- ID:
- ivo://CDS.VizieR/J/A+A/624/A10
- Title:
- Normalized Halpha line profiles of FGK stars
- Short Name:
- J/A+A/624/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The determination of stellar effective temperature (T_eff_) in F, G, and K stars using Halpha profile fitting is a quite remarkable and powerful tool because it does not depend on reddening and is only slightly sensitive to other atmospheric parameters. Nevertheless, this technique is not frequently used because of the complex procedure needed to recover the profile of broad lines in echelle spectra. As a consequence, tests performed on different models have sometimes provided ambiguous results. The main aim of this work is to test the ability of the Halpha profile fitting technique to derive T_eff. We also aim to improve the applicability of this technique to echelle spectra and to test how well 1D+LTE models perform on a variety of F-K stars. We also apply the technique to HARPS spectra and test the reliability and the stability of the HARPS response over several years using the Sun. We have developed a normalization method for recovering undistorted Halpha profiles and we have first applied it to spectra acquired with the single-order coude instrument (resolution R=45000) at do Pico dos Dias Observatory to avoid the problem of blaze correction. The continuum location around Halpha is optimised using an iterative procedure, where the identification of minute telluric features is performed. A set of spectra was acquired with the MUSICOS echelle spectrograph (R=40000) to independently validate the normalization method. The accuracy of the method and of the 1D+LTE model is determined using coude/HARPS/MUSICOS spectra of the Sun and coude-only spectra of a sample of ten Gaia Benchmark Stars with T_eff_ determined from interferometric measurements. HARPS, coude, and MUSICOS spectra are used to determine T_eff_ of 43 sample stars. We find that a proper choice of spectral windows of fits plus the identification of telluric features allow for a very careful normalization of the spectra and produce reliable H{alpha} profiles. We also find that the most used solar atlases cannot be used as templates for Halpha temperature diagnostics without renormalization. The comparison with the Sun shows that H{alpha} profiles from 1D+LTE models underestimate the solar T_eff_ by 28K. We find the same agreement between Halpha and interferometry and between Halpha and Infrared Flux Method: a shallow dependency on metallicity according to the relation T_eff_=T_eff_^Halpha^-159[Fe/H]+28K within the metallicity range -0.70 to +0.40dex. The comparison with the Infrared Flux Method shows a scatter of 59K dominated by photometric errors (52K). In order to investigate the origin of this dependency, we analysed spectra from 3D models and found that they produce hotter temperatures, and that their use largely improves the agreement with the interferometric and Infrared Flux Method measurements. Finally, we find HARPS spectra to be fully suitable for Halpha profile temperature diagnostics; they are perfectly compatible with the coude spectra, and lead to the same T_eff_ for the Sun as that found when analysing HARPS spectra over a timespan of more than 7 years.
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- ID:
- ivo://CDS.VizieR/J/A+A/390/235
- Title:
- OI and FeII equivalent widths in metal-poor stars
- Short Name:
- J/A+A/390/235
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The table gives equivalent widths (in m{AA}) of OI and FeII lines for 35 metal-poor main sequence and subgiant stars as measured from high resolution, high S/N spectra observed with the ESO VLT/UVES spectrograph, during three observing runs: April 8-12, 2000, July 22-24, 2000, and April 10-12, 2001.
- ID:
- ivo://CDS.VizieR/J/A+A/499/129
- Title:
- Old MS stars in young moving groups
- Short Name:
- J/A+A/499/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The associations and moving groups of young stars are excellent laboratories to investigate the stellar formation in the solar neighborhood. Past results confirmed that a non-negligible fraction of old main-sequence stars is present in the lists of members of the young stellar kinematic groups. A detailed study on the properties of these samples is needed to separate the young stars from old main-sequence stars with similar space motion, in order to identify the origin of these structures. Our intention is to characterize the sample of stars members of the young moving groups and determine their age distribution to quantify the contamination by old main-sequence stars, in particular, in the Local Association. For our study, we used the sample of stars possible members of the young (~10-650Myr) moving groups from the literature. In order to determine the age of the stars, we used several age indicators well suited for young main sequence stars: X-ray fluxes from the Rosat All-sky Survey database, photometric data from the Tycho-2, Hipparcos, and 2MASS database. We also used spectroscopic data, in particular the equivalent width of the lithium line LiI lambda6707.8{AA} and Halpha, to constrain the range of ages of the stars in the sample. The combination of photometric and spectroscopic data permitted to separate the young stars (10-650Myr) from the old (>1Gyr) field ones. In particular, the member list of the Local Association results contaminated by ~30% of old field stars. This value must be considered as the contamination of our particular sample, not to the entire Local Association. In other young moving groups it is more difficult to estimate the fraction of old stars in the samples of possible members. However, the X-ray emission level can help to separate, at least, two age populations: stars with 200Myr and stars older than this. The samples of candidates of the classical moving groups contain a non-negligible amount of old field stars that should be considered in studies on the stellar birthrate in the solar neighborhood. Our results agree with the scenario of the moving groups being composed by groups of young stars formed in a recent star formation episode and old field stars with similar space motion. Only combining both X-ray and optical spectroscopic data it is possible to distinguish between the two age populations.
- ID:
- ivo://CDS.VizieR/J/other/RMxAA/56.139
- Title:
- On the evolution of angular momentum
- Short Name:
- J/other/RMxAA/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Selecting the best quality data, I find that nearly all 0.5 to 1.2M_{sun}_ main sequence stars converge to a single rotational mass dependent sequence after 750Myr; when the mass is larger than 0.8M_{sun}_, most of them converge in ~120Myr. If stars rotate as rigid bodies, the angular momentum of the vast majority is within clearly outlined bounds. The lower boundary defines a terminal main sequence rotational isochrone, the upper one coincides with slow rotators from the Pleiades and stars from Praesepe delineate a third one. Mass dependent exponential relationships between angular momentum and age are determined from these isochrones. Age estimates based on the angular momentum, are acceptable in middle aged stars older than 750Myr and more massive than 0.6-0.7M_{sun}_. The evolution of the Rossby number indicates that the Parker dynamo may cease early on in stars where M/M_{sun}_>=1.1. An empirical formula for the torque, an idealized model for it and a relation between rotational period and magnetic field, lead to a formula for the evolution of the mass loss rate, predicting that the present solar rate is close to a minimum and that it was around five times more vigorous when life on Earth started.
- ID:
- ivo://CDS.VizieR/J/ApJ/612/481
- Title:
- Optical brightness of {epsilon} Eri dust ring
- Short Name:
- J/ApJ/612/481
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The STIS CCD camera on the Hubble Space Telescope (HST) was used to take deep optical images near the K2 V main-sequence star {epsilon} Eridani in an attempt to find an optical counterpart of the dust ring previously imaged by submillimeter observations. Upper limits for the optical brightness of the dust ring are determined and discussed in the context of the scattered starlight expected from plausible dust models.
- ID:
- ivo://CDS.VizieR/J/AJ/160/235
- Title:
- Optical photometry and RVs of TOI-481b and TOI-892b
- Short Name:
- J/AJ/160/235
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery of two new 10 day period giant planets from the Transiting Exoplanet Survey Satellite mission, whose masses were precisely determined using a wide diversity of ground-based facilities. TOI-481b and TOI-892b have similar radii (0.99{+/-}0.01R_Jup_ and 1.07{+/-}0.02R_Jup_, respectively), and orbital periods (10.3311days and 10.6266days, respectively), but significantly different masses (1.53{+/-}0.03M_Jup versus 0.95{+/-}0.07M_Jup_, respectively). Both planets orbit metal-rich stars ([Fe/H]=+0.26{+/-}0.05dex and [Fe/H]=+0.24{+/-}0.05 for TOI-481 and TOI-892, respectively) but at different evolutionary stages. TOI-481 is a M_*_=1.14{+/-}0.02M_{odot}_, R_*_=1.66{+/-}0.02R_{odot}_ G-type star (Teff=5735{+/-}72K), that with an age of 6.7Gyr, is in the turn-off point of the main sequence. TOI-892 on the other hand, is a F-type dwarf star (Teff=6261{+/-}80K), which has a mass of M_*_=1.28{+/-}0.03M_{odot}_ and a radius of R_*_=1.39{+/-}0.02R_{odot}_. TOI-481b and TOI-892b join the scarcely populated region of transiting gas giants with orbital periods longer than 10days, which is important to constrain theories of the formation and structure of hot Jupiters.
- ID:
- ivo://CDS.VizieR/J/A+A/338/1066
- Title:
- Optical Spectra of DENIS Brown Dwarf Candidate
- Short Name:
- J/A+A/338/1066
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Optical spectra for candidate brown dwarfs from the DENIS Mini-survey are provided. These are the spectra used to in Figure 1 of the paper.
- ID:
- ivo://CDS.VizieR/J/MNRAS/373/705
- Title:
- Optical spectroscopy of high proper motion stars
- Short Name:
- J/MNRAS/373/705
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spectra of 59 nearby star candidates, M dwarfs and white dwarfs, previously identified using high proper motion catalogues and the DENIS database. We review the existing spectral classification schemes and spectroscopic parallax calibrations in the near-infrared J band and derive spectral types and distances of the nearby candidates. Forty-two stars have spectroscopic distances smaller than 25pc, three of them being white dwarfs. Two targets lie within 10pc, one M8 star at 10.0pc (APMPM J0103-3738), and one M4 star at 8.3pc (L 225-57). One star, LHS 73, is found to be among the few subdwarfs lying within 20pc. Furthermore, together with LHS 72, it probably belongs to the closest pair of subdwarfs we know.
- ID:
- ivo://CDS.VizieR/J/AJ/152/11
- Title:
- Orbits of four triple stars
- Short Name:
- J/AJ/152/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Each of the nearby triple systems HIP 7601, 13498, 23824, and 113597 (HD 10800, 18198, 35877, 217379) consist of solar-type dwarfs with comparable masses, where all three components are resolved spectrally, while the outer pairs are resolved both visually and spectrally. These stars are relatively young (between 100 and 600Myr) and chromospherically active (X-ray sources), although they rotate slowly. I determine the spectroscopic orbits of the inner subsystems (periods 19.4, 14.1, 5.6, 20.3days) and the orbits of the outer systems (periods 1.75, 51, 27, 500years, respectively). For HIP 7601 and 13498, the combined spectro-interferometric outer orbits produce direct measurement of the masses of all of the components, allowing for a comparison with stellar models. The 6708{AA} lithium line is present and its strength is measured in each component individually by subtracting the contributions of the other components. The inner and outer orbits of HIP 7601 are nearly circular, likely co-planar, and have a modest period ratio of 1:33. This study contributes to the characterization of hierarchical multiplicity in the solar neighborhood and provides data for testing stellar evolutionary models and chronology.
- ID:
- ivo://CDS.VizieR/J/ApJ/757/164
- Title:
- Oxygen abundances of dwarf stars
- Short Name:
- J/ApJ/757/164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Oxygen abundances of 67 dwarf stars in the metallicity range -1.6<[Fe/H]<-0.4 are derived from a non-LTE analysis of the 777nm OI triplet lines. These stars have precise atmospheric parameters measured by Nissen and Schuster (Cat. J/A+A/511/L10), who find that they separate into three groups based on their kinematics and {alpha}-element (Mg, Si, Ca, Ti) abundances: thick disk, high-{alpha} halo, and low-{alpha} halo. We find the oxygen abundance trends of thick-disk and high-{alpha} halo stars very similar. The low-{alpha} stars show a larger star-to-star scatter in [O/Fe] at a given [Fe/H] and have systematically lower oxygen abundances compared to the other two groups. Thus, we find the behavior of oxygen abundances in these groups of stars similar to that of the {alpha} elements. We use previously published oxygen abundance data of disk and very metal-poor halo stars to present an overall view (-2.3<[Fe/H]<+0.3) of oxygen abundance trends of stars in the solar neighborhood. Two field halo dwarf stars stand out in their O and Na abundances. Both G53-41 and G150-40 have very low oxygen and very high sodium abundances, which are key signatures of the abundance anomalies observed in globular cluster (GC) stars. Therefore, they are likely field halo stars born in GCs. If true, we estimate that at least 3%+/-2% of the local field metal-poor star population was born in GCs.
