- ID:
- ivo://CDS.VizieR/J/ApJS/220/18
- Title:
- BDKP IV. RVs of late-M and L dwarfs with MagE
- Short Name:
- J/ApJS/220/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radial velocity measurements are presented for 85 late M- and L-type very low-mass stars and brown dwarfs obtained with the Magellan Echellette spectrograph. Targets primarily have distances within 20pc of the Sun, with more distant sources selected for their unusual spectral energy distributions. We achieved precisions of 2-3km/s, and combined these with astrometric and spectrophotometric data to calculate UVW velocities. Most are members of the thin disk of the Galaxy, and velocity dispersions indicate a mean age of 5.2+/-0.2Gyr for sources within 20pc. We find significantly different kinematic ages between late-M dwarfs (4.0+/-0.2Gyr) and L dwarfs (6.5+/-0.4Gyr) in our sample that are contrary to predictions from prior simulations. This difference appears to be driven by a dispersed population of unusually blue L dwarfs which may be more prevalent in our local volume-limited sample than in deeper magnitude-limited surveys. The L dwarfs exhibit an asymmetric U velocity distribution with a net inward flow, similar to gradients recently detected in local stellar samples. Simulations incorporating brown dwarf evolution and Galactic orbital dynamics are unable to reproduce the velocity asymmetry, suggesting non-axisymmetric perturbations or two distinct L dwarf populations. We also find the L dwarfs to have a kinematic age-activity correlation similar to more massive stars. We identify several sources with low surface gravities, and two new substellar candidate members of nearby young moving groups: the astrometric binary DENIS J08230313-4912012AB, a low-probability member of the {beta} Pictoris Moving Group; and 2MASS J15104786-2818174, a moderate-probability member of the 30-50Myr Argus Association.
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Search Results
- 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/PASP/110/533
- Title:
- BR photometry of Fornax bright stars
- Short Name:
- J/PASP/110/533
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present accurate photometry on the Johnson B, Kron-Cousins R photometric system for approximately 100,000 stars in a 1/3deg^2^ field centered on the dwarf spheroidal galaxy in Fornax. We identify numerous probable short-period variable stars, blue stars that appear to be the main sequence of a small population with an age of order 108yr, and two distinct types of luminous red star: an extended sequence of primarily carbon stars and a clump of mostly M giants slightly more luminous than the giant-branch tip. The spatial distribution of each of these subpopulations within the Fornax dwarf galaxy is considered.
- ID:
- ivo://CDS.VizieR/J/MNRAS/289/729
- Title:
- BVRIJHK photometry of red LMC supergiants
- Short Name:
- J/MNRAS/289/729
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (BV)_J_(RI)_C_ observations for 185 and additional JHK observations for 53 red supergiant candidates in the Large Magellanic Cloud (LMC) are presented. The data have been reduced discussing carefully the dependence of effective wavelengths on the spectral energy distribution of the star, which is very strong especially for the Cousins R band. Non-linear colour dependences of transformation coefficients vor the V magnitude and the R-I colour have been taken into account. The mean error of the BVRI data is 0.03 to 0.04 mag, while that of the JHK observations is 0.02mag. The MK types are not given to the stars, as the classifications given in the literature are mostly very uncertain. The spectra we have obtained for 88 of the stars will be discussed in a forthcoming paper where we will give directly physical properties like Mbol and Teff instead of MK types. Most of the stars are supergiants of type late K to early M.
- ID:
- ivo://CDS.VizieR/J/A+A/177/131
- Title:
- CaII and MgII excess flux density in cool stars
- Short Name:
- J/A+A/177/131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relation between the CaII H and K line-tore flux density and rotation period is studied for a sample of 313 cool stars of luminosity classes ranging from II-III to V, and compared to similar relations for MgII h and k and soft X-ray.
- 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/AJ/131/2959
- Title:
- Candidate low-mass PMS in 25 Orionis group
- Short Name:
- J/AJ/131/2959
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar group surrounding the Be (B1Vpe) star 25 Ori was discovered to be a pre-main-sequence (PMS) population by the CIDA Variability Survey of Orion (Cat. J/AJ/129/907) and subsequent spectroscopy. We analyze Sloan Digital Sky Survey multiepoch photometry to map the southern extent of the 25 Ori group and characterize its PMS population. We compare this group to the neighboring Orion OB1a and OB1b subassociations and to active star formation sites (NGC 2068/NGC 2071) within the LDN 1630 dark cloud. We find that the 25 Ori group has a radius of 1.4{deg}, corresponding to 8-11pc at the distances of Orion OB1a and OB1b.
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/3133
- Title:
- Candidate Neptunes around late-type dwarfs
- Short Name:
- J/MNRAS/437/3133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Studies of transiting Neptune-size planets orbiting close to nearby bright stars can inform theories of planet formation because mass and radius and therefore mean density can be accurately estimated and compared with interior models. The distribution of such planets with stellar mass and orbital period relative to their Jovian-mass counterparts can test scenarios of orbital migration, and whether "hot" (period <10d) Neptunes evolved from "hot" Jupiters as a result of mass loss. We searched 1763 late K and early M dwarf stars for transiting Neptunes by analyzing photometry from the Wide Angle Search for Planets and obtaining high-precision (<=10^-3^) follow-up photometry of stars with candidate transit signals. We identified 92 candidate signals among 80 other stars and carried out 148 observations of predicted candidate transits with 1-2m telescopes.
- ID:
- ivo://CDS.VizieR/J/ApJ/735/41
- Title:
- Carbon and oxygen abundances in FGK stars
- Short Name:
- J/ApJ/735/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present carbon and oxygen abundances for 941 FGK stars -the largest such catalog to date. We find that planet-bearing systems are enriched in these elements. We self-consistently measure N_C_/N_O_, which is thought to play a key role in planet formation. We identify 46 stars with N_C_/N_O_>=1.00 as potential hosts of carbon-dominated exoplanets. We measure a downward trend in [O/Fe] versus [Fe/H] and find distinct trends in the thin and thick disks, supporting the work of Bensby et al. Finally, we measure sub-solar N_C_/N_O_=0.40^+0.11^_-0.07_, for WASP-12, a surprising result as this star is host to a transiting hot Jupiter whose dayside atmosphere was recently reported to have N_C_/N_O_>=1 by Madhusudhan et al. Our measurements are based on 15,000 high signal-to-noise spectra taken with the Keck 1 telescope as part of the California Planet Search. We derive abundances from the [OI] and CI absorption lines at {lambda}=6300 and 6587{AA} using the SME spectral synthesizer.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A112
- Title:
- Carbon and oxygen in 107 dwarf stars
- Short Name:
- J/A+A/621/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results from the determination of stellar masses, carbon and oxygen abundances in the atmospheres of 107 stars from the CHEPS program. Our stars are drawn from a population with a significantly super-solar metallicity. At least 10 of these stars are known to host orbiting planets. In this work, we set out to understand the behavior of carbon and oxygen abundance in stars with different spectral classes, metallicities and Vsini, within the metal-rich stellar population. Masses of these stars were determined using the data from Gaia DR2 release. The oxygen and carbon abundances were determined by fitting the absorption lines. Oxygen abundances were determined by fits to the 6300.304{AA} OI line, and for the determination of the carbon abundances we used 3 lines of the CI atom and 12 lines of C_2_ molecule for the determination of carbon abundances. We determine masses and abundances of 107 CHEPS stars. There is no evidence that the [C/O] ratio depends on V sin i or the mass of the star, within our constrained range of masses, i.e. 0.82<M*/M_{sun}_<1.5 and metallicities -0.27<[Fe/H]<+0.39 and we confirm that metal-rich dwarf stars with planets are more carbon-rich in comparison with non-planet host stars, with a statistical significance of 96%. We find tentative evidence that there is a slight offset to lower abundance and a greater dispersion in oxygen abundances relative to carbon, and interpret this as potentially arising from the production of the oxygen being more effective at more metal-poor epochs. We also find evidence that for lower mass star's the angular momentum loss in star's with planets as measured by Vsini is steeper than star's without planets. In general, we find that the fast rotators (Vsini>5km/s) are massive stars.
