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α Centauri A in the far infrared: First measurement of the temperature minimum of a star other than the Sun

Liseau, R. and Montesinos, B. and Olofsson, G. and Bryden, G. and Marshall, J. P. and Ardila, D. and Aran, A. Bayo and Danchi, W. C. and del Burgo, C. and Eiroa, C. and Ertel, S. and Fridlund, M. C. W. and Krivov, A. V. and Pilbratt, G. L. and Roberge, A. and Thébault, P. and Wiegert, J. and White, G. J. (2013) α Centauri A in the far infrared: First measurement of the temperature minimum of a star other than the Sun. Astronomy and Astrophysics, 549 . Art. No. L7. ISSN 0004-6361.

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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 α   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 α   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 α   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 α   Cen   A in the far infared. Results. Similar to the Sun, the far infrared (FIR) emission of α   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 α   Cen   A appears marginally cooler, T_(min) ~ T_(160) μm = 3920 ± 375 K. Beyond the minimum near 160 μm, the brightness temperatures increase, and this radiation very likely originates in warmer regions of the chromosphere of α   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.

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Additional Information:© 2013 ESO. Received 22 November 2012. Accepted 14 December 2012. Published online 10 January 2013. Based on observations with Herschel, which is an ESA space observatory with science instruments provided by the European-led Principal Investigator consortia and with important participation from NASA. We thank Dr. K. Eriksson for the special computations of the α Cen A-Uppsala model. The Swedish authors appreciate the continued support by the Swedish National Space Board (SNSB) for our Herschel-projects. C. Eiroa, J. P. Marshall, and B. Montesinos are partially supported by Spanish grant AYA 2011/02622. A. Bayo was co-funded under the Marie Curie Actions of the European Comission (FP7-COFUND). S. Ertel thanks the French National Research Agency (ANR) for financial support through contract ANR-2010 BLAN-0505-01 (EXOZODI).
Funding AgencyGrant Number
Swedish National Space Board (SNSB)UNSPECIFIED
Spanish grantAYA 2011/02622
European Comission Marie Curie Actions (FP7-COFUND)UNSPECIFIED
French National Research Agency (ANR) EXOZODIANR-2010 BLAN-0505-01
Subject Keywords:stars: individual: α Cen – stars: atmospheres – stars: chromospheres – circumstellar matter – infrared: stars – submillimeter: stars
Record Number:CaltechAUTHORS:20130226-094232353
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Official Citation:α Centauri A in the far infrared - First measurement of the temperature minimum of a star other than the Sun R. Liseau, B. Montesinos, G. Olofsson, G. Bryden, J. P. Marshall, D. Ardila, A. Bayo Aran, W. C. Danchi, C. del Burgo, C. Eiroa, S. Ertel, M. C. W. Fridlund, A. V. Krivov, G. L. Pilbratt, A. Roberge, P. Thébault, J. Wiegert and G. J. White A&A 549 L7 (2013) DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37134
Deposited By: Ruth Sustaita
Deposited On:26 Feb 2013 21:45
Last Modified:03 Oct 2019 04:44

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