We report on a mechanism which may lead to a spinup of the surface of a rotating single star leaving the Hayashi line, which is much stronger than the spin-up expected from the mere contraction of the star. By analyzing rigidly rotating, convective stellar envelopes, we qualitatively work out the mechanism through which these envelopes may be spun up or down by mass loss through their lower or ...

We discuss the various post-main sequence phases of massive stars, focusing on Wolf-Rayet stars, Luminous Blue Variables, plus connections with other early-type and late-type supergiants. End states for massive stars are also investigated, emphasising connections between Supernovae originating from core-collapse massive stars and Gamma Ray Bursts.

After a brief review of the observational evidences indicating how the populations of Be stars, red/blue supergiants, Wolf-Rayet stars vary as a function of metallicity, we discuss the implications of these observed trend for our understanding of the massive star evolution. We show how the inclusion of the effects of rotation in stellar models improves significantly the correspondence between t...

A previously unpublished ultralow–dispersion spectrum of Sanduleak -69 202, the stellar progenitor of SN 1987A, is presented and the uncertain presupernova evolution of Sanduleak -69 202 is discussed. Subject headings: Supernovae: individual (SN 1987A) — techniques: ultralow– dispersion spectra — Large Magellanic Cloud — supergiants — stars: Sanduleak -69 202

We study the origin of the bi-stability jump in the terminal velocity of the winds of supergiants near spectral type B1. Observations show that here the ratio v∞/vesc drops steeply from about 2.6 at types earlier than B1 to a value of v∞/vesc=1.3 at types later than B2. To this purpose, we have calculated wind models and mass-loss rates for early-type supergiants in a Teff grid covering the ran...

1 Visiting Astronomer at the Infrared Telescope Facility which is operated by the University of Hawaii under contract to the National Aeronautics and Space Administration 2 ABSTRACT The first measurement of the photospheric abundances in a star at the Galactic Center are presented. A detailed abundance analysis of the Galactic Center M2 supergiant IRS 7 was carried out using high-resolution nea...

We discuss HST FOS ultraviolet spectroscopy and NICMOS near-infrared photometry of four young super star clusters in the central region of the irregular starburst galaxy NGC 1569. The new observations coupled with previous HST WFPC2 photometry and ground-based optical spectroscopy allow us to isolate and age-date the hot and cool stellar components of these massive clusters. We analyze the two ...

We present a detailed LTE chemical analysis of 10 optically bright F-type post-AGB objects on the basis of the analysis of high-resolution optical spectra and compare the results with similar objects discussed in the literature. The iron content is low on average, and so confirms the old and hence low-mass nature of the supergiants, with a noticable exception of HD 95767. We emphasize the fact ...

Context. Thermal wind emission in the form of free-free and free-bound emission is known to show up in the infrared and radio continuum of hot and massive stars. For OB supergiants with moderate mass loss rates and a wind velocity distribution with β ≃ 0.8 . . . 1.0, no influence of the wind to the optical continuum, i.e. for λ <∼ 1.0 μm, is expected. Investigations of stellar and wind paramete...

Context. The outer Galactic disc contains some features such as the warp and flare, whose origin is still debated. Gaia data provide an excellent opportunity to probe at large distances study these features. Aims. We derive density distributions of average (old) whole population supergiants (representative a young population), we use them constrain their flare. By comparing results, how propert...