5.1 The ionizing spectrum

The hydrogen-deficient synthetic spectra of Abell48 was modelled using stellar model atmospheres produced by the Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres (Hamann & Gräfener, 2004; Gräfener et al., 2002). It solves the non-local thermodynamic equilibrium (non-LTE) radiative transfer equation in the comoving frame, iteratively with the equations of statistical equilibrium and radiative equilibrium, for an expanding atmosphere under the assumptions of spherical symmetry, stationarity and homogeneity. The result of our model atmosphere is shown in Fig.5. The model atmosphere calculated with the PoWR code is for the stellar surface abundances H:He:C:N:O = 10:85:0.3:5:0.6 by mass, the stellar temperature $T_{\rm eff}$=70kK, the transformed radius $R_{\rm t}=0.54$R ${}_{\bigodot}$ and the wind terminal velocity $v_{\infty}=1000$ kms$^{-1}$. The best photoionization model was obtained with an effective temperature of 70kK (the same as PoWR model used by Todt et al., 2013) and a stellar luminosity of $L_{\rm\star}/$L $_{\bigodot}$= 5500, which is close to $L_{\star}/$L $_{\bigodot}$= 6000 adopted by Todt et al. (2013). This stellar luminosity was found to be consistent with the observed H$\beta$ luminosity and the flux ratio of $[$O III$]$/H$\beta$. A stellar luminosity higher than 5500L $_{\bigodot}$ produces inconsistent results for the nebular photoionization modelling. The emission-line spectrum produced by our adopted stellar parameters was found to be consistent with the observations.

Table 8: Input parameters for the MOCASSIN photoionization model.

Stellar and Nebular			Nebular Abundances
Parameters			Model	Obs.
$T_{\rm eff}$(kK)	70	He/H	0.120	0.124
$L_{\rm\star}$(L $_{\bigodot}$)	5500	C/H  $\times 10^{3}$	3.00	-
$N_{\rm H}$ (cm$^{-3}$)	800-1200	N/H  $\times 10^{5}$	6.50	4.30
$D$(kpc)	1.9	O/H  $\times 10^{4}$	1.40	1.59
$r_{\rm out}$(arcsec)	23	Ne/H  $\times 10^{5}$	6.00	6.36
$\delta r$(arcsec)	13	S/H  $\times 10^{6}$	6.00	6.73
$h$(arcsec)	23	Ar/H  $\times 10^{6}$	1.20	1.48