STScI

Wide Field and Planetary Camera 2 Instrument Handbook for Cycle 14

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6.1 System Throughput


A decision on a suitable exposure time will require the combination of

When the transmissions of filters T() are combined with the overall system response Q(), we obtain detector quantum efficiency (DQE) plots (electrons-per-photon as a function of ) for each filter. These DQE plots link the output of the CCD to the photon flux at the input to an unobscured 2.4 m telescope.

These calibrations exist in the STScI Calibration Data Base, and are accessible with the STSDAS SYNPHOT package or with the XCAL software. The XCAL and SYNPHOT Users Guides should be consulted for further details.

The throughput calibration presented here is accurate to at least 10%-which is sufficient for planning observations, but not for the analysis of many programs. Investigators wishing to do photometry on WFPC2 images should refer to the HST Data Handbook for an explanation of the conventions used in determining WFPC2 zeropoints and should use the zeropoints given in Table 5.1 of the WFPC2 Data Handbook (Version 4.0, January 2002). For the most accurate and up-to-date calibrations, users should examine the on-line version of the Data Handbook to verify that no numbers of interest have changed since the last paper publication. A recent study has examined the issue of WFPC2 zeropoints (Heyer, et al. 2004, WFPC2 ISR 04-01) and is recommending using the zeropoints of Dolphin (2002, private communication) on his web site at http://www.noao.edu/staff/dolphin/wfpc2_calib/

In Table 6.1 the dimensionless efficiency and the mean wavelength for each filter are tabulated together with the effective width, the equivalent Gaussian dimensionless width, the maximum transmission, the derivative of the mean wavelength with respect to spectral index, the pivot wavelength, average wavelength, and wavelength of maximum transmission. The parameters are defined as follows. The dimensionless efficiency is

The mean wavelength is defined in Schneider, Gunn, and Hoessel (1993, ApJ 264, 337).

This rather unconventional definition has the property that the correspondingly defined mean frequency is just . It is in some sense halfway between the conventional frequency mean and the wavelength mean.

The pivot wavelength is defined as

The average wavelength is that defined in the simplest sense

The effective dimensionless Gaussian width is defined implicitly by

The effective width of the bandpass is

We note that all of the above integrals have been evaluated over the range to so as to avoid unrealistic contributions from imperfect blocking far from the bandpass. Where necessary, the integration range was further constrained to the range 1000 to 11000.

Parameters and are the respective parameters at the peak throughput.

The parameter is defined in section Count Rates for Power Law Sources.

The final two columns in Table 6.1 are defined as follows. In the next-to-last column me/sec is the zero-point magnitude for 1 e- s-1 (with AB=0). The final column gives twfsky, which is the exposure time (in seconds) needed to make the sky noise equal to 5 e- RMS (i.e. ~read noise) in the WFC for a sky level of V=23.3 mag arcsec-2.

Table 6.1: System Efficiencies and Zeropoints. See Section 6.1 for definitions. 1
Filter
QT d/
QTmax
d/d
p
<>
max
me/sec
twfsky
F122M
0.00010
1305.6
239.1
0.0778
0.00107
7.90
1321.6
1326.2
1260
18.48
1.1E+07
F130LP
0.10175
4285.9
4755.4
0.4712
0.13936
951.53
5814.6
6137.5
6398
26.01
1.9E+02
F160BW
0.00024
1473.0
449.1
0.1295
0.00074
24.69
1521.9
1534.9
1400
19.46
9.2E+05
F165LP
0.10091
4494.4
4528.9
0.4279
0.14066
823.00
5852.9
6155.6
6400
26.00
1.9E+02
F170W
0.00057
1707.7
545.1
0.1355
0.00169
31.37
1769.7
1786.3
1857
20.38
2.3E+06
F185W
0.00038
1941.6
334.3
0.0731
0.00196
10.38
1962.3
1967.7
1940
19.93
7.3E+06
F218W
0.00059
2177.4
395.0
0.0770
0.00286
12.92
2203.1
2209.6
2242
20.42
5.4E+06
F255W
0.00080
2577.7
395.1
0.0651
0.00462
10.92
2599.4
2604.9
2536
20.76
2.6E+06
F300W
0.00571
2919.8
740.2
0.1077
0.01974
33.84
2986.8
3004.3
2804
22.89
6.7E+04
F336W
0.00497
3329.3
374.3
0.0477
0.03558
7.59
3344.4
3348.2
3454
22.74
3.6E+04
F343N
0.00003
3426.9
23.5
0.0029
0.00397
0.03
3426.9
3427.0
3432
17.27
4.7E+06
F375N
0.00008
3732.2
24.4
0.0028
0.00983
0.03
3732.3
3732.3
3736
18.24
1.1E+06
F380W
0.00779
3940.5
681.8
0.0735
0.03752
21.27
3982.7
3993.1
3999
23.22
7.1E+03
F390N
0.00031
3888.0
45.0
0.0049
0.01999
0.09
3888.2
3888.2
3889
19.72
2.1E+05
F410M
0.00183
4085.7
146.8
0.0153
0.04027
0.95
4087.6
4088.1
4097
21.65
2.7E+04
F437N
0.00022
4369.1
25.2
0.0025
0.03065
0.03
4369.2
4369.2
4368
19.37
1.7E+05
F439W
0.00576
4292.6
473.2
0.0468
0.03903
9.41
4311.3
4316.0
4318
22.90
7.1E+03
F450W
0.01678
4483.6
950.8
0.0901
0.08671
36.36
4555.4
4573.0
5069
24.06
2.0E+03
F467M
0.00250
4667.7
166.5
0.0151
0.05582
1.07
4669.8
4670.4
4731
21.99
1.2E+04
F469N
0.00027
4694.4
25.0
0.0023
0.03784
0.02
4694.4
4694.4
4698
19.56
1.1E+05
F487N
0.00034
4865.1
25.9
0.0023
0.04811
0.02
4865.2
4865.2
4864
19.81
8.1E+04
F502N
0.00041
5012.4
26.9
0.0023
0.05800
0.03
5012.4
5012.4
5009
20.04
5.9E+04
F547M
0.01342
5467.8
483.2
0.0375
0.11515
7.70
5483.3
5487.1
5558
23.81
1.6E+03
F555W
0.03012
5336.8
1228.4
0.0977
0.11194
50.99
5439.0
5464.6
5550
24.69
7.3E+02
F569W
0.02343
5582.3
965.7
0.0735
0.11518
30.13
5642.0
5657.4
5549
24.42
8.9E+02
F588N
0.00145
5893.2
49.0
0.0035
0.13078
0.07
5893.5
5893.5
5896
21.40
1.3E+04
F606W
0.04513
5860.1
1502.4
0.1089
0.14220
69.46
5996.8
6030.8
6185
25.13
4.2E+02
F622W
0.02882
6137.4
917.1
0.0635
0.14096
24.71
6186.2
6198.6
6405
24.64
6.3E+02
F631N
0.00084
6306.4
30.9
0.0021
0.12632
0.03
6306.4
6306.4
6301
20.81
2.1E+04
F656N
0.00049
6563.8
21.5
0.0014
0.11273
0.01
6563.8
6563.8
6562
20.21
3.5E+04
F658N
0.00068
6590.8
28.5
0.0018
0.11443
0.02
6590.8
6590.8
6591
20.58
2.5E+04
F673N
0.00113
6732.2
47.2
0.0030
0.11978
0.06
6732.3
6732.3
6730
21.12
1.4E+04
F675W
0.02344
6677.4
866.8
0.0551
0.13604
20.29
6717.4
6727.6
6624
24.42
7.0E+02
F702W
0.03429
6818.0
1384.7
0.0862
0.14185
50.71
6918.5
6944.3
6513
24.83
4.6E+02
F785LP
0.00900
8627.9
1381.2
0.0680
0.04831
39.88
8707.0
8727.5
8226
23.38
1.3E+03
F791W
0.01694
7811.2
1230.7
0.0669
0.09530
34.97
7880.6
7898.4
7397
24.07
7.6E+02
F814W
0.01949
7904.8
1539.4
0.0827
0.10343
54.06
8012.2
8040.3
7255
24.22
6.5E+02
F850LP
0.00473
9086.1
1037.5
0.0485
0.03939
21.37
9128.8
9139.8
8810
22.68
2.4E+03
F953N
0.00016
9544.7
52.5
0.0023
0.02213
0.05
9544.9
9545.0
9525
19.00
6.9E+04
F1042M
0.00017
10220.5
448.9
0.0187
0.00481
3.56
10227.6
10229.4
10110
19.10
6.0E+04
FQUVN-A
0.00033
3764.4
73.2
0.0083
0.01326
0.26
3764.5
3764.6
3801
19.78
2.5E+05
FQUVN-B
0.00030
3829.3
57.3
0.0064
0.01557
0.15
3829.5
3829.6
3828
19.68
2.4E+05
FQUVN-C
0.00037
3912.6
59.5
0.0065
0.01900
0.16
3912.9
3913.0
3909
19.92
1.7E+05
FQUVN-D
0.00047
3991.8
63.6
0.0068
0.02329
0.18
3992.2
3992.3
3989
20.17
1.2E+05
FQCH4N-A
0.00076
5435.3
34.4
0.0027
0.09537
0.04
5435.4
5435.4
5442
20.70
2.9E+04
FQCH4N15-B
0.00088
6199.2
33.8
0.0023
0.12242
0.03
6199.4
6199.4
6202
20.85
2.0E+04
FQCH4N33-B
0.00087
6199.3
33.8
0.0023
0.12165
0.03
6199.4
6199.4
6202
20.85
2.0E+04
FQCH4N-C
0.00070
7278.5
38.1
0.0022
0.10275
0.04
7278.5
7278.5
7278
20.60
2.1E+04
FQCH4N-D
0.00021
8930.2
54.9
0.0026
0.02917
0.06
8930.2
8930.2
8930
19.31
5.0E+04
POLQ_par
0.06695
4978.4
4226.0
0.3605
0.09998
646.91
6099.9
6355.5
6493
25.56
-
POLQ_per
0.01494
6257.6
5233.7
0.3552
0.04268
789.39
7613.6
7843.4
8001
23.93
-
1All values have been computed using the WF3 chip, except for the Quad filters.


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