WFPC2 1-Gyro Test Results
Matt McMaster
Marco Sirianni
1
The Test
•
Program 11077 was initially designed for ACS/HRC using the TGM original
program test as a template.
•
11077 was converted to WFPC2/PC by Matt McMaster maintaining an
observational strategy very close to the original.
•
Attention was focused on the PC because the undersampling was less
severe than for the WFs WFPC2/PC 0.46 mas (ACS/HRC 0.26 mas)
•
The program consisted of multiple exposures of two rich star clusters: NGC
5904 and NGC 6341.
•
Two sets of observation were taken, one on Jan 29 in 2-gyro mode and the
other on Jan 31 in 1-gyro mode.
Target
RA (2000)
Dec (2000)
Guide Star
Brightness
Exptime
(Sec)
Number of
Images
NGC 5904
15 18 28.14
+02 07 9.80
V≈14
10,100,400
28
NGC 6341
17 17 7.05
+43 17 58.25
V≈13 and 14
10,100,400
140
2
The Analysis
• The software developed for the TGM test was modified to be
used with WFPC2 data.
• The FWHM of the PSF for stars with S/N > 10 was calculated
by fitting a gaussian profile to the stellar light profile
– Resulted in tens to hundreds of measurement per image
depending on exposure time and richness of the cluster
• All of the measurements in each image were averaged to
produce a mean PSF for the observation
2-Gyro
1-Gyro
3
Results
PSF FWHM distribution
(unit: PC pixel -all data included)
2- Gyro
Mean
Min
Max
: 1.67 pix ± 0.16
: 1.13
: 1.99
Mean
Min
Max
: 1.65 pix ± 0.14
: 1.09
: 1.89
1- Gyro
The average PSF FWHM is remarkably similar indicating no obvious
degradation in performance in 1-Gyro mode
4
Results – (cont.)
As done for the TGM test, the dependence of the FWHM
on exposure time, guide star brightness, and position on
the sky was analyzed:
Guide Star Brightness (Mag)
V=12.91
V=13.86
There is no difference
between images taken
with a V=13 and V=14
guide star
There are small
differences in the PSF
width due to the
exposure time duration.
10 sec
1 - gyro
2 - gyro
FWHM
1.63
1.65
s
100 sec
1 - gyro
2 - gyro
FWHM
1.71
1.70
s
400 sec
1 - gyro
2 - gyro
FWHM
1.82
1.85
s
Average
1 - gyro
2 - gyro
FWHM
1.68
1.70
s
5
0.01
0.01
FWHM
s
1.62 0.01
1.67 0.01
0.01
0.01
FWHM
s
1.69 0.01
1.70 0.01
0.02
0.04
FWHM
s
1.82 0.03
1.86 0.03
0.01
0.02
FWHM
s
1.68 0.02
1.72 0.02
Data from NGC 6341 only
Results - (cont.)
2 – GYRO
Exptime
FWHM
10 sec
100 sec
400 sec
1.66 ± 0.03
1.70 ± 0.03
1.85 ± 0.04
1 – GYRO
Exptime
FWHM
10 sec
100 sec
400 sec
1.63 ± 0.02
1.70 ± 0.04
1.82 ± 0.05
Such differences were also noted during the original 2-Gyro on orbit
verification test with the ACS/HRC.
6
Results – (Cont.)
The average PSF width in NGC 5904 data is systematically
smaller than in NGC 6341, but there is no dependency on the
gyro guiding configuration.
Target
1 Gyro
2 Gyro
NGC 5904
1.41 ±0.04
1.46 ±0.07
NGC 6341
1.68 ±0.01
1.71 ±0.01
A similar result was found for the clusters observed in the
original 2-gyro on-orbit test with HRC
7
Conclusions
There is no evidence that
the quality of the science
data obtained in 1-gyro
mode is any worse than
in 2-gyro mode.
NGC 6341 /PC
1-Gyro mode
F555W -100 sec
8