The Rotation of M Dwarfs Observed by the Apache Point Galactic Evolution Experiment

Abstract

We present the results of a spectroscopic analysis of rotational velocities in 714 M-dwarf stars observed by the SDSS-III Apache Point Galactic Evolution Experiment (APOGEE) survey. We use a template-fitting technique to estimate v i sin while simultaneously estimating g log , M H [ ], and T eff . We conservatively estimate that our detection limit is 8 km s −1 . We compare our results to M-dwarf rotation studies in the literature based on both spectroscopic and photometric measurements. Like other authors, we find an increase in the fraction of rapid rotators with decreasing stellar temperature, exemplified by a sharp increase in rotation near the M4 transition to fully convective stellar interiors, which is consistent with the hypothesis that fully convective stars are unable to shed angular momentum as efficiently as those with radiative cores. We compare a sample of targets observed both by APOGEE and the MEarth transiting planet survey and find no cases where the measured v i sin and rotation period are physically inconsistent, requiring i sin 1 > . We compare our spectroscopic results to the fraction of rotators inferred from photometric surveys and find that while the results are broadly consistent, the photometric surveys exhibit a smaller fraction of rotators beyond the M4 transition by a factor of ∼2. We discuss possible reasons for this discrepancy. Given our detection limit, our results are consistent with a bimodal distribution in rotation that is seen in photometric surveys.

Temperatures and Metallicities of M Dwarfs in the APOGEE Survey

“…A number of studies out of the M-dwarf ancillary survey have already been conducted to measure reliable fundamental atmospheric parameters and make kinematic measurements using spectral synthesis of atmo-spheric model grids. These studies include Deshpande et al (2013) and Gilhool et al (2018) which have studied the radial and rotational kinematics for 700+ sources; Souto et al (2017) and Souto et al (2018) which have modeled three exoplanet-hosting M dwarfs , determining T eff /log g/metallicity + 13 elemental abundances; Rajpurohit et al (2018) which tested BT-Settl Allard et al (2012) and MARCS Gustafsson et al (2008) model grids on 45 M dwarfs to estimate T eff /log g/metallicity; and Skinner et al (2018) which identified and measured mass ratios and radial velocities for 44 M-dwarf spectroscopic binaries. This work complements existing studies by producing a model-independent catalog of spectroscopic temperatures and metallicities to test against model predictions for the entire APOGEE M-dwarf sample, which we quantify to contain at least 10,000 sources to date (DR14).…”

Efficient and precise transit light curves for rapidly-rotating, oblate stars

“…These rapidly-rotating stars can be significantly oblate due to the centrifugal force pulling the equator outwards. Additionally, pre-main sequence stars and some young main sequence M dwarfs have been shown to display very rapid rotation (Rebull et al 2016(Rebull et al , 2017(Rebull et al , 2018(Rebull et al , 2020Stauffer et al 2018;Gilhool et al 2018) and are therefore also likely to be oblate. Other kinds of stars such as binary stars and exoplanet hosts may also exhibit deviations from spherical geometry due to tidal forces in addition to rotation (Prša 2018;Welsh et al 2010).…”

Photometric rotation periods for 107 M dwarfs from the APACHE survey

“…With TESS now beginning to survey the northern hemisphere, the study presented here is particularly timely, as all of the bright M dwarfs in the sample objective of this work are prime targets for the potential identification of transiting small planets amenable to high-precision mass determination and further atmospheric characterization measurements (TESS mission Level 1 Requirement). Our sample of rotation periods can also be used to further our understanding of important issues of stellar astrophysics pertaining to partly and fully convective stars, such as differences in rotational evolution (e.g., Gilhool et al 2018, and references therein) and the age-rotation-activity relation (e.g., Wright et al 2018;González-Álvarez et al 2019).…”