- ID:
- ivo://CDS.VizieR/J/A+A/581/A73
- Title:
- Luhman 16AB X-shooter spectra
- Short Name:
- J/A+A/581/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained high signal-to-noise intermediate-resolution (R~6000-11000) optical (600-1000nm) and near-infrared (1000-2480nm) spectra of each component of the the closest brown dwarf binary, Luhman 16AB, with X-Shooter on the Very Large Telescope (VLT). We classify the primary and secondary as L6-L7.5 and T0+/-1, respectively, in agreement with previous measurements. We present measurements of the lithium pseudo-equivalent widths, which appears of similar strength on both components. The presence of lithium (^7^Li) in both components imply masses below 0.06M_{sun} while comparison with models suggests lower limits of 0.04M_{sun}. The detection of lithium in the T component is the first of its kind. Similarly, we assess the strength of other alkali lines (e.g. 6-7{AA} for RbI and 4-7{AA} for CsI features) and compare them with estimates for L and T dwarfs. We also derive effective temperatures and luminosities of each component of the binary (-4.66dex, 1305K) and (-4.68dex, 1320K) for the L and T dwarf, respectively. Using our radial velocity determinations, the binary does not appear to belong to any of the well-known moving group. Our preliminary theoretical analysis of the optical and J-band spectra indicates that the L- and T-type spectra can be reproduced with a single temperature and gravity but different relative chemical abundances which impact strongly the spectral energy distribution of L/T transition objects.
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- ID:
- ivo://CDS.VizieR/J/AJ/133/439
- Title:
- Luminosity function of M7-L8 ultracool dwarfs
- Short Name:
- J/AJ/133/439
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a 20pc, volume-limited sample of M7-L8 dwarfs created through spectroscopic follow-up of sources selected from the Two Micron All Sky Survey Second Incremental Release Point Source Catalog. In this paper we present optical spectroscopy of 198 candidate nearby ultracool dwarfs, including 12 late-M and L dwarfs likely to be within 20pc of the Sun and 94 more distant late-type dwarfs. We have also identified five ultracool dwarfs with spectral signatures of low gravity. Combining these data with previous results, we define a sample of 99 ultracool dwarfs in 91 systems within 20pc. These are used to estimate the J- and K-band luminosity functions for dwarfs with optical spectral types between M7 and L8 (10.5<M_J_<15, 9.5<M_Ks_<13). We find a space density of 4.9x10^-3^/pc^3^ for late-M dwarfs (M7-M9.5) and a lower limit of 3.8x10^-3^/pc^3^ for L dwarfs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/478/3138
- Title:
- Luminous cool supergiants in Magellanic Clouds
- Short Name:
- J/MNRAS/478/3138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The empirical upper luminosity boundary L_max_ of cool supergiants, often referred to as the Humphreys-Davidson limit, is thought to encode information on the general mass-loss behaviour of massive stars. Further, it delineates the boundary at which single stars will end their lives stripped of their hydrogen-rich envelope, which in turn is a key factor in the relative rates of Type-II to Type-Ibc supernovae from single star channels. In this paper we have revisited the issue of L_max_ by studying the luminosity distributions of cool supergiants (SGs) in the Large and Small Magellanic Clouds (LMC/SMC). We assemble highly-complete samples of cool SGs in each galaxy, and determine their spectral energy distributions from the optical to the mid-infrared using modern multi-wavelength survey data. We show that in both cases L_max_ appears to be lower than previously quoted, and is in the region of logL/L_{sun}_=5.5. There is no evidence for L_max_ being higher in the SMC than in the LMC, as would be expected if metallicity-dependent winds were the dominant factor in the stripping of stellar envelopes. We also show that L_max_ aligns with the lowest luminosity of single nitrogen-rich Wolf-Rayet stars, indicating of a change in evolutionary sequence for stars above a critical mass. From population synthesis analysis we show that the Geneva evolutionary models greatly over-predict the numbers of cool SGs in the SMC. We also argue that the trend of earlier average spectral types of cool SGs in lower metallicity environments represents a genuine shift to hotter temperatures. Finally, we use our new bolometric luminosity measurements to provide updated bolometric corrections for cool supergiants.
- ID:
- ivo://CDS.VizieR/J/A+A/409/1017
- Title:
- Magnetic activity of 6 young solar stars. II
- Short Name:
- J/A+A/409/1017
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The present paper is the second of a series dedicated to the study of the magnetic activity in a selected sample of young solar analogues. The sample includes five single G0-G5V stars with ages between ~=130Myr and 700Myr: EK Dra, {pi}^1^ UMa, HN Peg, {kappa}^1^ Cet and BE Cet. In this study we also include the Pleiades-age (~=130Myr) K0V star DX Leo. Our analysis is based on high precision photometric observations carried out as part of "The Sun in Time" project, aimed at a multiwavelength study of stars with solar-like global properties, but with different ages and thus at different stages of evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A22
- Title:
- Magnetic fields of HD9472 and HD190771
- Short Name:
- J/A+A/619/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the measurement of stellar longitudinal magnetic fields (H_eff_), using machine learning algoritmhs (MLA). We applied the MLA approach in the analysis of two stars, namely, HD 190771 and HD 9471. We present in electronic format the two data sets, one per star, used in the training of the MLA.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/2157
- Title:
- Main-sequence star chromospheres
- Short Name:
- J/MNRAS/403/2157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on high-resolution observations of two dM1 stars: Gl 867A, an active dM1e star, and Gl 205, a less active dM1 star. The wavelength coverage is from 3890 to 6820{AA} with a resolving power of about 45000. The difference spectrum of these two stars allows us to make a survey of spectral lines sensitive to magnetic activity.
- ID:
- ivo://CDS.VizieR/J/A+A/467/665
- Title:
- Manganese abundances in the Galactic disk
- Short Name:
- J/A+A/467/665
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Manganese is an iron-peak element and although the nucleosynthesis path that leads to its formation is fairly well understood, it remains unclear which objects, SN II and/or SN Ia, that contribute the majority of Mn to the interstellar medium. It also remains unclear to which extent the supernovae Mn yields depend on the metallicity of the progenitor star or not.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A119
- Title:
- Masses and luminosities for 342 stars
- Short Name:
- J/A+A/587/A119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present revised basic astrophysical stellar parameters: the masses, luminosities, ages, and radii for 342 stars from the PennState-Torun Centre for Astronomy Planet Search. For 327 stars the atmospheric parameters were already available in the literature. For the other 15 objects we also present spectroscopic atmospheric parameters: the effective temperatures, surface gravities, and iron abundances. Spectroscopic atmospheric parameters were obtained with a standard spectroscopic analysis procedure, using ARES and MOOG, or TGVIT codes. To refine the stellar masses, ages, and luminosities, we applied a Bayesian method.
- ID:
- ivo://CDS.VizieR/J/A+A/320/79
- Title:
- Mass-luminosity relation of low-mass stars
- Short Name:
- J/A+A/320/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To construct the MLR, empirical data for 56 stars in 30 low mass multiple systems, main sequence components of spectral class M0 and later were collected and processed. We considered only those systems where the determination of dynamical masses of components is possible, that is, where masses are derived directly from celestial mechanical considerations rather than from relations between mass and some observational parameter.
- ID:
- ivo://CDS.VizieR/J/ApJ/476/311
- Title:
- 2MASS M-dwarf discoveries
- Short Name:
- J/ApJ/476/311
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained follow-up spectroscopy of eight late dwarf candidates discovered in a 105deg^2^ area observed with the 2MASS (2 Micron All-Sky Survey) Prototype Camera during test runs between 1992 and 1994. These objects were chosen because of their red infrared colors (e.g., J-Ks>=1.10) and/or red OIR colors (e.g., R-Ks>=6.00). All eight are late M dwarfs, six of which have spectral types later than van Biesbroeck 8 (type M7 V). Despite the fact that we have only followed up a fraction of the reddest sources discovered, the number of known M dwarfs of type M7 and cooler has been increased by 30%. Extrapolation of these results alone shows that over 2000 dwarfs of similar spectral type and with Ks<=14.0 will be imaged by 2MASS over the entire sky. One of these new discoveries is astonishingly cool and has a tentative type of >=M10V. This dwarf, one of the least luminous objects yet discovered, could itself be a high-mass brown dwarf, thus providing another empirical data point in a regime where few such objects are now recognized. Only the substellar suspect GD 165 B and the bona fide brown dwarf GL 229 B, both discovered as companions to known stars, are cooler. Thus, this 2MASS discovery becomes the coolest isolated object so far identified.
