alpha Centauri A in the far infrared - First measurement of the temperature minimum of a star other than the Sun
Journal article, 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.
solar chromosphere
circumstellar matter
binary-system
atmosphere
free absorption coefficient
components
submillimeter
infrared:
stars: individual: alpha Cen
camera
model
continuum
stars: chromospheres
stars: atmospheres
millimeter
Author
René Liseau
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
B. Montesinos
Centro de Astrobiologia (CAB)
G. Olofsson
Stockholm University
G. Bryden
Jet Propulsion Laboratory, California Institute of Technology
J. P. Marshall
Universidad Autonoma de Madrid (UAM)
D. R. Ardila
European Space Astronomy Centre (ESAC)
National Aeronautics and Space Administration (NASA)
A. B. Aran
European Southern Observatory Santiago
Max Planck Society
W. Danchi
NASA Goddard Space Flight Center
C. del Burgo
National Institute of Astrophysics, Optics and Electronics
C. Eiroa
Universidad Autonoma de Madrid (UAM)
S. Ertel
Grenoble Alpes University
M. Fridlund
European Space Research and Technology Centre (ESA ESTEC)
A. Krivov
Friedrich Schiller University Jena
G.L. Pilbratt
European Space Research and Technology Centre (ESA ESTEC)
A. Roberge
NASA Goddard Space Flight Center
P. Thebault
Observatoire de Paris-Meudon
Joachim Wiegert
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
G. J. White
STFC Rutherford Appleton Laboratory
Open University
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 549 L7Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201220776