Dynamics of Rotation in M Dwarfs: Indications for a Change in the Dynamo Regime in Stars at the Onset of Complete Convection

Abstract

We have measured v sin i with high precision for a sample of dM3 stars (86 targets). We detected rotation in 82 stars (73 dM3 stars, and 9 dM3e stars). We compare our measurements of v sin i for all the stars in our dM0, dM2, dM3 and dM4 samples to those from other authors. We find a good agreement down to v sin i values of less than 1 km s −1 . The mean of the differences between measurements is only 0.42 km s −1 .We find that the distribution of P/sini for our dM3 stars is different from the distribution of P/sini among our samples of dM2 and dM4 stars. The mean rotation rate for the dM3 stars (excluding dM3e and sdM3 stars) is significantly slower (25.8 days) than for dM2 (14.4 days) and dM4 stars (11.4 days). Analogous behavior also emerges among the faster rotators (dMe stars): we find that a longer rotation period also occurs at spectral sub-type dM3e. Our data suggest that, as regards the rotational properties of lower main sequence stars, spectral sub-type dM3 stands out as exhibiting unusual slow rotation compared to that of adjoining sub-types. Our data lead us to suggest that the unusual rotational properties of M3 dwarfs may represent a signature of the transition to complete convection (TTCC).

ROTATION–ACTIVITY CORRELATIONS IN K AND M DWARFS. I. STELLAR PARAMETERS AND COMPILATIONS OF v sin i AND P/sin i FOR A LARGE SAMPLE OF LATE-K AND M DWARFS*

“…In total, the present compilation of P/sin i measures includes measurements for 418 different K and M dwarfs. As already reported in Paper XVI and in Houdebine & Mullan (2015, hereafter HM), we confirm here that these distributions vary with spectral subtype: the distributions among dK6, dM2, dM3, and dM4 stars are statistically different from one another. These findings imply that in order to study RACs one must construct RACs separately for each different spectral subtype.…”

“…As a preliminary to constructing RACs in K and M dwarfs, over the past several years we have reported improved spectroscopic measurements of rotational broadening vsini in stars of spectral subtypes dK4 (Houdebine 2011a, PaperXVI thereafter), dK6 (present study), dM2 (Houdebine 2008, Paper VIII, Houdebine 2010a, PaperXIV), dM3 (Houdebine & Mullan 2015), and dM4 (Houdebine 2012a, PaperXVII). An important aspect of our vsini measurements has to do with the use of the HARPS and SOPHIE spectrographs: these spectrographs are designed initially for exoplanet searches and are therefore very stable in wavelength in the long term (about 1 m s −1 for HARPS).…”

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

“…For example, the model suite may not span a large enough range of surface gravity at low temperatures, resulting in artificially inflated v i sin at low effective temperature if there is a physical correlation between g log and T eff . However, no such systematic effect has been found by other authors using PHOENIX templates (Houdebine & Mullan 2015;Maldonado et al 2017). Tests with template grids spanning a wide range of g log ( g 4.5 log 5.5   ) indicate that systematic bias of v i sin with g log is small and does not have a large impact on our detection threshold.…”

Magnetic Fields on the Flare Star Trappist-1: Consequences for Radius Inflation and Planetary Habitability

“…If the distinction between stars with or without a tachocline carried over in a one-to-one manner to dynamo operation, we might expect to observe a change in coronal emission (which is magnetically driven) at the transition to complete convection (TTCC at spectral type M3 [Houdebine and Mullan 2015;Houdebine et al 2017]). We might also expect to observe a clear change in magnetic topology at the TTCC as well.…”