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

The Logic Structure of Pictorial Representation

This paper articulates the logical structure of pictorial representation, through an interpretation and defence of the role of resemblance. As a means to this, the discussion critically engages with existing theories, notably those of Schier, Goodman, and Margolis. The fundamental argument of the essay is that what makes pictorial representation logically distinctive is the fact that, once learned, it can be applied without recourse to ad hoc external conventions. Such conventions are required in order to secure exact denotation, but for something to count as a picture as such, we require only that it is formally organized so as to resemble some kind of three-dimensional object or scene.This paper articulates the logical structure of pictorial representation, through an interpretation and defence of the role of resemblance. As a means to this, the discussion critically engages with existing theories, notably those of Schier, Goodman, and Margolis. The fundamental argument of the essay is that what makes pictorial representation logically distinctive is the fact that, once learned, it can be applied without recourse to ad hoc external conventions. Such conventions are required in order to secure exact denotation, but for something to count as a picture as such, we require only that it is formally organized so as to resemble some kind of three-dimensional object or scene