Related papers: Quantitative Spectroscopy of Supergiants
Red Supergiants (RSGs) are cool (~4000K), highly luminous stars (L - 10^5 Lsun), and are among the brightest near-infrared (NIR) sources in star-forming galaxies. This makes them powerful probes of the properties of their host galaxies,…
Massive star evolution is still poorly understood, and observational tests are required to discriminate between different implementations of physical phenomenon in stellar evolution codes. By confronting stellar evolution models with…
Blue stragglers (BSS) are stars whose position in the Color-Magnitude Diagram (CMD) places them above the main sequence turn-off (TO) point of a star cluster. Using data from the core of 47 Tuc in the ultraviolet (UV), we have identified…
We present the analysis of the rest frame ultraviolet and optical spectra of 30 bright blue quasars at $z\sim3$, selected to examine the suitability of AGN as cosmological probes. In our previous works, we found an unexpectedly high…
The blue supergiant (BSG) problem, namely, the overabundance of BSGs inconsistent with classical stellar evolution theory, remains an open question in stellar astrophysics. Several theoretical explanations have been proposed, which may be…
Regular intrinsic brightness variations observed in many stars are caused by pulsations. These pulsations provide information on the global and structural parameters of the star. The pulsation periods range from seconds to years, depending…
B[e] stars are among the most peculiar objects in the sky. This spectral type, characterised by allowed and forbidden emission lines, and a large infrared excess, does not represent an homogenous class of objects, but instead, a mix of…
In the standard view of massive star evolution, luminous blue variables (LBVs) are transitional objects between the most massive O-type stars and Wolf-Rayet (WR) stars. With short lifetimes, these stars should all be found near one another.…
Dwarf elliptical (dE) galaxies, with blue absolute magnitudes typically fainter than $M_B = -16$, are the most numerous type of galaxy in the nearby universe. Tremendous advances have been made over the past several years in delineating the…
(abridged) The flux-weighted gravity-luminosity relationship (FGLR) of blue supergiant stars (BSG) links their absolute magnitude to the spectroscopically determined flux-weighted gravity log g = Teff^4. BSG are the brightest stars in the…
A search for a correlation between the luminosities of the brightest stars and luminosities of their host galaxies was carried out on archived Hubble Space Telescope (HST) F606W or F555W (V) and F814W (I) images of about 150 nearby…
Dwarf galaxies play an important role in our understanding of galaxy formation and evolution, and starbursts are believed to strongly affect their structure and evolution. Here we present a study of 12 of the nearest dwarf galaxies thought…
We have developed a new non-gray theory of the evolution, spectra, and colors of extrasolar giant planets (EGPs) and brown dwarfs that reveals their exotic nature and uniqueness. We have discovered that the fluxes of such objects for…
A massive star can enter the blue supergiant region either evolving directly from the main-sequence, or evolving from a previous red supergiant stage. The fractions of the blue supergiants having different histories depend on the internal…
We present an atlas composed of more than 1500 spectra of late-type stars (spectral types from G to M) observed simultaneously in the optical and calcium triplet spectral ranges. These spectra were obtained as part of a survey to search for…
Owing to their extreme crowding and high and variable extinction, stars in the Galactic Bulge, within +-2 degrees of the Galactic plane, and especially those in the Nuclear Star Cluster, have only rarely been targeted for an analyses of…
Lasting anywhere from a few milliseconds to several minutes, GRBs shine hundreds of times brighter than a typical supernova, making them briefly the brightest source of cosmic gamma-ray photons in the observable Universe. This thesis…
B supergiants (BSGs) are evolved stars with effective temperatures between 10 to 30 kK and are important to understand massive star evolution. Located on the edge of the line-driven wind regime, the study of their atmospheres is helpful to…
The most luminous galaxies in the blue passband have a larger correlation amplitude than L* galaxies. They do not appear to be preferentially located in rich clusters or groups, but a significant fraction of them seem to be in systems which…
Massive stars typically undergo short-lived post-main sequence evolutionary phases with strong mass loss and occasional mass eruptions. Many of such massive stars in transition phases have been identified based on their dusty envelopes. The…