High-Precision Astrometry of the S5 polarcap sources

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)

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

GLOBAL HIGH-PRECISION ASTROMETRY


We can study astrometric variations in time and/or frequency

Epoch 1 Epoch 2



astrometric variations in time and/or frequency







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

PHASE-DELAY ASTROMETRY

• Relative separation determination by means of least squares fits:

• Homogeneous sampling of all sources at different frequencies.

2

2T n

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

The Fitting Model

30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)

0-300 ps

(t) =

+ str (,t) +


instrum (t)

geo (t) +

1 ps/s

TECTONICS, T

IDES,

AND RELATIV

ISTIC

MODELS

The Fitting Model

30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)

0-300 ps

(t) =

+ str (,t) +


instrum (t)

geo (t) +

1 ps/s

TECTONICS, T

IDES,

AND RELATIV

ISTIC

MODELS

METEOROLOGY

MEASUREM

ENTS

The Fitting Model

30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)

0-300 ps

(t) =

+ str (,t) +


instrum (t)

geo (t) +

1 ps/s

TECTONICS, T

IDES,

AND RELATIV

ISTIC

MODELS

METEOROLOGY

MEASUREM

ENTS

GPS (IONEX T

ABLES)

The Fitting Model

30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)

0-300 ps

(t) =

+ str (,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

The Fitting Model

30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)

0-300 ps

(t) =

+ str (,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 Model

30 ms 5-9 ns (E=90º) 0.1-3 ns (E=90º)

0-300 ps

(t) =

+ str (,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

• 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

-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

Phase closures should be NULL for point-like sources,

or for observables from which we extract all the

source structure information.

Check Phase Closures

Phase closures should be NULL for point-like sources,

or for observables from which we extract all the

source structure information.

Check Phase Closures

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.

(Simulations)

Baselines:

Closures:

Corrected baselines:

Automatic Phase Connector

Antenna-based corrections:

Antenna-based corrections:

Antenna: OV

Source: 04

Nº of ambs: +1

The phase connection completed (undifferenced):

The phase connection completed (undifferenced):

The phase connection completed (differenced):

When things are not as expected...


Baselines with SC

Weather dependent...

Residual delay rate (ps/s)


The phase connection completed (differenced):

Triangles = RA uncertaintiesSquares = Dec uncertainties

Relative Position Uncertainty

Relative Position Uncertainty

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

15 GHz

Some ResultsAstrometry of 0212+735


43 GHz

15 GHz



Ros et al. 2000


Ros et al. 2000

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

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


C1985.8

X2004.53

X2001.09

X1991.89

X1988.83Q1999.01

Q2004.62

K1999.57

K2000.46

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


C1985.8

X2004.53

X2001.09

X1991.89

X1988.83Q1999.01

Q2004.62

K1999.57

K2000.46

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


C1985.8

X2004.53

X2001.09

X1991.89

X1988.83Q1999.01

Q2004.62

K1999.57

K2000.46

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


C1985.8

X2004.53

X2001.09

X1991.89

X1988.83Q1999.01

Q2004.62

K1999.57

K2000.46

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

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

• 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

Documents

High-Precision Astrometry of the S5 polarcap sources