Properties of the CO and H2O MOLsphere of the red supergiant Betelgeuse from VLTI/AMBER observations
Aims: We intend to investigate the shape and composition of the close molecular layer (also known as the MOLsphere) that surrounds the star. This analysis is part of a wider program that aims at understanding the dynamics of the circumstellar envelope of Betelgeuse.
Methods: On January and February 2011, Betelgeuse was observed using the Astronomical Multi-BEam combineR (AMBER) instrument of the Very Large Telescope Interferometer (VLTI) in the H and K bands. Using the medium spectral resolution of the instrument (R ~ 1500), we were able to investigate the carbon monoxide band heads and the water-vapor bands. We used two different approaches to analyse our data: a model fit in both the continuum and absorption lines and then a fit with a radiative hydrodynamics (RHD) simulation.
Results: Using the continuum data, we derive a uniform disk diameter of 41.01 ± 0.41 mas, a power law type limb-darkened disk diameter of 42.28 ± 0.43 mas and a limb-darkening exponent of 0.155 ± 0.009. Within the absorption lines, using a single layer model, we obtain parameters of the MOLsphere. Using a RHD simulation, we unveil the convection pattern in the visibilities.
Conclusions: We derived a new value of the angular diameter of Betelgeuse in the K band continuum. Our observations in the absorption lines are well reproduced by a molecular layer at 1.2 stellar radii containing both CO and H2O. The visibilities at higher spatial frequencies are matching a convection pattern in a RHD simulation.
Astronomy and Astrophysics
- Pub Date:
- December 2014
- infrared: stars;
- techniques: interferometric;
- stars: late-type;
- stars: atmospheres;
- stars: individual: Betelgeuse;
- Astrophysics - Solar and Stellar Astrophysics
- 13 pages, 11 figures, accepted for publication in Astronomy &