- ID:
- ivo://CDS.VizieR/J/ApJ/794/146
- Title:
- M dwarfs with IR excess
- Short Name:
- J/ApJ/794/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) spectroscopic catalog, we searched the WISE AllWISE catalog to investigate the occurrence of warm dust, as inferred from IR excesses, around field M dwarfs (dMs). We developed SDSS/WISE color selection criteria to identify 175 dMs (from 70841) that show IR flux greater than the typical dM photosphere levels at 12 and/or 22{mu}m, including seven new stars within the Orion OB1 footprint. We characterize the dust populations inferred from each IR excess and investigate the possibility that these excesses could arise from ultracool binary companions by modeling combined spectral energy distributions. Our observed IR fluxes are greater than levels expected from ultracool companions (>3{sigma}). We also estimate that the probability the observed IR excesses are due to chance alignments with extragalactic sources is <0.1%. Using SDSS spectra we measure surface gravity-dependent features (K, Na, and CaH 3) and find <15% of our sample indicates low surface gravities. Examining tracers of youth (H{alpha}, UV fluxes, and Li absorption), we find <3% of our sample appear young, indicating we are observing a population of field stars >~1Gyr, likely harboring circumstellar material. We investigate age-dependent properties probed by this sample, studying the disk fraction as a function of Galactic height. The fraction remains small and constant to |Z|~700pc and then drops, indicating little to no trend with age. Possible explanations for disks around field dMs include (1) collisions of planetary bodies, (2) tidal disruption of planetary bodies, or (3) failed planet formation.
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- ID:
- ivo://CDS.VizieR/J/A+A/638/A20
- Title:
- M dwarfs X-ray activity and rotation relations
- Short Name:
- J/A+A/638/A20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relation of activity to rotation in M dwarfs is of high astrophysical interest because it provides observational evidence of the stellar dynamo, which is poorly understood for low-mass stars, especially in the fully convective regime. Previous studies have shown that the relation of X-ray activity to rotation consists of two different regimes: the saturated regime for fast-rotating stars and unsaturated regime for slowly rotating stars. The transition between the two regimes lies at a rotation period of ~10d. We present here a sample of 14 M dwarf stars observed with XMM-Newton and Chandra, for which we also computed rotational periods from Kepler Two-Wheel (K2) Mission light curves. We compiled X-ray and rotation data from the literature and homogenized all data sets to provide the largest uniform sample of M dwarfs (302 stars) for X-ray activity and rotation studies to date. We then fit the relation between LX-Prot using three different mass bins to separate partially and fully convective stars. We found a steeper slope in the unsaturated regime for fully convective stars and a nonconstant LX level in the saturated regime for all masses. In the LX/Lbol-R_O_ space we discovered a remarkable double gap that might be related to a discontinuous period evolution. Then we combined the evolution of Prot predicted by angular momentum evolution models with our new results on the empirical LX-Prot relation to provide an estimate for the age decay of X-ray luminosity. We compare predictions of this relationship with the actual X-ray luminosities of M stars with known ages from 100Myr to a few billion years. We find remarkably good agreement between the predicted LX and the observed values for partially convective stars. However, for fully convective stars at ages of a few billion years, the constructed LX-age relation overpredicts the X-ray luminosity because the angular momentum evolution model underpredicts the rotation period of these stars. Finally, we examine the effect of different parameterizations for the Rossby number (R_O_) on the shape of the activity-rotation relation in LX/Lbol-R_O_ space, and we find that the slope in the unsaturated regime and the location of the break point of the dual power-law depend sensitively on the choice of R_O_.
- ID:
- ivo://CDS.VizieR/J/ApJ/812/3
- Title:
- MEarth mid-to-late M dwarfs rotation & kinematics
- Short Name:
- J/ApJ/812/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using spectroscopic observations and photometric light curves of 238 nearby M dwarfs from the MEarth exoplanet transit survey, we examine the relationships between magnetic activity (quantified by H{alpha} emission), rotation period, and stellar age. Previous attempts to investigate the relationship between magnetic activity and rotation in these stars were hampered by the limited number of M dwarfs with measured rotation periods (and the fact that v sin i measurements probe only rapid rotation). However, the photometric data from MEarth allows us to probe a wide range of rotation periods for hundreds of M dwarf stars (from shorter than one to longer than 100 days). Over all M spectral types that we probe, we find that the presence of magnetic activity is tied to rotation, including for late-type, fully convective M dwarfs. We also find evidence that the fraction of late-type M dwarfs that are active may be higher at longer rotation periods compared to their early-type counterparts, with several active, late-type, slowly rotating stars present in our sample. Additionally, we find that all M dwarfs with rotation periods shorter than 26 days (early-type; M1-M4) and 86 days (late-type; M5-M8) are magnetically active. This potential mismatch suggests that the physical mechanisms that connect stellar rotation to chromospheric heating may be different in fully convective stars. A kinematic analysis suggests that the magnetically active, rapidly rotating stars are consistent with a kinematically young population, while slow-rotators are less active or inactive and appear to belong to an older, dynamically heated stellar population.
- ID:
- ivo://CDS.VizieR/J/ApJ/818/153
- Title:
- MEarth photometry: nearby M-dwarf magnitudes
- Short Name:
- J/ApJ/818/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The MEarth Project is a photometric survey systematically searching the smallest stars near the Sun for transiting rocky planets. Since 2008, MEarth has taken approximately two million images of 1844 stars suspected to be mid-to-late M dwarfs. We have augmented this survey by taking nightly exposures of photometric standard stars and have utilized this data to photometrically calibrate the MEarth system, identify photometric nights, and obtain an optical magnitude with 1.5% precision for each M dwarf system. Each optical magnitude is an average over many years of data, and therefore should be largely immune to stellar variability and flaring. We combine this with trigonometric distance measurements, spectroscopic metallicity measurements, and 2MASS infrared magnitude measurements in order to derive a color-magnitude-metallicity relation across the mid-to-late M dwarf spectral sequence that can reproduce spectroscopic metallicity determinations to a precision of 0.1 dex. We release optical magnitudes and metallicity estimates for 1567 M dwarfs, many of which did not have an accurate determination of either prior to this work. For an additional 277 stars without a trigonometric parallax, we provide an estimate of the distance, assuming solar neighborhood metallicity. We find that the median metallicity for a volume-limited sample of stars within 20pc of the Sun is [Fe/H]=-0.03+/-0.008, and that 29/565 of these stars have a metallicity of [Fe/H]=-0.5 or lower, similar to the low-metallicity distribution of nearby G dwarfs. When combined with the results of ongoing and future planet surveys targeting these objects, the metallicity estimates presented here will be important for assessing the significance of any putative planet-metallicity correlation.
- ID:
- ivo://CDS.VizieR/J/A+A/551/A36
- Title:
- Metallicity of M dwarfs. III.
- Short Name:
- J/A+A/551/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this work is the study of the planet-metallicity and the planet-stellar mass correlations for M dwarfs from the HARPS GTO M dwarf subsample. We use a new method that takes advantage of the HARPS high-resolution spectra to increase the precision of metallicity, using previous photometric calibrations of [Fe/H] and effective temperature as starting values.
- ID:
- ivo://CDS.VizieR/J/PASJ/33/107
- Title:
- M giants in Cassiopeia
- Short Name:
- J/PASJ/33/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Coordinates and identifications for M-type stars in Cassiopeia
- ID:
- ivo://CDS.VizieR/J/MNRAS/337/519
- Title:
- M giants in MACHO, DENIS and ISOGAL
- Short Name:
- J/MNRAS/337/519
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A 'complete' sample of 174 M giants classified in the mid-1980s by Blanco (1986AJ.....91..290B) and later than subtype M0 in the NGC 6522 Baade's Window clear field has been investigated to establish some general properties of cool bulge stars. Photometric information has been obtained from the MACHO data base to search for variability and, where possible, to determine periods. Near- and mid-infrared magnitudes have been extracted from DENIS (<B/denis>) and ISOGAL (<II/243>). 46 semiregular variables (SRVs) and two irregular variables were found amongst the 174. Many M5 and all stars M6 or later show variation, whereas earlier subtypes (M1-M4) do not.
- ID:
- ivo://CDS.VizieR/J/A+AS/105/311
- Title:
- M giants spectra and photometry
- Short Name:
- J/A+AS/105/311
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From a sample of 97 very bright M-giant stars in the Solar neighbourhood, high-quality `intrinsic' spectra in the spectral range [380-900]nm for all M-spectral subclasses of the Case and MK classification systems are obtained. The results are fitted to photospheric synthetic spectra in the range [99-12500]nm in order to infer the corresponding continua. The synthetic spectra are also compared to the intrinsic spectra. The effective temperatures are derived and mathematical spectral classification criteria are found. The (UB)j(VRI)c(JHKLM)eso photometric data of the sample are also given.
- ID:
- ivo://CDS.VizieR/J/AJ/128/245
- Title:
- M giant stars in the Sagittarius dwarf galaxy
- Short Name:
- J/AJ/128/245
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained moderate resolution (~6km/s) spectroscopy of several hundred M giant candidates selected from Two Micron All Sky Survey photometry (Cat. <II/246>). Radial velocities are presented for stars mainly in the southern Galactic hemisphere, and the primary targets have Galactic positions consistent with association to the tidal tail system of the Sagittarius (Sgr) dwarf galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJ/670/346
- Title:
- M giant stars in the Sagittarius dwarf galaxy. V.
- Short Name:
- J/ApJ/670/346
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present reliable measurements of the metallicity distribution function (MDF) at different points along the tidal stream of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy, based on high-resolution, echelle spectroscopy of candidate M giant members of the Sgr system.
