FGS 2 Dark + Background Count Determination
The FGS 2 Dark and Background counts were determined from a failed acquisition on 2009:229:05:23, two
time segments were examined. This analysis determines the Dark + Background counts, since they cannot be
separated when the FGS is searching in the Field-Of-View. The results are consistent with each other and are
presented in the following Table.
Data Collection
Start Time
05:35:57.215
05:27:26.940
Data Collection
End Time
05:37:24.715
05:33:54.215
XA PMT
(counts)
1.91
1.83
XB PMT
(counts)
3.35
3.33
YA PMT
(counts)
0.63
0.61
YB PMT
(counts)
1.79
1.76
Total PMT
Counts
7.67
7.54
FGS 2 - 15 arcmin x 15 arcmin
Background measurements done at center of FOV, RA = 107.96905 deg, DEC = -26.09807 deg.
The FGS 2 Dark counts were determined from the SM4 Acceptance Test on 2009:138:16:17, while the HST
was still attached to the Shuttle. The results are presented in the following Table. The results are disappointing,
it would appear that some light was leaking into the OTA, while HST was on the Shuttle.
Data Collection
Start Time
16:17:06.444
Data Collection
End Time
16:20:18.144
XA PMT
(counts)
2.66
XB PMT
(counts)
5.25
YA PMT
(counts)
0.26
YB PMT
(counts)
2.15
Total PMT
Counts
10.33
As an alternative to the SM4 AT data, eight data sets from the day 159 and day 160 Astrometry observation sets
were examined. These results are presented in the following Table and agree better with the Dark+Background
measurements presented earlier. Just based on the number of points in each data set, the 3rd data set which has
the maximum number, should be used as the FGS 2 baseline values for this point in time.
Data Collection
Start Time
160:01:44:38.509
160:03:19:29.434
159:15:54:11.458
159:17:33:40.458
160:01:45:57.609
160:03:19:57.584
159:16:05:57.583
159:17:41:57.583
Data Collection
End Time
01:45:56.659
03:19:56.659
16:05:56.658
17:41:56.658
01:46:22.459
03:21:06.484
16:06:32.483
17:42:38.533
XA PMT
(counts)
1.62
1.65
1.61
1.62
1.60
1.61
1.69
1.61
XB PMT
(counts)
3.20
3.13
3.13
3.14
3.17
3.09
3.22
3.12
The plots for these data sets follow the SM4 AT plot.
YA PMT
(counts)
0.26
0.22
0.26
0.27
0.32
0.22
0.24
0.29
YB PMT
(counts)
1.43
1.39
1.43
1.42
1.45
1.41
1.37
1.41
Total PMT
Counts
6.51
6.40
6.44
6.45
6.55
6.33
6.53
6.43
No.
Points
3127
1090
28209
19849
995
2757
1397
1639