- ID:
- ivo://CDS.VizieR/J/ApJS/258/43
- Title:
- Light curves of AGBs in Galactic open clusters
- Short Name:
- J/ApJS/258/43
- Date:
- 15 Feb 2022 09:28:18
- Publisher:
- CDS
- Description:
- Benefiting from the GAIA second and early third releases of photometric and astrometric data we examine the population of asymptotic giant branch (AGB) stars that appear in the fields of intermediate-age and young open star clusters. We identify 49 AGB star candidates, brighter than the tip of the red giant branch, with a good-to-high cluster membership probability. Among them we find 19 TP-AGB stars with known spectral type: 4 M stars, 3 MS/S stars and 12 C stars. By combining observations, stellar models, and radiative transfer calculations that include the effect of circumstellar dust, we characterize each star in terms of initial mass, luminosity, mass-loss rate, core mass, period and mode of pulsation. The information collected helps us shed light on the TP-AGB evolution at solar-like metallicity, placing constraints on the third dredge-up process, the initial masses of carbon stars, stellar winds, and the initial-final mass relation (IFMR). In particular, we find that two bright carbon stars, MSB 75 and BM IV 90, members of the clusters NGC 7789 and NGC 2660 (with similar ages of about 1.2-1.6 Gyr and initial masses between 2.1 and 1.9 solar masses), have unusually high core masses, about 0.67-0.7 solar masses. These results support the findings of a recent work (Marigo et al., 2020NatAs...4.1102M) that identified a kink in the IFMR, which interrupts its monotonic trend just at the same initial masses. Finally, we investigate two competing scenarios to explain the Mc data: the role of stellar winds in single-star evolution, and binary interactions through the blue-straggler channel.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/632/A95
- Title:
- Light curves of NGC 6910 pulsating stars
- Short Name:
- J/A+A/632/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this study is to obtain the age of the open cluster NGC 6910 by means of ensemble asteroseismology of the early-type pulsating members, to derive their stellar parameters, and to classify the excited modes. We used time-series analysis, performed photometric and spectroscopic mode identification, and calculated grids of evolutionary and seismic models to apply the procedure of ensemble asteroseismology for nine pulsating members of NGC 6910. With two iterations of the procedure of ensemble asteroseismology we derived an age of 10.6^+0.9^_-0.8_Myr for NGC 6910. We also identified the degree l for 8 of 37 modes detected in these stars and classified all modes in terms of p, g, and mixed-mode pulsations. Of the nine pulsating stars examined in the paper, eight are {beta} Cep stars, including three that are hybrid {beta} Cep and slowly pulsating B-type (SPB) pulsators, and one is an SPB star. Interestingly, the least massive {beta} Cep star, NGC 6910-38, has a mass of about 5.6 solar masses. The present theory does not predict unstable p modes in B-type stars with such a low mass. The g modes with relatively high frequencies (>3.5d^-1^), observed in three members of the cluster, are also stable according to seismic modelling. Both findings pose a challenge for theoretical calculations and prompt a revision of the opacities. The procedure of ensemble asteroseismology was found to be successful for NGC 6910 and {chi} Per on the basis of pulsating B-type stars and can therefore be applied to other young open clusters that are rich in such stars.
- ID:
- ivo://CDS.VizieR/J/PASP/131/D4101
- Title:
- Likely Pleiades members with Gaia DR2
- Short Name:
- J/PASP/131/D4101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents an investigation on fundamental astrophysical properties of the Pleiades cluster (M 45) using high-precision astrometric and photometric data from the Gaia Data Release 2 (Gaia-DR2). To obtain reliable cluster members, a machine-learning (ML) method is used to compute membership probabilities for 31462 sample stars within a radius of 6.5{deg} from the cluster center, both the astrometric and photometric data are taken into account. We obtain a total number of 1454 likely cluster members with membership probabilities larger than 0.6, including a well-known white dwarf (LB 1497) with a high membership probability of ~0.96. We find a well-defined relationship between the parallaxes and proper motions of the cluster members, the most likely explanation for the relationship is that the depth effect of the cluster along the line of sight must be taken into consideration. Using Monte Carlo simulations, the most likely distance, proper motion, and radial velocity of the cluster are determined to be D=136.0+/-0.1pc, (<{mu}_{alpha}_cos{delta}>, <{mu}_{delta}_>)=(+20.141+/-0.093, -45.536+/ -0.081)mas/yr, and <V_r_>=+5.8+/-0.1km/s, respectively. It is found that the likely cluster members extend outward to a limiting radius of R_lim_=310'+/-12' (12.3+/-0.5pc) from the cluster center, and the total mass of the cluster within this radius is M_tot_=721+/-93M_{sun}_. We find clear evidence for the presence of spatial mass segregation in this young cluster by analyzing the photometry and spatial positions of the likely cluster members. Interestingly, we also find that four high-mass cluster members with high membership probabilities (>0.99) are being ejected from the inner region of the cluster, they may have formed via close encounters between single and binary stars.
- ID:
- ivo://CDS.VizieR/J/A+A/489/403
- Title:
- Line abundances for solar stars
- Short Name:
- J/A+A/489/403
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the abundance measurements of several elements (Fe, Ca, Na, Ni, Ti, Al, Cr, Si) for 20 solar-type stars belonging to four Galactic open clusters: NGC 3680, IC 4651, Praesepe, and M 67. Oxygen abundances were in addition measured for most stars in each cluster apart from IC 4651. For NGC 3680, accurate abundance determinations using high-resolution spectra covering a large spectral domain are computed for the first time. We used UVES high-resolution, high signal-to-noise (S/N) ratio spectra and performed a differential analysis with respect to the sun, by measuring equivalent widths and assuming LTE.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A51
- Title:
- Line list for abundance determination in Sun siblings
- Short Name:
- J/A+A/575/A51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this paper is to find lost siblings of the Sun by analyzing high resolution spectra. Finding solar siblings will enable us to constrain the parameters of the parental cluster and the birth place of the Sun in the Galaxy. The solar siblings can be identified by accurate measurements of metallicity, stellar age and elemental abundances for solar neighbourhood stars. The solar siblings candidates were kinematically selected based on their proper motions, parallaxes and colours. Stellar parameters were determined through a purely spectroscopic approach and partly physical method, respectively. Comparing synthetic with observed spectra, elemental abundances were computed based on the stellar parameters obtained using a partly physical method. A chemical tagging technique was used to identify the solar siblings. We present stellar parameters, stellar ages, and detailed elemental abundances for Na, Mg, Al, Si, Ca, Ti, Cr, Fe, and Ni for 32 solar sibling candidates. Our abundances analysis shows that four stars are chemically homogeneous together with the Sun. Technique of chemical tagging gives us a high probability that they might be from the same open cluster. Only one candidate, HIP 40317, which has solar metallicity and age could be a solar sibling. We performed simulations of the Sun's birth cluster in analytical Galactic model and found that most of the radial velocities of the solar siblings lie in the range -10<=Vr<=10km/s, which is smaller than the radial velocity of HIP 40317 (Vr=34.2km/s), under different Galactic parameters and different initial conditions of the Sun's birth cluster. The sibling status for HIP 40317 is not directly supported by our dynamical analysis.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/4301
- Title:
- Line list for red giants in open clusters
- Short Name:
- J/MNRAS/450/4301
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed high-dispersion echelle spectra of red giant members in the five open clusters (OCs) NGC 1342, NGC 1662, NGC 1912, NGC 2354 and NGC 2447 and determined their radial velocities and chemical compositions. These are the first chemical abundance measurements for all but NGC 2447. We combined our clusters from this and previous papers with a sample drawn from the literature for which we remeasured the chemical abundances to establish a common abundance scale. With this homogeneous sample of OCs, we study the relative elemental abundances of stars in OCs in comparison with field stars as a function of age and metallicity. We find a range of mild enrichment of heavy (Ba-Eu) elements in young OC giants over field stars of the same metallicity. Our analysis supports that the youngest stellar generations in cluster might be underrepresented by the solar neighbourhood field stars.
- ID:
- ivo://CDS.VizieR/J/A+A/372/862
- Title:
- Lithium abundances in IC 2602 and IC 2391
- Short Name:
- J/A+A/372/862
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Lithium abundances and [Fe/H] for a sample of late-type stars in the young open clusters IC 2602 and IC 2391. Abundances are based on high resolution spectra obtained at ESO (3.6m + CASPEC) and CTIO (4m + echelle spectrograph)
- ID:
- ivo://CDS.VizieR/J/A+A/613/A63
- Title:
- Lithium content for 148 Pleiades stars
- Short Name:
- J/A+A/613/A63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolution of lithium abundance over a star's lifetime is indicative of transport processes operating in the stellar interior. Aims. We revisit the relationship between lithium content and rotation rate previously reported for cool dwarfs in the Pleiades cluster. Methods. We derive new LiI 670.8nm equivalent width measurements from high-resolution spectra obtained for low-mass Pleiades members. We combine these new measurements with previously published ones, and use the Kepler/K2 rotational periods recently derived for Pleiades cool dwarfs to investigate the lithium-rotation connection in this 125Myr-old cluster. Results. The new data confirm the correlation between lithium equivalent width and stellar spin rate for a sample of 51 early K-type members of the cluster, where fast rotating stars are systematically lithium-rich compared to slowly rotating ones. The correlation is valid for all stars over the (J-Ks) color range 0.50-0.70mag, corresponding to a mass range from about 0.75 to 0.90M_{sun}_, and may extend down to lower masses. Conclusions. We argue that the dispersion in lithium equivalent widths observed for cool dwarfs in the Pleiades cluster reflects an intrinsic scatter in lithium abundances, and suggest that the physical origin of the lithium dispersion pattern is to be found in the pre-main sequence rotational history of solar-type stars.
- ID:
- ivo://CDS.VizieR/J/A+A/541/A150
- Title:
- Lithium in M67 and Hyades
- Short Name:
- J/A+A/541/A150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Lithium abundances in open clusters are a very effective probe of mixing processes, and their study can help to understand the large depletion of lithium in the Sun. Due to its age and metallicity, the open cluster M67 is especially interesting on this regard. Many studies on lithium abundances in M67 have already been performed, but a homogeneous global analysis of lithium in stars from subsolar up to the most massive members, was never accomplished for a large sample based on high-quality spectra. We tested our non-standard models, which were calibrated using the Sun with observational data. We collected literature data to follow, for the first time in a homogeneous way, NLTE lithium abundances of all observed single stars in M67 more massive than about 0.9 solar masses.
520. Lithium in Praesepe
- ID:
- ivo://CDS.VizieR/J/AJ/106/1080
- Title:
- Lithium in Praesepe
- Short Name:
- J/AJ/106/1080
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Echelle observations are presented of lithium in 63 F and G dwarfs of the Praesepe cluster. For stars earlier than about G0V, Praesepe follows the same trends seen in the Hyades, which has approximately the same age and composition. Stars in Praesepe later than about G5V have more Li than their Hyades counterparts, possibly because Praesepe is slightly younger than the Hyades or has slightly lower metallicity. Significant differences in the abundance of Li are seen among stars of the same color, and, as in the Hyades, there is a tendency for the deviant stars to be binaries to the extent that duplicity in Praesepe is known. There are also stars with much less Li than most cluster members yet which appear to be true members of Praesepe. The close binary KW 181 has a normal Li abundance, despite the fact that similar close binaries in the Hyades are Li rich.