Observations et mod\'elisations spectro-interf\'erom\'etriques longue base des \'etoiles et de leur environnement proche

TL;DR

This paper demonstrates the use of VLTI/AMBER spectro-interferometry to analyze fast rotating stars, developing digital tools and a semi-analytical model to measure stellar parameters and surface features with high precision.

Contribution

It introduces a chromatic semi-analytical model and digital reduction tools for interpreting interferometric data of rapidly rotating stars, enabling detailed stellar surface characterization.

Findings

Measured flattening and rotation velocities of four massive stars

Estimated temperature and gravity distribution across stellar surfaces

Opened pathways for systematic studies of star-environment interactions

Abstract

With the construction of the VLTI (Very Large Telescope Interferometer of the European Observatory ESO for the southern hemisphere) it is now possible to make observations with resolutions of the order of milli-arc-seconds, especially in IR with AMBER instrument (Astronomical Multi Beam Recombine). These new capabilities allow us to better constrain the stellar structures such as polar jets, equatorial disks and flattened photospheres of rotating stars. Thus the estimation of stellar fundamental parameters allows to explore in detail the mechanisms of mass loss, pulsation and magnetism governing the variability and the evolution of the stars. This thesis presents the results of fast rotating stars observations carried out on the AMBER spectro-interferometer VLTI in its high \& medium spectral resolutions modes. The observations were highly degraded by the optical defects of AMBER and their analysis required the development of specific digital reduction tools to reach the necessary precision for the interferometric measurements interpretation. In order to interpret those measures I developed a chromatic semi-analytical model of rapidly rotating star that allowed me to estimate, from the differential phases; the degree of flattening, the equatorial radius, the rotation velocity, the angle of inclination, the position angle of the star rotation axis in the sky, the local distribution of the effective temperature and the surface gravity of the star within the von Zeipel theorem. The results for four massive stars of spectral types B, A and F have allowed me to characterize the mechanisms discussed above and thus open some prospect for more systematic studies of similar objects, with extending later these studies to the relationship photosphere - circumstellar envelope.