- ID:
- ivo://CDS.VizieR/J/ApJ/854/184
- Title:
- Abundances of stars in 3 open clusters
- Short Name:
- J/ApJ/854/184
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Single stars in open clusters with known distances are important targets in constraining the nucleosynthesis process since their ages and luminosities are also known. In this work, we analyze a sample of 29 single red giants of the open clusters NGC2360, NGC3680, and NGC5822 using high-resolution spectroscopy. We obtained atmospheric parameters, abundances of the elements C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd, as well as radial and rotational velocities. We employed the local thermodynamic equilibrium atmospheric models of Kurucz and the spectral analysis code moog. Rotational velocities and light-element abundances were derived using spectral synthesis. Based on our analysis of the single red giants in these three open clusters, we could compare, for the first time, their abundance pattern with that of the binary stars of the same clusters previously studied. Our results show that the abundances of both single and binary stars of the open clusters NGC 2360, NGC 3680, and NGC 5822 do not have significant differences. For the elements created by the s-process, we observed that the open clusters NGC2360, NGC3680, and NGC5822 also follow the trend already raised in the literature that young clusters have higher s-process element abundances than older clusters. Finally, we observed that the three clusters of our sample exhibit a trend in the [Y/Mg]-age relation, which may indicate the ability of the [Y/Mg] ratio to be used as a clock for the giants.
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- ID:
- ivo://CDS.VizieR/J/AJ/154/69
- Title:
- ACRONYM II. The {beta} Pictoris Moving Group
- Short Name:
- J/AJ/154/69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We confirm 66 low-mass stellar and brown dwarf systems (K7-M9) plus 19 visual or spectroscopic companions of the {beta} Pictoris moving group (BPMG). Of these, 41 are new discoveries, increasing the known low-mass members by 45%. We also add four objects to the 14 known with masses predicted to be less than 0.07 M_{sun}_. Our efficient photometric + kinematic selection process identified 104 low-mass candidates, which we observed with ground-based spectroscopy. We collected infrared observations of the latest spectral types (>M5) to search for low-gravity objects. These and all <M5 candidates were observed with high-resolution optical spectrographs to measure the radial velocities and youth indicators, such as lithium absorption and H{alpha} emission, needed to confirm BPMG membership, achieving a 63% confirmation rate. We also compiled the most complete census of BPMG membership, with which we tested the efficiency and false-membership assignments using our selection and confirmation criteria. Using the new census, we assess a group age of 22+/-6 Myr, consistent with past estimates. With the now-densely sampled lithium depletion boundary, we resolve the broadening of the boundary by either an age spread or astrophysical influences on lithium-burning rates. We find that 69% of the now-known members with AFGKM primaries are M stars, nearing the expected value of 75%. However, the new initial mass function for the BPMG shows a deficit of 0.2-0.3 M_{sun}_ stars by a factor of ~2. We expect that the AFGK census of the BPMG is also incomplete, probably due to biases of searches toward the nearest stars.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A4
- Title:
- Activity and accretion in {gamma} Vel and Cha I
- Short Name:
- J/A+A/575/A4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the fundamental parameters (effective temperature, surface gravity, lithium abundance, and radial velocity) delivered by the GES consortium in the first internal data release to select the members of Gamma Vel and Cha I among the UVES and GIRAFFE spectroscopic observations. A total of 140 Gamma Vel members and 74 Cha I members were studied. The procedure adopted by the GES to derive stellar fundamental parameters provided also measures of the projected rotational velocity (vsini). We calculated stellar luminosities through spectral energy distributions, while stellar masses were derived by comparison with evolutionary tracks. The spectral subtraction of low-activity and slowly rotating templates, which are rotationally broadened to match the vsini of the targets, enabled us to measure the equivalent widths (EWs) and the fluxes in the H{alpha} and H{beta} lines. The H{alpha} line was also used for identifying accreting objects, on the basis of its equivalent width and the width at the 10% of the line peak (10%W), and for evaluating the mass accretion rate (M_acc_). The distribution of vsini for the members of Gamma Vel displays a peak at about 10km/s with a tail toward faster rotators. There is also some indication of a different vsini distribution for the members of its two kinematical populations. Most of these stars have H{alpha} fluxes corresponding to a saturated activity regime. We find a similar distribution, but with a narrower peak, for Cha I. Only a handful of stars in Gamma Vel display signatures of accretion, while many more accretors were detected in the younger Cha I, where the highest H{alpha} fluxes are mostly due to accretion, rather than to chromospheric activity. Accreting and active stars occupy two different regions in a T_eff-flux diagram and we propose a criterion for distinguishing them. We derive M_acc in the ranges 10^-11^-10^-9^M_{sun}_/yr and 10^-10^-10^-7^M_{sun}_/yr for Gamma Vel and Cha I accretors, respectively.
- ID:
- ivo://CDS.VizieR/J/AJ/156/61
- Title:
- A study of the H{alpha} variability of Be stars
- Short Name:
- J/AJ/156/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the results of 4 years of high-resolution spectral observations of 69 emission-line stars, 54 of them being newly discovered sources. We classified the stars on the basis of their position in the two-color IR diagram and some additional criteria: shape and width of the H{alpha} profile, presence of He lines, proper motion and parallax, membership to open cluster and associations. Sixty of our targets turned out to be Be stars. We also found four late giants, four pre-MS stars, and one late dwarf. The H{alpha} emission profiles of our Be stars range from single peaked to typical shell profiles that can also be highly asymmetric or single-peaked profiles with a narrow absorption core. The emission profiles appear almost constant with time or highly variable in intensity and in their V/R ratio. The detected long-term variability of the H{alpha} emission is important for investigating the on/off switch phenomenon of Be stars. Our study led to an increase of the number of the emission-line stars of 16 open clusters.
- ID:
- ivo://CDS.VizieR/J/AJ/134/1298
- Title:
- CaII equivalent widths in 29 Galactic clusters
- Short Name:
- J/AJ/134/1298
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From observations of almost 500 red giant branch stars in 29 Galactic open and globular clusters, we have investigated the behavior of the infrared Ca II triplet (8498, 8542, and 8662{AA}) in the age range 13Gyr<=age<=0.25Gyr and the metallicity range -2.2<=[Fe/H]<=+0.47. These are the widest ranges of ages and metallicities in which the behavior of the Ca II triplet lines has been investigated in a homogeneous way. We report the first empirical study of the variation of the Ca II triplet lines' strength, for given metallicities, with respect to luminosity.
- ID:
- ivo://CDS.VizieR/J/A+A/465/185
- Title:
- Element abundances of 7 stars of NGC 6253
- Short Name:
- J/A+A/465/185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a big FLAMES survey of 10 Galactic open clusters aiming at different goals. One of them is the determination of chemical abundances, in order to put constraints on the radial metallicity gradient in the disk and its evolution. One of the sample clusters is the very metal rich NGC 6253. We have obtained UVES high resolution spectra of seven candidate clusters members (from the turn off up to the red clump) with the goal of determining the chemical composition of NGC 6253 and to investigate its origin and role in the interpretation of the radial metallicity gradient in the disk.
- ID:
- ivo://CDS.VizieR/J/MNRAS/434/1681
- Title:
- Extremely metal-poor stars CaII triplet
- Short Name:
- J/MNRAS/434/1681
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We extend our previous calibration of the infrared CaII triplet (CaT) as a metallicity indicator to the metal-poor regime by including observations of 55 field stars with [Fe/H] down to -4.0dex. While we previously solved the saturation at high metallicity using a combination of a Lorentzian and a Gaussian to reproduce the line profiles, in this paper we address the non-linearity at low metallicity following the suggestion of Starkenburg et al. of adding two non-linear terms to the relation among the [Fe/H], luminosity and strength of the calcium triplet lines. Our calibration thus extends from -4.0 to +0.5 in metallicity and is presented using four different luminosity indicators: V-V_HB_, M_V_, M_I_ and M_K_. The calibration obtained in this paper results in a tight correlation between [Fe/H] abundances measured from high-resolution spectra and [Fe/H] values derived from the CaT, over the whole metallicity range covered.
- ID:
- ivo://CDS.VizieR/J/MNRAS/407/465
- Title:
- Fast-rotating M dwarfs in NGC2516
- Short Name:
- J/MNRAS/407/465
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report radial velocities (RVs), projected equatorial velocities (vsini) and CaII triplet (CaT) chromospheric activity indices for 237 late-K to mid-M candidate members of the young open cluster NGC 2516. These stars have published rotation periods between 0.1 and 15d. Intermediate-resolution spectra were obtained using the Giraffe spectrograph at the Very Large Telescope. Membership was confirmed on the basis of their RVs for 210 targets.
- ID:
- ivo://CDS.VizieR/J/A+A/612/A99
- Title:
- Gaia-ESO Survey in 7 open star cluster fields
- Short Name:
- J/A+A/612/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas. We describe the methodologies that, taking advantage of Gaia-DR1 and the Gaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators. We perform a homogeneous analysis of eight open clusters using the Gaia-DR1 TGAS catalogue for bright members and information from the Gaia-ESO Survey for fainter stars. Cluster membership probabilities for the Gaia-ESO Survey targets are derived based on several spectroscopic tracers. The Gaia-ESO Survey also provides the cluster chemical composition. We obtain cluster parallaxes using two methods. The first one relies on the astrometric selection of a sample of bona fide members, while the other one fits the parallax distribution of a larger sample of TGAS sources. Ages and reddening values are recovered through a Bayesian analysis using the 2MASS magnitudes and three sets of standard models. Lithium depletion boundary (LDB) ages are also determined using literature observations and the same models employed for the Bayesian analysis. For all but one cluster, parallaxes derived by us agree with those presented in Gaia Collaboration (2017A&A...601A..19G, Cat. J/A+A/601/A19), while a discrepancy is found for NGC 2516; we provide evidence supporting our own determination. Inferred cluster ages are robust against models and are generally consistent with literature values. The systematic parallax errors inherent in the Gaia DR1 data presently limit the precision of our results. Nevertheless, we have been able to place these eight clusters onto the same age scale for the first time, with good agreement between isochronal and LDB ages where there is overlap. Our approach appears promising and demonstrates the potential of combining Gaia and ground-based spectroscopic datasets.
- ID:
- ivo://CDS.VizieR/J/AJ/153/99
- Title:
- Galactic outer disk: a field toward Tombaugh 1
- Short Name:
- J/AJ/153/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We employ optical photometry and high-resolution spectroscopy to study a field toward the open cluster Tombaugh 1, where we identify a complex population mixture that we describe in terms of young and old Galactic thin disks. Of particular interest is the spatial distribution of the young population, which consists of dwarfs with spectral types as early as B6 and is distributed in a blue plume feature in the color-magnitude diagram. For the first time, we confirm spectroscopically that most of these stars are early-type stars and not blue stragglers or halo/thick-disk subdwarfs. Moreover, they are not evenly distributed along the line of sight but crowd at heliocentric distances between 6.6 and 8.2 kpc. We compare these results with present-day understanding of the spiral structure of the Galaxy and suggest that they trace the outer arm. This range of distances challenges current Galactic models adopting a disk cutoff at 14 kpc from the Galactic center. The young dwarfs overlap in space with an older component, which is identified as an old Galactic thin disk. Both young and old populations are confined in space since the disk is warped at the latitude and longitude of Tombaugh 1. The main effects of the warp are that the line of sight intersects the disk and entirely crosses it at the outer arm distance and that there are no traces of the closer Perseus arm, which would then be either unimportant in this sector or located much closer to the formal Galactic plane. Finally, we analyze a group of giant stars, which turn out to be located at very different distances and to possess very different chemical properties, with no obvious relation to the other populations.
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