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

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-v sin i 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-v sin i 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(R HK ) and v sin i 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-v sin i 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.

Dynamical Packing in the Habitable Zone: The Case of Beta CVn

“…As expected, the K values are well below that required of the RV data presented in this work, but may be feasible with developing facilities (Fischer et al 2016). Additionally, the work of Herrero et al (2012) showed that Beta CVn has a relatively high probability that the inclination of the equatorial plane is > 80°relative to the plane of the sky (see Section 3.1), and so the transit probabilities are likely underestimated.…”

“…Given the quiet nature of the star, the question arises as to the stellar equatorial plane relative to the plane of the sky since this will influence the detectability of planetary signatures, assuming those orbits are coplanar with the stellar equator. In order to optimize blind transit searches, Herrero et al (2012) provided a catalog of stars whose inclination of the equatorial plane is likely > 80°relative to the plane of the sky. They adopt a rotational velocity of = v i sin 2.9 km s −1 and activity index of ¢ = -R log 4.885 HK ( ) for Beta CVn, and their methodology predicts a high probability (50% larger than the average of their sample) of the star having an inclination >  80 .…”

HIP 114328: a new refractory-poor and Li-poor solar twin

“…There are not many studies of HIP 114328 in the literature, only two papers are reported by SIMBAD, one on stellar activity (Jenkins et al 2011) and the other one on a list of candidates for targeted transit searches (Herrero et al 2012). There are three earlier papers on delta Scuti stars, but they are actually misidentifications, and refer to DY Peg (HD 218549) and not to HIP 114328 (HD 218544).…”

HADES RV programme with HARPS-N at TNG

“…Using the radii and v sin i measurements from Maldonado et al (2017) combined with our rotation period determinations it is possible to estimate the inclination of the star's pole to the line A89, page 9 of 17 of sight. Even for those stars where the period could not be determined from the time series, we have an estimation based on the mean level of chromospheric activity (Table A.3) in a similar way as in Herrero et al (2012). The parameters and uncertainties are calculated by bootstrapping simulations.…”