VSOP2 Astrometry: Astrometric Accuracy Made with Phase Referencing

1
VSOP-2 Astrometry Astrometric Accuracy Made with
Phase Referencing

• Yoshiharu Asaki (ISAS)
• (VSOP-2 Symposium, Dec 3-7, 2007)

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Outline

• Background
• VLBI Observation Simulation Software
• VSOP-2 Phase Referencing Simulations
• Astrometric Accuracy
• Calibrator Candidate
• Comments

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Background
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VLBI Phase Referencing Astrometry Era
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Galactic Water Maser Source, S Per
Asaki et al., IAUS-242, 2007
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Galactic Water Maser Source S Per(relative
position to a continuum source, KR 143)
Asaki et al., IAUS-242, 2007
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Galactic Water Maser Source S Per(relative
position to a continuum source, KR 143)
Asaki et al., IAUS-242, 2007
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S Per Annual Parallax 0.399 0.014
mas?Distance2.51 0.09 kpc
Asaki et al., IAUS-242, 2007
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VERA VLBI Phase Referencing Astrometry
(Oral talk given by M. Honma, and several poster
presentations downstairs)
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VSOP-2Phase Referencing
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VLBI Observation Simulation Software
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Simulation Investigations for VLBI Phase
Referencing Astrometry

• Pradel et al. 2006, AAp, 452, 1099
• VLBA, EVN, VLBAEVN
• Asaki et al. 2007, PASJ, 59, 397
• VSOP-2

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Astronomical Radio Interferometer Simulator (ARIS)

• VLBI Phase Referencing Simulation
• Error sources
• Space-VLBI Observation Simulations
• Orbit determination (OD) errors
• Attitude control errors
• Operation satellite tracking schedule

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Simulated Fringe with ARIS
Before Phase Referencing
After Phase Referencing
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Characteristic Phase Errors related to ASTRO-G

• Pointing Error
• Attitude error and telescope optics design
• Antenna Position Error
• Orbit determination (OD)

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Delay Error Related to the Attitude
Wave Front
Right Attitude
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Delay Error due to the Attitude Error
Wave Front
Right Attitude
Pointing Error
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Delay Error due to the Attitude Error
Wave Front
Right Attitude
Pointing Error
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Attitude Error ? Delay Error

• Specification of Pointing Requirement lt 5/1000
  

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Attitude Error ? Delay Error

• Specification of Pointing Requirement lt 5/1000

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OD Error Model
cross track
True Trajectory
along track
OD
radial
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OD Error Model

• Tracking Stations
• Red ISAS, Usuda
• Yellowish green NRAO, Green Bank
• Blue DSN, Robled
• Light blue DSN, Tid
• Pink DSN, Goldstone
• Arrow Displacement vector of the satellite
  position.

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OD Error Model for ASTRO-G(Typical Profile)
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OD Error Model for ASTRO-G(Typical Profile)
Apogee
Apogee
Perigee
Perigee
Perigee
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Before Phase Referencing(Pointing Error OD
Error)
Observation Frequency 43GHz Pointing Error (3s)
5/1000 OD Error 4cm at apogee, 1cm at
perigee
Target Calibrator
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After Phase Referencing(Pointing Error OD
Error)
Observation Frequency 43GHz Pointing Error (3s)
5/1000 OD Error 4cm at apogee, 1cm at
perigee
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VSOP-2 Phase Referencing Simulations
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Simulation Conditions

• Array
• VLBA (NRAO) ASTRO-G
• GRTs lowest elevation 20 deg
• Switching Cycle Time 60 sec
• Observation Time
• 15 hours (2 orbital periods of ASTRO-G)
• Target Calibrator
• Point sources
• Total Flux Density 1 Jy
• Declination 59
• Tropospheric Turbulence
• Stable condition for 43-GHz observations
• Typical condition for 22- and 8-GHz observations

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Simulation Conditions

• Array
• VLBA (NRAO) ASTRO-G
• GRTs lowest elevation 20 deg
• Switching Cycle Time 60 sec
• Observation Time
• 15 hours (2 orbital periods of ASTRO-G)
• Target Calibrator
• Point sources
• Total Flux Density 1 Jy
• Declination 59
• Tropospheric Turbulence
• Stable condition for 43-GHz observations
• Typical condition for 22- and 8-GHz observations

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Simulation Conditions

• Array
• VLBA (NRAO) ASTRO-G
• GRTs lowest elevation 20 deg
• Switching Cycle Time 60 sec
• Observation Time
• 15 hours (2 orbital periods of ASTRO-G)
• Target Calibrator
• Point sources
• Total Flux Density 1 Jy
• Declination 59
• Tropospheric Turbulence
• Stable condition for 43-GHz observations
• Typical condition for 22- and 8-GHz observations

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Simulation Conditions

• Array
• VLBA (NRAO) ASTRO-G
• GRTs lowest elevation 20 deg
• Switching Cycle Time 60 sec
• Observation Time
• 15 hours (2 orbital periods of ASTRO-G)
• Target Calibrator
• Point sources
• Total Flux Density 1 Jy
• Declination 59
• Tropospheric Turbulence
• Stable condition for 43-GHz observations
• Typical condition for 22- and 8-GHz observations

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Simulation Conditions

• Array
• VLBA (NRAO) ASTRO-G
• GRTs lowest elevation 20 deg
• Switching Cycle Time 60 sec
• Observation Time
• 15 hours (2 orbital periods of ASTRO-G)
• Target Calibrator
• Point sources
• Total Flux Density 1 Jy
• Declination 59
• Tropospheric Turbulence
• Stable condition for 43-GHz observations
• Typical condition for 22- and 8-GHz observations

Not Included
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ON-source Time for ASTRO-G and the VLBA
VLBA
ASTRO-G
VLBA
2 separation 60-s switching cycle
ASTRO-G
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Typical (u, v) Coverage(2 pair, 43 GHz)
Target Calibrator
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ARIS AIPSImaging Simulations
0.5 separation 2-cm OD Error

• ARIS (Fringe Generation)
• Phase Referencing
• FITS-IDI save
• AIPS (Image Synthesis)
• FITS-IDI load
• No Calibration
• CLEAN

Synthesized Image with AIPS ?
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ARIS AIPSImaging Simulations
0.5 separation 2-cm OD Error

• ARIS (Fringe Generation)
• Phase Referencing
• FITS-IDI save
• AIPS (Image Synthesis)
• FITS-IDI load
• No Calibration
• CLEAN

Synthesized Image with AIPS ?
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Astromertric Accuracyin this study
Synthesized Image
Astrometric Accuracy E ( r )
r
Declination
The point source model position
The brightest position of a synthesized image
Right Ascension
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OD Error Tropospheric EPL Bias Error
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OD Error (apogee) 2cm, 4cm, 8cm, 16cm, 32cm
EPL Bias Error 4cm (1s)
8GHz
22GHz
43GHz
VLBA
EPL Bias Error 2cm (1s)
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Q-band CLEAN Image
Q-band CLEAN Image (no VLBI error, no noise)
VLBA
ASTRO-G VLBA
Model
15-hour observation with the VLBA
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Q-band CLEAN Image
Q-band CLEAN Image (no VLBI error, no noise)
VLBA
ASTRO-G VLBA
15-hour observation with the VLBA
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Required calibrator flux density

• Image coherence loss as a function of SNR of a
  single calibrator ON-source duration
• SNR5 coherence loss of less than 2
• SNR4 coherence loss of 2-4
• SNR3 coherence loss of about 10
• Required calibrator flux density for SNR of 4
  (with a VLBA antenna, ON-source duration of 20 s,
  and BW of 256MHz)
• 8.4 GHz 63 mJy
• 22GHz 84 mJy
• 43GHz 154 mJy

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VCS (VLBA Calibrator Survey)

• Catalogues VCS1, VCS2, VCS3, VCS4, VCS5, and
  2005f_astro.
• UV FITS files and text catalogue file are
  available via internet
• http//vlbi.gsfc.nasa.gov/solutions/2005f_astro/
• http//www.vlba.nrao.edu/astro/calib/vlbaCalib.txt
  
• Sizes and strengths of the VCS sources are
  estimated by Gaussian fitting.

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Basic Ideas to Estimate Flux Densities at 8.4,
22, 43 GHz with a Space Baseline

• F F0(?) exp-2(pD?s(?))2
• Flux density F0(?) ??-a
• Size s(?) ??-ß

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Basic Ideas to Estimate Flux Densities at 8.4,
22, 43 GHz with a Space Baseline

• F F0(?) exp-2(pD?s(?))2
• Flux density F0(?) ??-a
• a log(Fx)-log(Fs) / log(?s)-log(?x)
• ? explog(Fx)log(?s)-log(Fs)log(?x) /
  log(?s)-log(?x)
• Size s(?) ??-ß
• ß log(sx)-log(ss) / log(?s)-log(?x)
• ? explog(sx)log(?s)-log(ss)log(?x) /
  log(?s)-log(?x)
• If ss0 or sx0, s(?)sx.

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Examples of the Gaussian Fitting(J10330711)
X-band
S-band
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Calibrator Candidate Distribution Estimated from
the VCS
8.4GHz gt 60 mJy 22GHz gt 80 mJy 43GHz
gt 150 mJy
8.4GHz lt 5 22GHz lt 3 43GHz
lt 2
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VCS Monte Carlo Simulation(Northern Sky)
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Comments
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Comments 1/3

• VLBI Phase Referencing Astrometry Simulations
• ARIS AIPS
• Characteristic Space-VLBI Phase Errors with
  ASTRO-G
• Attitude error (pointing error)
• OD error ? baseline vector error

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Comments 2/3

• VSOP-2 astrometry will be twice or more accurate
  than astrometric observations with ground VLBI
  arrays for a complete point target
• With less than 10-cm OD accuracy
• With effective atmospheric EPL errors

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Comments 3/3

• A careful preparation will be needed for each
  target especially at 22 and 43 GHz in terms of
  the calibrator.