East Asian VLBI activities

VERA&

JVN

KVN

CVN

VSOP/VSOP2

Parallax measurements of H2O maser source beyond 5 kpc with VERA

Mizusawa-VERA observatory, NAOJ

Mareki Honma & VERA project member

Contents

Based on astrometry of S269 (at ~5kpc), we present the results on

• Parallax

• Proper motions

• Galactc rotation velocity at S269

Star Forming Region S269S269 : Massive SFR toward anti-center regions

Near-IR view of S269

VERA array

Ishigaki-jima Ogasawara

Iriki

Mizusawa

Max. baseline : 2300 km

2004~ observations started

VERA : VLBI array dedicated to astrometrynew technology : dual-beam phase referencing

S269 H2O maser

• Intensity 　 200 Jy

• Reference ： J0613+1305,

(0.7 deg separation)

0.4 mas linear structure with velocity gradient

Accretion disk around YSO ?

Cross-power spectrum

posi

tion

Parallax measurement

• Motions of S269 H2O maser

East-West motion for 1 yr

π ： 189 +/-16 μas D ： 5.30 +/- 0.44 kpc

World record for smallest parallax !

1yr

North-South motion for 1 yr

S269 in the Milky Way

• S269

　　 ～ 5.3 kpc

c.f. R0 ~ 8 kpc

Ready to perform Galaxy-scale astrometry

Sun

~30 kpc

S 269 proper motion

S269 motion with respect to LSR

(V_l, V_b) = (-4.6, -4.1) km/s

much smaller than galactic

rotation (c.f. ~200 km/s)

> similar galactic rotation

velocity at the Sun and at

S269

Galactic rotation velocity at S269

• Rotation velocity

determination from V_l

obs. V_l = -5 +/-5 km/s

Vc_S269 /Vc_sun =

1.00 +/- 0.03

(accuracy 3% ！ )

• Radial velocity is consistent

with the above results

Tangential vel.

Radial vel.

Vc_S269 /Vc_Sun

Vr

, V_l

Constraint on the rotation curve

• Strong constraint from one objects

Flat rotation curve out to 13 kpc

Summary

• We have successfully measured the parallax and proper motions of S269 with VERA.

• Galactic rotation velocity at S269 is the same to that at LSR within 3%.

> Strong constraint on outer rotation curve

　 --- 　 these results demonstrate power of high-precision astrometry !

Announcement

• VERA will be open to international use from this observational season (2006/07)

• Dual-beam mode at 22 GHz will be open.

• Call for proposal will be in Oct 2006, and deadline will be the end of October.

--- If you are interested, please contact us !