alpha Centauri A in the far infrared - First measurement of the temperature minimum of a star other than the Sun
Artikel i vetenskaplig tidskrift, 2013

Context. Chromospheres and coronae are common phenomena on solar-type stars. Understanding the energy transfer to these heated atmospheric layers requires direct access to the relevant empirical data. Study of these structures has, by and large, been limited to the Sun thus far. Aims. The region of the temperature reversal can be directly observed only in the far infrared and submillimetre spectral regime. We aim at determining the characteristics of the atmosphere in the region of the temperature minimum of the solar sister star alpha Cen A. As a bonus this will also provide a detailed mapping of the spectral energy distribution, i.e. knowledge that is crucial when searching for faint, Kuiper belt-like dust emission around other stars. Methods. For the nearby binary system alpha Cen, stellar parameters are known with high accuracy from measurements. For the basic model parameters T-eff, log g and [Fe/H], we interpolate stellar model atmospheres in the grid of Gaia/PHOENIX and compute the corresponding model for the G2 V star alpha Cen A. Comparison with photometric measurements shows excellent agreement between observed photospheric data in the optical and infrared. For longer wavelengths, the modelled spectral energy distribution is compared to Spitzer-MIPS, Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry. A specifically tailored Uppsala model based on the MARCS code and extending further in wavelength is used to gauge the emission characteristics of alpha Cen A in the far infared. Results. Similar to the Sun, the far infrared (FIR) emission of alpha Cen A originates in the minimum temperature region above the stellar photosphere in the visible. However, in comparison with the solar case, the FIR photosphere of alpha Cen A appears marginally cooler, T-min similar to T-160 (mu m) = 3920 +/- 375 K. Beyond the minimum near 160 mu m, the brightness temperatures increase, and this radiation very likely originates in warmer regions of the chromosphere of alpha Cen A. Conclusions. To the best of our knowledge, this is the first time a temperature minimum has been directly measured on a main-sequence star other than the Sun.

free absorption coefficient






stars: atmospheres



solar chromosphere



stars: chromospheres

circumstellar matter

stars: individual: alpha Cen


René Liseau

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

B. Montesinos

CSIC-INTA - Centro de Astrobiologia (CAB)

G. Olofsson

Stockholms universitet

G. Bryden

Jet Propulsion Laboratory, California Institute of Technology

J. P. Marshall

Universidad Autonoma de Madrid (UAM)

D. R. Ardila

European Space Astronomy Centre

National Aeronautics and Space Administration

A. B. Aran

European Southern Observatory Santiago

Max Planck-institutet

W. Danchi

NASA Goddard Space Flight Center

C. del Burgo

Instituto Nacional de Astrofisica Optica y Electronica

C. Eiroa

Universidad Autonoma de Madrid (UAM)

S. Ertel


M. Fridlund


A. Krivov

Friedrich-Schiller-Universität Jena

G.L. Pilbratt


A. Roberge

NASA Goddard Space Flight Center

P. Thebault

GEPI - Galaxies, Etoiles, Physique, Instrumentation

Joachim Wiegert

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

G. J. White

Open University

Rutherford Appleton Laboratory

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 549 L7


Astronomi, astrofysik och kosmologi