The zero magnitude of a given ISOPHOT 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(

) = 3.900, 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, [6], and Walker & Cohen 1992, [55].

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

where $F_{\nu}(measured)$ is the AAR flux density. The values for $F_{\nu,0}$ with filter identifier and reference wavelength ${\lambda}_{ref}$ are listed in Table D.1.

For completeness, we have included in Table D.1 the corresponding powers on the detector $P_0({\lambda}_{ref})$ , the ideal Vega flux density at the reference wavelength $F_{\nu}({\lambda}_{ref})$ , and the colour correction

$P_0({\lambda}_{ref})$ can be applied to the SPD products, thereby taking into account the point spread function correction, see Equations 5.8 and 5.9. The values of

are very close to the ones which have been derived for a 10000 K blackbody, see Table C.2.

**Table D.1:** *Zero magnitude flux densities of ISOPHOT filter bands.*
filter	${\lambda}_{ref}$	$P_0({\lambda}_{ref})$	$F_{\nu,0}({\lambda}_{ref})$	$F_{\nu}({\lambda}_{ref})$
ID	[ $\mu$ m]	[W]	[Jy]	[Jy]	[ ]
P_3.29	3.3	4.60E13	312.0	318.2	0.981
P_3.6	3.6	2.15E12	284.7	270.9	1.051
P_4.85	4.8	1.24E12	163.2	152.1	1.072
P_7.3	7.3	1.01E12	79.96	71.09	1.125
P_7.7	7.7	1.61E13	65.14	64.23	1.014
P_10	10	1.77E13	39.40	38.60	1.021
P_11.3	11.3	3.94E14	29.96	30.40	0.985
P_12.8	12.8	5.71E13	35.47	26.97	1.315
P_16	15	1.26E13	24.21	23.79	1.018
P_11.5	12	5.46E14	17.25	17.40	0.991
P_20	20	5.17E14	9.940	9.840	1.010
P_25	25	3.47E14	8.109	6.307	1.286
P_60	60	7.29E16	1.233	1.087	1.135
P_100	100	3.55E16	0.4068	0.3866	1.052
C_50	65	5.76E16	1.197	0.9245	1.295
C_60	60	7.60E16	1.153	1.087	1.061
C_70	80	5.22E16	0.7489	0.6075	1.233
C_90	90	8.45E16	0.5597	0.4787	1.169
C_100	100	4.03E16	0.4261	0.3866	1.102
C_105	105	2.25E16	0.3683	0.3503	1.052
C_120	120	1.15E16	0.3253	0.2672	1.217
C_135	150	1.32E16	0.1862	0.1698	1.096
C_160	170	1.60E16	0.1587	0.1316	1.205
C_180	180	6.92E17	0.1288	0.1172	1.099
C_200	200	2.27E17	0.0972	0.0945	1.028

D. Magnitude System in ISOPHOT