Optimizing exoplanet transit searches around low-mass stars with inclination constraints^⋆

¹ Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB, Facultat de Ciències, Torre C5 parell, 2a pl, 08193 Bellaterra, Spain
e-mail: eherrero@ice.cat; iribas@ice.cat
² Dept. d’Astronomia i Meteorologia, Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), Martí Franquès 1, 08028 Barcelona, Spain
e-mail: carme.jordi@ub.edu
³ Department of Astronomy & Astrophysics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085, USA
e-mail: edward.guinan@villanova.edu; sengle01@villanova.edu

Received: 2 August 2011
Accepted: 25 October 2011

Abstract

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 $\log \mathrm{\left(}{\mathit{R}}_{\mathit{HK}}^{\mathrm{\prime }}\mathrm{\right)}$ 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.