WFC3IR Minimum Exposure Times and Subarrays
WFC3/IR is a multi-accum detector. There are many timing sequences, with the possibility
of using 1 to 15 reads for each. The total integration time depends on the type of timing
sequence, the number of reads (NSAMP), and the size of the selected array. Subarrays have
shorter integration times than full arrays for the same timing sequence name. The
integration times are shown in tables in the Phase II Proposal Instructions.
The read noise depends on the NSAMP. The ETC uses a value of read noise that assumes
NSAMP=15. It underestimates the read noise for smaller NSAMP. The ETC accepts or computes
only a total integration time, so observers should check the possible integration times
and keep in mind the assumption of NSAMP=15 for the read noise.
WFC3 Filters and Dispersers
The following tables show the filter and disperser properties.
WFC3 UVIS Filters and Grism
Name |
Description |
Pivot (A) |
Width (A) |
Peak Transmission |
UVIS Long-Pass (LP) and Extremely Wide (X) Filters |
|
|
|
|
F200LP |
Clear; grism reference |
5686.9 |
|
0.98 |
F300X |
Extremely wide UV |
2829.8 |
753.0 |
0.53 |
F350LP |
Long pass |
6812.0 |
|
0.98 |
F475X |
Extremely wide blue |
4917.1 |
2199.6 |
0.94 |
F600LP |
Long pass |
8430.2 |
|
0.99 |
F850LP |
SDSS z’ |
9756.4 |
|
0.96 |
UVIS Wide-Band(W) Filters |
|
|
|
|
F218W |
ISM feature |
2183.0 |
351.7 |
0.23 |
F225W |
UV wide |
2341.0 |
547.3 |
0.32 |
F275W |
UV wide |
2715.3 |
480.8 |
0.46 |
F336W |
U, Stromgren u |
3361.1 |
553.8 |
0.75 |
F390W |
Washington C |
3904.6 |
953.0 |
0.96 |
F438W |
WFPC2 B |
4318.7 |
676.8 |
0.84 |
F475W |
SDSS g’ |
4760.6 |
1488.9 |
0.92 |
F555W |
WFPC2 V |
5309.8 |
1595.1 |
0.95 |
F606W |
WFPC2 Wide V |
5907.0 |
2304.2 |
0.99 |
F625W |
SDSS r’ |
6254.0 |
1575.4 |
0.95 |
F775W |
SDSS i’ |
7733.6 |
1486.0 |
0.85 |
F814W |
WFPC2 Wide I |
8304.7 |
2543.3 |
0.97 |
UVIS Medium-Band (M) Filters |
|
|
|
|
F390M |
Ca II continuum |
3893.8 |
210.5 |
0.88 |
F410M |
Stromgren v |
4107.0 |
182.8 |
0.98 |
FQ422M |
Blue continuum |
4217.7 |
113.3 |
0.69 |
F467M |
Stromgren b |
4680.7 |
218.0 |
0.98 |
F547M |
Stromgren y |
5447.0 |
714.0 |
0.88 |
F621M |
11% passband |
6216.7 |
631.0 |
0.99 |
F689M |
11% passband |
6886.0 |
708.6 |
0.94 |
F763M |
11% passband |
7636.3 |
798.6 |
0.97 |
F845M |
11% passband |
8468.9 |
886.7 |
0.96 |
UVIS Narrow-Band (N) Filters |
|
|
|
|
FQ232N |
C II] 2326 |
2326.9 |
32.2 |
0.12 |
FQ243N |
[Ne IV] 2425 |
2420.6 |
34.8 |
0.15 |
F280N |
Mg II 2795/2802 |
2796.8 |
22.9 |
0.27 |
F343N |
[Ne V] 3426 |
3438.0 |
140.0 |
0.78 |
F373N |
[O II] 3726/3728 |
3729.6 |
39.2 |
0.78 |
FQ378N |
z ([O II] 3726) |
3790.9 |
89.2 |
0.83 |
FQ387N |
[Ne III] 3868 |
3873.0 |
23.1 |
0.72 |
F395N |
Ca II 3933/3968 |
3953.7 |
72.9 |
0.86 |
FQ436N |
H 4340 + [O III] 4363 |
4366.7 |
35.7 |
0.67 |
FQ437N |
[O III] 4363 |
4370.6 |
24.6 |
0.70 |
F469N |
He II 4686 |
4687.5 |
37.2 |
0.69 |
F487N |
H 4861 |
4870.7 |
48.4 |
0.85 |
FQ492N |
z (H) |
4932.1 |
101.0 |
0.85 |
F502N |
[O III] 5007 |
5009.0 |
57.8 |
0.87 |
FQ508N |
z ([O III] 5007) |
5089.7 |
117.9 |
0.87 |
FQ575N |
[N II] 5754 |
5755.9 |
12.9 |
0.78 |
FQ619N |
CH4 6194 |
6197.5 |
61.6 |
0.89 |
F631N |
[O I] 6300 |
6303.0 |
43.1 |
0.86 |
FQ634N |
6194 continuum |
6347.5 |
66.2 |
0.88 |
F645N |
Continuum |
6451.6 |
85.0 |
0.86 |
F656N |
H 6562 |
6561.1 |
13.9 |
0.86 |
F657N |
Wide H + [N II] |
6565.1 |
96.3 |
0.90 |
F658N |
[N II] 6583 |
6585.2 |
23.6 |
0.92 |
F665N |
z (H + [N II]) |
6654.4 |
109.0 |
0.90 |
FQ672N |
[S II] 6717 |
6716.1 |
14.9 |
0.89 |
F673N |
[S II] 6717/6731 |
6764.5 |
100.5 |
0.91 |
FQ674N |
[S II] 6731 |
6729.5 |
10.0 |
0.68 |
F680N |
z (H + [N II]) |
6878.6 |
323.6 |
0.95 |
FQ727N |
CH4 7270 |
7274.7 |
64.8 |
0.89 |
FQ750N |
7270 continuum |
7500.6 |
68.8 |
0.85 |
FQ889N |
CH4 25 km-agt |
8891.8 |
93.7 |
0.90 |
FQ906N |
CH4 2.5 km-agt |
9056.7 |
94.0 |
0.92 |
FQ924N |
CH4 0.25 km-agt |
9246.3 |
89.2 |
0.94 |
FQ937N |
CH4 0.025 km-agt |
9371.1 |
91.9 |
0.91 |
F953N |
[S III] 9532 |
9529.7 |
84.6 |
0.90 |
UVIS Grism (G) |
|
|
|
|
G280 |
UV Grism |
|
1850 |
0.4 |
WFC3 IR Channel Filters and Grisms
Name |
Description |
Pivot (nm) |
Width (nm) |
Peak Transmission |
IR Wide-Band(W) Filters |
|
|
|
|
F105W |
Wide Y |
1048.95 |
292.30 |
0.98 |
F110W |
Wide YJ |
1141.40 |
503.40 |
0.99 |
F125W |
Wide J |
1245.90 |
301.50 |
0.98 |
F140W |
Wide JH gap; red grism reference |
1392.10 |
399.00 |
0.99 |
F160W |
WFC3 H |
1540.52 |
287.88 |
0.98 |
IR Medium-Band(M) Filters |
|
|
|
|
F098M |
Blue grism reference |
982.93 |
169.48 |
0.97 |
F127M |
H2O/CH4 continuum |
1273.64 |
68.79 |
0.98 |
F139M |
H2O/CH4 line |
1383.80 |
64.58 |
0.98 |
F153M |
H2O and NH3 |
1533.31 |
68.78 |
0.98 |
IR Narrow-Band(N) Filters |
|
|
|
|
F126N |
[Fe II] |
1258.26 |
11.83 |
0.90 |
F128N |
Paschen |
1283.30 |
13.54 |
0.94 |
F130N |
Paschen continuum |
1300.62 |
13.28 |
0.96 |
F132N |
Paschen (redshifted) |
1319.04 |
13.07 |
0.91 |
F164N |
[Fe II] |
1645.13 |
17.48 |
0.93 |
F167N |
[Fe II] continuum |
1667.26 |
17.16 |
0.93 |
IR Grisms (G) |
|
|
|
|
G102 |
“Blue” high-resolution grism |
|
250 |
|
G141 |
“Red” low-resolution grism |
|
600 |
|
WFC3 Scan Mode
Spatial scan mode is available for IR imaging observations, IR spectroscopic observations,
and UVIS imaging observations. The target is moved along the detector at a fixed rate during the
exposure time. The ETC requires a pair of input parameters to describe the scan: either scan
rate (arcsec per sec) and scan length (arcsec) or exposure time (sec) and scan length (arcsec).
For the imaging modes, the height and width of the region that will be used for SNR calculations
is selected. For the IR spectroscopic mode, only the height of the region is selected. For that
mode, the width will be 1 pixel for computing the count rate and one spectral resolution
element (2 pixels) for computing counts.
The scan rate can be any number between 0.0 and 7.84 arcseconds/sec. Rates higher
than 5 arcseconds/sec are performed under gyro control. The scan length or exposure time should
be chosen to fit the array or subarray used for the exposure.