STScI Logo

Hubble Space Telescope
Magnitude Types

The default is to input 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
J. Biretta (STScI) and Hans-Martin Adorf (ST-ECF)