We present near-IR interferometric measurements of the K1.5 giant Arcturus (α Bootis), obtained at the IOTA interferometer with the FLUOR instrument, in four narrow filters with central wavelengths ranging from 2.03μm to 2.39μm. These observations were expected to allow us to quantify the wavelength dependence of the diameter of a typical K giant. They are compared to predictions from both plan...

We propose a scenario to form low-mass, single, slow rotating white dwarfs from a solar-like star accompanied by a massive planet, or a brown dwarf, in a relatively close orbit (e.g. HD 89707). Such white dwarfs were recently found by Maxted & Marsh (1998). When the solar-like star ascends the giant branch it captures the planet and the subsequent spiral-in phase expels the envelope of the gian...

Photoevaporation driven by the ultraviolet radiation from massive stars severely limits the lifetime of protoplanetary discs around stars formed within stellar clusters. I investigate the resulting influence of clustered environments on the probability of giant planet formation, and show that for clusters as rich, or richer than, Orion, the time available for planet formation is likely to be li...

Giant planets orbiting stars other than the Sun are clearly detectable through precise radial-velocity measurements of the orbital reflex motion of the parent star. In the four years since the discovery 1 of the companion to the star 51 Peg, similar low-amplitude " Doppler star wobbles " have revealed the presence of some 20 planets orbiting nearby solar-type stars. Several of these newly-disco...

The giant galaxies located at the centers of cluster cooling flows are frequently sites of vigorous star formation. In some instances, star formation appears to have been triggered by the galaxy’s radio source. The colors and spectral indices of the young populations are generally consistent with short duration bursts or continuous star formation for durations ≪ 1 Gyr, which is less than the pr...

Light element (Li, Li and Be) depletion isochrones for halo stars have been calculated with standard stellar evolution models. These models include the latest available opacities and are computed through the sub-giant branch. If Li is not produced in appreciable amounts by stellar flares, then the detection of Li in HD 84937 by Smith, Lambert & Nissen (1993) is compatible with standard stellar ...

We observed with Chandra two peculiar galactic X–ray sources, 4U 1700+24 and 4U 1954+319, which are suspected to have a M-type giant star as optical counterpart, in order to get an high-precision astrometric position for both of them. The peculiarity of these sources lies in the fact that these are the only two cases among low-mass X–ray binaries (LMXBs), besides the confirmed case of GX 1+4, f...

The existence of Uranus and Neptune presents severe difficulties for the core accretion model for the formation of ice giant planets. We suggest an alternative mechanism, namely disk instability leading to the formation of gas giant protoplanets, coagulation and settling of dust grains to form ice/rock cores at their centers, and photoevaporation of their gaseous envelopes by a nearby OB star, ...

Based on the large number of elliptical planetary nebulae I argue that ∼ 55% of all progenitors of planetary nebulae have planets around them. The planets spin up the stars when the later evolve along the red giant branch or along the asymptotic giant branch. The arguments, which were presented in several of my earlier works, and are summarized in the paper, suggest that the presence of four ga...

We report on HST/ACS photometry of the rich intermediate-age star cluster NGC 1846 in the Large Magellanic Cloud, which clearly reveals the presence of a double main sequence turn-off in this object. Despite this, the main sequence, sub-giant branch, and red giant branch are all narrow and well-defined, and the red clump is compact. We examine the spatial distribution of turn-off stars and demo...