The standard picture holds that giant elliptical galaxies formed in a single burst at high redshift. Aging of their stellar populations subsequently caused them to fade and become redder. The Canada-France Redshift Survey provides a sample of about 150 galaxies with the luminosities and colours of passively evolving giant ellipticals and with 0.1 < z < 1. This sample is inconsistent with the st...

We model the evolution of the abundances of light elements in carbon-enhanced metalpoor (CEMP) stars, under the assumption that such stars are formed by mass transfer in a binary system. We have modelled the accretion of material ejected by an asymptotic giant branch star on to the surface of a companion star. We then examine three different scenarios: one in which the material is mixed only by...

Context. Over the last decade, several groups of young (mainly low-mass) stars have been discovered in the solar neighbourhood (closer than ∼100 pc), thanks to cross-correlation between X-ray, optical spectroscopy and kinematic data. These young local associations – including an important fraction whose members are Hipparcos stars – offer insights into the star formation process in low-density ...

We study the response of the structure of an asymptotic giant branch (AGB) star to the accretion of a brown dwarf or planet in its interior. In particular, we examine the case in which the brown dwarf spirals-in, and the accreted matter is deposited at the base of the convective envelope and in the thin radiative shell surrounding the hydrogen burning shell. In our spherically symmetric simulat...

The nearby face-on spiral galaxy M101 has been observed with the Far-Infrared Surveyor (FIS) onboard AKARI. The far-infrared four-band images reveal fine spatial structures of M101, which include global spiral patterns, giant H II regions embedded in outer spiral arms, and a bar-like feature crossing the center. The spectral energy distribution of the whole galaxy shows the presence of the cold...

Over the last decade, several groups of young (mainly low-mass) stars have been discovered in the solar neighbourhood (closer than∼ 100 pc), thanks to cross-correlation between X-ray, optical spectroscopy and kinematic data. These young local associations including an important fraction whose members are Hipparcos stars offer insights into the star formation process in low-density environments,...

We investigate the gravitational interaction of a Jovian mass protoplanet with a gaseous disc with aspect ratio and kinematic viscosity expected for the protoplanetary disc from which it formed. Different disc surface density distributions have been investigated. We focus on the tidal interaction with the disc with the consequent gap formation and orbital migration of the protoplanet. Nonlinear...

We present the first detailed analysis of resolved stellar populations in the dwarf galaxies NGC 185 and NGC 205 based on archival V-and I-band WFPC2 pointings. For NGC 185 we deduce from the brightest main sequence and blue loop stars that star formation was probably still active about 4×10 8 yr ago; and have three key abundance-related results: (1) We identify ancient stars with [Fe/H]-1.5 de...

Stars generally form faster than the ambipolar diffusion time, suggesting that several processes short circuit the delay and promote a rapid collapse. These processes are considered here, including turbulence compression in the outer parts of giant molecular cloud (GMC) cores and GMC envelopes, GMC core formation in an initially supercritical state, and compression-induced triggering in dispers...