Benchmarking the fundamental parameters of Ap stars with optical long-baseline interferometric measurements
Context. The variety of physical processes at play in chemically peculiar stars makes it difficult to determine their fundamental parameters. In particular, for the magnetic ones, called Ap stars, the strong magnetic fields and the induced spotted stellar surfaces may lead to biased effective temperatures when these values are derived through spectro-photometry. <BR /> Aims: […]
Calibrating the surface brightness – color relation for late-type red giants stars in the visible domain using VEGA/CHARA interferometric observations
Context. The surface brightness – color relationship (SBCR) is a poweful tool for determining the angular diameter of stars from photometry. It was for instance used to derive the distance of eclipsing binaries in the Large Magellanic Cloud (LMC), which led to its distance determination with an accuracy of 1%. <BR /> Aims: We calibrate […]
Visible and near-infrared spectro-interferometric analysis of the edge-on Be star o Aquarii
<BR /> Aims: We present a detailed visible and near-infrared spectro-interferometric analysis of the Be-shell star o Aquarii from quasi-contemporaneous CHARA/VEGA and VLTI/AMBER observations. <BR /> Methods: We analyzed spectro-interferometric data in the Hα (VEGA) and Brγ (AMBER) lines using models of increasing complexity: simple geometric models, kinematic models, and radiative transfer models computed with […]
NAOMI: the adaptive optics system of the Auxiliary Telescopes of the VLTI
Context. The tip-tilt stabilisation system of the 1.8 m Auxiliary Telescopes of the Very Large Telescope Interferometer was never dimensioned for robust fringe tracking, except when atmospheric seeing conditions are excellent. <BR /> Aims: Increasing the level of wavefront correction at the telescopes is expected to improve the coupling into the single-mode fibres of the […]
Spectro-interferometric observations of a sample of Be stars. Setting limits to the geometry and kinematics of stable Be disks
Context. Be stars are rapid rotators surrounded by a gaseous disk envelope whose origin is still under debate. This envelope is responsible for observed emission lines and large infrared excess. <BR /> Aims: To progress in the understanding of the physical processes involved in the disk formation, we estimate the disk parameters for a sample […]
Fibered visible interferometry and adaptive optics: FRIEND at CHARA
<BR /> Aims: In the context of the future developments of long baseline interferometry at visible wavelengths, we have built a prototype instrument called Fibered spectrally Resolved Interferometer – New Design (FRIEND) based on single mode fibers and a new generation detector called Electron Multiplying Charge-Coupled Device (EMCCD). Installed on the Center for High Angular […]
Physical properties of β Lyrae A and its opaque accretion disk
Mass exchange and mass loss in close binaries can significantly affect their evolution, but a complete self-consistent theory of these processes is still to be developed. Processes such as radiative shielding due to a hot-spot region, or a hydrodynamical interaction of different parts of the gas stream have been studied previously. In order to test […]
Multi-epoch VLTI-PIONIER imaging of the supergiant V766 Cen
Context. The star V766 Cen (=HR 5171A) was originally classified as a yellow hypergiant but lately found to more likely be a 27-36 M<SUB>☉</SUB> red supergiant (RSG). Recent observations indicated a close eclipsing companion in the contact or common-envelope phase. <BR /> Aims: Here, we aim at imaging observations of V766 Cen to confirm the […]
Flattening and surface-brightness of the fast-rotating star δ Persei with the visible VEGA/CHARA interferometer
Context. Rapid rotation is a common feature for massive stars, with important consequences on their physical structure, flux distribution and evolution. Fast-rotating stars are flattened and show gravity darkening (non-uniform surface intensity distribution). Another important and less studied impact of fast-rotation in early-type stars is its influence on the surface brightness colour relation (hereafter SBCR), […]
VEGA/CHARA interferometric observations of Cepheids. I. A resolved structure around the prototype classical Cepheid δ Cep in the visible spectral range
Context. The B-W method is used to determine the distance of Cepheids and consists in combining the angular size variations of the star, as derived from infrared surface-brightness relations or interferometry, with its linear size variation, as deduced from visible spectroscopy using the projection factor. The underlying assumption is that the photospheres probed in the […]