VERA project
description
Transcript of VERA project
VERA project
H.Kobayashi
NAOJ,VERA project
VLBA 10th Anniversary Conference
(Socorro, June 12, 2003)
Project members
13 scientists (NAOJ, Kagoshima Univ.) H.Kobayashi, S.Manabe, N.Kawaguchi, T.Omodaka, K.Shib
ata, O.Kameya, Y.Tamura, M.Honma, K.Hirota, Y.Kanya, T.Jike, H. Ishituka, M.Rijoha
7 technicians T.Miyaji, K.Horiai, S.Kuji, K.Iwadate, K.Satou, H.Sakai, T.
Bushimata
8 graduate students T.Oyama, T.Kurayama, R.Kamohara, H.Suda, S.Sakakibara,
K.Nakashima, R.Shimizu, Y.Che
Scientific goal
Astrometry with 10μarcsec. accuracy between background object and galactic object within 2.2 degree separation Proper motion and parallax measurements
3D map and velocity field of the Galaxy Detailed 3D velocity structure of molecular gas around evolved
stars and star forming regions
Phase referencing to improve sensitivity with long integration
Specifications
Antenna diameter ; 20m Observing bands ; 2GHz, 8GHz,
22GHz 、 43GHz Tape recording rate ; 1Gbps 2 beam system for phase referencing Path error between 2 beam; 100μm
Construction of the antenna
Panel adjustment Surface accuracy
0.15mm rms Panel; 0.1 mm rms Panel adjustment; 0.1 m
m rms Sub ref.: 0.03mm rms
Cooled HEMT receiver
Trx = 60 K @ 22GHz
40K@22GHz
Trx=130K @ 43GHz
70K@43GHz
Discrete HEMT MMIC HEMT
Radiator on the antenna surface
Noise source on the dish Symmetric distribution of
4 noise sources Instrumental phase error is
estimated by the average of 4.
Instrumental phase correction
Phase difference of surface radiator between 2 beams
Less than 1degree measurement accuracy is achieved
2B phase response from surface radiator depend on beam separation
First phase variations between 2 beams
Fringe phase of W49N,OH43 and difference
Allan variance of them
Coherence improvement
Coherence drop of 1B and 2B fringe
Fringe detection with 20 min. integration, GRB030329
Geodesy observations
Combine with the world coordinate by SX observations Combined with Tsukuba 32m of Japanese GSI
Baseline determination Required accuracy 2mm 22GHz wideband observations SX conventional observations
1Gbps recorder & correlation
•SONY DIR2000 1024Mbps
80 min/tape
•Mitaka FX correlator
5 station correlation with 1Gbps
Output to CODA system
Convert correlation data to FITS
Test observations
Phase referencing check 22GHz
SgrB2-SgrA*, W51N, W49N, Orion-KL, W3OHVX-Sgr, VY-CMa, etc
43GHzOrion-KL
Fringe check and calibrators Strong H2O masers (>20Jy), Calibrator candidates
Improvement of sensitivity 22GHz
Before improvement
After improvement
Atmospheric loss τ=0.2 66K τ=0.2 66K
Ground coupling 25K 25K
Fee dome loss -0.6 dB 54K -0.1dB 9K
Receiver 80K 112K 40K 50K
System noise Tsys* 232K 155K
Improvement of sensitivity 43 GHz
Before improvement
After improvement
Atmospheric loss τ=0.15 49K τ=0.15 49K
Ground coupling 29K 29K
Fee dome loss -1 dB 90K -0.15dB 12K
Receiver 130K 190K 70K 84K
System noise Tsys* 358K 174K
Expected sensitivity 1
22GHz 43GHz
separation 0 deg. 2 deg. 0 deg. 2 deg.
Antenna aperture eff.
50%* 48% 45% 36%
Tsys 150 K 150 K 180 K 180 K
* Measured value
Expected Sensitivity 2
22GHz 22GHz 43GHz 43GHz
Continum Maser Continum Maser
Integ. Time
100 3600 100 3600
7σ
Sensitivity
0.1 Jy 1.2 Jy 0.25 Jy 1.9Jy
Integ. Time
3600 100 3600 100
7σ
Sensitivity
0.02 Jy 7.2 Jy 0.04 Jy 11.4Jy
Plan of VERA
2002 : Fringe detection / 2B fringe test
2003: Feasibility check of 2B interferometer
Test observations for astrometry
2004: Test observations for astrometry
Improvement of system sensitivity
2005: Complete