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48 results for “M Dwarfs”
Atmospheric Parameters and Abundances for Half a Million M Dwarfs via Cycle-StarNet
<p>Final version for submission.</p>
Brightest M Dwarfs in the Northern Sky Spectroscopic Catalog
This table contains a spectroscopic catalog of the 1564 brightest (J < 9<sup>m</sup>) M-dwarf candidates in the northern sky, as selected from the SUPERBLINK proper-motion catalog (Lepine and Shara 2005, AJ, 129, 1483). Observations confirm 1408 of the candidates to be late-K and M dwarfs with spectral subtypes K7 - M6. From the low (mu > 40 mas yr<sup>-1</sup>) proper motion limit and high level of completeness of the SUPERBLINK catalog in that magnitude range, the authors estimate that their spectroscopic census most likely includes > 90% of all existing, northern-sky M dwarfs with apparent magnitude J < 9<sup>m</sup>. Only 682 stars in this sample are listed in the Third Catalog of Nearby Stars (CNS3, Gliese and Jahreiss 1991); most others are relative unknowns and have spectroscopic data presented here for the first time. Spectral subtypes are assigned based on spectral index measurements of CaH and TiO molecular bands; a comparison of spectra from the same stars obtained at different observatories, however, reveals that spectral band index measurements are dependent on spectral resolution, spectrophotometric calibration, and other instrumental factors. As a result, the authors find that a consistent classification scheme requires that spectral indices be calibrated and corrected for each observatory/instrument used. After systematic corrections and a recalibration of the subtype-index relationships for the CaH2, CaH3, TiO5, and TiO6 spectral indices, the authors find that they can consistently and reliably classify all the stars to a half-subtype precision. The use of corrected spectral indices further requires them to recalibrate the zeta parameter, a metallicity indicator based on the ratio of TiO and CaH optical bandheads. However, the authors find that their zeta values are not sensitive enough to diagnose metallicity variations in dwarfs of subtypes M2 and earlier (+/- 0.5 dex accuracy) and are only marginally useful at later M3-M5 subtypes (+/- 0.2 dex accuracy). Fits of their spectra to the Phoenix atmospheric model grid are used to estimate effective temperatures. These suggest the existence of a plateau in the M1-M3 subtype range, in agreement with model fits of infrared spectra but at odds with photometric determinations of T<sub>eff</sub>. Existing geometric parallax measurements are extracted from the literature for 624 stars, and are used to determine spectroscopic and photometric distances for all the other stars. Active dwarfs are identified from measurements of H-alpha equivalent widths, and the authors find a strong correlation between H-alpha emission in M dwarfs and detected X-ray emission from ROSAT and/or a large UV excess in the GALEX point source catalog. Proper motion data and photometric distances are combined in order to evaluate the (U, V, W) distribution in velocity space, which is found to correlate tightly with the velocity distribution of G dwarfs in the solar neighborhood. However, active stars show a smaller dispersion in their space velocities, which is consistent with those stars being younger on average. The authors state that this catalog will be very useful for guiding the selection of the best M dwarf targets for exoplanet searches, in particular those using high-precision radial velocity measurements. This online catalog was created by the HEASARC in June 2013 based on a machine-readable version of Tables 1, 3 and 7 from the paper which were obtained from the AJ website (Tables 1 and 3) or from the first author (Table 7). This is a service provided by NASA HEASARC .
Bright M Dwarf All-Sky Catalog
This table contains an all-sky catalog of M dwarf stars with apparent infrared magnitude J < 10. The 8889 stars are selected from the ongoing SUPERBLINK survey of stars with proper motion mu > 40 mas yr<sup>-1</sup>, supplemented on the bright end with the Tycho-2 catalog. Completeness tests which account for kinematic (proper motion) bias suggest that this catalog represents ~75% of the estimated ~11,900 M dwarfs with J < 10 expected to populate the entire sky. The catalog is, however, significantly more complete for the northern sky (~90%) than it is for the south (~60%). Stars are identified as cool, red M dwarfs from a combination of optical and infrared color cuts, and are distinguished from background M giants and highly reddened stars using either existing parallax measurements or, if such measurements are lacking, using their location in an optical-to-infrared reduced proper motion diagram. These bright M dwarfs are all prime targets for exoplanet surveys using the Doppler radial velocity or transit methods; the combination of low-mass and bright apparent magnitude should make possible the detection of Earth-size planets on short-period orbits using currently available techniques. Parallax measurements, when available, and photometric distance estimates are provided for all stars, and these place most systems within 60 pc of the Sun. Spectral type estimated from V-J color shows that most of the stars range from K7 to M4, with only a few late M dwarfs, all within 20 pc. Proximity to the Sun also makes these stars good targets for high-resolution exoplanet imaging searches, especially if younger objects can be identified on the basis of X-ray or UV excess. For that purpose, we include X-ray flux from ROSAT and FUV/NUV ultraviolet magnitudes from GALEX for all stars for which a counterpart can be identified in those catalogs. Additional photometric data include optical magnitudes from Digitized Sky Survey plates and infrared magnitudes from the Two Micron All Sky Survey. This table was first created by the HEASARC in October 2011 based on electronic versions of Tables 1 and 2 from the reference paper which were obtained from the AJ web site. A slightly revised version based on corrected versions of the input tables received from the author was ingested in December 2011. This is a service provided by NASA HEASARC .
UV/X-Ray Data for M Dwarfs Within 10 Parsecs
M dwarfs are the most numerous stars in the galaxy. They are characterized by strong magnetic activity. The ensuing high-energy emission is crucial for the evolution of their planets and the eventual presence of life on them. The authors systematically study the X-ray and ultraviolet emission of a subsample of M dwarfs from a recent proper-motion survey, selecting all M dwarfs within 10 pc to obtain a nearly volume-limited sample (~90% completeness). Archival ROSAT, XMM-Newton and GALEX data are combined with published spectroscopic studies of H-alpha emission and rotation to obtain a broad picture of stellar activity on M dwarfs. The authors make use of synthetic model spectra to determine the relative contributions of photospheric and chromospheric emission to the ultraviolet flux. They also analyze the same diagnostics for a comparison sample of young M dwarfs in the TW Hya association (~10 Myr old). The authors find that generally the emission in the GALEX bands is dominated by the chromosphere but the photospheric component is not negligible in early-M field dwarfs. The surface fluxes for the H-alpha, near-ultraviolet, far-ultraviolet and X-ray emission are connected via a power-law dependence. The authors present in the reference paper for the first time such flux-flux relations involving broad-band ultraviolet emission for M dwarfs. Activity indices are defined as the flux ratios between the activity diagnostics and the bolometric flux of the star in analogy to the Ca II R'(HK) index. For a given spectral type, these indices display a spread of 2-3 dex which is largest for M4-type stars. Strikingly, at mid-M spectral types, the spread of rotation rates is also at its highest level. The mean activity index for fast rotators, likely representing the saturation level, decreases from X-rays over the FUV to the NUV band and H-alpha, i.e. the fractional radiation output increases with atmospheric height. The comparison to the ultraviolet and X-ray properties of TW Hya members shows a drop of nearly three orders of magnitude for the luminosity in these bands between ~10 Myr and a few Gyr age. A few young field dwarfs (<1 Gyr) in the 10-pc sample bridge the gap indicating that the drop in magnetic activity with age is a continuous process. The slope of the age decay is steeper for the X-ray than for the UV luminosity. This sample is based on the All-Sky Catalog of bright M dwarfs published by Lepine & Gaidos (2011, AJ, 142, 138, <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/AJ/142/138">CDS Cat. J/AJ/142/138</a>, available at the HEASARC as the MDWARFASC table). The authors selected all 163 stars from this reference that are within 10pc. Four of these stars that were discovered to be actually late K-type stars were removed from this initial sample, leaving a final sample of 159 stars. This table was created by the HEASARC in July 2017 based upon <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/MNRAS/431/2063">CDS Catalog J/MNRAS/431/2063</a> files table1.dat and table2.dat. The positions of the stars were not explicitly given in these tables, but were taken by the HEASARC from the All-Sky Catalog of Bright M Dwarfs published by Lepine & Gaidos (2011, AJ, 142, 138, <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/AJ/142/138">CDS Cat. J/AJ/142/138</a>, available at the HEASARC as the MDWARFASC table). The version of Table 2 used by the HEASARC is the corrected one given in the Erratum (Stelzer et al. 2014) rather than the version given in the original paper (Stelzer et al. 2013). This is a service provided by NASA HEASARC .
PPM-XL Bright M Dwarfs Catalog
Using the Position and Proper Motion Extended-L (PPMXL) catalog, the authors have used optical and near-infrared color cuts together with a reduced proper motion cut to find bright M dwarfs for future exoplanet transit studies. PPMXL's low proper-motion uncertainties allow them to probe down to smaller proper motions than previous similar studies. The authors have combined unique objects found with this method to that of previous work to produce 8,479 K < 9th magnitude M dwarfs. Low-resolution spectroscopy was obtained of a sample of the objects found using this selection method to gain statistics on their spectral type and physical properties. Results show a spectral-type range of K7 to M4V. This catalog is the most complete collection of K < 9 M dwarfs currently available and is made available herein. The PPMXL catalog (Roeser et al. 2010) represents a combination of the USNO-B1.0 and Two Micron All-Sky Survey (2MASS) catalogs mapped on to the International Celestial Reference Frame (ICRF), which allows proper motions to be described in a quasi-absolute manner as opposed to relative. PPMXL now provides low uncertainties for both the proper motion and position for many of the objects within the two catalogs. Typical uncertainties for proper motions are 4 - 10 mas/yr. The NIR JHK magnitudes from 2MASS and the optical BVRI magnitudes from USNO-B1.0 also provide very useful color information about the objects and are used during the sample selection process. In this work, the authors classified 4,054 M dwarfs with magnitudes of K < 9 from the PPMXL catalog. By probing down to lower proper motions, this work has produced 1,193 new bright M dwarf candidates that were not included in previous catalogs. By combining these objects with M dwarfs from Lepine & Gaidos (2011, AJ, 142, 138) the authors obtained a final catalog with 8,479 K < 9 late K and M dwarfs suitable for future exoplanet transit studies. This table was created by the HEASARC in February 2015 based on the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/MNRAS/435/2161">CDS Catalog J/MNRAS/435/2161</a> file table3.dat. This is a service provided by NASA HEASARC .
Near-UV Detected Bright Early-M Dwarf Star Catalog
Planets orbiting within the close-in habitable zones of M dwarf stars will be exposed to elevated high-energy radiation driven by strong magnetohydrodynamic dynamos during stellar youth. Near-ultraviolet (NUV) irradiation can erode and alter the chemistry of planetary atmospheres, and a quantitative description of the evolution of NUV emission from M dwarfs is needed when modeling these effects. The authors investigated the NUV luminosity evolution of early M-type dwarfs by cross-correlating the Lepine & Gaidos (LG11: 2011, AJ, 142, 138) catalog of bright M dwarfs (available at the HEASARC as the MDWARFASC table) with the Galaxy Evolution Explorer (GALEX) catalog of NUV (1771-2831 Angstrom) sources. Of the 4,805 sources with GALEX counterparts, 797 have NUV emission significantly (> 2.5 sigma) in excess of an empirical basal level. The authors inspected these candidate active stars using visible-wavelength spectra, high-resolution adaptive optics imaging, time-series photometry, and literature searches to identify cases where the elevated NUV emission is due to unresolved background sources or stellar companions; they estimated the overall occurrence of these "false positives" (FPs) as ~ 16%. The authors constructed an NUV luminosity function that accounted for FPs, detection biases of the source catalogs, and GALEX upper limits. They found the NUV luminosity function to be inconsistent with predictions from a constant star-formation rate and simplified age-activity relation defined by a two-parameter power law. This table was created by the HEASARC in March 2015 based on an electronic versions of Table 4 from the reference paper which was obtained from the ApJ web site. This is a service provided by NASA HEASARC .
New M Dwarfs in the Solar Neighborhood
This table contains the results from a spectroscopic study of 1080 nearby active M dwarfs, selected by correlating the Two Micron All Sky Survey (2MASS) and ROSAT catalogs at galactic latitudes greater than 15 degrees above or below the Galactic Plane and using a matching radius of 20 arcseconds, as well as color cuts (J-H < 0.75, H-K > 0.15 and 0.8 < J-K < 1.1) designed to select M dwarfs. The authors have derived the spectral types and estimated distances for all of their stars. The spectral types range between K5 and M6. Nearly half of the stars lie within 50 pc. The authors have measured the equivalent width of the H-alpha emission line. Their 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,the authors have derived the stellar X-ray luminosities. Their stars display a "saturation-type" relation between the chromospheric and coronal activity. The relation is such that log L<sub>X</sub>/L<sub>bol</sub> remains "saturated" at a value of approximately -3 for varying H-alpha equivalent width. The authors have found 568 matches in the USNO-B catalog and have derived the tangential velocities v<sub>tan</sub> for these stars. There is a slight trend of decreasing chromospheric activity with age, such that the stars with higher v<sub>tan</sub> values have lower H-alpha equivalent widths. The coronal emission, however, remains saturated at a value of log L<sub>X</sub>/L<sub>bol</sub> ~ -3 for varying tangential velocities, suggesting that the coronal activity remains saturated with age. The authors do not find any break in the saturation-type relation at the spectral type at which stars become fully convective (~M3.5). Most of the stars in their sample show more coronal emission than the dMe stars in the Hyades and Praesepe clusters and have v<sub>tan</sub> < 40 km s<sup>-1</sup>, suggesting that they belong to a young population. This table was created by the HEASARC in March 2010 based on the (corrected) electronic version of Table 1 from the reference paper which was obtained from the Astronomical Journal web site. This is a service provided by NASA HEASARC .
scripts to reproduce simulations from Simulations of dynamo action in slowly rotating M dwarfs: Dependence on dimensionless parameters
<p>Scripts with .in and .local files to re-run the simulations presented in the paper Simulations of dynamo action in slowly rotating M dwarfs: Dependence on dimensionless parameters.</p>
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