Fundamental parameters of 16 late-type stars derived from their angular diameter measured with VLTI/AMBER★

Abstract

Thanks to their large angular dimension and brightness, red giants and\nsupergiants are privileged targets for optical long-baseline interferometers.\nSixteen red giants and supergiants have been observed with the VLTI/AMBER\nfacility over a two-years period, at medium spectral resolution (R=1500) in the\nK band. The limb-darkened angular diameters are derived from fits of stellar\natmospheric models on the visibility and the triple product data. The angular\ndiameters do not show any significant temporal variation, except for one\ntarget: TX Psc, which shows a variation of 4% using visibility data. For the\neight targets previously measured by Long-Baseline Interferometry (LBI) in the\nsame spectral range, the difference between our diameters and the literature\nvalues is less than 5%, except for TX Psc, which shows a difference of 11%. For\nthe 8 other targets, the present angular diameters are the first measured from\nLBI. Angular diameters are then used to determine several fundamental stellar\nparameters, and to locate these targets in the Hertzsprung-Russell Diagram\n(HRD). Except for the enigmatic Tc-poor low-mass carbon star W Ori, the\nlocation of Tc-rich stars in the HRD matches remarkably well the\nthermally-pulsating AGB, as it is predicted by the stellar-evolution models.\nFor pulsating stars with periods available, we compute the pulsation constant\nand locate the stars along the various sequences in the Period -- Luminosity\ndiagram. We confirm the increase in mass along the pulsation sequences, as\npredicted by the theory, except for W Ori which, despite being less massive,\nappears to have a longer period than T Cet along the first-overtone sequence.\n