Volume 548, December 2012
|Number of page(s)||11|
|Published online||13 November 2012|
A time evolution model of chromospheric activity on the main sequence
1 European Space Agency, ESTEC – Postbus 299, 2200 AG Noordwijk, The Netherlands
2 Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
3 INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
4 Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
5 Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
6 Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
7 Laboratoire d’Astrophysique de Marseille, 38 rue Frdric Joliot-Curie, 13388 Marseille Cedex 13, France
Received: 23 February 2012
Accepted: 21 September 2012
Aims. The present study reports measurements of the rotation period of a young solar analogue, estimates of its surface coverage by photospheric starspots and of its chromospheric activity level, and derivations of its evolutionary status. Detailed observations of many young solar-type stars, such as the one reported in the present paper, provide insight into rotation and magnetic properties that may have prevailed on the Sun in its early evolution.
Methods. Using a model based on the rotational modulation of the visibility of active regions, we analysed the high-accuracy CoRoT lightcurve of the active star CoRoT 102899501. Spectroscopic follow-up observations were used to derive its fundamental parameters. We compared the chromospheric activity level of Corot 102899501 with the R′HK index distribution vs age established on a large sample of solar-type dwarfs in open clusters. We also compared the chromospheric activity level of this young star with a model of chromospheric activity evolution established by combining relationships between the R′HK index and the Rossby number with a recent model of stellar rotation evolution on the main sequence.
Results. We measure the spot coverage of the stellar surface as a function of time and find evidence for a tentative increase from 5 − 14% at the beginning of the observing run to 13−29% 35 days later. A high level of magnetic activity on Corot 102899501 is corroborated by a strong emission in the Balmer and Ca ii H and K lines (R′HK ~ -4). The starspots used as tracers of the star rotation constrain the rotation period to 1.625 ± 0.002 days and do not show evidence for differential rotation. The effective temperature (Teff = 5180 ± 80 K), surface gravity (log g = 4.35 ± 0.1), and metallicity ([M/H] = 0.05 ± 0.07 dex) indicate that the object is located near the evolutionary track of a 1.09 ± 0.12 M⊙ pre-main sequence star at an age of 23 ± 10 Myr. This value is consistent with the “gyro-age” of about 8−25 Myr, inferred using a parameterization of the stellar rotation period as a function of colour index and time established for the I-sequence of stars in stellar clusters.
Conclusions. We conclude that the high magnetic activity level and fast rotation of CoRoT 102899501 are manifestations of its stellar youth consistent with its estimated evolutionary status and with the detection of a strong Li i λ6707.8 Å absorption line in its spectrum. We argue that a magnetic activity level comparable to that observed on CoRot 102899501 could have been present on the Sun at the time of planet formation.
Key words: stars: activity / stars: atmospheres / stars: late-type / stars: magnetic field / stars: rotation / starspots
Based on observations obtained with CoRoT, a space project operated by the French Space Agency, CNES, with participation of the Science Programme of ESA, ESTEC/RSSD, Austria, Belgium, Brazil, Germany and Spain.
Based on observations made with the Anglo-Australian Telescope; the 2.1-m Otto Struve telescope at McDonald Observatory, Texas, USA; the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, in time allocated by the NOT “Fast-Track” Service Programme, OPTICON, and the Spanish Time Allocation Committee (CAT).
© ESO, 2012
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