The fundamental parameters of the Ap star 78 Virginis. Could 78 Vir be a rapidly oscillating Ap star?
Context. Determining the effective temperature of Ap stars, including the roAp stellar pulsators, is a difficult task owing to their strong magnetic field and their related spotted surfaces. It is, however, an important step towards constraining models of their complex atmosphere and testing proposed pulsation excitation mechanisms. <BR /> Aims: Using the unique angular resolution […]
The peculiar fast-rotating star 51 Ophiuchi probed by VEGA/CHARA
Context. Stellar rotation is a key in our understanding of both mass-loss and evolution of intermediate and massive stars. It can lead to anisotropic mass-loss in the form of radiative wind or an excretion disk. <BR /> Aims: We wished to spatially resolve the photosphere and gaseous environment of 51 Oph, a peculiar star with […]
Spectral and spatial imaging of the Be+sdO binary <ASTROBJ>ϕ Persei</ASTROBJ>
<BR /> Aims: The rapidly rotating Be star <ASTROBJ>ϕ Persei</ASTROBJ> was spun up by mass and angular momentum transfer from a now stripped-down, hot subdwarf companion. Here we present the first high angular resolution images of <ASTROBJ>ϕ Persei</ASTROBJ> made possible by new capabilities in long-baseline interferometry at near-IR and visible wavelengths. We analyzed these images […]
Benchmark stars for Gaia Fundamental properties of the Population II star HD 140283 from interferometric, spectroscopic, and photometric data
Metal-poor halo stars are important astrophysical laboratories that allow us to unravel details about many aspects of astrophysics, including the chemical conditions at the formation of our Galaxy, understanding the processes of diffusion in stellar interiors, and determining precise effective temperatures and calibration of colour-effective temperature relations. To address any of these issues the fundamental […]
Improving the surface brightness-color relation for early-type stars using optical interferometry⋆
Context. The method of distance determination of eclipsing binaries consists in combining the radii of both components determined from spectro-photometric observations with their respective angular diameters derived from the surface brightness-color relation (SBC). However, the largest limitation of the method comes from the uncertainty on the SBC relation: about 2% for late-type stars (or 0.04 […]
V838 Monocerotis: the central star and its environment a decade after outburst
<BR /> Aims: V838 Monocerotis erupted in 2002, brightened in a series of outbursts, and eventually developed a spectacular light echo. A very red star emerged a few months after the outburst. The whole event has been interpreted as the result of a merger. <BR /> Methods: We obtained near- and mid-IR interferometric observations of […]
Beyond the diffraction limit of optical/IR interferometers. II. Stellar parameters of rotating stars from differential phases
Context. As previously demonstrated on Achernar, one can derive the angular radius, rotational velocity, axis tilt, and orientation of a fast-rotating star from the differential phases obtained by spectrally resolved long baseline interferometry using earth-rotation synthesis. <BR /> Aims: We applied this method on a small sample of stars for different spectral types and classes, […]
The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in the common envelope phase
Context. Only a few stars are caught in the very brief and often crucial stages when they quickly traverse the Hertzsprung-Russell diagram, and none has yet been spatially resolved in the mass transfer phase. <BR /> Aims: We initiated long-term optical interferometry monitoring of the diameters of massive and unstable yellow hypergiants (YHG) with the […]
Spectrally resolved interferometric observations of α Cephei and physical modeling of fast rotating stars
Context. When a given observational quantity depends on several stellar physical parameters, it is generally very difficult to obtain observational constraints for each of them individually. Therefore, we studied under which conditions constraints for some individual parameters can be achieved for fast rotators, knowing that their geometry is modified by the rapid rotation which causes […]
Evidence of an asymmetrical Keplerian disk in the Brγ and He I emission lines around the Be star HD 110432
Context. HD 110432 was classified as a γ Cas X-ray analog” since it has similar peculiar X-ray and optical characteristics