Spectro-interferometry of 8 evolved stars

We determine the physical parameters of the outer atmosphere of a sample of eight evolved stars, including the red supergiant {alpha} Scorpii, the red giant branch stars {alpha} Bootis and {gamma} Crucis, the K giant {lambda} Velorum, the normal M giants BK Virginis and SW Virginis, and the Mira star W Hydrae (in two different luminosity phases) by spatially resolving the stars in the individual carbon monoxide (CO) first overtone lines.

We used the Astronomical Multi-BEam combineR (AMBER) instrument at the Very Large Telescope Interferometer (VLTI), in high-resolution mode ({lambda}/{Delta}{lambda}~=12000) between 2.28 and 2.31um in the K band. The maximal angular resolution is 10mas, obtained using a triplet telescope configuration, with baselines from 7 to 48m. By using a numerical model of a molecular atmosphere in a spherical shells (MOLsphere), called PAMPERO (an acronym for the 'physical approach of molecular photospheric ejection at high angular resolution for evolved stars'), we add multiple extended CO layers above the photospheric MARCS model at an adequate spatial resolution.