Optimizing exoplanet transit searches around low-mass stars with inclination constraints⋆
E. Herrero1,2, I. Ribas1, C. Jordi2, E. F. Guinan3 and S. G. Engle3
1 Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB, Facultat de Ciències, Torre C5 parell, 2a pl, 08193 Bellaterra, Spain
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2 Dept. d’Astronomia i Meteorologia, Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), Martí Franquès 1, 08028 Barcelona, Spain
3 Department of Astronomy & Astrophysics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085, USA
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Received: 2 August 2011
Accepted: 25 October 2011
Aims. We investigate a method to increase the efficiency of a targeted exoplanet search with the transit technique by preselecting a subset of candidates from large catalogs of stars. Assuming spin-orbit alignment, this can be achieved by considering stars that have a higher probability to be oriented nearly equator-on (inclination close to 90°).
Methods. We used activity-rotation velocity relations for low-mass stars with a convective envelope to study the dependence of the position in the activity-vsini diagram on the stellar axis inclination. We composed a catalog of G-, K-, M-type main-sequence simulated stars using isochrones, an isotropic inclination distribution and empirical relations to obtain their rotation periods and activity indexes. Then the activity-vsini diagram was completed and statistics were applied to trace the areas containing the higher ratio of stars with inclinations above 80°. A similar statistics was applied to stars from real catalogs with and vsini data to find their probability of being oriented equator-on.
Results. We present our method to generate the simulated star catalog and the subsequent statistics to find the highly inclined stars from real catalogs using the activity-vsini diagram. Several catalogs from the literature are analyzed and a subsample of stars with the highest probability of being equator-on is presented.
Conclusions. Assuming spin-orbit alignment, the efficiency of an exoplanet transit search in the resulting subsample of probably highly inclined stars is estimated to be two to three times higher than with a general search without preselection.
Key words: stars: activity / planets and satellites: detection / stars: rotation
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