- ID:
- ivo://CDS.VizieR/J/A+A/588/A148
- Title:
- NGC 6397 stars MUSE spectra
- Short Name:
- J/A+A/588/A148
- Date:
- 23 Mar 2022 16:26:54
- Publisher:
- CDS
- Description:
- We demonstrate the high multiplex advantage of crowded field 3D spectroscopy with the new integral field spectrograph MUSE by means of a spectroscopic analysis of more than 12000 individual stars in the globular cluster NGC 6397. The stars are deblended with a point spread function fitting technique, using a photometric reference catalogue from HST as prior, including relative positions and brightnesses. This catalogue is also used for a first analysis of the extracted spectra, followed by an automatic in-depth analysis via a full-spectrum fitting method based on a large grid of PHOENIX spectra. We analysed the largest sample so far available for a single globular cluster of 18 932 spectra from 12 307 stars in NGC 6397. We derived a mean radial velocity of v_rad_=17.84+/-0.07km/s and a mean metallicity of [Fe/H]=-2.120+/-0.002, with the latter seemingly varying with temperature for stars on the red giant branch (RGB). We determine Teff and [Fe/H] from the spectra, and log g from HST photometry. This is the first very comprehensive Hertzsprung-Russell diagram (HRD) for a globular cluster based on the analysis of several thousands of stellar spectra, ranging from the main sequence to the tip of the RGB. Furthermore, two interesting objects were identified; one is a post-AGB star and the other is a possible millisecond-pulsar companion.
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- ID:
- ivo://CDS.VizieR/J/A+A/631/A14
- Title:
- NGC 2808 stellar population spectra
- Short Name:
- J/A+A/631/A14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic globular clusters (GCs) are now known to host multiple populations displaying particular abundance variations. The different populations within a GC can be well distinguished following their position in the pseudo two-colors diagrams, also referred to as "chromosome maps". These maps are constructed using optical and near-UV photometry available from the Hubble Space Telescope (HST) UV survey of GCs. However, the chemical tagging of the various populations in the chromosome maps is hampered by the fact that HST photometry and elemental abundances are both available only for a limited number of stars. The spectra collected as part of the MUSE survey of globular clusters provide a spectroscopic counterpart to the HST photometric catalogs covering the central regions of GCs. In this paper, we use the MUSE spectra of 1155 red giant branch (RGB) stars in NGC 2808 to characterize the abundance variations seen in the multiple populations of this cluster. We use the chromosome map of NGC 2808 to divide the RGB stars into their respective populations. We then combine the spectra of all stars belonging to a given population, resulting in one high signal-to-noise ratio spectrum representative of each population. Variations in the spectral lines of O, Na, Mg, and Al are clearly detected among four of the populations. In order to quantify these variations, we measured equivalent width differences and created synthetic populations spectra that were used to determine abundance variations with respect to the primordial population of the cluster. Our results are in good agreement with the values expected from previous studies based on high-resolution spectroscopy. We do not see any significant variations in the spectral lines of Ca, K, and Ba. We also do not detect abundance variations among the stars belonging to the primordial population of NGC 2808.
- ID:
- ivo://CDS.VizieR/J/ApJS/116/1
- Title:
- Old Stellar Populations. VI. Absorption-Line
- Short Name:
- J/ApJS/116/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present absorption-line strengths on the Lick/IDS line-strength system of 381 galaxies and 38 globular clusters in the 4000--6400 angstrom region. All galaxies were observed at Lick Observatory between 1972 and 1984 with the Cassegrain Image Dissector Scanner spectrograph, making this study one of the largest homogeneous collections of galaxy spectral line data to date. We also present a catalogue of nuclear velocity dispersions used to correct the absorption-line strengths onto the stellar Lick/IDS system. Extensive discussion of both random and systematic errors of the Lick/IDS system is provided. Indices are seen to fall into three families: alpha-element-like indices (including CN, Mg, Na D, and TiO2) that correlate positively with velocity dispersion; Fe-like indices (including Ca, the G band, TiO1, and all Fe indices) that correlate only weakly with velocity dispersion and the alpha indices; and Hbeta which anti-correlates with both velocity dispersion and the alpha indices. C2 4668 seems to be intermediate between the alpha and Fe groups. These groupings probably represent different element abundance families with different nucleosynthesis histories.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A79
- Title:
- ONC stars masses from literature
- Short Name:
- J/A+A/626/A79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- ALMA observations of the Serpens South star-forming region suggest that stellar protoclusters may be completely mass segregated at birth. Independent observations also suggest that embedded clusters form segregated by mass. As the primordial mass segregation seems to be lost over time, we aim to study on which timescale an initially perfectly mass-segregated star cluster becomes indistinguishable from an initially not mass-segregated cluster. As an example, the Orion Nebula Cluster (ONC) is also discussed. We used N-body simulations of star clusters with various masses and two different degrees of primordial mass segregation. We analysed their energy redistribution through two-body relaxation to quantify the time when the models agree in terms of mass segregation, which sets in only dynamically in the models that are primordially not mass segregated. A comprehensive cross-matched catalogue combining optical, infrared, and X-ray surveys of ONC members was also compiled and made available. The models evolve to a similar radial distribution of high-mass stars after the core collapse (about half a median two-body relaxation time, t_rh_) and become observationally indistinguishable from the point of view of mass segregation at time tau_v_~3.3t_rh_. In the case of the ONC, using the distribution of high-mass stars, we may not rule out either evolutionary scenario (regardless of whether they are initially mass segregated). When we account for extinction and elongation of the ONC, as reported elsewhere, an initially perfectly mass-segregated state seems to be more consistent with the observed cluster.
- ID:
- ivo://CDS.VizieR/I/348
- Title:
- Orbital parameters in Milky-Way-like potentials
- Short Name:
- I/348
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Orbital parameters, such as eccentricity and maximum vertical excursion, of stars in the Milky Way are an important tool for understanding its dynamics and evolution, but calculation of such parameters usually relies on computationally-expensive numerical orbit integration. We present and test a fast method for estimating these parameters using an application of the Sackel fudge, used previously for the estimation of action-angle variables. We show that the method is highly accurate, to a level of <1% in eccentricity, over a large range of relevant orbits and in different Milky Way-like potentials, and demonstrate its validity by estimating the eccentricity distribution of the RAVE-TGAS data set and comparing it to that from orbit integration. Using the method, the orbital characteristics of the ~7 million Gaia DR2 stars with radial velocity measurements are computed with Monte Carlo sampled errors in ~116 hours of parallelised cpu time, at a speed that we estimate to be ~3 to 4 orders of magnitude faster than using numerical orbit integration. We demonstrate using this catalogue that Gaia DR2 samples a large range of orbits in the solar vicinity, down to those with r_peri_<~2.5kpc, and out to r_ap_>~13kpc. We also show that many of the features present in orbital parameter space have a low mean zmax, suggesting that they likely result from disk dynamical effects.
- ID:
- ivo://CDS.VizieR/J/AJ/113/1733
- Title:
- Orion Nebula Cluster population
- Short Name:
- J/AJ/113/1733
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the first phase of a study of the stellar population comprising the Orion Nebula Cluster (ONC). Approximately 50% of the ~3500 stars identified to date within ~2.5pc of the namesake Trapezium stars are optically visible, and in this paper we focus on that sample with I<2.5mag. The large number and number density of stars (n_peak_>10^4^pc^-3^), the wide range in the stellar mass (~0.1-50M_{sun}_), and the extreme youth (<1-2Myr) of the stellar population, make the ONC the best site for investigating: (1) the detailed shape of a truly "initial" mass spectrum; (2) the apparent age spread in a region thought to have undergone triggered star formation; (3) the time sequence of star formation as a function of stellar mass; and (4) trends of all of the above with cluster radius.
- ID:
- ivo://CDS.VizieR/J/MNRAS/313/347
- Title:
- Pleiades low-mass stars and brown dwarfs
- Short Name:
- J/MNRAS/313/347
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a six-square-degree Pleiades survey in I and Z, which is photometrically complete to approximately I_KP_=19.2mag (I_C_=19.6 in the Pleiades). We remove non-cluster contamination on the basis of proper motions and infrared photometry, and present 339 candidate cluster members, 30 of which are fainter than I_KP_=17.5, and are thus strong brown-dwarf candidates.
- ID:
- ivo://CDS.VizieR/J/AJ/153/101
- Title:
- Pleiades members stellar properties
- Short Name:
- J/AJ/153/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Precise measurements of eclipsing binary parameters and statistical studies of young clusters have suggested that some magnetically active low-mass dwarfs possess radii inflated by ~5%-15% relative to theoretical expectations. If true, this effect should be pronounced in young open clusters, due to the rapid rotation and strong magnetic activity of their most extreme members. We explore this possibility by determining empirical radii for 83 members of the nearby Pleiades open cluster, using spectral energy distribution fitting to establish F_bol_ with a typical accuracy of ~3% together with color and spectro-photometric indices to determine T_eff_. We find several Pleiades members with radii inflated above radius-T_eff_ models from state-of-the-art calculations, and apparent dispersions in radii for the K-dwarfs of the cluster. Moreover, we demonstrate that this putative radius inflation correlates strongly with rotation rate, consistent with inflation of young stars by magnetic activity and/or starspots. We argue that this signal is not a consequence of starspot-induced color anomalies, binarity, or depth effects in the cluster, employing Gaia DR1 distances as a check. Finally, we consider the lithium abundances of these stars, demonstrating a triple correlation between rotation rate, radius inflation, and enhanced lithium abundance. Our result-already significant to ~99.99% confidence-provides strong support for a magnetic origin of the inflated radii and lithium dispersion observed in young, low-mass stars.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A4
- Title:
- Praesepe (NGC 2632) and its tidal tails
- Short Name:
- J/A+A/627/A4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Within a 400pc sphere around the Sun, we search for Praesepe's tidal tails in the Gaia Data Release 2 (DR2) data set. We used a modified convergent-point method to find stars with space velocities close to the space velocity of the Praesepe cluster. We find a clear indication for the existence of Praesepe's tidal tails, both extending up to 165pc from the centre of the cluster. A total of 1393 stars populate the cluster and its tails, giving a total mass of 794M_{sun}_. We determined a tidal radius of 10.77pc for the cluster and a tidal mass of 483M_{sun}_. The corresponding half-mass radius is 4.8pc. We also found a clear indication for mass segregation in the cluster. The tidal tails outside 2 tidal radii are populated by 389 stars. The total contamination of our sample by field stars lies between 50 and 100 stars or 3.6-7.2%. We used an astrometrically and photometrically clean subsample of Gaia DR2, which makes our Praesepe sample incomplete beyond M~12.0mag; this corresponds to about 0.25M_{sun}_. A comparison with an N-body model of the cluster and its tails shows remarkably good coincidence. Three new white dwarfs are found in the tails.
- ID:
- ivo://CDS.VizieR/J/AJ/156/142
- Title:
- Precision cluster abund. for APOGEE using SDSS DR14
- Short Name:
- J/AJ/156/142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to produce a comprehensive, uniform, infrared-based spectroscopic data set for hundreds of open clusters, and to constrain key Galactic dynamical and chemical parameters from this sample. This second contribution from the OCCAM survey presents analysis of 259 member stars with [Fe/H] determinations in 19 open clusters, using Sloan Digital Sky Survey Data Release 14 (SDSS/DR14) data from the Apache Point Observatory Galactic Evolution Experiment and ESA Gaia. This analysis, which includes clusters with R_GC_ ranging from 7 to 13 kpc, measures an [Fe/H] gradient of -0.061+/-0.004 dex/kpc. We also confirm evidence of a significant positive gradient in the {alpha}-elements ([O/Fe], [Mg/Fe], and [Si/Fe]) and present evidence for a significant negative gradient in iron-peak elements ([Mn/Fe] and [Ni/Fe]).
