margoniner, V.E., Palma, C., Pereyra, A., Rodrigues, C.V., Schutte, A., Sitko, M.L., Tornikoski, M., van der Walt, J,, van Wyk, F., Whitelock, P.A., Wolk, S.J.: Multiwavelength monitoring of the BL Lac object PKS 2155-304 in May 1994: III. The Ground-Based Campaign. Astrophysical Journal, Vol. 486, 1997, p. 770-783.
12. Pohjolainen, S., Valtaoja, E., Urpo, S.: Impulsive acceleration during gradual type solar radio flares. Advances in Space Research, Vol. 20, 1997 p. 2337-2340.
13. Schwarz, U., Kurths, J., Kliem, B., Krüger, A., Urpo, S.: Multiresolution analysis of solar mm-wave bursts. Astronomy and Astrophysics, Suppl. Series, Vol. 127, 1997, p. 309-318.
14. Wehrle, A.E., Pian, E., Urry, C.M., Maraschi, L., Ghisellini, G., Hartman, R.C., Madejski, G.M., Makino, F., Marscher, A.P., McHardy, I.M., Wagner, S.J., Webb, J.R., Aldering, G.S., Aller, M.F., Aller, H.D., Backman, D.E., Balonek, T.J., Boltwood, P., Bonnell, J., Capinger, J., Celotti, A., Collmar, W., Dalton, J., Drucker, A., Falomo, R., Fichtel, C.E., Freudling, W., Gear, W.K., Gonzalez-Perez, N., Hall, P., Inoue, H., Johnson, W.N., Kazanas, D., Kidger, M.R., Kii, T., Kollgaard. R.I., Kondo, Y., Kurfess, J., Lawson, A. J., Lin, Y.C., McCollum, B., McNaron-Brown, K., Nagase, F., Nair, A. D., Penton, S., Pesce, J.E,, Pohl, M., Raiteri, C.M., Renda, M., Robson, E.I., Sambruna, R.M., Schirmer, A.F., Shrader, C., Sikora, M., Sillanpää, A., Smith, P.S., Stevens, J.A., Stocke, J., Takalo, L.O., Teräsranta, H., Thompson, D.J., Tornikoski, M., Tosti, G., Turcotte, P., Treves, A., Unwin, S.C., Valtaoja, E., Villata, M., Xu, W., Yamashita, A., Zook, A.: Multiwavelength Observations of a Dramatic High Energy Flare in the Blazar 3C 279. Astrophysical Journal, accepted 1997.
15. Hildebrandt, J., Krüger, A., Stepanov, A.V., Urpo, S., Zaitsev, V.: Thermal and nonthermal radio emission: Spectra and diagnostics of coronal microwave sources. Astronomy and Astrophysics, submitted, 1997.
16. Leppänen, K., Mass, M., Rioja, M., Sanghera, H.: High dynamic range imaging with the EVN. Vistas in Astronomy (EVN/JIVE Symposium Special Issue), accepted, 1997.
17. Takalo, L.O., Sillanpää, A., Valtaoja, E., Katajainen, S., Nilsson, K., Pursimo, T., Heinämäki, P., Villata, M., Raiteri, C.M., Ghisellini, G., De Francesco, G., Lanteri, L., Chiaberge, M., Peila, A., Boltwood, P., Tosti, G., Fiorucci, M., Teräsranta, H., Tornikoski, M., Teerikorpi, P.: Monitoring of AO 0235+164 during a faint state. Astronomy and Astrophysics, accepted, 1997.
18. Zaitsev, V.V., Stepanov, A.V., Urpo, S., Pohjolainen, S.: LRC-circuit analog of current-carrying magnetic loop: Diagnostics of electric parameters. Astron. Astrophys., submitted 1997.
19. Leppänen, K., Liljeström, T., Diamond, P., Kemball, A.: Submilliarcsecond linear polarization observations of water masers in W51 M. Astrophysical Journal, submitted, 1997.
20. Zaitsev, V.V., Stepanov, A.V., Urpo, S., Pohjolainen, S.: Diagnostics of electric currents in coronal magnetic loops (in Russian). Astronomical Journal (Russia), submitted, 1997.
21. Urpo, S., Riehokainen, A.: The high latitude mm-wave solar sources and their relation to other solar phenomena such as polar faculae. Hvar Observatory Bulletin, submitted, 1997.

International Conferences

1. Wiik, K., Valtaoja, E.: Three epoch VLBI observations of a sample of 15 AGN at 22 GHz: Comparison of total flux and VLBI properties. Proceedings of the IAU Colloquium 164: Radio emission from galactic and extragalactic compact sources, Socorro, USA, April 21-26, 1997, in press.
2. Valtaoja, E.: Structure and properties of AGN cores from VLBI and total flux density variations. Proceedings of the IAU Colloquium 164: Radio emission from galactic and extragalactic compact sources, Socorro, USA, April 21-26, 1997, in press.
3. Leppänen, K., Liljeström, T., Diamond, P., Kemball, A., Gwinn, C.: Polarization VLBI observations of water masers in star forming regions. Proceedings of the IAU Colloquium 164: Radio emission from galactic and extragalactic compact sources, Socorro, USA, April 21-26, 1997, in press.
4. Liljeström, T.: Shock structure of high-velocity water masers in W49 N. Proceedings of the IAU Colloquium 164: Radio emission from galactic and extragalactic compact sources, Socorro, USA, April 21-26, 1997, in press.
5. Garrett, M.A., Leppänen, K., Porcas, R.W., Patnaik, A.R., Nair, S., Teräsranta, H.: VLBA $\lambda 7$ mm polarisation observations. Proceedings of the IAU Colloquium 164: Radio emission from galactic and extragalactic compact sources, Socorro, USA, April 21-26, 1997, in press.
6. Lähteenmäki, A.: Limiting brightness temperature for synchrotron sources. Proceedings of the IAU Colloquium 164: Radio emission from galactic and extragalactic compact sources, Socorro, USA, April 21-26, 1997, in press.
7. Jauncey, D. L., Tingay, S. J., Preston, R. A., Reynolds, J. E., Lovell, J.E.J., McCulloch, P.M., Costa, M.E., Koekemoer, A., Tornikoski, M., Kedziora-Chudczer, L., Campbell-Wilson, D., Nicolson, G.D.: PKS 1718-649, the nearest GPS radio source. Proceedings of the IAU Colloqium 164: Radio emission from galactic and extragalactic compact sources, Socorro, USA, April 21-26, 1997, in press.
8. Kaufman, M., Liljeström, T., Gwinn, C.: 321 GHz and 22 GHz observations of water masers in the W49N star forming regions. Proceedings of the Star Formation Symposium, Astron. Soc. of Pacific, San Francisco, 1997, in press.
9. Mukherjee, R., Bertsch, D.L., Bloom, S.D., Dingus, B.L., Esposito, J.A., Hartman, R.C., Hunter, S.D., Kanbach, G., Kniffen, D.A., Kraus, A., Krichbaum, T.P., Lin, Y.C., Mahoney, W.A., Marscher, A.P., Mayer-Hasselwander, H.A., Michelson, P.F., Von Montigny, C., Muecke, A., Nolan, P.L., Pohl, M., Reimer, O., Schneid, E., Sreekumar, P., Teräsranta, H., Thompson, D.J., Tornikoski, M., Valtaoja, E., Wagner, S., Witzel, A.: EGRET observations of PKS 0528+134 from 1991 to 1997. Proceedings of the 4th Compton Symposium, Williamsburg, USA, eds. C.D. Dermer, M.S. Strickman, and J.D. Kurfess, American Institute of Physics, 1997, p. 1346-1350.
10. Wehrle, A., Pian, E., Urry, M., Maraschi, L., Ghisellini, G., Hartman, R.C., Madejski, G., Makino, F., Marscher, A.P., McHardy, I.M., Webb, J.R., Aldering, G.S., Aller, M.F., Aller, H.D., Backman, D.E., Balonek, T., Boltwood, P., Bonnell, J., Caplinger, J., Celotti, A., Collmar, W., Dalton, J., Drucker, A., Falomo, R., Fichtel, C.E., Freudling, W., Gear, W.K., Gonzalez-Perez, J.N., Hall, P., Inoue, H., Johnson, W.N., Kidger, M.R., Kollgaard, R.I., Kondo, Y., Kurfess, J., Lawson, A.J., McCollum, B., McNaron-Brown, K., Nair, D., Penton, S., Pohl, M., Raiteri, C.M., Renda, M., Robson, E.I., Sambruna, R.M., Schirmer, A.F., Shrader, C., Sikora, M., Sillanpää, A., Smith, P., Stevens, J.A., Stocke, J., Takalo, L.O., Teräsranta, H., Thompson, T.J., Thompson, R., Tornikoski, M., Tosti, G., Turcotte, P., Treves, A., Unwin, S.C., Valtaoja, E., Villata, M., Wagner, S.J., Xu, W., Zook, A.: Multiwavelength flaring of the quasar 3C 279. Proceedings of the 4th Compton Symposium, Williamsburg, USA, eds. C.D. Dermer, M.S. Strickman, and J.D. Kurfess, American Institute of Physics, 1997, p. 1417-1420.
11. Aller, M.F., Marscher, A.P., Hartman, R.C., Aller, H.D., Aller, M.C., Balonek, T.J., Begelman, M.C., Chiaberge, M., Clements, S.D., Collmar, W., DeFrancesco, G., Gear, W.K., Georganopoulos, M., Ghisellini, G., Glass, I.S., Gonzalez-Peres, J.N., Heinämäki, P., Herter, M., Hooper, E.J., Hughes, P.A., Johnson, W.N., Katajainen, S., Kidger, M.R., Kraus, A., Lanteri, L., Lawrence, G.F., Lichti, G.G., Lin, Y.C., Madejski, G.M., McNaron-Brown, K., Moore, E.M., Mukherjee, R., Nair, A.D., Nilsson, K., Peila, A., Pierkowski, D.B., Pohl, M., Pursimo, T., Raiteri, C.M., Reich, W., Robson, E.I., Sillanpää, A., Sikora, A., Smith, A.G., Steppe, H., Stevens, J., Takalo, L.O., Teräsranta, H., Tornikoski, M., Valtaoja, E., von Montigny, C., Villata, M., Wagner, S., Wichmann, R., Witzel, A.: Radio to Gamma-ray Observations of 3C 454.3: 1993-1995. Proceedings of the 4th Compton Symposium, Williamsburg, USA, eds. C.D. Dermer, M.S. Strickman, and J.D. Kurfess, American Institute of Physics, 1997, p. 1423-1427.
12. Edwards, P.G., Lovell, J.E.J., Hartman, R.C., Tornikoski, M., Lainela, M., McCulloch, P.M., Gaensler, B.M., Hunstead, R.W.: Multi-wavelength Radio Monitoring of EGRET Sources and Candidates. Proceedings of the 4th Compton Symposium, Williamsburg, USA, eds. C.D. Dermer, M.S. Strickman, and J.D. Kurfess, American Institute of Physics, 1997, p. 1428-1432.
13. Teräsranta., H.: The burst activity at millimeter wavelengths compared to gamma-activity of AGN. Proceedings of the 4th Compton Symposium, Williamsburg, USA, eds. C.D. Dermer, M.S. Strickman, and J.D. Kurfess, American Institute of Physics, 1997, p. 1447-1451.
14. Lähteenmäki, A., Teräsranta, H., Wiik. K., and Valtaoja, E.: Relationships between radio and gamma-ray properties in active galactic nuclei. Proceedings of the 4th Compton Symposium, Williamsburg, USA, eds. C.D. Dermer, M.S. Strickman, and J.D. Kurfess, American Institute of Physics, 1997, p. 1452-1456.
15. Ogura, L., Nakano, M., Sugitani, K., Liljeström, T.: SEST observations of the HH 135/136 complex. Proceedings of the IAU Symposium 182: Low-mass star formation - from infall to outflow, eds. F. Malbet, A. Castets, Laboratoire d'Astrophysique, Observatoire de Grenoble, Grenoble, 1997, p. 166-167.
16. Pohjolainen, S., Urpo, S.: Solar active region development at millimetre wavelengths. 5th SOHO Workshop 'The corona and solar wind near minimum activity', Oslo, 1997. ESA SP-404, 1997, 619-622.
17. Brajša, R., Ruždjak, V., Vršnak, B., Pohjolainen, S., Urpo, S., Sakurai, T., Wöhl, H.: Soft X-ray, microwave and He I measurements of coronal holes. IAU 23, Kyoto, Japan, August 17-30, 1997.
18. Tornikoski, M., Teräsranta, H., Valtaoja, E.: The radio behaviour of BL Lacertae during the 1997 optical outburst. Multifrequency monitoring of blazars, OJ-94 annual meeting, 6-10 September 1997, Perugia, Italy, 1997, in press.
19. Tornikoski, M., Valtaoja, E.: The radio vs. optical behaviour in OJ 287; Multifrequency monitoring of blazars, OJ-94 annual meeting, 6-10 September 1997, Perugia, Italy, 1997, in press.
20. Pohjolainen, S., Valtaoja, E., Urpo, S.: Impulsive acceleration during gradual type solar radio flares. 31st COSPAR Scientific Assembly, Birmingham, England, 1996. Adv. Space Res., Vol. 20, No. 12, 1997, p. 2337-2340.
21. Pohjolainen, S.: Millimetre wave radio emission from solar active regions and the observed correlation with other wavelength data. 2nd Advances in Solar Physics Euroconference, Preveza, Greece, 1997. Astronomical Society of the Pacific Conference Series, submitted, 1997.

Laboratory Reports

1. Urpo, S. (editor): Metsähovi Radio Research Station Annual Report 1996. Helsinki University of Technology, Metsähovi Radio Research Station, Series B, Report 12, 1997.
2. Zaitsev, V.V., Stepanov, A.V., Urpo, S., Pohjolainen, S.: LRC-circuit analog of current carrying magnetic loop: Diagnostics of electric parameters. Helsinki University of Technology, Metsähovi Radio Research Station, Series A, Report 25, 1997.
3. Urpo, S., Pohjolainen S., Heikkilä J., Wiik K.: Solar observations at Metsähovi in 1994-1995. Helsinki University of Technology, Metsähovi Radio Research Station, Series A, Report 26, 1997.

Other Publications

1. Urpo, S., Gibson, R., Fischer, H., Rinaldini, C.: Evaluation of the Joint Research Centre 1992-1996. COM(97)164 final, Office for Official Publications of the European Communities, Brussels, 1997.
2. Valtaoja, E.: Finnish participation in the VSOP Space VLBI program. Finnish COSPAR, January 10-11, 1997, Report Series Turku-FL-L23, University of Turku, Department of Physics, 1997, E13.
3. Tornikoski, M., Teräsranta, H.: The role of radio monitoring data for satellite observations of AGN (in Finnish). Finnish COSPAR, January 10-11, 1997, Report Series Turku-FL-L23, University of Turku, Department of Physics, 1997, E11.
4. Lähteenmäki, A., Valtaoja. E., and Teräsranta, H.: Gamma-ray variations in active galactic nuclei observed with the Compton gamma-ray satellite and the connection to radio outbursts. Finnish COSPAR, January 10-11, 1997, Report Series Turku-FL-L23, University of Turku, Department of Physics, 1997, P18.
5. Pohjolainen, S., Urpo, S., Valtaoja, E.: Directivity effects in solar limb flares observed by ground-based and satellite instruments. Finnish COSPAR, January 10-11, 1997, Report Series Turku-FL-L23, University of Turku, Department of Physics, 1997, E10.
6. Koistinen, O., Karlamaa, K., Peltonen, J., Urpo, S.: 43 GHz low noise receiver for VLBI research. Finnish COSPAR, January 10-11, 1997, Report Series Turku-FL-L23, University of Turku, Department of Physics, 1997, E12.
7. Wiik, K.: Preparing for the VLBI space observatory programme (VSOP) mission: comparing two-epoch ground-based 22 GHz VLBI survey and total flux density observations. Finnish COSPAR, January 10-11, 1997, Report Series Turku-FL-L23, University of Turku, Department of Physics, 1997, P7.
8. Engelberg, J.: GPS satellite receivers performance at the Metsähovi Radio Research Station. Finnish COSPAR, January 10-11, 1997, Report Series Turku-FL-L23, University of Turku, Department of Physics, 1997, P19.
9. Mujunen, A., Ritakari, J.: Acquiring and storing HRDL data during AMS space shuttle mission. Finnish COSPAR, January 10-11, 1997, Report Series Turku-FL-L23, University of Turku, Department of Physics, 1997, P16.
10. Liljeström, T.: Water maser observing programs with the VSOP very long baseline interferometry satellite. Finnish COSPAR, January 10-11, 1997, Report Series Turku-FL-L23, University of Turku, Department of Physics, 1997, P6.
11. Ritakari, J., Mujunen, A.: Data Communications on space shuttle mission STS-91. Finnish COSPAR, January 10-11, 1997, Report Series Turku-FL-L23, University of Turku, Department of Physics, 1997, E28.
12. Pohjolainen S., Urpo S., Valtaoja E.: Emission mechanisms in solar flares at millimetre wavelengths. Proceedings of the XXXI Annual Conference of the Finnish Physical Society. University of Helsinki, Report Series in Physics, HU-P-262(1997), 1997, p. 3.06.
13. Wiik, K., Valtaoja, E.: Total flux density monitoring data as a predictor for the space VLBI missions.Proceedings of the XXXI Annual Conference of the Finnish Physical Society, Report Series in Physics HU-P-262 (1997), Helsinki, 1997, p. 3.38.
14. Lähteenmäki, A., Teräsranta, H., and Valtaoja, E.: Gamma-ray and radio variations in active galactic nuclei. Proc. XXXI Annual Conference of the Finnish Physical Society, University of Helsinki, Report Series in Physics HU-P-262, 1997, p. 3.37.
15. Lähteenmäki, A.: Doppler boosting factors and viewing angles for active galactic nuclei. Proc. Nordic-Baltic graduate student meeting on extragalactic astronomy, Seili, Finland, ed. M. Hanski, Tuorla Observatory Reports Informo No. 179, 1997.

Visits to Foreign Institutes

Alpha Magnetic Spectrometer (AMS) HRDL pre-ESTL verification tests, CERN, Geneva, Switzerland, 6.1.-8.1.1997, A. Mujunen, J. Ritakari

Alpha Magnetic Spectrometer (AMS) HRDL NASA ESTL tests, NASA Johnson Space Center, Houston, TX, USA, 10.2.-14.2.1997, A. Mujunen, J. Ritakari

Alpha Magnetic Spectrometer (AMS) HRDL Ground Operations Safety Review and Ground Operations Working Group meetings, NASA Kennedy Space Center, Cape Canaveral, FL, USA, 17.2.-22.2.1997, A. Mujunen

Observations with the SEST Telescope, La Silla, Chile, 8-15.2.1997, A. Lähteenmäki

Observations with the SEST telescope, La Silla, Chile, 27.3.-5.4.1997, M. Tornikoski.

Observations with the Nordic Optical Telescope, La Palma, Spain, 4-11.7.1997, A. Lähteenmäki and E. Valtaoja

Observations with the SEST telescope, La Silla, Chile, 26.8.-4.9.1997, H. Teräsranta.

EVN R/W, VIV (VLBA to Mark IV) kick-off meeting, Joint Institute for VLBI in Europe (JIVE), Dwingeloo, The Netherlands, 10.10.1997, A. Mujunen

FS Support, support for FS Linux migration to Debian 1.3.1 under contract with JIVE/EVN, NASA Goddard Space Flight Center, Baltimore, MD, USA, 16.10.-23.10.1997, A. Mujunen

Observations with the SEST telescope, La Silla, Chile, 30.10.-11.11.1997, K. Karlamaa.

Alpha Magnetic Spectrometer (AMS) HRDL detector tests, ETHZ, Zürich, Switzerland, 13.11.- 15.11.1997 and 24.11.-27.11.1997, A. Mujunen, J. Ritakari

Alpha Magnetic Spectrometer (AMS) HRDL Rack Shipment and Installation, ETHZ, Zürich, Switzerland, 21-28.11.1997, J. Engelberg, E. Oinaskallio

AMS HRDL Rack Shipment and Installation, ETH-Zentrum, Zürich, Switzerland, 21-28.11.1997, J. Engelberg, E. Oinaskallio

Alpha Magnetic Spectrometer (AMS) HRDL GSE setup and initial tests, NASA Kennedy Space Center, Cape Canaveral, FL, USA, 13.12.-20.12.1997, J. Engelberg, A. Mujunen

Observations with the SEST telescope, La Silla, Chile, 25.12.1997-4.1.1998, M. Tornikoski.

Visiting Scientists

Michael Wunderlich, Max Planck Institute für Radioastronomie, Bonn, Germany, 10-14.5.1997

Leslie Parry, Nuffield Radio Astronomy Laboratory, University of Manchester, Jodrell Bank, United Kingdom, 10-14.5.1997

Ed Himwich, NASA GSFC, USA, 24-27.6.1997.

A.V. Stepanov, Main Astronomical Observatory, Pulkovo, 12-26.5.1997

V.V. Zaitsev, Institute of Applied Physics, Nizhny Novgorod, 12-26.5.1997

Theses

No theses were submitted in 1997 by the Metsähovi personnel.

Teaching

Lecture on astronomy and space science at Mäkelänrinteen aikuislukio, 28.1.1997, S. Pohjolainen.

Lectures about astronomy, astronomical instrumentation and the work of an astronomer to the speciality course of astronomy at the junior high school Anttilan Yläaste of Lohja, 20.3., 16.9. and 2.11.1997, M. Tornikoski.

Participation in the science project of the Ladue Jr. High School, Missouri, USA, as a specialist, via electronic mail, M. Tornikoski.

``GPS paikkatiedon tuotannossa ja navigoinnissa maalla, merellä ja ilmassa'', Metsähovi, 4.4.1997, J. Engelberg, E. Oinaskallio

Course for graduate students on cosmology, Helsinki University of Technology, Electrical Department, spring 1997, S. Urpo

Other Activities

Evaluation of docent application of Dr. P. Eskelinen, Lappeenranta University of Technology, S. Urpo

Participation in Boards and Committees

AAS, American Astronomical Society, member S. Urpo

Academy of Finland, member of expert panel S. Urpo

AMS, TEKES Guiding Group, member S. Urpo

CESRA (Community of European Solar Radio Astronomers) Meeting to be held in June 9-13, 1998. Local Organizing Committee, chair S. Pohjolainen, members S. Urpo and S. Hurtta, Scientific Organizing Committee, member S. Urpo

CMVA (Coordinated Millimeter VLBI Array) Directors Meeting, Bonn, Germany, 16.12.1997, S. Pohjolainen, K. Wiik

COSPAR, Committee on Space Research, Finnish National Committee, chairman S. Urpo

COSPAR, Finnish National Representative S, Urpo

COSPAR, Commission E2, Solar Physics, member S. Urpo

EAS, European Astronomical Society, founding member S. Urpo

ESA (European Space Agency) SPC (Science Programme Committee) delegate S. Urpo

ESA SPC, Paris, France, 18-19.2.1997, S. Urpo

ESA SPC, Paris, France, 2-3.6.1997, S. Urpo

ESA SPC, Oxford, UK, 9-11.9.1997, S. Urpo

ESA SPC, Paris, France, 17-18.11.1997, S. Urpo

ESF/CRAF European Science Foundation/Committee for Radio Astronomy Frequencies Meeting, ETH-Zentrum, Switzerland, 20-21.10.1997, J. Engelberg.

EVN (European VLBI Network) Board of Directors, member S. Urpo

EVN Board of Directors Meeting, Jodrell Bank, UK, 22-25.3.1997, S. Urpo

EVN Board of Directors Meeting, Onsala, Sweden, 24.10. 1997, S. Pohjolainen

EVN TWG (Technical Working Group) Meeting, Siikaranta, Espoo, Finland, 24-27.6.1997, organizer K. Wiik.

Finnish Space Committee, permanent adviser S. Urpo

Finnish Space Committee, ESTEC, Noordwijk, The Netherlands, 9-10.12.1997, S. Urpo

Hvar Observatory Bulletin, Board of Editors S. Urpo

IAG, associate member S. Urpo

IAU, Finnish National Committee, member S. Urpo

INTAS project INTAS-RFBR-95-316, coordinator S. Urpo

National UMTS (Universal Mobile Telecommunications System) Working Group, 8.12.1997, J. Engelberg

OECD Mega Science Forum, Working Group on Radio Astronomy, Paris, France, 3-5.12.1997, S. Urpo

Radio Administration Advisory Group, several meetings during 1997, J. Engelberg.

RISC (Radioastron International Science Committee) member S. Urpo

RISC, Moscow, Russia, 1-5.4.1997, S. Urpo

Sodankylä Geophysical Observatory, member of the Board S. Urpo

Sodankylä Geophysical Observatory Board, Sodankylä, Finland, 31.7-1.8.1997, S. Urpo

Tuorla Observatory, member of the Board S. Urpo

URSI, National Representative of Commission J, Radio Astronomy S. Urpo

URSI, Finnish National Committee, vice member S. Urpo

Working Group for Finnish-Russian Cooperation in Space Field, member S. Urpo

International Meetings and Talks

IAU Colloquium 164: Radio emission from galactic and extragalactic compact sources, Socorro, USA, 21-26.4.1997. A. Lähteenmäki poster: Limiting brightness temperature for synchrotron sources. K. Wiik poster: Three epoch VLBI observations of a sample of 15 AGN at 22 GHz: Comparison of total flux and VLBI properties. E. Valtaoja poster: Structure and properties of AGN cores from VLBI and total flux density variations. T. Liljeström poster: Polarization VLBI observations of water masers in star forming regions. T. Liljeström poster: Shock structure of high-velocity water masers in W49 N. H. Teräsranta poster: VLBA $\lambda 7$ mm polarisation observations. M. Tornikoski poster: PKS 1718-649, the nearest GPS radio source.

4th Compton Symposium on Gamma-Ray Astronomy and Astrophysics, Williamsburg, USA, 28-30.4. A. Lähteenmäki, H. Teräsranta, K. Wiik poster:: Relationships between radio and gamma-ray properties in active galactic nuclei. H. Teräsranta, M. Tornikoski poster: EGRET observations of PKS 0528+134 from 1991 to 1997. H. Teräsranta, M. Tornikoski poster: Multiwavelength flaring of the quasar 3C 279. H. Teräsranta, M. Tornikoski poster: Radio to Gamma-ray Observations of 3C 454.3: 1993-1995. M. Tornikoski poster: Multi-wavelength Radio Monitoring of EGRET Sources and Candidates. H. Teräsranta poster: The burst activity at millimeter wavelengths compared to gamma-activity of AGN.

The OJ-94 annual meeting 1997, Multifrequency monitoring of blazars in Perugia, Italy, September 8-9th. M. Tornikoski talk: The radio behaviour of BL Lacertae during the 1997 optical outburst, and talk: The radio vs. optical behaviour in OJ 287.

Fifth SOHO Workshop, Oslo, Norway, June 17-20, 1997. S. Pohjolainen poster: Solar Active Region Development at Millimetre Wavelengths.

Summer School in Space Solar Physics, Orsay, France, Sept. 1-13, 1997. S. Pohjolainen, participation in the course.

2nd ASPE Euroconference Three Dimensional Structure of Solar Active Regions, Preveza, Greece, October 7-11, 1997. S. Pohjolainen talk: Millimetre wave radio emission from solar active regions and the observed correlation with other wavelength data.

Hvar Astrophysical Colloquium, Hvar Observatory, Hvar, Croatia, June 28 - July 5, 1997. S. Urpo talk: The high latitude mm-wave solar sources and their relation to other solar phenomena such as polar faculae.

National Meetings and Talks

VI Suomen avaruustutkijoiden COSPAR-kokous, Turku, Finland, 10-11.1.1997. M. Tornikoski talk The role of radio monitoring data for satellite observations of AGN (in Finnish). S. Pohjolainen, talk: Directivity effects in solar limb flares observed by ground-based and satellite instruments. O. Koistinen talk: 43 GHz low noise receiver for VLBI research. J. Ritakari talk: Data Communications on space shuttle mission STS-91. K. Wiik poster: Preparing for the VLBI space observatory programme (VSOP) mission: comparing two-epoch ground-based 22 GHz VLBI survey and total flux density observations. J. Engelberg poster: GPS satellite receivers performance at the Metsähovi Radio Research Station. A. Mujunen poster: Acquiring and storing HRDL data during AMS space shuttle mission. T. Liljeström poster: Water maser observing programs with the VSOP very long baseline interferometry satellite. A. Lähteenmäki poster: Gamma-ray variations in active galactic nuclei observed with the Compton gamma-ray satellite and the connection to radio outbursts.

Nordic-Baltic graduate student meeting on extragalactic astronomy, A. Lähteenmäki talk: Doppler boosting factors and viewing angles for active galactic nuclei. Seili, Finland, 27-29.1.1997.

XXXI Annual Conference of the Finnish Physical Society, Helsinki, Finland, 13-15.3.1997. A. Lähteenmäki poster: Gamma-ray and radio variations in active galactic nuclei. S. Pohjolainen talk: Emission mechanisms in solar flares at millimetre wavelengths. K. Wiik poster: Total flux density monitoring data as a predictor for the space VLBI missions.

EVN (European VLBI Network) TWG, Espoo 27-28.6.1997, J. Engelberg, J. Heikkilä, K. Karlamaa, A. Mujunen, J. Ritakari, P. Suvikunnas, K. Wiik.

Research Seminar on High-Energy Astrophysics, University of Helsinki, Observatory, December 3, 1997. S. Pohjolainen talk: SOHO/SUMER observations of the Solar UV radiation.

Public Relations

Lecture about galaxies, their classification and properties to the amateur astronomy club Lohjan Ursa, 26.3.1997, M. Tornikoski.

Lecture about active galactic nuclei, radio astronomy and Metsähovi research projects to the amateur astronomy club Pollux, 26.10.1997, M. Tornikoski.

Personnel in 1997

Permanent Positions funded by the Helsinki University of Technology

 
Urpo, Seppo, Prof., Dr.Tech., 		 Director of the institute,  		 Seppo.Urpo@hut.fi

docent on leave of absence as

senior researcher for the

Academy of Finland

(Aug 1, 1997- Jul 31, 1998)

Engelberg, Jan, Eng. Operations engineer Jan.Engelberg@hut.fi

Hurtta, Solveig, Ms. Secretary Solveig.Hurtta@hut.fi

Oinaskallio, Erkki, Mr. Technician Erkki.Oinaskallio@hut.fi

Peltonen, Juhani, Dr.Tech. Laboratory engineer jussi@kurp.hut.fi

Scientific and Technical Staff Funded by Research Contracts

 
Heikkilä, Juho, student      		 Research aid, part time      		 Juho.Heikkila@hut.fi

from Jun 1, 1997

Karlamaa, Kirsi, student Research aid Kirsi.Karlamaa@hut.fi

Koistinen, Olli, Lic.Tech. Research scientist Olli.Koistinen@hut.fi

Liljeström, Tarja, Lic.Phil. Research scientist, in Aug Tarja.Liljestrom.hut.fi

and Dec, 1997

Lähteenmäki, Anne, M.Sc. Research scientist Anne.Lahteenmaki@hut.fi

Mujunen, Ari, M.Sc.(Eng) Research scientist Ari.Mujunen@hut.fi

Pohjolainen, Silja, Dr.Phil. Research scientist, acting Silja.Pohjolainen@hut.fi

director of the institute

(Aug 1, 1997-Jul 31, 1998)

Ritakari, Jouko, M.Sc.(Eng) Research scientist, part time jr@kurp.hut.fi

Rönnberg, Henry, Mr. Mechanic

Suvikunnas, Pasi, student Research aid,

Jun 1-Aug 31, 1997

Teräsranta, Harri, Dr.Tech. Research scientist hte@kurp.hut.fi

Tornikoski, Merja, Dr.Tech. Research scientist Merja.Tornikoski@hut.fi

Turtiainen, Esa, Lic.Tech. Research scientist, until

Jun 30, 1997

Wiik, Kaj, M.Sc.(Eng) Research scientist Kaj.Wiik@hut.fi

Metsähovi Advisory Committee

 
Juuti, Pauli., M.Sc. (Eng)        		 Tiuri, Martti, Prof.emer., M.P. (Chair)

Pellinen, Risto, Prof. Valtonen, Mauri, Prof.

Somervuo, Pekka, Dr.Tech. Urpo, Seppo, Prof. (Secretary)

Tanskanen, Pekka, Prof.

\

Reports published by Metsähovi

Report Series A - Metsähovi Publications on Radio Science

Seppo Urpo, Silja Pohjolainen, Harri Teräsranta (1987): Solar microwave radiation maps measured at Metsähovi Radio Research Station in 1978-1979. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 1.

Seppo Urpo, Silja Pohjolainen, Harri Teräsranta (1988): Solar microwave radiation maps measured at Metsähovi Radio Research Station in 1980-1981. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 2.

Seppo Urpo, Silja Pohjolainen, Harri Teräsranta (1988): Solar microwave radiation maps measured at Metsähovi Radio Research Station in 1982-1983. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 3.

Seppo Urpo, Silja Pohjolainen, Harri Teräsranta (1989): Solar microwave radiation maps measured at Metsähovi Radio Research Station in 1984-1986. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 4.

Seppo Urpo, Silja Pohjolainen, Harri Teräsranta, Kirsi Karlamaa (1991): Solar microwave radiation maps measured at Metsähovi Radio Research Station in 1987-1988. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 5.

Seppo Urpo, Silja Pohjolainen, Harri Teräsranta, Kirsi Karlamaa (1991): Solar microwave radiation maps measured at Metsähovi Radio Research Station in 1989. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 6.

Seppo Urpo, Silja Pohjolainen, Harri Teräsranta, Kirsi Karlamaa (1991): Report microwave radiation maps measured at Metsähovi Radio Research Station in 1990. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 7.

S. Wiren, E. Valtaoja, H. Teräsranta, J. Kotilainen (1991): A complete sample of northern hemisphere active galactic nuclei - differences in flux and spectra at high radio frequencies. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 8.

E. Valtaoja, A. Lähteenmäki, H. Teräsranta (1991): A northern 2 Jy Sample of compact extragalactic radio sources suitable for millimeter and space VLBI observations. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 9.

Seppo Urpo, Kirsi Karlamaa, Silja Pohjolainen, Harri Teräsranta (1992): Solar microwave radiation maps measured at Metsähovi Radio Research Station in 1991. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 10.

Seppo Urpo, Silja Pohjolainen, Harri Teräsranta (1992): Solar Radio Flares 1989-1991; Solar microwave flares observed at Metsähovi Radio Research Station in 1989-1991. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 11.

Seppo Urpo, Silja Pohjolainen, Harri Teräsranta (1992): Solar observations at Metsähovi in January - June 1992. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 12.

Seppo Urpo, Silja Pohjolainen, Harri Teräsranta (1993): Solar observations at Metsähovi in July - December 1992. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 13.

Silja Pohjolainen, Kimmo Lehtinen (1993): Finnish Astronomy Days 1992 and 1993, Proceedings of the Finnish Astronomical Society. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 14.

M. Tornikoski, E. Valtaoja, H. Teräsranta, A.G. Smith, A.D. Nair, S.D. Clements, R.J. Leacock (1993): Correlated radio and optical variations in a sample of AGN. M. Tornikoski, E. Valtaoja, H. Teräsranta, M. Okyudo (1993): A simultaneous radio-optical flare in BL Lacertae. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 15.

Seppo Urpo, Silja Pohjolainen, Harri Teräsranta (1994): Solar observations at Metsähovi in 1993. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 16.

Merja Tornikoski (1994): Studies of extragalactic radio sources: observations and analysis of multifrequency spectra and variability (Dr.Tech. Thesis). Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 17.

Harri Teräsranta (1994): Observations of extragalactic sources with the Metsähovi radio telescope at 22-87 GHz (Dr.Tech. Thesis). Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 19.

Kari Leppänen (1995): 22 GHz Polarimetric Imaging with the Very Long Baseline Array (Dr.Tech. Thesis). Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 20.

S. Pohjolainen, E. Valtaoja, S. Urpo, H. Aurass (1996): Microwave emission from coronal heights: study of a non-thermal radio flare. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 21.

Alexander Riehokainen, Seppo Urpo, Esko Valtaoja (1996): Solar rotation rates at high latitudes determined from microwave observations. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 22.

Alexander Riehokainen, Seppo Urpo, Esko Valtaoja (1996): The relationship between enhanced temperature microwave regions and other solar activity at low and high latitudes. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 23.

Silja Pohjolainen (1996): Energy release by solar flares: Observations at radio and X-ray wavelengths (Dr.Phil. Thesis). Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 24.

V.V. Zaitsev, A.V. Stepanov, S. Urpo, S. Pohjolainen (1997): LRC-circuit analog of current-carrying magnetic loop: Diagnostics of electric parameters. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 25.

S. Urpo, S. Pohjolainen, J. Heikkilä, K. Wiik (1997): Solar observations at Metsähovi in 1994-1995. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series A, Report 26.

S. Pohjolainen (Editor) (1998): CESRA Workshop on Coronal Explosive Events. Metsähovi Publications on Radio Science. HUT-MET-27.

Report Series B - Metsähovi Reports

Seppo Urpo, Silja Pohjolainen (ed.) (1989): Metsähovi Radio Research Station Annual Report 1988. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 1.

Vesa Wäyrynen (1989): Solar Observation System. Program Document. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 2.

Heikki Laurila, Niklas Holsti, Harri Teräsranta, Seppo Urpo, Tero Jankko (1989): A Computer Program for Point-Source Microwave Continuum Observation (FIVE). Program Document Vol. I-III. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 3.

Seppo Urpo, Silja Pohjolainen (ed.) (1990): Metsähovi Radio Research Station Annual Report 1989. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 4.

Seppo Urpo (ed.) (1991): Metsähovi Radio Research Station Annual Report 1990. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 5.

Seppo Urpo (ed.) (1992) Metsähovi Radio Research Station Annual Report 1991. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 6.

Seppo Urpo (ed.) (1993): Metsähovi Radio Research Station Annual Report 1992. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 7.

Seppo Urpo, E. Valtaoja (toimittajat) (1993): Avaruustutkimuksen ja radiotieteen uudet ulottuvuudet. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 8.

Seppo Urpo (ed.) (1994): Metsähovi Radio Research Station Annual Report 1993. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 9.

Seppo Urpo (ed.) (1995): Metsähovi Radio Research Station Annual Report 1994. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 10.

Seppo Urpo (ed.) (1996): Metsähovi Radio Research Station Annual Report 1995. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 11.

Seppo Urpo (ed.) (1997): Metsähovi Radio Research Station Annual Report 1996. Helsinki University of Technology, Metsähovi Radio Research Station, Report Series B, Report 12.

Silja Pohjolainen (Editor) (1998): Metsähovi Radio Observatory Annual Report 1997. Metsähovi Reports, HUT-KURP-13.