- ID:
- ivo://CDS.VizieR/J/ApJ/869/157
- Title:
- ASTRAL: reference spectra for evolved M stars
- Short Name:
- J/ApJ/869/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hubble Space Telescope (HST) Treasury Program Advanced Spectral Library Project: Cool Stars was designed to collect representative, high-quality UV spectra of eight evolved F-M type cool stars. The Space Telescope Imaging Spectrograph (STIS) echelle spectra of these objects enable investigations of a broad range of topics, including stellar and interstellar astrophysics. This paper provides a guide to the spectra of the two evolved M stars, the M2 Iab supergiant {alpha}Ori and the M3.4 giant {gamma}Cru, with comparisons to the prototypical K1.5 giant {alpha}Boo. It includes identifications of the significant atomic and molecular emission and absorption features and discusses the character of the photospheric and chromospheric continua and line spectra. The fluorescent processes responsible for a large portion of the emission-line spectrum, the characteristics of the stellar winds, and the available diagnostics for hot and cool plasmas are also summarized. This analysis will facilitate the future study of the spectra, outer atmospheres, and winds, not only of these objects but of numerous other cool, low-gravity stars, for years to come.
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- ID:
- ivo://CDS.VizieR/J/AJ/161/78
- Title:
- Astrometry for 14 debris disk stars with SPHERE
- Short Name:
- J/AJ/161/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Debris disk stars are good targets for high-contrast imaging searches for planetary systems, since debris disks have been shown to have a tentative correlation with giant planets. We selected 20 stars identified as debris disk hosts by the WISE mission, with particularly high levels of warm dust. We observed these with the VLT/SPHERE high-contrast imaging instrument with the goal of finding planets and imaging the disks in scattered light. Our survey reaches a median 5{sigma} sensitivity of 10.4MJ at 25au and 5.9MJ at 100au. We identified three new stellar companions (HD18378B, HD19257B, and HD133778B): two are mid-M-type stars and one is a late-K or early-M star. Three additional stars have very widely separated stellar companions (all at >2000au) identified in the Gaia catalog. The stars hosting the three SPHERE-identified companions are all older (>~700Myr), with one having recently left the main sequence and one a giant star. We infer that the high volumes of dust observed around these stars has been caused by a recent collision between the planets and planetesimal belts in the system, although for the most evolved star, mass loss could also be responsible for the infrared excess. Future mid-infrared spectroscopy or polarimetric imaging may allow the positions and spatial extent of these dust belts to be constrained, thereby providing evidence as to the true cause of the elevated levels of dust around these old systems. None of the disks in this survey is resolved in scattered light.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A42
- Title:
- A study of dust nucleation in Mira. Part I.
- Short Name:
- J/A+A/592/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dust is efficiently produced by cool giant stars, but the condensation of inorganic dust is poorly understood. Observations of key aluminum bearing molecules around evolved stars has enabled us to investigate the nucleation of alumina (Al_2_O_3_) dust in the gas. Aims. We aim to identify and characterize aluminum bearing species in the circumstellar gas of Mira (o Ceti) in order to elucidate their role in the production of Al_2_O_3_ dust. We used multiepoch spectral line observations at (sub-)millimeter, far-infrared, and optical wavelengths including: maps with ALMA that probe the gas distribution in the immediate vicinity of the star at ~30mas; observations with ALMA, APEX, and Herschel in 2013-2015 for studying cycle and inter-cycle variability of the rotational lines of Al-bearing molecules; optical records as far back as 1965 to examine variations in electronic transitions over time spans of days to decades; and velocity measurements and excitation analysis of the spectral features that constrain the physical parameters of the gas.
- ID:
- ivo://CDS.VizieR/J/other/Nat/594.365
- Title:
- Betelgeuse during its Great Dimming
- Short Name:
- J/other/Nat/594.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Red supergiants represent the most common final stage of the evolution of stars with initial masses between 8 and 30-35 times the mass of the Sun. During this phase of lifetime ~10^5 yrs, they experience substantial mass loss of unknown mechanism (Arroyo-Torres et al., 2015A&A...575A..50A). This mass loss can affect their evolutionary path, collapse, future supernova light curve, and ultimate fate as a neutron star or a black hole. From November 2019 to March 2020, the second closest red supergiant (RSG, 222^+48^_-34_pc) Betelgeuse experienced a historic dimming of its visible brightness, witnessed worldwide. Usually between 0.1 and 1.0mag, it went down to 1.614+/-0.008mag around 7-13 February 2020. Here we report high angular resolution observations showing that the southern hemisphere of the star was ten times darker than usual in the visible. Observations and modeling support the scenario of a dust clump recently formed in the vicinity of the star due to a local temperature decrease in a cool patch appearing on the photosphere. The directly imaged brightness variations of Betelgeuse evolved on a timescale of weeks. This event suggests that an inhomogeneous component of red supergiant mass loss is linked to a very contrasted and rapidly changing photosphere.
- ID:
- ivo://CDS.VizieR/J/MNRAS/479/1332
- Title:
- Binaries with F, G or K primaries and M dwarfs
- Short Name:
- J/MNRAS/479/1332
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigated almost 500 stars distributed among 193 binary or multiple systems made of late-F, G-, or early-K primaries and late-K or M dwarf companion candidates. For all of them, we compiled or measured coordinates, J-band magnitudes, spectral types, distances, and proper motions. With these data, we established a sample of 192 physically bound systems. In parallel, we carried out observations with HERMES/Mercator and obtained high-resolution spectra for the 192 primaries and five secondaries. We used these spectra and the automatic STEPAR code for deriving precise stellar atmospheric parameters: Teff, logg, {xi}, and chemical abundances for 13 atomic species, including [Fe/H]. After computing Galactocentric space velocities for all the primary stars, we performed a kinematic analysis and classified them in different Galactic populations and stellar kinematic groups of very different ages, which match our own metallicity determinations and isochronal age estimations. In particular, we identified three systems in the halo and 33 systems in the young Local Association, Ursa Major and Castor moving groups, and IC 2391 and Hyades Superclusters. We finally studied the exoplanet-metallicity relation in our 193 primaries and made a list 13 M-dwarf companions with very high metallicity that can be the targets of new dedicated exoplanet surveys. All in all, our dataset will be of great help for future works on the accurate determination of metallicity of M dwarfs.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A14
- Title:
- Blind photometric study of NGC 2264 region
- Short Name:
- J/A+A/621/A14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Thanks to their extensive and homogeneous sky coverage, deep, large-scale, multi-wavelength surveys are uniquely suited to statistically identify and map young star clusters in our Galaxy. Such studies are crucial to address themes like the initial mass function, or the modes and dynamics of star cluster formation and evolution. We aim to test a purely photometric approach to statistically identify a young clustered population embedded in a large population of field stars, with no prior knowledge on the nature of stars in the field. We conducted our blind test study on the NGC 2264 region, which hosts a well-known, richly populated young cluster (~3Myr-old) and several active star-forming sites. We selected a large (4 deg^2^) area around the NGC 2264 cluster, and assembled an extensive r, i, J catalog of the field from pre-existing large-scale surveys, notably Pan-STARRS1 and UKIDSS. We then mapped the stellar color locus on the (i-J, r-i) diagram to select M-type stars, which offer the following observational advantages with respect to more massive stars: i) they comprise a significant fraction of the Galactic stellar population; ii) their pre-main sequence phase lasts significantly longer than for higher-mass stars; iii) they exhibit the strongest luminosity evolution from the pre-main sequence to the main sequence; iv) their observed r, i, J colors provide a direct and empirical estimate of AV. A comparative analysis of the photometric and spatial properties of M-type stars as a function of AV enabled us to probe the structure and stellar content of our field. Using only r, i, J photometry, we could identify two distinct populations in our field: a diffuse field population and a clustered population in the center of the field. The presence of a concentration of occulting material, spatially associated with the clustered population, allowed us to derive an estimate of its distance (800-900pc) and age (0.5-5Myr); these values are overall consistent with the literature parameters for the NGC 2264 star-forming region. The extracted clustered population exhibits a hierarchical structure, with two main clumps and peaks in number density of objects around the most extincted locations within the field. An excellent agreement is found between the observed substructures for the clustered population and a map of the NGC 2264 subregions reported in the literature. Our selection of clustered members is coherent with the literature census of the NGC 2264 cluster for about 95% of the objects located in the inner regions of the field, where the estimated contamination rate by field stars in our sample is only 2%. In addition, the availability of a uniform dataset for a large area around the NGC 2264 region enabled us to discover a population of about a hundred stars with indications of statistical membership to the cluster, therefore extending the low-mass population census of NGC 2264 to distances of 10-15pc from the cluster cores. By making use solely of deep, multi-band (r, i, J) photometry, without assuming any further knowledge on the stellar population of our field, we were able to statistically identify and reconstruct the structure of a very young cluster that has been a prime target for star formation studies over several decades. The method tested here can be readily applied to surveys such as Pan-STARRS and the future LSST to undertake a first complete census of low-mass, young stellar populations down to distances of several kpc across the Galactic plane.
- ID:
- ivo://CDS.VizieR/J/MNRAS/426/1591
- Title:
- CaII equivalent widths of dM1 stars
- Short Name:
- J/MNRAS/426/1591
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 187 high-resolution spectra for 62 different M1 dwarfs from observations obtained with the FIbre-fed Echelle Spectrograph (FIES) on the Nordic Optical Telescope (NOT) and from observations with the Fibre-fed Extended Range Echelle Spectrograph (FEROS) from the European Southern Observatory (ESO) data base. We also compiled other measurements available in the literature.
- ID:
- ivo://CDS.VizieR/J/ApJ/833/281
- Title:
- Candidate rotating M dwarfs from PS1-MDS
- Short Name:
- J/ApJ/833/281
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on an ongoing project to investigate activity in the M dwarf stellar population observed by the Pan-STARRS1 Medium-Deep Survey (PS1-MDS). Using a custom-built pipeline, we refine an initial sample of ~4 million sources in PS1-MDS to a sample of 184148 candidate cool stars using color cuts. Motivated by the well-known relationship between rotation and stellar activity, we use a multiband periodogram analysis and visual vetting to identify 270 sources that are likely rotating M dwarfs. We derive a new set of polynomials relating M dwarf PS1 colors to fundamental stellar parameters and use them to estimate the masses, distances, effective temperatures, and bolometric luminosities of our sample. We present a catalog containing these values, our measured rotation periods, and cross-matches to other surveys. Our final sample spans periods of <~1-130 days in stars with estimated effective temperatures of ~2700-4000K. Twenty-two of our sources have X-ray cross-matches, and they are found to be relatively X-ray bright as would be expected from selection effects. Our data set provides evidence that Kepler-based searches have not been sensitive to very slowly rotating stars (P_rot_>~70 day), implying that the observed emergence of very slow rotators in studies of low-mass stars may be a systematic effect. We also see a lack of low-amplitude (<2%) variability in objects with intermediate (10-40 day) rotation periods, which, considered in conjunction with other observational results, may be a signpost of a loss of magnetic complexity associated with a phase of rapid spin-down in intermediate-age M dwarfs. This work represents just a first step in exploring stellar variability in data from the PS1-MDS and, in the farther future, Large Synoptic Survey Telescope.
- ID:
- ivo://CDS.VizieR/J/A+A/577/A128
- Title:
- CARMENES input catalogue of M dwarfs. I
- Short Name:
- J/A+A/577/A128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CARMENES is a stabilised, high-resolution, double-channel spectrograph at the 3.5m Calar Alto telescope. It is optimally designed for radial-velocity surveys of M dwarfs with potentially habitable Earth-mass planets. We prepare a list of the brightest, single M dwarfs in each spectral subtype observable from the northern hemisphere, from which we will select the best planet-hunting targets for CARMENES. In this first paper on the preparation of our input catalogue, we compiled a large amount of public data and collected low-resolution optical spectroscopy with CAFOS at the 2.2m Calar Alto telescope for 753 stars. We derived accurate spectral types using a dense grid of standard stars, a double least-squares minimisation technique, and 31 spectral indices previously defined by other authors. Additionally, we quantified surface gravity, metallicity, and chromospheric activity for all the stars in our sample. We calculated spectral types for all 753 stars, of which 305 are new and 448 are revised. We measured pseudo-equivalent widths of H{alpha} for all the stars in our sample, concluded that chromospheric activity does not affect spectral typing from our indices, and tabulated 49 stars that had been reported to be young stars in open clusters, moving groups, and stellar associations. Of the 753 stars, two are new subdwarf candidates, three are T Tauri stars, 25 are giants, 44 are K dwarfs, and 679 are M dwarfs. Many of the 261 investigated dwarfs in the range M4.0-8.0 V are among the brightest stars known in their spectral subtype.
- ID:
- ivo://CDS.VizieR/J/A+A/597/A47
- Title:
- CARMENES input catalogue of M dwarfs II
- Short Name:
- J/A+A/597/A47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We search for low-mass companions of M dwarfs and characterize their multiplicity fraction with the purpose of helping in the selection of the most appropriate targets for the CARMENES exoplanet survey. We obtained high-resolution images in the I band with the lucky imaging instrument FastCam at the 1.5m Telescopio Carlos Sanchez for 490 mid- to late-M dwarfs. For all the detected binaries, we measured angular separations, position angles, and magnitude differences in the I band. We also calculated the masses of each individual component and estimated orbital periods, using the available magnitude and colour relations for M dwarfs and our own M_J_-spectral type and mass-M_I_ relations. To avoid biases in our sample selection, we built a volume-limited sample of M0.0-M5.0 dwarfs that is complete up to 86% within 14pc.
