(National Astronomical Observatory of Japan) 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 Construction started 2002 Array construction completed 2002 System evaluation as single dish, sigle-beam VLBI 2003 System evaluation as dual-beam VLBI 2004~ Evaluation of astrometric precision Geodetic observations VLBI with universities 2003/04~ Common-use (domestic only) 2004~ 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 4 x 20m radio telescopes Completed in 2002 Iriki Mizusawa Ishigaki 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 ! Normal VLBI station VERA station reference atmosphere Target source 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 Parallax measurement target accuracy : 10 micro-arcsec ! 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 SIM space opt ～2009 10 μas or higher 10^4 GAIA ～2012 10 μas 10^9 JASMINE IR 2013 ? 10^8 VERA VLBI radio 2004 10^3

Target source : masers H2O maser (22GHz) SiO masers (43GHz) Maser from outflow in SFR H2O maser (22GHz) SiO masers (43GHz) 　　Star Forming Regions (H2O) 　　AGB stars (H2O, SiO) distribution of H2O maser sources 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 メーザーの固有運動と視線速度を利用 10000 AU 3000 AU W49N : D = 11.5 +/- 1.5 kpc Gwinn et al. (1992) OH 43.8-0.1 with VERA D = 2.8 +/- 0.5 kpc Honma et al. (2005) Vflow ~ 200 km/s Vflow ~ 8 km/s

W49N - OH43.8-0.1 pair W49N Milky Way in summer 2 mas OH43