Evolutionary helium and CNO anomalies in the atmospheres and winds of massive hot stars

The ubiquitous evidence for processed materials in the atmospheres, winds, and circumstellar ejecta of massive stars is reviewed. A broad array of normal and peculiar evolutionary stages is considered, up to and including Type II supernova progenitors. The quantitative analysis of these spectra is difficult, and until recently for the most part only qualitative or approximate results have been available. However, several important current programs promise reliable abundance calculations. A significant emerging result is that the morphologically normal majority of both hot and cold supergiants may already display an admixture of CNO-cycle products in their atmospheres. It may become possible in this way to identify blue supergiants returning from the red supergiant region, as appears to have been the case for the SN 1987A progenitor

Spectral Classification of O2-3.5If*/WN5-7 stars

An updated classification scheme for transition O2-3.5If*/WN5-7 stars is presented, following recent revisions to the spectral classifications for O and WN stars. We propose that O2-3.5If*, O2-3.5If*/WN5-7 and WN5-7 stars may be discriminated using the morphology of Hbeta to trace increasing wind density as follows: purely in absorption for O2-3.5If* stars in addition to the usual diagnostics from Walborn et al.; P Cygni for O2-3.5If*/WN5-7 stars; purely in emission for WN stars in addition to the usual diagnostics from Smith et al. We also discuss approximate criteria to discriminate between these subtypes from near-IR spectroscopy. The physical and wind properties of such stars are qualitatively discussed together with their evolutionary significance. We suggest that the majority of O2-3.5If*/WN5-7 stars are young, very massive hydrogen-burning stars, genuinely intermediate between O2-3.5If* and WN5-7 subtypes, although a minority are apparently core helium-burning stars evolving blueward towards the classical WN sequence. Finally, we reassess classifications for stars exhibiting lower ionization spectral features plus Hbeta emission.Comment: 16 pages, 8 figures, accepted for MNRA

Very Massive Stars and the Eddington Limit

We use contemporary evolutionary models for Very Massive Stars (VMS) to assess whether the Eddington limit constrains the upper stellar mass limit. We also consider the interplay between mass and age for the wind properties and spectral morphology of VMS, with reference to the recently modified classification scheme for O2-3.5If*/WN stars. Finally, the death of VMS in the local universe is considered in the context of pair instability supernovae.Comment: 6 pages, 4 figures, from "Four Decades of Massive Star Research" (Quebec, Jul 2011), ASP Conf Ser, in press (L. Drissen, C. Robert, N. St-Louis, A.F.J. Moffat, eds.

HDE 269896: una supergigante especial de la nube mayor de Magallanes

The star HDE 269896, a hypergiant in the Large Magellanic Cloud, with spectral type ON9.7 Ia+, is a special case within the known OB Zoo. We have discovered strong emission from the N II 5000 ˚A complex in its spectrum, and the previously known He II λ4686 emission, with an anomalous strength for the spectral type, has also been observed. Comparing HDE 269896 with other objects that show N II emission lines, such as WN10 and WN11 types, we find that this star is highly evolved, albeit less so than the latter stars. Thus, it is reasonable to propose that HDE 269896 should be in an immediate pre-WNVL (Very Late WN) state. Another characteristic of this star is the unusually wide range of ionization present in its extended atmosphere. Subsequent analysis of its spectrum will permit a better understanding of both the relevant atomic physics and the structure of this unusual atmosphere.La estrella HDE 269896, hipergigante de la Nube Mayor de Magallanes, con tipo espectral ON9.7 Ia+, es un caso particular dentro del zoológico OB conocido. Hemos encontrado en su espectro, una intensa emisión del complejo N II 5000 A y se ha observado también una emisión ˚ de He II λ4686, la cual por su intensidad, resulta anómala para su tipo espectral. Comparando a HDE 269896 con otros objetos que muestran líneas de emisión de N II, como ser WN10 y WN11, resulta evidente que HDE 269896 es un objeto altamente evolucionado, aunque lo es menos que las estrellas WN10 y WN11. Por esto, resulta razonable proponer que HDE 269896 debe hallarse en un estado inmediato de pre-WNVL (Very Late WN). Otra particularidad presente en HDE 269896, es el inusualmente amplio rango de ionización que tiene lugar en su atmósfera extendida. Análisis posteriores de su espectro permitirán comprender mejor tanto la física atómica involucrada como la estructura de esta atmósfera inusual.Fil: Corti, Mariela Alejandra. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Walborn, Nolan Revere. Space Telescope Science Institute; Estados Unido

The Correlation between X-Ray Line Ionization and Optical Spectral Types of the OB Stars

Marked correlations are reported between the ionization of the X-ray line spectra of normal OB stars, as observed by the Chandra X-Ray Observatory, and their optical spectral types. These correlations include the progressive weakening of the higher ionization relative to the lower ionization X-ray lines with advancing spectral type, and the similarly decreasing intensity ratios of the H-like to He-like lines of the alpha ions. These relationships were not predicted by models, nor have they been clearly evident in astrophysical studies of a few objects; rather, they have emerged from morphological analysis of an adequate (albeit still small) sample, from which known peculiar objects such as magnetic stars and very rapid rotators have been isolated to reveal the normal trends. This process is analogous to that which first demonstrated the strong relationships between the UV wind profiles and the optical spectral types of normal OB stars, which likely bear a physical as well as a historical connection to the present X-ray results. Since the optical spectral types are calibrated in terms of fundamental stellar parameters, it follows that the winds and X-ray spectra are determined by the latter. These observations provide strong guidance for further astrophysical modeling of these phenomena.Comment: 19 pages, 7 figures, 2 tables; ApJ accepte