- ID:
- ivo://CDS.VizieR/J/MNRAS/390/567
- Title:
- Magnetic field and velocity of mid M dwarfs
- Short Name:
- J/MNRAS/390/567
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present in this paper, the first results of a spectropolarimetric analysis of a small sample (~20) of active stars ranging from spectral type M0 to M8, which are either fully convective or possess a very small radiative core. This study aims at providing new constraints on dynamo processes in fully convective stars. This paper focuses on ve stars of spectral type ~M4, i.e. with masses close to the full convection threshold (0.35M_{sun}_), and with short rotational periods. Tomographic imaging techniques allow us to reconstruct the surface magnetic topologies from the rotationally modulated time-series of circularly polarized profiles. We find that all stars host mainly axisymmetric large-scale poloidal fields. Three stars were observed at two different epochs separated by 1yr; we find the magnetic topologies to be globally stable on this time-scale. We also provide an accurate estimation of the rotational period of all stars, thus allowing us to start studying how rotation impacts the large-scale magnetic field.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/615/L12
- Title:
- 2MASS J04183483+2131275 spectrum
- Short Name:
- J/A+A/615/L12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used the 10.4-m Gran Telescopio Canarias (GTC) with its low-dispersion optical spectrograph to obtain 10 spectra of 2277s each covering the range 6300-10300 Angstroms with a resolving power of R~500 for the Hyades brown dwarf 2MASSJ04183483+2131275. We detect lithium in absorption and Halpha in emission in this combined spectrum.
- ID:
- ivo://CDS.VizieR/J/A+A/357/225
- Title:
- Mass loss of M supergiants
- Short Name:
- J/A+A/357/225
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The following tables present near-infrared photometry and millimeter observations of a sample of optical M supergiants, together with estimations of their luminosity and dust mass-loss rate. Near-infrared observations were done in February 1995 with the ESO T2.2m-IRAC1 and T3.6m-TIMMI instruments, millimeter observations were made in December 1994 with the IRAM-30m-telescope and in February 1995 with the SEST. For a description of the (N1-N3) and (JHKL) photometric system, see e.g. <GCPD/39> and <GCPD/09>, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJ/756/74
- Title:
- 2MASS view of Sgr dSph. VII. Kinematics
- Short Name:
- J/ApJ/756/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have assembled a large-area spectroscopic survey of giant stars in the Sagittarius (Sgr) dwarf galaxy core. Using medium resolution (R~15000), multifiber spectroscopy we have measured velocities of these stars, which extend up to 12{deg} from the galaxy's center (3.7 core radii or 0.4 times the King limiting radius). From these high-quality spectra we identify 1310 Sgr members out of 2296 stars surveyed, distributed across 24 different fields across the Sgr core. Additional slit spectra were obtained of stars bridging from the Sgr core to its trailing tail. Our systematic, large-area sample shows no evidence for significant rotation, a result at odds with the ~20km/s rotation required as an explanation for the bifurcation seen in the Sgr tidal stream; the observed small (<=4km/s) velocity trend primarily along the major axis is consistent with models of the projected motion of an extended body on the sky with no need for intrinsic rotation. The Sgr core is found to have a flat velocity dispersion (except for a kinematically colder center point) across its surveyed extent and into its tidal tails, a property that matches the velocity dispersion profiles measured for other Milky Way dwarf spheroidal (dSph) galaxies. We comment on the possible significance of this observed kinematical similarity for the dynamical state of the other classical Milky Way dSphs in light of the fact that Sgr is clearly a strongly tidally disrupted system.
- ID:
- ivo://CDS.VizieR/J/other/RAA/15.1182
- Title:
- M Dwarf catalog of LAMOST DR1
- Short Name:
- J/other/RAA/15.1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic catalog of 93 619 M dwarfs from the first data release of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) general survey. During sample selection, M giant contamination was eliminated using 2MASS photometry and CaH/TiO molecular indices. For each spectrum, the spectral subtype and values are provided including radial velocity, H{alpha} equivalent width, a series of prominent molecular band indices, and the metal-sensitive parameter {zeta}, as well as distances and the space motions for high S/N objects. In addition, H{alpha} emission lines are measured to examine the magnetic activity properties of M dwarfs and 7179 active ones are found. In particular, a subsample with significant variation in magnetic activity is revealed through observations from different epochs. Finally, statistical analysis for this sample is performed, including the metallicity classification, the distribution of molecular band indices and their errors.
- ID:
- ivo://CDS.VizieR/VI/156
- Title:
- M-dwarf Lum-Temp-Radius relationships
- Short Name:
- VI/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There is growing evidence that M-dwarf stars suffer radius inflation when compared to theoretical models, suggesting that models are missing some key physics required to completely describe stars at effective temperatures (TSED) less than about 4000K. The advent of Gaia DR2 distances finally makes available large datasets to determine the nature and extent of this effect.We employ an all-sky sample, comprising of >15000 stars, to determine empirical relation-ships between luminosity, temperature and radius.This is accomplished using only geometric distances and multiwave-band photometry, by utilising a modified spectral energy distribution fitting method. The radii we measure show an inflation of 3-7% compared to models, but nomore than a 1-2% intrinsic spread in the inflated sequence. We show that we are currently able to determine M-dwarf radii to an accuracy of 2.4% using our method. However, we determine that this is limited by the precision of metallicity measurements, which contribute 1.7% to the measured radius scatter. We also present evidence that stellar magnetism is currently unable to explain radius inflation in M-dwarfs.
- ID:
- ivo://CDS.VizieR/J/AJ/156/45
- Title:
- M-dwarf multiples in the SDSS-III/APOGEE
- Short Name:
- J/AJ/156/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Binary stars make up a significant portion of all stellar systems. Consequently, an understanding of the bulk properties of binary stars is necessary for a full picture of star formation. Binary surveys indicate that both multiplicity fraction and typical orbital separation increase as functions of primary mass. Correlations with higher-order architectural parameters such as mass ratio are less well constrained. We seek to identify and characterize double-lined spectroscopic binaries (SB2s) among the 1350 M-dwarf ancillary science targets with APOGEE spectra in the SDSS-III Data Release 13. We measure the degree of asymmetry in the APOGEE pipeline cross-correlation functions (CCFs) and use those metrics to identify a sample of 44 high-likelihood candidate SB2s. At least 11 of these SB2s are known, having been previously identified by Deshpande et al. (2013, J/AJ/146/156) and/or El-Badry et al. (2018MNRAS.476..528E). We are able to extract radial velocities (RVs) for the components of 36 of these systems from their CCFs. With these RVs, we measure mass ratios for 29 SB2s and five SB3s. We use Bayesian techniques to fit maximum-likelihood (but still preliminary) orbits for four SB2s with eight or more distinct APOGEE observations. The observed (but incomplete) mass-ratio distribution of this sample rises quickly toward unity. Two-sided Kolmogorov-Smirnov tests find probabilities of 18.3% and 18.7%, demonstrating that the mass-ratio distribution of our sample is consistent with those measured by Pourbaix et al. (2004, Cat. B/sb9) and Fernandez et al. (2017PASP..129h4201F), respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/541/A9
- Title:
- M dwarfs activity and radial velocity
- Short Name:
- J/A+A/541/A9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Due to their low mass and luminosity, M dwarfs are ideal targets if one hopes to find low-mass planets similar to Earth by using the radial velocity (RV) method. However, stellar magnetic cycles could add noise or even mimic the RV signal of a long-period companion. Following our previous work that studied the correlation between activity cycles and long-term RV variations for K dwarfs we now expand that research to the lower-end of the main sequence. Our objective is to detect any correlations between long-term activity variations and the observed RV of a sample of M dwarfs. We used a sample of 27 M-dwarfs with a median observational timespan of 5.9 years. The cross-correlation function (CCF) with its parameters RV, bisector inverse slope (BIS), full-width-at-half- maximum (FWHM) and contrast have been computed from the HARPS spectrum. The activity index have been derived using the Na I D doublet. These parameters were compared with the activity level of the stars to search for correlations. We detected RV variations up to ~5m/s that we can attribute to activity cycle effects. However, only 36% of the stars with long-term activity variability appear to have their RV affected by magnetic cycles, on the typical timescale of ~6 years. Therefore, we suggest a careful analysis of activity data when searching for extrasolar planets using long-timespan RV data.
- ID:
- ivo://CDS.VizieR/J/AJ/159/52
- Title:
- M dwarfs at high spectral-resolution in Y band
- Short Name:
- J/AJ/159/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In young Sun-like stars and field M-dwarf stars, chromospheric and coronal magnetic activity indicators such as H{alpha}, X-ray, and radio emission are known to saturate with low Rossby number (Ro<~0.1), defined as the ratio of rotation period to convective turnover time. The mechanism for the saturation is unclear. In this paper, we use photospheric TiI and CaI absorption lines in the Y band to investigate magnetic field strength in M dwarfs for Rossby numbers between 0.01 and 1.0. The equivalent widths of the lines are magnetically enhanced by photospheric spots, a global field, or a combination of the two. The equivalent widths behave qualitatively similar to the chromospheric and coronal indicators: we see increasing equivalent widths (increasing absorption) with decreasing Ro and saturation of the equivalent widths for Ro<~0.1. The majority of M dwarfs in this study are fully convective. The results add to mounting evidence that the magnetic saturation mechanism occurs at or beneath the stellar photosphere.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A52
- Title:
- M dwarfs HeI infrared triplet variability
- Short Name:
- J/A+A/640/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The HeI infrared (IR) triplet at 10830{AA} is an important activity indicator for the Sun and in solar-type stars, however, it has rarely been studied in relation to M dwarfs to date. In this study, we use the time-averaged spectra of 319 single stars with spectral types ranging from M0.0 V to M9.0V obtained with the CARMENES high resolution optical and near-infrared spectrograph at Calar Alto to study the properties of the HeI IR triplet lines. In quiescence, we find the triplet in absorption with a decrease of the measured pseudo equivalent width (pEW) towards later sub-types. For stars later than M5.0 V, the HeI triplet becomes undetectable in our study. This dependence on effective temperature may be related to a change in chromospheric conditions along the Mdwarf sequence. When an emission in the triplet is observed, we attribute it to flaring. The absence of emission during quiescence is consistent with line formation by photo-ionisation and recombination, while flare emission may be caused by collisions within dense material. The HeI triplet tends to increase in depth according to increasing activity levels, ultimately becoming filled in; however, we do not find a correlation between the pEW(He IR) and X-ray properties. This behaviour may be attributed to the absence of very inactive stars (LX/Lbol<-5.5) in our sample or to the complex behaviour with regard to increasing depth and filling in.
