8.4 Sensitivities and Exposure-Time Estimation

Table 8.2 lists current estimates of the detection limits for slitless spectroscopy with the UVIS and IR modes. The numbers in the table are the V magnitudes of point sources for which a 1-hour exposure yields a spectrum with a S/N of 5 per resolution element, with extraction boxes of 1 × 5 and 1 × 3 pixels for the UVIS and IR, respectively. V magnitudes are given for three different assumed source spectral types.

Table 8.2: V-band detection limits for the WFC3 grism modes for 1-hour exposure and 5σ detection.

Mode

Spectral Type

Wavelength
(nm)

O3 V

A0 V (Vega)

G2 V

UVIS2/G280

25.0

21.9

18.2

250

IR/G102

21.3

22.0

22.9

1050

IR/G141

20.5

21.3

22.8

1550


For more accurate estimations of exposure times, observers should use the WFC3 Exposure Time Calculator (ETC). The ETC supports all three spectroscopic modes.