1. 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)

2. 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

3. 3

4. GLOBAL HIGH-PRECISION ASTROMETRY

5. GLOBAL HIGH-PRECISION ASTROMETRY

6. GLOBAL HIGH-PRECISION ASTROMETRY
Epoch 1
Epoch 2
We can study astrometric variations in time and/or frequency

7. GLOBAL HIGH-PRECISION ASTROMETRY
astrometric variations in time and/or frequency

8. GLOBAL HIGH-PRECISION ASTROMETRY
astrometric variations in time and/or frequency

9. GLOBAL HIGH-PRECISION ASTROMETRY
astrometric variations in time and/or frequency

10. GLOBAL HIGH-PRECISION ASTROMETRY
astrometric variations in time and/or frequency

11. VLBA OBSERVATIONS Epoch Frequency (GHz) 8.4 15.4 43 1997.93  1999.41           11

12. PHASE-DELAY ASTROMETRY
Relative separation determination by means of least squares fits:
Homogeneous sampling of all sources at different frequencies.

13. The Fitting Model  (t) = + str (,t) + trop (E(t)) +
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 13

14. The Fitting Model  (t) = + str (,t) + trop (E(t)) +
TECTONICS, TIDES,
AND RELATIVISTIC
MODELS
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 14

15. The Fitting Model  (t) = + str (,t) + trop (E(t)) +
TECTONICS, TIDES,
AND RELATIVISTIC
MODELS
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
METEOROLOGY
MEASUREMENTS 15

16. The Fitting Model  (t) = + str (,t) + trop (E(t)) +
TECTONICS, TIDES,
AND RELATIVISTIC
MODELS
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
GPS (IONEX TABLES)
METEOROLOGY
MEASUREMENTS 16

17. The Fitting Model  (t) = + str (,t) + trop (E(t)) +
TECTONICS, TIDES,
AND RELATIVISTIC
MODELS
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
GPS (IONEX TABLES)
METEOROLOGY
MEASUREMENTS
MAPS OF
RADIOSOURCES 17

18. The Fitting Model  (t) = + str (,t) + trop (E(t)) +
TECTONICS, TIDES,
AND RELATIVISTIC
MODELS
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
GPS (IONEX TABLES)
METEOROLOGY
MEASUREMENTS
MAPS OF
RADIOSOURCES
WLSF ESTIMATE 18

19. The Fitting Model The Fitting Software
TECTONICS, TIDES,
AND RELATIVISTIC
MODELS
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
GPS (IONEX TABLES)
METEOROLOGY
MEASUREMENTS
MAPS OF
RADIOSOURCES
WLSF ESTIMATE
The Fitting Software
Geometric model and fitting procedures computed with the University of Valencia Precision Astrometry Package (UVPAP):
- Possibility of multisource differential astrometry 19

20. The Fitting Strategy
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).

21. EPOCH 2000.46, 15GHz PHASE-CONNECTION -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

23. Check Phase Closures
Phase closures should be NULL for point-like sources, or for observables from which we extract all the source structure information.

24. Check Phase Closures
Phase closures should be NULL for point-like sources, or for observables from which we extract all the source structure information. 24

25. Automatic Phase Connector
The Algorithm:
- For a given scan:
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.
Applies the set of corrections found for the actual scan to the next scan,
before it computes the closures of that new scan.

26. Automatic Phase Connector
(Simulations)
Baselines:
Corrected baselines:
Closures:

31. Antenna-based corrections:

32. Antenna-based corrections:
Antenna: OV
Source: 04
Nº of ambs: +1 32

33. The phase connection completed (undifferenced):

34. The phase connection completed (undifferenced):34

35. The phase connection completed (differenced):35

36. When things are not as expected...

37. When things are not as expected...
Residual delay rate (ps/s)
Baselines with SC
Weather dependent...

38. When things are not as expected...

39. The phase connection completed (differenced):39

40. Relative Position Uncertainty
Triangles = RA uncertainties
Squares = Dec uncertainties

41. Relative Position Uncertainty

42. 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:
278as in RA
170as in DEC

43. Some Results
Astrometry of
15 GHz

44. Some Results
Astrometry of
15 GHz
43 GHz

45. Some Results
Astrometry of

46. Some Results
Astrometry of
Ros et al. 2000

47. Some Results
Astrometry of
Ros et al. 2000

48. Results:1928+738 time series Q1999.01 X1988.83 K1999.57 X1991.89
43 GHz
15.4 GHz
8.4 GHz Q X K X K X Q
C1985.8 X

49. Results:1928+738 time series Q1999.01 X1988.83 K1999.57 X1991.89
43 GHz
15.4 GHz
8.4 GHz Q X K X K X Q
C1985.8 X

50. Results:1928+738 time series Q1999.01 X1988.83 K1999.57 X1991.89
43 GHz
15.4 GHz
8.4 GHz Q X K X K X Q
C1985.8 X

51. Results:1928+738 time series Q1999.01 X1988.83 K1999.57 X1991.89
43 GHz
15.4 GHz
8.4 GHz Q X K X K X Q
C1985.8 X

52. Results:1928+738 time series Q1999.01 X1988.83 K1999.57 X1991.89
43 GHz
15.4 GHz
8.4 GHz Q X K X K X Q
C1985.8 X

53. Some results: opacity effects
8.4/43 GHz astrometry for
+ 43 GHz
+ 8.4 GHz + +
8.4 GHz
8.4 GHz
43GHz
 = mas
 = 0.45 mas

54. Some results: opacity effects
8.4/43 GHz astrometry for
+ 43 GHz
+ 8.4 GHz + +
8.4 GHz
8.4 GHz
43GHz
 = 0.23 mas
 = 0.14 mas

55. Conclusions
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 55