Input the surface brightness in magnitudes per square arcsecond.
The default is to use Johnson Visual magnitudes, but you can use the menu to select other Johnson-Cousins magnitudes, or AB magnitudes.
U, B, V, R, and I are standard magnitudes in the Johnson-Cousins system. (U, B, and V are from Johnson, and R and I are from Cousins. V and Visual magnitude are equivalent.) The table below is used to convert the input magnitudes to V before calculation:
Color Spectral Type
----- ------------------------------------------------------------------------
O5 B0 A0 F0 G0 G5 K0III M0III gE Sa Sbc Scd IrI
U-V -1.43 -1.36 0.04 0.31 0.65 0.82 1.86 3.46 1.64 1.62 1.28 0.51 0.05
B-V -0.30 -0.29 0.02 0.25 0.54 0.62 0.91 1.44 0.99 0.98 0.91 0.50 0.37
V-R -0.14 -0.15 0.01 0.17 0.36 0.40 0.51 0.89 0.53 0.48 0.43 0.36 0.28
V-I -0.31 -0.27 0.03 0.36 0.73 0.76 0.95 1.74 1.10 0.99 0.90 0.70 0.66
Stellar colors are from SYNPHOT runs using Bruzual synthetic spectra. Galaxy U-B and B-V colors are drawn from Longo and deVaucouleurs 1983 for representative objects;V-R and R-I are estimated from WFPC2 Handbook Table 6.1. Galaxy colors are probably accurate to only to ~20%.
AB_xxxxx are AB magnitudes at the standard WFPC2 filter bands. For example AB_F555W means AB at the effective wavelength of the F555W filter (5398 Angstroms). AB magnitudes are defined as:
AB = -2.5 log10(F(nu)) - 48.60
where F(nu) is the flux in erg sec-1 cm-2 Hz-1.
Band Effective Wavelength (Ang.) ------- --------------------------- F160BW 1492 F218W 2192 F255W 2586 F300W 2943 F336W 3342 F439W 4300 F555W 5398 F675W 6696 F814W 7921 F1042M 10184