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Transcript
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