1 International Conference on RadioAstron Mission November 2003, Moscow ASTROMETRIC GOALS OF THE RADIOASTRON MISSION V.E.ZHAROV 1, A.E.RODIN 2, I.A.GERASIMOV 1, Yu.P.ILYASOV 2, K.V.KUIMOV 1 1 Sternberg State Astronomical Institute, Russia 2 Puschino Radio Astronomical Observatory of Lebedev Physical Institute, Russia

2 RADIOASTRON MISSION Orbital parameters Orbital period p = 9.5 days Semi-major axis a = km Eccentricity e = Perigee height H = 2000 km Optimized launch date is March 15, 2006.

3 The fringe sizes (in micro arc seconds) for the apogee B max (km) Band / (cm) P / 92L / 18C / 6.2K /

4 Main scientific goals of the mission Astrophysics problems: Study of radio galaxies, quasars, black holes, neutron stars with very high angular resolution; cosmological evolution of compact extragalactic radio sources; determination of fundamental cosmological parameters and study of gravitational lenses and the nature of dark matter. Astrometry problems: Precise astrometry on level of several microarcseconds, determinations of the distances to pulsars as well as evaluations of their velocities by the measurements of parallax and proper motion; link of kinematical and dynamical celestial reference frames; measurements of secular aberration (motion of the Solar system in Galaxy); search of the weak microlensing events – study of apparent motions of compact extragalactic radio sources; direct measurements of distances using spherical wave front.

5 Modern and future radio and optical catalogs Radio Optical

6 Defining sources for improved ICRF and its distribution S/N=10 S min ~ 30 mJy Defining sources with S>1 Ju S/N>30 s t  300 ps Each source will be observed more than 100 times Uncertainty of coordinate will be < 10 m as

7 Weak Microlensing Sazhin M.V., Zharov V.E., et al., Microarcsecond instability of the celestial reference frame. Monthly Notices of Roy. Astron. Soc., 300, p (1998)

8 List of reference pulsars Pulsar list B h 32 m s±0.0005s 54 o 34 ' ' '± ' ' B h 58m s ±0.003s 54 o 13' ' ' ± 0.1' ' B h 53m 09.30s ± 0.01s 07 o 55' ' ‘± 0.07 ' ' B h 35m s ± 0.006s 16 o 16 ' 40.07' ' ± 0.27' ' B h 22m s ± 0.005s 51 o 54 ' ' ' ± 0.01' ' Eulerian angles Link of the celestial frames DE200 and ICRF by pulsar positions VLBI Timing B (Rodin, Sekido, 2000) (Downs, Reichly, 1983) B (Bartel, Nunes, 1996) (Wolszczan, 1999) B (Bartel, et.al, 1996) (Kaspi, et. al, 1994) B (Campbell, et.al, 1996) (Downs, Reichly, 1983) Eulerian angles (mas) from DE200 to ICRF Finger, Folkner, Folkner et al., Rodin, Sekido, LLR & VLBI LLR & VLBI Pulsar VLBI & timing (TDA Progr. Report (A&A, 287, (AP–RASC Conf. Digest, 42–109, JPL, CA) p. 279–289) Chuo Univ., Tokyo, p.388) Ax 1 ± 3 – 2 ± 2 – 4 ± 2 Ay –10 ± 3 –12 ± 3 –13 ± 2 Az – 4 ± 5 – 6 ± 3 –17 ± 6

9 Secular aberration Solar system velocity V= 220 km/s, orbit radius R= 8,5 kpc maximum secular aberration = 2.5 min of arc Annual change of the direction of the Solar system velocity = 50 m as (secular aberration per year = 4 m as )

10 List of Sources for the Secular Aberration Measurement Name R.A. Dec. Gal. b Gal. l D O O D D C O O C C C C C C C C Name R.A. Dec. Gal. b Gal. l C O C D C D D C D D C D C D D C C D C C

11 CONCLUSION Generation of precise fundamental celestial reference frame Link of kinematical and dynamical celestial reference frames Precise measurement of radio telescopes positions in geocentric terrestrial reference frame Parallax and proper motion measurements of pulsars Tests of Theory of Relativity measurements of secular aberration (motion of the Solar system).

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