High-Precision Astrometry of the S5 polarcap sources
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Transcript of High-Precision Astrometry of the S5 polarcap sources
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High-Precision Astrometry of the S5
polarcap sources
Jose C. Guirado (Univ. Valencia)
&
J.M. Marcaide (UV), I. Martí-Vidal (MPIfR), S. Jiménez (UV),
E. Ros (UV)
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The S5 Polar Cap Sample
• Studied in MPIfR since 80s (Eckart et al., 1987, Witzel et al., 1988, etc.)
• Flat spectrum Radiosources:
• 8 QSOs • 5 BL-Lac objects
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GLOBAL HIGH-PRECISION ASTROMETRY
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GLOBAL HIGH-PRECISION ASTROMETRY
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We can study astrometric variations in time and/or frequency
Epoch 1 Epoch 2
GLOBAL HIGH-PRECISION ASTROMETRY
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GLOBAL HIGH-PRECISION ASTROMETRY
astrometric variations in time and/or frequency
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GLOBAL HIGH-PRECISION ASTROMETRY
astrometric variations in time and/or frequency
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GLOBAL HIGH-PRECISION ASTROMETRY
astrometric variations in time and/or frequency
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GLOBAL HIGH-PRECISION ASTROMETRY
astrometric variations in time and/or frequency
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VLBA OBSERVATIONS
2004.62
2005.45
2004.53
2001.71
2001.09
2001.04
2000.46
1999.57
1999.41
1997.93
4315.48.4
Frequency (GHz)Epoch
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PHASE-DELAY ASTROMETRY
• Relative separation determination by means of least squares fits:
• Homogeneous sampling of all sources at different frequencies.
2
2T n
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The Fitting Model
30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)
0-300 ps
(t) =
+ str (,t) +
trop (E(t)) + ion (,E(t)) +
instrum (t)
geo (t) +
1 ps/s
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The Fitting Model
30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)
0-300 ps
(t) =
+ str (,t) +
trop (E(t)) + ion (,E(t)) +
instrum (t)
geo (t) +
1 ps/s
TECTONICS, T
IDES,
AND RELATIV
ISTIC
MODELS
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The Fitting Model
30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)
0-300 ps
(t) =
+ str (,t) +
trop (E(t)) + ion (,E(t)) +
instrum (t)
geo (t) +
1 ps/s
TECTONICS, T
IDES,
AND RELATIV
ISTIC
MODELS
METEOROLOGY
MEASUREM
ENTS
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The Fitting Model
30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)
0-300 ps
(t) =
+ str (,t) +
trop (E(t)) + ion (,E(t)) +
instrum (t)
geo (t) +
1 ps/s
TECTONICS, T
IDES,
AND RELATIV
ISTIC
MODELS
METEOROLOGY
MEASUREM
ENTS
GPS (IONEX T
ABLES)
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The Fitting Model
30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)
0-300 ps
(t) =
+ str (,t) +
trop (E(t)) + ion (,E(t)) +
instrum (t)
geo (t) +
1 ps/s
TECTONICS, T
IDES,
AND RELATIV
ISTIC
MODELS
METEOROLOGY
MEASUREM
ENTS
GPS (IONEX T
ABLES)
MAPS O
F
RADIOSOURCES
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The Fitting Model
30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)
0-300 ps
(t) =
+ str (,t) +
trop (E(t)) + ion (,E(t)) +
instrum (t)
geo (t) +
1 ps/s
TECTONICS, T
IDES,
AND RELATIV
ISTIC
MODELS
METEOROLOGY
MEASUREM
ENTS
GPS (IONEX T
ABLES)
MAPS O
F
RADIOSOURCES
WLSF E
STIMATE
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The Fitting Model
30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)
0-300 ps
(t) =
+ str (,t) +
trop (E(t)) + ion (,E(t)) +
instrum (t)
geo (t) +
1 ps/s
TECTONICS, T
IDES,
AND RELATIV
ISTIC
MODELS
METEOROLOGY
MEASUREM
ENTS
GPS (IONEX T
ABLES)
MAPS O
F
RADIOSOURCES
WLSF E
STIMATE
The Fitting Software• Geometric model and fitting procedures computed with the University of
Valencia Precision Astrometry Package (UVPAP):
- Possibility of multisource differential astrometry
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• Find a preliminary model by fitting the clock drifts and the atmospheric zenith delays to the GROUP DELAY data.
• Use the resulting model to estimate the phase ambiguities of the PHASE DELAY (pre-connection).
• Refine the phase connection and perform the astrometric analysis (check the quality of the differential observables).
The Fitting Strategy
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-Time between obs. ~ 120 s-2 cycle at 15 GHz ~ 65 ps
THUS,
-Residual rates should be lower than
33ps/120ps ~ 0.3 ps/s
EPOCH 2000.46, 15GHz
PHASE-CONNECTION
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Phase closures should be NULL for point-like sources,
or for observables from which we extract all the
source structure information.
Check Phase Closures
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Phase closures should be NULL for point-like sources,
or for observables from which we extract all the
source structure information.
Check Phase Closures
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Automatic Phase Connector
• Finds which baseline appears more times in the set of non-zero closures.
• Adds and subtracts 1 phase cycle to the delay of that baseline. Computes the score corresponding to each of these corrections:
score = (# of closures moved closer to 0) – (# of closures moved away from zero).
• The highest score will determine which correction is applied definitely.
• Recomputes the closures and repeats the previous steps until all closures are zero.
The Algorithm:- For a given scan:
Applies the set of corrections found for the actual scan to the next scan, before it computes the closures of that new scan.
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(Simulations)
Baselines:
Closures:
Corrected baselines:
Automatic Phase Connector
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Antenna-based corrections:
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Antenna-based corrections:
Antenna: OV
Source: 04
Nº of ambs: +1
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The phase connection completed (undifferenced):
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The phase connection completed (undifferenced):
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The phase connection completed (differenced):
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When things are not as expected...
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When things are not as expected...
Baselines with SC
Weather dependent...
Residual delay rate (ps/s)
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When things are not as expected...
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The phase connection completed (differenced):
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Triangles = RA uncertaintiesSquares = Dec uncertainties
Relative Position Uncertainty
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Relative Position Uncertainty
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Results: differential positions
We find some large corrections of the relative sources coordinates with respect to the ICRF positions. Nevertheless, our astrometric results are not directly comparable to the ICRF:
-Our astrometric corrections are defined with respect to the “phase centers” of the maps. Our astrometry considers, then, the structures of the sources.
-Source opacity effects could be present while comparing the source positions observed at 15GHz and 8.4/2.3 GHz
-Mean corrections are:
278as in RA
170as in DEC
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15 GHz
Some ResultsAstrometry of 0212+735
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Some ResultsAstrometry of 0212+735
43 GHz
15 GHz
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Some ResultsAstrometry of 1928+738
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Some ResultsAstrometry of 1928+738
Ros et al. 2000
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Some ResultsAstrometry of 1928+738
Ros et al. 2000
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1928+738
-0,8
-0,6
-0,4
-0,2
0
0,2
0,4
0,6
0,8
1
-0,8-0,6-0,4-0,200,20,40,6
RA
DE
C
43 GHz
15.4 GHz
8.4 GHz
Results:1928+738 time series
C1985.8
X2004.53
X2001.09
X1991.89
X1988.83Q1999.01
Q2004.62
K1999.57
K2000.46
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1928+738
-0,8
-0,6
-0,4
-0,2
0
0,2
0,4
0,6
0,8
1
-0,8-0,6-0,4-0,200,20,40,6
RA
DE
C
43 GHz
15.4 GHz
8.4 GHz
Results:1928+738 time series
C1985.8
X2004.53
X2001.09
X1991.89
X1988.83Q1999.01
Q2004.62
K1999.57
K2000.46
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1928+738
-0,8
-0,6
-0,4
-0,2
0
0,2
0,4
0,6
0,8
1
-0,8-0,6-0,4-0,200,20,40,6
RA
DE
C
43 GHz
15.4 GHz
8.4 GHz
Results:1928+738 time series
C1985.8
X2004.53
X2001.09
X1991.89
X1988.83Q1999.01
Q2004.62
K1999.57
K2000.46
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1928+738
-0,8
-0,6
-0,4
-0,2
0
0,2
0,4
0,6
0,8
1
-0,8-0,6-0,4-0,200,20,40,6
RA
DE
C
43 GHz
15.4 GHz
8.4 GHz
Results:1928+738 time series
C1985.8
X2004.53
X2001.09
X1991.89
X1988.83Q1999.01
Q2004.62
K1999.57
K2000.46
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1928+738
-0,8
-0,6
-0,4
-0,2
0
0,2
0,4
0,6
0,8
1
-0,8-0,6-0,4-0,200,20,40,6
RA
DE
C
43 GHz
15.4 GHz
8.4 GHz
Results:1928+738 time series
C1985.8
X2004.53
X2001.09
X1991.89
X1988.83Q1999.01
Q2004.62
K1999.57
K2000.46
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Some results: opacity effects8.4/43 GHz astrometry for 1928+738
+ 43 GHz
+ 8.4 GHz
8.4 GHz
8.4 GHz
43GHz
++
= - 0.07 mas
= 0.45 mas
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Some results: opacity effects
+ 43 GHz
+ 8.4 GHz
8.4 GHz 43GHz8.4 GHz
8.4/43 GHz astrometry for 1803+784
++
= 0.23 mas
= 0.14 mas
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• We have performed high-precision, wide-angle, astrometry analysis of a radio sample.
• The phase delays have been well connected and we have checked the good quality of differenced delays in the astrometric fit. The use of these observables improves the accuracy of the astrometry by a factor of 2-3 (the main source of uncertainties comes from the modeling of the tropospheric delay). We obtain differential astrometry precisions ranging from ~10 to ~500 mas (depending on source separations), which are ~10 times higher than the precisions achivevable with the phase-reference technique…
• …But, at 15 and 43 GHz the success of the analysis depends much of the weather
• Combination with other epochs provide precise kinematics (where’s the core?)
• Combination with other freqs provide precise spectral information
ConclusionsConclusions