Volume 553, May 2013
|Number of page(s)||8|
|Published online||18 April 2013|
Spatially resolved, high-spectral resolution observation of the K giant Aldebaran in the CO first overtone lines with VLTI/AMBER⋆
Max−Planck−Institut für Radioastronomie,
Auf dem Hügel 69,
Received: 31 January 2013
Accepted: 9 March 2013
Aims. We present a high-spatial and high-spectral resolution observation of the well-studied K giant Aldebaran with AMBER at the Very Large Telescope Interferometer (VLTI). Our aim is to spatially resolve the outer atmosphere (so-called MOLsphere) in individual CO first overtone lines and derive its physical properties, which are important for understanding the mass-loss mechanism in normal (i.e., non-Mira) K−M giants.
Methods. Aldebaran was observed between 2.28 and 2.31 μm with a projected baseline length of 10.4 m and a spectral resolution of 12 000.
Results. The uniform-disk diameter observed in the CO first overtone lines is 20−35% larger than is measured in the continuum. We have also detected a signature of inhomogeneities in the CO-line-forming region on a spatial scale of ~45 mas, which is more than twice as large as the angular diameter of the star itself. While the MARCS photospheric model reproduces the observed spectrum well, the angular size in the CO lines predicted by the MARCS model is significantly smaller than observed. This is because the MARCS model with the parameters of Aldebaran has a geometrical extension of only ~2% (with respect to the stellar radius). The observed spectrum and interferometric data in the CO lines can be simultaneously reproduced by placing an additional CO layer above the MARCS photosphere. This CO layer is extended to 2.5 ± 0.3 R⋆ with CO column densities of 5 × 1019−2 × 1020 cm-2 and a temperature of 1500 ± 200 K.
Conclusions. The high spectral resolution of AMBER has enabled us to spatially resolve the inhomogeneous, extended outer atmosphere (MOLsphere) in the individual CO lines for the first time in a K giant. Our modeling of the MOLsphere of Aldebaran suggests a rather small gradient in the temperature distribution above the photosphere up to 2−3 R⋆.
Key words: infrared: stars / techniques: interferometric / stars: mass-loss / stars: late-type / stars: atmospheres / stars: individual: Aldebaran
© ESO, 2013
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.