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Red Leaks in UV Filters
STScI

WFPC2 Instrument Handbook for Cycle 11

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Red Leaks in UV Filters

The "red leaks" in the UV filters are shown in Figure 3.10 for F122M, F160BW (the new Wood's filter), F170W, F185W, F218W F255W, F300W, and F336W. The presence of significant red leaks in the UV filters, together with the much greater sensitivity and wavelength coverage in the red part of the spectrum, makes calibration of UV observations difficult. Table 3.13 shows red leak estimates as a percentage of the total detected flux from de-reddened stellar sources, ordered by spectral type. In each column, the red leak is defined as the percentage of the detected flux longward of the cutoff wavelength in the third row. In the presence of interstellar reddening, the red leaks will be larger.

Figure 3.10: UV Filter Red Leaks. Includes the on-orbit measurements of system response.  
 

Table 3.13: Red Leak in UV Filters. A synthetic photometry calculation with de-reddened BPGS stellar spectra and system response from on-orbit data.
Filter
Central (nm)
Cutoff (nm)		 F122M 122
140		 F160BW 160
240		 F170W
170
260		 F185W
185
260		 F218W
218
280		 F255W
255
310		 F300W
300
400		 F336W 336
400		 F122M
122
380		 F160BW
160
380		 F170W
170
380		 F185W
185
380		 F218W
218
380		 F255W|
255
380		 F300W
300
380		 F336W
336
380
9 SGR
O5
16.9
0.7
0.4
0.2
0.3
0.1
0.3
0.1
0.5
0.1
9 SGE
O8F
16.9
0.7
0.4
0.2
0.3
0.1
0.3
0.1
0.5
0.1
HR 8D23
O6
21.8
1.0
0.5
0.3
0.4
0.1
0.6
0.1
0.6
0.1
-1935
B1V
20.1
0.8
0.4
0.3
0.4
0.1
0.6
0.1
0.6
0.2
60 CYG
B1V
20.1
0.8
0.4
0.3
0.4
0.1
0.6
0.1
0.6
0.2
102 HER
B2V
22.5
1.2
0.6
0.4
0.4
0.1
0.1
1.1
0.2
0.1
0.8
0.2
ETA HYA
B3V
22.7
1.2
0.6
0.4
0.5
0.1
0.1
1.3
0.3
0.1
0.9
0.2
IOTA HER
B3V
22.7
1.2
0.6
0.4
0.5
0.1
0.2
1.3
0.3
0.1
0.9
0.2
HR 7899
B4V
22.7
1.2
0.6
0.4
0.5
0.1
0.2
1.4
0.3
0.1
0.9
0.2
38 OPH
A1V
30.0
1.6
0.7
0.5
0.5
0.1
0.2
2.9
0.5
0.1
1.1
0.3
HR 7174
B6V
30.7
1.8
0.8
0.5
0.5
0.1
0.3
3.8
0.7
0.2
0.1
1.3
0.4
9 VUL
B7V
30.8
1.8
0.8
0.5
0.5
0.1
0.3
3.9
0.7
0.2
0.1
1.4
0.4
HD 189689
B9V
41.1
2.4
0.9
0.5
0.6
0.2
0.3
7.4
1.0
0.2
0.1
1.6
0.4
THETA VIR
A0V
59.6
4.0
1.2
0.6
0.8
0.3
0.6
20.3
2.2
0.4
0.1
0.1
2.5
0.7
NU CAP
B9V
58.6
3.7
1.2
0.6
0.8
0.3
0.5
18.3
2.0
0.4
0.1
0.1
2.2
0.6
HR 6169
A2V
59.5
4.0
1.2
0.6
0.8
0.3
0.6
20.1
2.2
0.4
0.1
0.1
2.3
0.7
HD 140849A
A1V
73.7
3.8
1.1
0.6
0.7
0.3
0.5
23.7
2.0
0.4
0.1
0.1
2.0
0.6
69 HER
A2V
59.5
3.9
1.2
0.6
0.8
0.3
0.6
20.0
2.2
0.4
0.1
0.1
2.2
0.7
HD 140849B
A3V
89.0
6.5
1.5
0.8
1.0
0.4
0.6
44.0
3.9
0.6
0.1
0.2
2.4
0.7
58 AQL
A0V
75.5
4.3
1.3
0.6
0.8
0.3
0.7
28.6
2.5
0.5
0.1
0.1
2.7
0.8
78 HER
B9V
75.0
4.2
1.2
0.6
0.7
0.3
0.7
27.5
2.4
0.5
0.1
0.1
2.4
0.8
HR 6570
A7V
89.7
7.0
1.6
0.8
1.0
0.4
0.7
47.6
4.4
0.7
0.1
0.2
2.6
0.9
HD 187754
A2V
97.9
11.0
2.1
0.9
1.2
0.5
0.9
64.4
7.4
1.0
0.2
0.2
3.2
1.1
THETA 1 SER
A5V
97.7
9.8
1.9
0.9
1.1
0.4
0.8
60.3
6.2
0.8
0.1
0.2
2.6
0.9
PRAESEPE 276
99.7
12.1
2.2
1.0
1.2
0.5
0.9
67.5
8.1
1.1
0.2
0.2
2.9
1.0
PRAESEPE 114
99.7
11.6
2.2
1.0
1.2
0.5
0.9
66.0
7.6
1.0
0.2
0.2
2.7
1.0
PRAESEPE 154
100.0
17.0
3.0
1.1
1.3
0.5
0.9
71.9
11.4
1.4
0.2
0.2
2.8
1.0
HD 140192
A5V
100.0
17.4
3.0
1.1
1.3
0.6
0.9
72.7
11.7
1.5
0.2
0.2
2.9
1.1
PRAESEPE 226
100.0
17.2
3.0
1.1
1.3
0.6
1.0
72.7
11.6
1.4
0.2
0.2
2.7
1.1
PRAESEPE 37
100.0
38.8
7.7
2.0
1.7
0.6
1.0
80.8
27.0
3.9
0.3
0.3
2.8
1.1
HD 191177
F4V
100.0
64.9
17.6
3.0
2.3
0.8
1.1
86.1
48.4
10.1
0.6
0.5
3.6
1.3
PRAESEPE 332
100.0
62.4
16.3
2.9
2.2
0.7
1.0
84.6
44.9
8.8
0.5
0.4
2.9
1.1
BD+293891
F6V
100.0
67.4
19.4
3.7
2.5
0.8
1.1
86.4
49.8
11.0
0.7
0.4
3.1
1.2
PRAESEPE 222
100.0
50.7
11.4
2.8
2.2
0.8
1.1
84.7
36.8
6.2
0.5
0.4
2.8
1.2
HD 35246
F8V
100.0
52.1
11.8
2.9
2.2
0.8
1.3
85.8
38.6
6.6
0.5
0.4
2.8
1.4
BD+263780
G0V
100.0
52.4
11.9
2.9
2.2
0.9
1.3
86.0
38.9
6.7
0.5
0.4
2.8
1.4
HD 148816
F9V
100.0
51.1
11.5
2.8
2.2
0.8
1.2
85.0
37.2
6.3
0.5
0.3
2.8
1.3
HD 155675
F8V
100.0
69.0
20.5
4.7
3.4
1.0
1.3
88.7
53.3
12.4
0.9
0.6
3.3
1.4
PRAESEPE 418
100.0
70.2
21.1
4.8
3.5
1.0
1.4
89.4
55.0
13.2
1.0
0.6
3.2
1.5
HYAD 1
100.0
71.4
21.9
4.8
3.5
1.1
1.5
90.0
56.8
14.1
1.0
0.6
3.4
1.6
HD 122693
F8V
100.0
71.6
22.1
4.9
3.5
1.1
1.6
90.1
57.1
14.2
1.1
0.6
3.5
1.7
HD 154417
F8V
100.0
70.6
21.4
4.8
3.5
1.1
1.4
89.5
55.5
13.4
1.0
0.6
3.2
1.5
HYAD 2
100.0
89.2
46.7
7.9
3.4
1.2
1.6
91.2
71.6
30.3
1.7
0.6
3.3
1.7
HD 227547
G5V
100.0
89.5
47.2
8.0
3.4
1.2
1.7
91.4
72.0
30.7
1.7
0.6
3.3
1.8
HD 154760
G2V
100.0
89.3
46.8
7.9
3.4
1.2
1.6
91.3
71.6
30.3
1.7
0.6
3.3
1.7
HD 140605
G2V
100.0
89.9
48.2
8.1
3.5
1.3
1.8
91.8
73.2
32.0
1.8
0.7
3.4
1.9
HYAD 15
100.0
90.1
48.5
8.0
3.5
1.3
1.8
92.1
73.7
32.5
1.8
0.7
3.4
1.9
HD 139777A
K0V
100.0
89.8
47.7
8.0
3.4
1.3
1.8
91.7
72.8
31.5
1.7
0.6
3.5
1.9
HD 136274
G8V
100.0
91.4
51.6
8.3
3.5
1.7
2.3
93.4
77.1
36.6
2.0
0.7
3.6
2.4
HYAD 26
100.0
91.6
52.3
8.3
3.6
1.7
2.3
93.5
77.6
37.3
2.1
0.7
3.6
2.4
HD 150205
G5V
100.0
91.7
52.3
8.4
3.6
1.7
2.4
93.5
77.6
37.4
2.1
0.8
3.8
2.4
HYAD 21
100.0
92.8
55.7
8.6
3.7
2.1
2.8
94.6
80.7
41.8
2.4
0.8
3.9
2.9
+02 3001
G8V
100.0
93.0
56.1
8.6
3.6
2.2
3.1
94.8
81.1
42.3
2.4
0.8
4.3
3.2
HD 190571
G8V
100.0
0.3
99.5
95.2
40.0
11.3
3.4
3.6
96.7
0.1
91.4
80.4
16.0
3.0
6.1
3.7
HYAD 183
100.0
0.3
99.6
96.0
41.6
11.7
4.3
4.6
97.5
0.1
93.1
83.8
18.3
3.4
6.7
4.7
HD 140470
K3V
100.0
0.3
99.6
96.2
42.2
11.9
4.5
4.8
97.5
0.1
93.3
84.4
19.0
3.5
7.0
4.9
HD 154712
K4V
100.0
0.2
99.7
95.7
45.7
15.8
6.6
6.7
98.3
0.1
95.3
87.4
24.6
5.4
9.4
6.8
HYAD 185
100.0
0.2
99.7
96.7
50.0
15.7
8.0
7.9
98.6
0.1
96.0
89.5
28.6
5.5
10.6
8.0
+382457
K8V
100.0
0.2
99.7
96.6
48.6
16.5
8.8
9.1
98.7
0.1
96.4
90.1
28.7
6.3
11.5
9.1
HYAD 173
100.0
0.1
99.5
93.8
32.0
8.5
11.8
12.8
99.0
96.9
88.7
19.8
3.8
14.3
12.9
GL 40
M0V
100.0
0.1
99.6
94.9
34.5
8.8
14.5
15.4
99.2
97.5
90.7
22.8
4.2
17.4
15.5
HYAD 189
100.0
0.1
99.6
95.3
35.8
9.1
15.7
16.8
99.3
97.7
91.5
24.3
4.4
18.4
16.9
HD 151288
K7V
100.0
0.1
99.7
95.6
37.0
9.4
16.5
17.4
99.3
97.8
91.9
25.5
4.7
19.3
17.4
HD 157881
K7V
100.0
0.1
99.7
95.6
36.6
9.2
16.7
17.6
99.3
97.8
91.9
25.2
4.5
19.4
17.7
HD 1326d3
M0V
100.0
0.1
99.7
95.8
37.5
9.4
17.7
18.9
99.4
97.9
92.3
26.2
4.7
20.5
18.9
GL 15A
M0V
100.0
0.1
99.8
97.7
48.6
11.5
27.3
26.7
99.6
0.1
98.8
95.6
38.8
6.7
30.4
26.8
GL 49
M2V
100.0
0.1
99.8
97.3
45.8
10.7
25.5
25.0
99.6
0.1
98.7
95.1
35.9
6.0
28.7
25.1
GL 1D9
M4V
100.0
0.1
99.9
98.2
54.5
12.5
34.1
32.2
99.7
0.1
99.1
96.7
46.1
7.9
37.2
32.3
GL 15B
M6V
100.0
0.2
99.9
99.2
69.7
17.7
51.1
46.0
99.9
0.1
99.6
98.4
64.0
13.3
53.5
46.1
GL 83.1
M8V
100.0
0.1
99.7
95.9
38.2
8.9
17.4
15.5
99.4
97.9
92.4
26.8
3.9
20.1
15.5
GL 65
M5V
100.0
0.1
99.8
97.0
43.3
9.2
22.4
17.8
99.6
98.5
94.4
33.0
4.3
25.2
17.9

 

Note that the SYNPHOT synthetic photometry package can be used to estimate the counts contributed by red leak for various particular situations, and for filters other than those plotted below.

There is significant variation of the UV throughput due to build-up of molecular contaminants on the CCD windows, and monthly decontamination procedures used to remove this contamination. See Short-term Time Dependence of UV Response

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