1. Globular Cluster Astrometry
(for fiber-positioning purposes)
Overview
Ata Sarajedini has MOSAIC data of many of our target globular clusters
Ata (et al.) uses IRAF to detect & center stars, and obtain photometry
Ata (et al.) provides (x,y,B,V) data per pointing
My task is to provide precise (a,d) per star
1) “undo” the standard chip metrology & telescope OFAD
2) apply Platais et al. (2002) chip metrology
3) transform to an astrometric system, with OFAD terms
T. Girard
SIM Group Meeting: Nov. 5, 2004 – CfA

2. Globular Cluster Astrometry
(for fiber-positioning purposes)
Current Astrometry-Reduction Status
Cluster Telesc. Frames Status (Ref. Cat.)
M3 0.9-m 3x2 done 12/02 USNO-A2
M5 0.9-m 4x2 completed UCAC2
M m 10x2 completed UCAC2
M m 3x2 completed UCAC2
M55 4-m 5x2 in progress USNO-A2
NGC m 9x2 in progress USNO-A2
M92 4-m 5x2 in limbo USNO-A2(?)
T. Girard
SIM Group Meeting: Nov. 5, 2004 – CfA

3. Globular Cluster Astrometry
(for fiber-positioning purposes)
Chip Metrology: NOAO (Davis) vs Platais
XY File: b1.dat (Davis)
Catalog: m12.ucac2
Tangent (a,d):
Offsets (x,y):
RA solution: Nref/poss = / Nterms = 8 Std Err = E-02
1 X E E (arcsec)
2 Y E E-06
3 const E E-03
4 X*X E E-10
5 X*Y E E-10
6 Y*Y E E-10
11 X*X*X E E-13
14 Y*Y*Y E E-13
XY File: b1i.dat (Platais)
RA solution: Nref/poss = / Nterms = 9 Std Err = E-02
1 X E E (arcsec)
2 Y E E-06
3 const E E-03
4 X*X E E-10
5 X*Y E E-10
6 Y*Y E E-10
12 X*X*Y E E-13
13 X*Y*Y E E-13
14 Y*Y*Y E E-13
T. Girard
SIM Group Meeting: Nov. 5, 2004 – CfA

4. Globular Cluster Astrometry
(for fiber-positioning purposes)
a,d Comparison of Two M3 Pointings: Davis metrology
T. Girard
SIM Group Meeting: Nov. 5, 2004 – CfA

5. Globular Cluster Astrometry
(for fiber-positioning purposes)
a,d Comparison of Two M3 Pointings: Platais metrology
T. Girard
SIM Group Meeting: Nov. 5, 2004 – CfA

6. Globular Cluster Astrometry
(for fiber-positioning purposes)
Reference Catalog: USNO-A2 vs UCAC2 (0.9-m)
Catalog: m12.usno_a2
Tangent (a,d):
Offsets (x,y):
RA solution: Nref/poss = / Nterms = 9 Std Err = E-01
1 X E E (arcsec)
2 Y E E-06
3 const E E-03
4 X*X E E-10
5 X*Y E E-10
6 Y*Y E E-10
12 X*X*Y E E-13
13 X*Y*Y E E-13
14 Y*Y*Y E E-13
Catalog: m12.ucac2
RA solution: Nref/poss = / Nterms = 9 Std Err = E-02
1 X E E (arcsec)
2 Y E E-06
3 const E E-03
4 X*X E E-10
5 X*Y E E-10
6 Y*Y E E-10
12 X*X*Y E E-13
13 X*Y*Y E E-13
14 Y*Y*Y E E-13
T. Girard
SIM Group Meeting: Nov. 5, 2004 – CfA

7. Globular Cluster Astrometry
(for fiber-positioning purposes)
Reference Catalog: USNO-A2 vs UCAC2 (4-m)
Catalog: m55.usno_a2
Tangent (a,d):
Offsets (x,y):
RA solution: Nref/poss = / Nterms = 9 Std Err = E-01
1 X E E (arcsec)
2 Y E E-06
3 const E E-03
4 X*X E E-10
5 X*Y E E-10
6 Y*Y E E-10
12 X*X*Y E E-13
13 X*Y*Y E E-13
14 Y*Y*Y E E-13
Catalog: m55.ucac2
Tangent (a,d):
RA solution: Nref/poss = / Nterms = 8 Std Err = E-02
1 X E E (arcsec)
2 Y E E-06
3 const E E-03
4 X*X E E-09
5 X*Y E E-09
6 Y*Y E E-09
12 X*X*Y E E-13
14 Y*Y*Y E E-13
T. Girard
SIM Group Meeting: Nov. 5, 2004 – CfA

8. Globular Cluster Astrometry
(for fiber-positioning purposes)
Estimated Astrometric Precision...
based on a,d comparisons of two pointings in M3 (0.9-m) is arcsec,
“ “ “ “ “ “ “ “ M12 “ “ arcsec,
but, is a function of magnitude (as one would expect).
The M12 data (0.9-m) indicate a precision of...
0.025 arcsec for B < 16.
T. Girard
SIM Group Meeting: Nov. 5, 2004 – CfA

9. Globular Cluster Astrometry
(for fiber-positioning purposes)
Summary
 Astrometric software/procedures for MOSAIC cluster data are working,
4 clusters are completed, (M3, M5, M12, M13)
 Platais metrology + UCAC2 produces good results for 0.9-m data,
precision is ~ 25 mas for well-measured stars,
~ 40 mas for all stars
 4-m cluster data is still being explored, to determine optimum procedures
T. Girard
SIM Group Meeting: Nov. 5, 2004 – CfA