UV(IUE) spectra of hot post-AGB candidates

Abstract

Analysis of the low resolution UV(IUE) spectra of 15 hot post-AGB candidates is presented. The UV(IUE) spectra of 10 stars suggest partial obscuration of the hot stars due to circumstellar dust. The reddened continua of these 10 stars were used to model and estimate the circumstellar extinction. The circumstellar extinction law was found to be linear in $\lambda^{-1}$ in the case of IRAS13266-5551 (CPD-55 5588), IRAS14331-6435 (Hen3-1013), IRAS16206-5956 (SAO 243756), IRAS17074-1845 (Hen3-1347), IRAS17311-4924 (Hen3-1428), IRAS18023-3409 (LSS 4634), IRAS18062+2410 (SAO 85766), IRAS18371-3159 (LSE 63), IRAS22023+5249 (LSIII +5224) and IRAS22495+5134 (LSIII +5142). There seems to be no significant circumstellar extinction in the case of IRAS17203-1534, IRAS17460-3114 (SAO 209306) and IRAS18379-1707 (LSS 5112). The UV(IUE) spectrum of IRAS12584-4837 (Hen3-847) shows several emission lines including that of HeII. It may be a massive young OB-supergiant or a low mass star in the post-AGB phase of evolution. IRAS16206-5956 (SAO 243756) and IRAS 18062+2410 (SAO 85766) show variability in the UV which in addition to stellar pulsations may be attributed to a dusty torus in motion around the hot central stars. The UV spectrum of the bipolar PPN, IRAS17423-1755 (Hen3-1475) indicates that the central B-type star is obscured by a dusty disk. The stars were placed on the log g$-$log T$_{\rm eff}$ diagram showing the post-AGB evolutionary tracks of Sch\"onberner. Terminal wind velocities of the stars were estimated from the CIV and NV stellar wind features. The presence of stellar wind in some of these stars indicates ongoing mass-loss.