Spatially resolved dusty torus toward the red supergiant WOH G64 in the Large Magellanic Cloud - AstrophysicsReportar como inadecuado

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Abstract: We present N-band spectro-interferometric observations of the red supergiantWOH G64 in the Large Magellanic Cloud LMC using MIDI at the Very LargeTelescope Interferometer VLTI. The location of WOH G64 on the H-R diagrambased on the previously estimated luminosities is in serious disagreement withthe current stellar evolution theory. The dust envelope around WOH G64 has beenspatially resolved with a baseline of ~60 m-the first MIDI observations toresolve an individual stellar source in an extragalactic system. The observedN-band visibilities show a slight decrease from 8 to 10 micron and a gradualincrease longward of 10 micron, reflecting the 10 micron silicate feature inself-absorption. The visibilities measured at four position angles differing by~60 degrees but at approximately the same baseline length ~60 m do not show anoticeable difference, suggesting that the object appears nearlycentrosymmetric. The observed N-band visibilities and spectral energydistribution can be reproduced by an optically and geometrically thick silicatetorus model viewed close to pole-on. The luminosity of the central star isderived to be 2.8 x 10^5 Lsun, which is by a factor of 2 lower than theprevious estimates based on spherical models. The lower luminosity newlyderived from our MIDI observations and two-dimensional modeling brings thelocation of WOH G64 on the H-R diagram in much better agreement withtheoretical evolutionary tracks for a 25 Msun star. We also identify the H2Oabsorption features at 2.7 and 6 micron in the spectra obtained with theInfrared Space Observatory and the Spitzer Space Telescope. The 2.7 micronfeature originates in the photosphere and-or the extended molecular layers,while the 6 micron feature is likely to be of circumstellar origin.

Autor: Keiichi Ohnaka, Thomas Driebe, Karl-Heinz Hofmann, Gerd Weigelt, Markus Wittkowski


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