Related papers: Optically observable zero-age main-sequence O star…
The systematics of OB spectra are reviewed in the optical domain, dominated by photospheric lines, and in the far ultraviolet (both IUE and FUSE ranges), in which the stellar-wind profiles dominate. First, the two-dimensional (temperature,…
The winds of stars with very specific temperatures and luminosities are ideal for determining the magnitude and nature of mass loss in OB stars. I identify these stars and analyze their wind lines. The results are discussed within the…
We present optical $I$-band light curves of the stars towards a star-forming region Cygnus OB7 from 17 nights photometric observations. The light curves are generated from a total of 381 image frames with very good photometric precision.…
Zero Age Main Sequence (ZAMS) models with updated physical inputs are presented for selected assumptions about the chemical composition, covering the ranges 0.6 < M/Mo < 1.2, 0.0001 < Z < 0.04, 0.23 < Y < 0.34.The HR diagram location of the…
We present synthetic spectra and SEDs computed along evolutionary tracks at Z=1/5 Zsun and Z=1/30 Zsun, for masses between 15 and 150 Msun. We predict that the most massive stars all start their evolution as O2 dwarfs at sub-solar…
Population III (Pop III) stars, the first generation of stars formed from primordial gas, played a fundamental role in shaping the early universe through their influence on cosmic reionization, early chemical enrichment, and the formation…
Context. Late O-type stars at luminosities $\log L/L_\odot \lesssim 5.2$ show weak winds with mass-loss rates lower than 10$^{-8} M_\odot$ yr$^{-1}$. This implies that their photospheric layers are not strongly affected by the stellar wind.…
MATISSE represents a great opportunity to image the environment around massive and evolved stars. This will allow one to put constraints on the circumstellar structure, on the mass ejection of dust and its reorganization , and on the…
I have isolated a population of numerous F stars that appear to be pre-main-sequence (PMS). The candidate PMS stars have been identified using CM diagram, reddening, flux excess in the UV and near-infrared, and luminosity anomaly. Negative…
We study the stellar and wind properties of a sample of Galactic O dwarfs to track the conditions under which weak winds (i.e mass loss rates lower than ~ 1e-8 Msol/yr) appear. The sample is composed of low and high luminosity dwarfs…
Context: Recent near-infrared data have contributed to the discovery of new (obscured) massive stellar clusters and massive stellar populations in previously known clusters in our Galaxy. These discoveries lead us to view the Milky Way as…
We present a study of the metal-poor (~6% Z_sun) massive (>8 M_sun) main-sequence star population in the star-forming dwarf galaxy Sextans A. By modeling near-UV to near-IR photometry of individual stars using the Bayesian Extinction and…
We develop a photometric search method for identifying smouldering galaxies at $5< z < 8$, which are defined to have weak emission lines and thus generally have low specific star formation rates and may even be in a state of (temporary)…
CONTEXT: The spectral analysis of hot, massive stars is a fundamental astrophysical method to obtain their intrinsic properties and their feedback. Quantitative spectroscopy for hot, massive stars requires detailed numerical modeling of the…
Non-variable OH/IR stars are thought to have just left the asymptotic giant branch (AGB) phase. In this conventional picture, they must still show strong circumstellar extinction caused by the dust ejected during the AGB phase, and the…
Small amounts of star formation in elliptical galaxies are suggested by several results: surprisingly young ages from optical line indices, cooling X-ray gas, and mid-IR dust emission. Such star formation has previously been difficult to…
We have identified six early-type galaxies at z>2.8 in the central 5.76 arcmin^2 Hubble Ultra Deep Field NICMOS region based on a pronounced broad-band discontinuity between the NICMOS F110W and F160W bandpasses. These galaxies have red…
Identifying stars formed in pristine environments (Pop III) within the first billion years is vital to uncovering the earliest growth and chemical evolution of galaxies. Pop III galaxies, however, are typically expected to be too faint and…
Formation of massive stars by accretion requires a high accretion rate of > 10^-4 M_sun/yr to overcome the radiation pressure barrier of the forming stars. Here, we study evolution of protostars accreting at such high rates, by solving the…
We have searched for visual binaries with projected separations in the range 200-3000 AU (0.1"-1.5") among a sample of 96 stars in the massive young NGC 6611 cluster, 60 of them being subsequently identified as high probability cluster…