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How dusty is ɑ Centauri? Excess or non-excess over the infrared photospheres of main-sequence stars

Wiegert, J. and Liseau, R. and Thébault, P. and Olofsson, G. and Mora, A. and Bryden, G. and Marshall, J. P. and Eiroa, C. and Montesinos, B. and Ardila, D. and Augereau, J. C. and Aran, A. Bayo and Danchi, W. C. and del Burgo, C. and Ertel, S. and Fridlund, M. C. W. and Hajigholi, M. and Krivov, A. V. and Pilbratt, G. L. and Roberge, A. and White, G. J. and Wolf, S. (2014) How dusty is ɑ Centauri? Excess or non-excess over the infrared photospheres of main-sequence stars. Astronomy and Astrophysics, 563 . Art. No. A102. ISSN 0004-6361.

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Context. Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby, solar-type binary α Centauri have metallicities that are higher than solar, which is thought to promote giant planet formation. Aims. We aim to determine the level of emission from debris around the stars in the α Cen system. This requires knowledge of their photospheres. Having already detected the temperature minimum, T_(min), of α Cen A at far-infrared wavelengths, we here attempt to do the same for the more active companion α Cen B. Using the α Cen stars as templates, we study the possible effects that T_(min) may have on the detectability of unresolved dust discs around other stars. Methods. We used Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry to determine the stellar spectral energy distributions in the far infrared and submillimetre. In addition, we used APEX-SHeFI observations for spectral line mapping to study the complex background around α Cen seen in the photometric images. Models of stellar atmospheres and of particulate discs, based on particle simulations and in conjunction with radiative transfer calculations, were used to estimate the amount of debris around these stars. Results. For solar-type stars more distant than α Cen, a fractional dust luminosity f_d ≡ L_(dust)/L_(star) ~ 2 × 10^(-7) could account for SEDs that do not exhibit the T_(min) effect. This is comparable to estimates of f_d for the Edgeworth-Kuiper belt of the solar system. In contrast to the far infrared, slight excesses at the 2.5σ level are observed at 24 μm for both α Cen A and B, which, if interpreted as due to zodiacal-type dust emission, would correspond to f_d ~ (1−3) × 10^(-5), i.e. some 10^2 times that of the local zodiacal cloud. Assuming simple power-law size distributions of the dust grains, dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the α Cen stars, viz. ≲ of 4 x 10^(-6) to M_☾ of 4 to 1000 μm size grains, distributed according to n(a) ∝ a^(−3.5). Similarly, for filled-in T_(min) emission, corresponding Edgeworth-Kuiper belts could account for ~10^(-3) M_☾ of dust. Conclusions. Our far-infrared observations lead to estimates of upper limits to the amount of circumstellar dust around the stars α Cen A and B. Light scattered and/or thermally emitted by exo-Zodi discs will have profound implications for future spectroscopic missions designed to search for biomarkers in the atmospheres of Earth-like planets. The far-infrared spectral energy distribution of α Cen B is marginally consistent with the presence of a minimum temperature region in the upper atmosphere of the star. We also show that an α Cen A-like temperature minimum may result in an erroneous apprehension about the presence of dust around other, more distant stars.

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Additional Information:© 2014 ESO. Article published by EDP Sciences. Published online 17 March 2014. Received 13 May 2013. Accepted 21 January 2014. Based on observations with Herschel which is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. And also based on observations with APEX, which is a 12 m diameter submillimetre telescope at 5100 m altitude on Llano Chajnantor in Chile. The telescope is operated by Onsala Space Observatory, Max-Planck-Institut für Radioastronomie (MPIfR), and European Southern Observatory (ESO). We thank the referee for the critical reading of the manuscript and the valuable suggestions that improved the quality of the paper. We are also grateful to H. Olofsson for granting his Director’s Discretionary Time to this project. We also wish to thank P. Bergman for his help with the APEX observations on such short notice and the swift reduction of the data. We appreciate the continued support of the Swedish National Space Board (SNSB) for our Herschel projects. The Swedish authors appreciate the continued support from 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 2011/26202. 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 2011/26202
European Comission Marie Curie Actions (FP7-COFUND) UNSPECIFIED
French National Research Agency (ANR) EXOZODIANR-2010 BLAN-0505-01
Subject Keywords:stars: individual: Alpha Centauri, binaries: general, circumstellar matter, infrared: stars, infrared: planetary systems, submillimeter: stars
Record Number:CaltechAUTHORS:20140509-085031864
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Official Citation:How dusty is α Centauri? - Excess or non-excess over the infrared photospheres of main-sequence stars J. Wiegert, R. Liseau, P. Thébault, G. Olofsson, A. Mora, G. Bryden, J. P. Marshall, C. Eiroa, B. Montesinos, D. Ardila, J. C. Augereau, A. Bayo Aran, W. C. Danchi, C. del Burgo, S. Ertel, M. C. W. Fridlund, M. Hajigholi, A. V. Krivov, G. L. Pilbratt, A. Roberge, G. J. White and S. Wolf A&A 563 A102 (2014) DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:45631
Deposited By: Ruth Sustaita
Deposited On:09 May 2014 22:18
Last Modified:09 May 2014 22:18

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