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 [1]

Description [2]

Pivot (A) [3]

Width (A) [4]

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 [5]

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 [6]

Description

Pivot [7] (nm)

Width [8] (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.