The zero magnitude of a given ISOCAM filter is defined as the signal of the `ideal' (i.e. model) Vega which would have been measured in that filter with an infinitely large aperture.

The ideal spectrum of Vega was derived from a Kurucz model with $T_{eff}$ = 9400 K , log

= 3.9, metal poor, $V_{turb}=$ 0.0 kms $^{-1}$ and no infrared excess due to circumstellar dust, extended to 300 $\mu$ m and absolutely calibrated as described by Cohen et al. 1992, [18] and Walker & Cohen 1992, [64].

The magnitude $m_{filter}$ can then be obtained from the CAM auto-analysis data product by applying the relation:

where $F_{\nu}(measured)$ is the flux density obtained from the ISOCAM data product (without colour correction). The values of $F_{\nu,0}$ for the different filter identifiers and reference wavelengths ${\lambda}_{ref}$ are listed in Table B.1.

For completeness, we have included in Table B.1 the ideal Vega flux density at the reference wavelength $F_{\nu}({\lambda}_{ref})$ , and the colour correction

The values of

are very close to the ones which have been derived for a 10000 K blackbody (see Appendix A).

**Table B.1:** *Zero magnitude flux densities of the different ISOCAM filter bands.*
filter	${\lambda}_{ref}$	$F_{\nu,0}({\lambda}_{ref})$	$F_{\nu}({\lambda}_{ref})$
ID	[ $\mu$ m]	[Jy]	[Jy]	[ ]
SW1	3.6	280.5	267.7	1.05
SW2	3.3	313.2	301.5	1.04
SW3	4.5	189.6	178.9	1.06
SW4	2.8	434.4	426.9	1.02
SW5	4.0	229.1	219.9	1.04
SW6	3.7	256.0	253.9	1.01
SW7	3.0	360.2	376.3	0.96
SW8	4.05	213.4	209.1	1.02
SW9	3.9	235.4	227.9	1.03
SW10	4.6	167.6	171.4	0.98
SW11	4.26	201.8	197.6	1.02

LW1	4.5	181.9	178.9	1.02
LW2	6.7	90.2	83.7	1.08
LW3	14.3	19.7	19.1	1.03
LW4	6.0	105.1	103.6	1.02
LW5	6.8	82.1	81.4	1.01
LW6	7.7	64.0	64.0	1.00
LW7	9.6	42.2	41.7	1.01
LW8	11.3	30.3	30.3	1.00
LW9	14.9	17.7	17.6	1.01
LW10	12.0	34.7	26.9	1.29

B. Magnitude System in ISOCAM