Exploring the Age-dependent Properties of M and L Dwarfs Using Gaia and SDSS

Abstract

We present a sample of 74, 216 M and L dwarfs a) constructed from two existing catalogs of cool dwarfs spectroscopically identified in the Sloan Digital Sky Survey (SDSS). We cross-matched the SDSS catalog with Gaia DR2 to obtain parallaxes and proper motions and modified the quality cuts suggested by the Gaia Collaboration to make them suitable for late-M and L dwarfs. We also provide relations between Gaia colors and absolute magnitudes with spectral type and conclude that (G − G RP ) has the tightest relation to spectral type for M and L dwarfs. In addition, we study magnetic activity as a function of position on the color-magnitude diagram, finding that Hα magnetically active stars have, on average, redder colors and/or brighter magnitudes than inactive stars. This effect cannot be explained by youth alone and might indicate that active stars are magnetically inflated, binaries and/or high metallicity. Moreover, we find that vertical velocity and vertical action dispersion are correlated with Hα emission, confirming that these two parameters are age indicators. We also find that stars below the main sequence have high tangential velocity which is consistent with a low metallicity and old population of stars that belong to the halo or thick disk.

Ross 19B: An Extremely Cold Companion Discovered via the Backyard Worlds: Planet 9 Citizen Science Project

“…The position of Ross 19A on a color-magnitude diagram compared to the well-characterized spectroscopic M dwarf sample of Kiman et al (2019) shows it is a typical mid-type M dwarf, with no clear deviation above or below the main sequence.…”

TESS Hunt for Young and Maturing Exoplanets (THYME). IV. Three Small Planets Orbiting a 120 Myr Old Star in the Pisces–Eridanus Stream*

“…TOI 451 B has Gaia DR2 parameters of B P −R P = 2.527 mag and T eff = 3507 K. The color corresponds to a spectral type of M3V according to Kiman et al (2019). TOI 451 B itself is likely a binary, as its Renormalized Unit Weight Error (RUWE; Lindegren et al 2018) 9 is RU W E = 1.24, higher than the distribution typically seen for single stars and indicative of binarity (Rizzuto et al 2018;Kraus et al, in preparation).…”

The population of M dwarfs observed at low radio frequencies

“…We detect 0.5 ± 0.1% of the stars in Gaia DR2 that are within 50 pc and which have spectral types M1.5 to M6.0. Each spectral type has an equal probability of detection, within uncertainty, although we note that the Gaia catalogue begins to become significantly incomplete for spectral types later than ∼M7 24 . Three of our detections (DG CVn, CR Dra, and GJ 3729) are known binaries with less than 3 AU separation, which is consistent with the known binarity rate of M dwarfs 25 .…”

“…After selecting all Gaia DR2 sources within 50 pc that are in the area so far surveyed by LoTSS, we followed the quality cuts outlined by Kiman et al 24 to form a clean sample of M dwarfs contained in Gaia DR2.…”