A.2 Converting Between Flux Density and Magnitudes

The conversion between magnitudes and flux density $F_\nu$ is given explicitly in equation A.1. All we need is to specify the zero-point flux, $F_{\nu_0}$.

The zero-point flux, $F_{\nu_0}$, is determined for a number of photometric systems. In Table A.2 we tabulate the zeropoints, $F_{\nu_0}$ and $F_{\lambda_0} = a_\lambda F_{\nu_0} / \lambda^2$, for IRAC.

Table A.2: The photometric zeropoints for the Spitzer/IRAC instrument.

$\lambda \; [\mu {\rm m}]$	$F_{\nu_0}$ [Jy]	$F_{\lambda_0}$ $[{\rm erg}\; {\rm cm}^{-2}\; {\rm s}^{-1} \;\mu {\rm m}^{-1}]$
3.6	277.5	$6.42\times 10^{-8}$
4.5	179.5	$2.66\times 10^{-8}$
5.8	116.6	$1.04\times 10^{-8}$
8.0	63.1	$2.96\times 10^{-9}$

In Table A.3, we display the zeropoints in the 2MASS passbands (see: http://www.ipac.caltech.edu/2mass/releases/second/doc/sec4_5.html).

Table A.3: The photometric zeropoints in the 2MASS filters.

Band	$\lambda [\mu m]$	$F_{\nu_0}$ [Jy]
J	1.235	1594
H	1.662	1024
Ks	2.159	666.7

In Table A.4 we tabulate the zeropoints, $F_{\nu_0}$ and $F_{\lambda_0} = a_\lambda F_{\nu_0} / \lambda^2$, adopted for NICMOS, based on the CIT system (Beckwith et al., 1976, ApJ, 208, 390).

Table A.4: The photometric zeropoints in the CIT system.

Band	$\lambda [\mu {\rm m}]$	$F_{\nu_0}$ [Jy]	$F_{\lambda_0}$ $[{\rm erg}\; {\rm cm}^{-2}\; {\rm s}^{-1} \;\mu {\rm m}^{-1}]$
V	0.56	3540	$3.39\times 10^{-5}$
R	0.70	2870	$1.76\times 10^{-5}$
I	0.90	2250	$8.83\times 10^{-6}$
J	1.25	1670	$3.20\times 10^{-6}$
H	1.65	980	$1.08\times 10^{-6}$
K	2.2	620	$3.84\times 10^{-7}$
L	3.4	280	$7.26\times 10^{-8}$
M	4.8	150	$1.95\times 10^{-8}$
N	10.1	37	$1.09\times 10^{-9}$
Q	20.0	10	$7.5 \times 10^{-11}$

In Table A.5, we display the zeropoints in the Johnson UBVRI+ system (see: Allen's Astrophysical Quantities, Fourth Edition, 2001, Arthur N. Cox (ed.), Springer-Verlag; Campins, Rieke, & Lebofsky 1985, AJ, 90, 896; Rieke, Lebofsky & Low 1985, AJ, 90, 900).

Table A.5: The photometric zeropoints in the Johnson UBVRI+ system.

Band	$\lambda [\mu m]$	$F_{\nu_0}$ [Jy]
U	0.36	1823
B	0.44	4130
V	0.55	3781
R	0.71	2941
I	0.97	2635
J	1.25	1603
H	1.60	1075
K	2.22	667
L	3.54	288
M	4.80	170
N	10.6	36
O	21.0	9.4

We have developed an online magnitude $\leftrightarrow$ flux density converter. Check the SSC tools website:

http://ssc.spitzer.caltech.edu/tools/