Diameter and photospheric structures of Canopus from ;AMBER/VLTI interferometry

Details Diameter and photospheric structures of Canopus from ;AMBER/VLTI interferometry Diameter and photospheric structures of Canopus from ;AMBER/VLTI interferometry

Oct 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008a%26a...489l...5d&link_type=abstract

Astronomy and Astrophysics, Volume 489, Issue 2, 2008, pp.L5-L8

Astronomy and Astrophysics

Astrophysics

6

Stars: Fundamental Parameters, Stars: Individual: Canopus, Supergiants, Methods: Observational, Techniques: High Angular Resolution, Techniques: Interferometric

Scientific paper

Context: Direct measurements of fundamental parameters and photospheric structures of post-main-sequence intermediate-mass stars are required for a deeper understanding of their evolution. Aims: Based on near-IR long-baseline interferometry we aim to resolve the stellar surface of the F0 supergiant star Canopus, and to precisely measure its angular diameter and related physical parameters. Methods: We used the AMBER/VLTI instrument to record interferometric data on Canopus: visibilities and closure phases in the H and K bands with a spectral resolution of 35. The available baselines (≃60-110 m) and the high quality of the AMBER/VLTI observations allowed us to measure fringe visibilities as far as in the third visibility lobe. Results: We determined an angular diameter of diameter=6.93±0.15 mas by adopting a linearly limb-darkened disk model. From this angular diameter and Hipparcos distance we derived a stellar radius R=71.4±4.0 R&sun;. Depending on bolometric fluxes existing in the literature, the measured diameter provides two estimates of the effective temperature: T_eff= 7284±107 K and T_eff= 7582±252 K. Conclusions: In addition to providing the most precise angular diameter obtained to date, the AMBER interferometric data point towards additional photospheric structures on Canopus beyond the limb-darkened model alone. A promising explanation for such surface structures is the presence of convection cells. We checked such a hypothesis using first order star-cell models and concluded that the AMBER observations are compatible with the presence of surface convective structures. This direct detection of convective cells on Canopus from interferometry can provide strong constraints to radiation-hydrodynamics models of photospheres of F-type supergiants.
Based on observations performed at the European Southern Observatory, Chile under ESO Program 079.D-0507.
Table 1 is only available in electronic form at http://www.aanda.org

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