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VERA project Mareki Honma (National Astronomical Observatory of Japan) 2/Mar/2005 @ Hokkaido Univ. Project Overview VERA: VLBI Exploration of Radio Astrometry • The first array dedicated to VLBI astrometry • New technique : dual-beam antenna • Target sources : maser sources • Science target : to establish 3D structure and dynamics of the Milky Way Science with VERA • Fundamental structure of the Galaxy • Physics of Mira variables, Period-Luminosity Relation • Outflows in star forming regions • High energy object (XRB, GRB etc.) • General relativity test Summary of Current status 2000 2002 2002 2003 2004~ Construction started Array construction completed System evaluation as single dish, sigle-beam VLBI System evaluation as dual-beam VLBI Evaluation of astrometric precision Geodetic observations VLBI with universities 2003/04~ 2004~ Common-use (domestic only) project observation 10~15 years to do astrometry of 1000 masers Future Extension: VLBI in East Asia • Japanese stations VERA, Hokkaido, Gifu, Yamaguchi, Kashima, Usuda, Tsukuba etc. • Korea KVN: 20m x 3 (to be completed in 2007) • China Shanghai, Urumqi (+ VSOP-2) will provide better sensitivity and better image Science : Galactic structures and AGNs VERA array Iriki 4 x 20m radio telescopes Completed in 2002 Ishigaki Mizusawa Ogasawara Max baseline : 2300 km VERA telescope : dual-beam antenna Dual-beam antenna : 2 receivers at focal plane Simultaneous observations of two adjacent sources can cancel out atmospheric fluctuation target accuracy : 10 micro-arcsec ! Target source Target source reference atmosphere atmosphere Normal VLBI station VERA station Schematic view of normal VLBI station and VERA station Dual-beam receiving system Dual-beam platform (Max. beam separation : 2.2 deg) dual-beam receivers (22GHz & 43GHz band receives) Astrometry of the Milky Way with VERA target accuracy : 10 micro-arcsec ! Parallax measurement VERA enables us to do astrometry of the Whole Milky Way Galaxy (c.f. GAIA, SIM) High-precision Astrometric Missions Near-future projects for 10 micro-arcsec astrometry name type band start year accuracy # of stars 10^4 SIM space opt ~2009 10 μas or higher GAIA space opt ~2012 10 μas 10^9 JASMINE space IR 2013 ? 10 μas 10^8 VERA VLBI radio 2004 10 μas 10^3 Target source : masers H2O maser (22GHz) SiO masers (43GHz) Star Forming Regions (H2O) AGB stars (H2O, SiO) distribution of H2O maser sources Maser from outflow in SFR Maser from TX Cam Fundamentals of the Galaxy Distance to the Sgr A* R0 Galactic Rotation velocity at the Sun θ0 Local disk density, local dark matter Structure of bulge and spiral arms Rotation curve → dark matter : where & how much ? Face-on view of Galactic maser distribution Astrometric Microlensing What’s Astrometric microlensing ? microlensing events detected through image position change Why Astrometric Microlensing ? 1) Large Lens size (high probability) 2) Independent observables from photometric events 3) Existence of high-precision missions in near future New tool to study dark object Example of image position change in astrometric microlensing Period Luminosity Relation of Mira • Another standard cosmic candle ? • Better understanding of stellar physics PL relation of Mira (Feast et al 1989) PL relation for AGBs (Wood 2000) High Energy Objects Natural laboratory of High Energy Physics X-ray binaries star + compact objects (WD, NS, BH ?) measurement of distance and orbital motion → mass, energy scale, nature of compact object GRO 1655-40 with VLBA Gamma-ray burst Gamma-ray burst origin : Super Nova relativistic jet (→ super-luminal motion expected) GRB030329 detected with VERA VERA Ishigaki-jima station Radio telescope in sub-tropical island General Relativity test • Gravitational Deflection of Light by the Sun Θ=(1+γ) / 2 (4GM / c2b) 1.75 arcsec for General Relativity Current value : γ= 1.000+/-0.001 from VLBI astrometry (with accuracy of 1 mas) Expected improvement by order of 2 (accuracy 1 mas to 10 micro-as) 運動学的距離決定 10000 AU メーザーの固有運動と視線速度を利用 W49N : D = 11.5 +/- 1.5 kpc Gwinn et al. (1992) Vflow ~ 200 km/s 3000 AU OH 43.8-0.1 with VERA D = 2.8 +/- 0.5 kpc Honma et al. (2005) Vflow ~ 8 km/s W49N - OH43.8-0.1 pair W49N 2 mas Milky Way in summer OH43