1. (National Astronomical Observatory of Japan)
VERA project
Mareki Honma
(National Astronomical Observatory of Japan)
Hokkaido Univ.

2. 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

3. 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

4. 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

5. 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

7. VERA array 4 x 20m radio telescopes Completed in 2002 Iriki Mizusawa
Ishigaki
Ogasawara
Max baseline : 2300 km

8. 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

9. Dual-beam receiving system
Dual-beam platform
(Max. beam separation : 2.2 deg)
dual-beam receivers
(22GHz & 43GHz band receives)

10. 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)

11. 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

12. 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

13. 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

14. 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

15. 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)

16. 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 with VLBA

17. Gamma-ray burst Gamma-ray burst origin ： Super Nova relativistic jet
(→　super-luminal motion expected)
GRB detected with VERA

18. VERA Ishigaki-jima station
Radio telescope
in sub-tropical island

19. 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= / from VLBI astrometry
(with accuracy of 1 mas)
Expected improvement by order of 2 (accuracy 1 mas to 10 micro-as)

20. 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 = /- 1.5 kpc
Gwinn et al. (1992)
OH with VERA
D = 2.8 +/- 0.5 kpc
Honma et al. (2005)
Vflow ~ 200 km/s
Vflow ~ 8 km/s

21. W49N - OH pair
W49N
Milky Way in summer
2 mas
OH43