Fundamental Parameters of Massive Stars

We discuss the determination of fundamental parameters of `normal' hot, massive OB-type stars, namely temperatures, luminosities, masses, gravities and surface abundances. We also present methods used to derive properties of stellar winds -- mass-loss rates and wind velocities from early-type stars.Comment: 21 pages, 3 figures, to appear in "Massive Stars: Formation, Evolution and Environment", eds. Heydari-Malayeri & Zahn (proceedings of 2002 Aussois summer school

Interstellar Ti II in the Milky Way and Magellanic Clouds

We discuss several sets of Ti II absorption-line data, which probe a variety of interstellar environments in our Galaxy and in the Magellanic Clouds. Comparisons of high-resolution (FWHM ~ 1.3-1.5 km/s) Ti II spectra of Galactic targets with corresponding high-resolution spectra of Na I, K I, and Ca II reveal both similarities and differences in the detailed structure of the absorption-line profiles -- reflecting component-to-component differences in the ionization and depletion behaviour of those species. Moderate-resolution (FWHM ~ 3.4-4.5 km/s) spectra of more heavily reddened Galactic stars provide more extensive information on the titanium depletion in colder, denser clouds -- where more than 99.9 per cent of the Ti may be in the dust phase. Moderate-resolution (FWHM ~ 4.5-8.7 km/s) spectra of stars in the Magellanic Clouds suggest that the titanium depletion is generally much less severe in the LMC and SMC than in our Galaxy [for a given N(H_tot), E(B-V), or molecular fraction f(H_2)] -- providing additional evidence for differences in depletion patterns in those two lower-metallicity galaxies. We briefly discuss possible implications of these results for the interpretation of gas-phase abundances in QSO absorption-line systems and of variations in the D/H ratio in the local Galactic ISM.Comment: 56 pages, 26 figures, accepted to MNRA

M4-18: The planetary nebula and its WC10 central star

We present a detailed analysis of the planetary nebula M4-18 (G146.7+07.6) and its WC10-type Wolf-Rayet central star, based on high quality optical spectroscopy (WHT/UES, INT/IDS, WIYN/DensPak) and imaging (HST/WFPC2). From a non-LTE model atmosphere analysis of the stellar spectrum, we derive Teff=31kK, log(Mdot/(Msun yr))=-6.05, v_inf=160 km/s and abundance number ratios of H/He<0.5, C/He=0.60 and O/He=0.10. These parameters are remarkably similar to He2-113 ([WC10]). Assuming an identical stellar mass to that determined by De Marco et al. for He2-113, we obtain a distance of 6.8kpc to M4-18 (E(B-V)=0.55mag from nebular and stellar techniques). This implies that the planetary nebula of M4-18 has a dynamical age of 3100 years, in contrast to >270 years for He2-113. This is supported by the much higher electron density of the latter. These observations may only be reconciled with evolutionary predictions if [WC]-type stars exhibit a range in stellar masses. Photo-ionization modelling of M4-18 is carried out using our stellar WR flux distribution, together with blackbody and Kurucz energy distributions obtained from Zanstra analyses. We conclude that the ionizing energy distribution from the Wolf-Rayet model provides the best consistency with the observed nebular properties, although discrepancies remain.Comment: 12 pages, 9 figures, accepted for MNRAS (latex uses mn.sty