Identification of New M Dwarfs in the Solar Neighborhood

Abstract

We present the results from a spectroscopic study of 1080 nearby active M dwarfs, selected by correlating the 2MASS and ROSAT catalogs. We have derived the spectral types and estimated distances for all of our stars. The spectral types range between K5 and M6. Nearly half of our stars lie within 50 pc. We have measured the equivalent width of the H alpha emission line. Our targets show an increase in chromospheric activity from early to mid-spectral types, with a peak in activity around M5. Using the count rate and hardness ratios obtained from the ROSAT catalog, we have derived the X-ray luminosities. Our stars display a "saturation-type" relation between the chromospheric and coronal activity. The relation is such that log (Lx/Lbol) remains "saturated" at a value of about -3 for varying H alpha equivalent width. We have found 568 matches in the USNO-B catalog, and have derived the tangential velocities for these stars. There is a slight trend of decreasing chromospheric activity with age, such that the stars with higher Vtan have lower H alpha equivalent widths. The coronal emission, however, remains saturated at a value of log (Lx/Lbol) -3 for varying tangential velocities, suggesting that the coronal activity remains saturated with age. We do not find any break in the saturation-type relation at the spectral type where stars become fully convective (~M3.5). Most of the stars in our sample show more coronal emission than the dMe stars in the Hyades and Praesepe clusters, and have Vtan< 40km/s, suggesting a young population.Comment: 24 pages, 8 figures, accepted for publication on A

2MASS 0213+3648 C: A wide T3 benchmark companion to an an active, old M dwarf binary

“…2MASS J0213+3648 was identified as an M dwarf in the solar neighbourhood with significant X-ray emission by Riaz et al (2006). Using low-resolution spectroscopy, they classified it as an M4.5 dwarf [a spectral type confirmed by Alonso-Floriano et al (2015)] with a spectrophotometric distance of 11 pc.…”

“…This object came into our input primary list from the nearby M dwarf catalogue of Lépine & Gaidos (2011). 2MASS J0213+3648 was discovered as an M4.5 by Riaz, Gizis & Harvin (2006) and identified as a close (0.217 arcsec) binary by Janson et al (2012), we refer to the unresolved M dwarf binary as 2MASS J0213+3648 AB. From the contrast ratio ( i = 2.16 ± 0.15 mag), Janson et al (2012) estimated a spectral type of M6.5 for the secondary component with the primary remaining an M4.5.…”

“…An iterative astrometric correction process is then used to determine the conversion from chip to celestial coordinates, minimizing the scatter between object positions on Janson et al (2014). c spectrum of combined object Riaz et al (2006). d based on flux ratio Janson et al (2012).…”

A Catalog of Galex Ultraviolet Emission From Spectroscopically Confirmed M Dwarfs*

“…However, several recent studies have examined the relationships between Hα and non-optical emission using data from all-sky surveys. In the X-ray, Riaz et al (2006) combined ROSAT data (Voges et al 1999) with sources in the Two Micron All Sky Survey (2MASS; Skrutskie et al 2006) to identify nearby M dwarfs for spectroscopic follow-up in order to examine the relationship between X-ray and Hα luminosity. They found that X-ray luminosity "saturates" (that there is an upper limit to the amount of quiescent X-ray emission) at a value of log(L X / L bol )∼−3.…”

“…When examining UV activity, it is likely necessary to account for this emission. We note that while Shkolnik & Barman (2014) and Ansdell et al (2015) use "saturation" to refer to the plateau of activity as a function of age for young stars, in this work we discuss saturation in the context of an upper limit to the level of emission in our most optically active stars (e.g., Riaz et al 2006).…”