Zodiacal Exoplanets in Time (ZEIT) III: A Neptune-sized planet orbiting a pre-main-sequence star in the Upper Scorpius OB Association
Authors:
Mann et al
Abstract:
We confirm and characterize a close-in (Porb = 5.425 days), super-Neptune sized (5.04+0.34−0.37 Earth radii) planet transiting EPIC 205117205 (2MASS J16101473-1919095), a late-type (M3) pre-main sequence (≃11 Myr-old) star in the Upper Scorpius subgroup of the Scorpius-Centaurus OB association. The host star has the kinematics of a member of the Upper Scorpius OB association, and its spectrum contains lithium absorption, an unambiguous sign of youth (less than 20 Myr) in late-type dwarfs. We combine photometry from K2 and the ground-based MEarth project to refine the planet's properties and constrain the average stellar density. We determine EPIC 205117205's bolometric flux and effective temperature from moderate resolution spectra. By utilizing isochrones that include the effects of magnetic fields, we derive a precise (6-7%) radius and mass for the host star, and a stellar age consistent with the established value for Upper Scorpius. Follow-up high-resolution imaging and Doppler spectroscopy confirm that the transiting object is not a stellar companion or a background eclipsing binary blended with the target. The shape of the transit, the constancy of the transit depth and periodicity over 1.5 years, and the independence with wavelength rules out stellar variability, or a dust cloud or debris disk partially occulting the star as the source of the signal; we conclude it must instead be planetary in origin. The existence of EPIC 205117205b suggests close-in planets can form in situ or migrate within ≃10 Myr, e.g., via interactions with a disk, and that long-timescale dynamical migration such as by Lidov-Kozai or planet-planet scattering is not responsible for all short-period planets.
Observations of exoplanets in time-evolving habitable zones of pre-main-sequence M dwarfs
Author:
Tian
Abstract:
It is recently proposed that planets in the habitable zones (HZ) of pre-main-sequence (PMS) M dwarfs are good targets for the detection of habitable environments. In this note we show that future ground-based telescopes will be able to observe planets in time-evolving HZ of PMS M dwarfs with duration 10–100 Myrs. Based on X-ray measurements, there are greater than 18 M0–M4 PMS stars within 10 pc, the characterization of potentially habitable exoplanets around which could provide highly valuable information regarding the evolution of habitable environments. There are tens of M dwarfs within 10 pc with X-ray to total luminosity ratios similar to that of the young Sun, the observations of potential planets around which could significantly improve our understanding of the physical states of early Solar System rocky planets.
