In the core accretion model, gas giant formation is a race between growth and migration; for a core to become a jovian planet, it must accrete its envelope before it spirals into the host star. We use a multizone numerical model to extend our previous investigation of the “window of opportunity” for gas giant formation within a disk. When the collision cross-section enhancement due to core atmo...

[Abridged] Most exoplanets detected so far are close-in planets, which likely to be affected by tidal dissipation in their host star. To get a complete picture of the evolution star-planet systems one needs consider impact tides within both stellar radiative and convective zones. We aim provide general formalism assess zones for all spectral types, allowing study dynamics given system throughou...

Radial velocity searches for extrasolar planets have discovered stars undergoing slow accelerations. The accelerations are likely due to one or more gas giant planets or brown dwarfs orbiting with period longer than the total time span of observations. The stellar acceleration is proportional to the mass of the companion divided by the square of its radius from the star. In this paper we predic...

We used the multifiber spectrograph FLAMES on the ESO Very Large Telescope UT2 to derive atmospheric parameters, metallicities and abundances of O and Na for 79 red giant stars in the Galactic globular cluster NGC 6218 (M 12). We analyzed stars in the magnitude range from about 1 mag below the bump to the tip of the Red Giant Branch. The average metallicity we derive is [Fe/H]=−1.31 ± 0.004 ± 0...

We present a photometric study of the stars in ionizing star clusters embedded in several giant HII regions of M33 (CC93, IC 142, NGC 595, MA2, NGC 604 and NGC 588). Our photometry are based on the HST-WFPC2 images of these clusters. Color-magnitude diagrams and color-color diagrams of these clusters are obtained and are used for estimating the reddenings and ages of the clusters. The luminosit...

We propose two statistical methods to derive oxygen abundances in HII regions and star forming galaxies and calibrate them with a sample of several hundred giant HII regions in spiral and blue compact galaxies as well as of galaxies from the Sloan Digital Sky Survey. We show the advantages of our new abundance indicators over previous ones.

The abundances of Fe, C, N, and Ba have been derived for the Carbon-Enhanced Metal-Poor star HE 1305+0132. The C and N abundances are typical of CEMP stars. The Ba abundance, derived for the first time for HE 1305+0132, is found to be enhanced relative to Fe, placing this star in the CEMP-s group. Combined with a previously derived highly enhanced abundance of F, the chemical composition of HE ...

Transient X-ray emission, with an approximate t−0.7 decay, was observed from SGR 1900+14 over 40 days following the the giant flare of 27 Aug 1998. We calculate in detail the diffusion of heat to the surface of a neutron star through an intense 1014 − 1015 G magnetic field, following the release of magnetic energy in its outer layers. We show that the power law index, the fraction of burst ener...

xvii Chapter 1 Motivation 1 Chapter 2 Stellar evolution, Compact Stars, Accretion discs and X-ray binaries 3 2.1 Stellar evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1 Star Formation . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1.1 Protostars . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1.2 Stellar Mass limits . . . . . . . . . . . . . . . . . . 5 ...

When a spinning-down neutron star undergoes a phase transition that produces quark matter in its core, a Super-Giant Glitch of the order ∆Ω/Ω ∼ 0.3 occurs on time scales from 0.05 seconds to a few minutes. The energy released is about 10 ergs and can account for Gamma Ray Bursts at cosmological distances. The estimated burst frequency, 10 per year per galaxy, is in very good agreement with obse...