This is preprint of a paper published in
Proc. 6th European VLBI Network Symposium,
June 25–28, 2002, Bonn, Germany
(eds.: E. Ros et al.), p. 19 – 20

Goals and results of the ad-hoc VLBI activity with Russian antennas


I. Molotov 1, S. Likhachev1, B. Lipatov2, A. Dementiev2, Yu. Gorshenkov3, A. Kovalenko1, A. Konovalenko4, C. Stanghellini5, G. Tuccari5, X. Hong6, X. Huang6, S. Dougherty7, R. Shanks7, X. Liu8, J. Zhang8, A. Kus9, K. Borkowski9, J. Quick10, G. Nicolson10, S. Ananthakrishnan11, M. Sankararaman11, I. Shmeld12, E. Bervalds12

1 Astro Space Center, LPI RAS, Profsoyuznaya str. 84/32, 117997 Moscow, Russia
2 Radiophysical Research Institute, B. Pecherskaya str. 25, 603950 N. Novgorod, Russia
3 Special Research Bureau, MPEI, Krasnokazarmennaya str. 14, 111250 Moscow, Russia
4 Institute of Radio Astronomy, NASU, Chervonopraporna str. 4, 310002 Kharkiv, Ukraine
5 Istituto di Radioastronomia, Contrada Renna Bassa, 96017 Noto (Siracusa), Italy
6 Shanghai Astronomical Observatory, NAO CAS, Nandan road 80, 200030 Shanghai, China
7 Dominion Radio Astrophysical Observatory, P.O. Box 248, V2A 6K3 Penticton B.C., Canada
8 Urumqi Astronomical Observatory, NAO CAS, S. Beijing Road 40, 830011 Urumqi, China
9 Torun Centre for Astronomy, NCU, Gagarina str. 11, 87-100 Torun, Poland
10 Hartebeesthoek Radio Astronomy Observatory, P.O. Box 443, 1740 Krugersdorp, South Africa
11 National Centre for Radio Astrophysics, TIFR, Post Bag 3, Ganeshkhind, 411007 Pune, India
12 University of Latvia, Astronomical Institute, Raina Bld. 19, 1586 Riga, Latvia
13 Ventspils International Radio Astronomy Center, Akademijas laukums 1, 1050 Riga, Latvia


Abstract. Low Frequency VLBI Network project was started in 1996 to involve some Russian radio telescopes in international VLBI activity. The 8 antennas in Russia, Ukraine, India and Latvia were equipped with repaired Mk-2 terminals from USA and 92 cm receivers. More modern S2 recorders were installed at Bear Lakes RT-64 and Puschino RT-22. Few Mk-2 and S2 experiments were arranged during 1997-2000 at 92-cm and 18-cm wavelengths using various combinations of these antennas and radio telescopes in USA, South Africa, China, Italy and Poland. The five sessions were processed by JPL/Caltech Block II and Penticton DRAO correlators. In the papers the scientific goals of this VLBI activity, results obtained so far and further plans are presented.


    1. Introduction

    The technique of Very Long Baseline Interferometry (VLBI) achieves the highest angular resolution and very actively used around the word for research of small-scale space phenomena and astrometry measurements. There are few large Russian radio telescopes suitable for VLBI observations: Bear Lakes RT-64, Kalyazin RT-64, Puschino RT-22 (near Moscow), Ussuriysk RT-70 (Far East), Svetloe RT-32 (near St.-Petersburg). Unfortunately Russians not participate in European VLBI programs since 1993. Main reason of it is the lack of compatible VLBI recorders (only modern VLBA terminal was returned to NRAO from Ussuriysk RT-70 in 1994). Therefore special program was started in 1996 in order to establish the international VLBI cooperation including some Russian radio telescopes with accessible and most cheap VLBI apparatuses – Mk-2 equipment received from JPL, USA for VLBI training goals and S2 equipment received from ISTC, Canada under grant of Russian Ministry of Science and Industry. The project was entitled as the Low Frequency VLBI Network (LFVN) and was partially supported by INTAS 96-0183 grant. Currently LFVN has few almost independent directions of development, each from which has own cooperation of observatories: Mk-2 sub-system at 92 cm wavelength for research of spikes, medium-sized irregularities of solar corona and wind, studying of limitations on VLBI caused by scattering effect, compiling of source list for Space VLBI Radioastron mission; international S2 ad-hoc array at 18 cm wavelength for survey of AGN (as pre-launch Radioastron, searching of CSO in the sample of GPS, properties of BL Lac objects) and OH-masers in evolved stars, SETI and attepts of stellar VLBI; VLBI radar (Evpatoria RT-70 transmitter + LFVN) at 6 cm wavelength for investigations of Earth group planets, near-Earth asteroids and space debris; integration with European VLBI Network basing on PC-disks recording terminals of new generation.

    2. LFVN development

    As first stage, the old Mk-2 equipment from JPL and NRAO was repaired and installed together with produced 92 cm receivers and one-channel base band converters at Bear Lakes RT-64, Puschino RT-22 (both near Moscow), St. Pustun RT-14 and Zimenki RT-15 (both near N. Novgorod) in Russia, Evpatoria RT-70 in Ukraine, Ventspils RT-32 in Latvia. GMRT (one 45 m antenna) at Pune and ORT (500x30 m parabolic cylinder) at Ooty in India also were equipped with Mk-2 terminals. The agreement about collaboration was obtained with observatories at Noto in Italy (RT-32), Urumqi in China (RT-25) and Torun in Poland (RT-15), which had 92 cm receiver and kept operational Mk-2 terminal. It was planned to use JPL/Caltech Block II correlator as LFVN Mk-2 processing center. In further, when Block II was unexpected stopped in 1998, the Russian Mk-2 correlator has been developed at RRI, N. Novgorod (first fringes in 2001). Block II can process only first INTAS1 LFVN experiment Noto-Puschino-St.Pustyn-GMRT-Ooty (the fringes were found between Noto-St. Pustyn-GMRT). The lot of further Mk-2 experiments waiting the processing at N. Novgorod. As results of INTAS1 experiment, 15 sources displayed unresolved components on baseline Noto-GMRT (5800 km) and were proposed as candidates for future Space VLBI observations, see Chuprikov (1999). Also obtained data on interplanetary medium added the previous experiments results and allowed to fix the limitations for elongation angles for VLBI were determined (coherency is absence closer 13o to the Sun) and to suppose the existing of average-scale irregularities of solar wind, see Altunin (2000).

 

     
a


b

Fig. 1. INTAS99.4: (u,v)-plane coverage (a) and image of source 1308+326 (Bear Lakes,
Puschino, Noto, Shanghai, Hartebeesthoek and Svetloe radio telescopes were used)


    On the second stage, two more modern Canadian S2 recording terminals (frequency bandwidth up to 64 MHz) were installed at Bear Lakes and Puschino. The direct connections were established with radio telescope stations around the world equipped with S2 system: Green Bank RT-43 (USA), Arecibo RT-300 (Puerto Rico), Shanghai RT-25 (China), Hartebeesthoek RT-26 (South Africa), and Svetloe RT-32 (Russia), and Penticton S2 correlators of DRAO (Canada). The first test S2 experiments were arranged and successfully processed at Penticton: INTAS98.2 (Bear Lakes-Hartebeesthoek-Green Bank) and INTAS98.5 (Bear Lakes-Puschino-Green Bank-Hartebeesthoek-Svetloe-Arecibo). The obtained results allowed to obtain an informal agreement about joint ad-hoc activity between Bear Lakes, Puschino, Noto, Shanghai and GMRT observatories, and Penticton correlator and new VLBI experiments at 18 cm wavelength were arranged: INTAS99.4 (Bear Lakes-Puschino-Noto-Shanghai-Hartebeesthoek-Svetloe) and INTAS00.3 (Bear Lakes-Puschino-Noto-Shanghai-Hartebeesthoek-GMRT). The observations programs were formed on base of requests of participating observatories. The trial post-processing of INTAS99.4 and INTAS00.3 (its correlation is not finished still), which was carried at Astro Space Center, showed that resulting (u,v) coverages seem rather regular and homogeneous. The figure 1. demonstrates the results for source 1308+326 in experiment INTAS99.4. Some images of 3C309.1 and 1156+295 were received from INTAS98.5, 1803+784, 1011+496 – from INTAS99.4, see Chuprikov (2202). The VLBI fringes were found for SETI source 37 Gem, Lamda And and T Tau stars.
    The first results of VLBI radar project presented at Tuccari (2002), the integrating with EVN project at Molotov (2002).

    3. Conclusion

    The LFVN began the regular operations and first scientific results were obtained. This activity allowed to keep in operation the large radio telescopes of former Soviet Union countries, to accumulate the necessary VLBI experience for new generation of antennas staff and create the necessary prerequisites for its integrating with EVN. The post-processing of all mentioned experiments will be continued (correlation of INTAS00.3 and OH-maser parts of both INTAS99.4 and INTAS00.3 must be finished soon). Also we plan to concentrate our special efforts on interpreting of solar wind results. There are the objectives for further LFVN developments under INTAS-IA-01-02. Our plan to continue the ad-hoc observations in 2002 and in future with involving of more quantity of radio telescopes. As nearest plans, the VLBR02.1 at 6 cm will be arranged in July and LFVN02.2 at 18 cm in December.


    References

Chuprikov, A.A., Girin, I.A., Likhachev, S.F., Molotov, I.E. et al. 1999, NewAR, 43, 8-10, 747
Altunin, V.I., Dementiev, A.F., Lipatov, B.N. et al. 2000, Radiophysics, XLIII, 3, 197
Chuprikov, A.A. 2002, These proceedings
Tuccari, G. et al. 2002, These proceedings
Molotov I.E. 2002, These proceedings