- ID:
- ivo://CDS.VizieR/VI/157
- Title:
- Full-spectrum fitting of simple stellar pop.
- Short Name:
- VI/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this second paper of a series on the accuracy and precision of the determination of age and metallicity of simple stellar populations (SSPs) by means of the full spectrum fitting technique, we study the influence of star cluster mass through stochastic fluctuations of the number of stars near the top of the stellar mass function, which dominate the flux in certain wavelength regimes depending on the age.We consider SSP models based on the Padova isochrones, spanning the age range 7.0<=log(age/yr)<=10.1. Simulated spectra of star clusters in the mass range 10^4^<=M/M_{sun}_<10^6^ are compared with SSP model spectra to determine best-fit ages and metallicities using a full-spectrum fitting routine in four wavelength regimes: the blue optical (0.35-0.70um), the red optical (0.6-1.0um), the near-IR (1.0-2.5um), and the mid-IR (2.5-5.0um). We compare the power of each wavelength regime in terms of both the overall precision of age and metallicity determination, and of its dependence on cluster mass. We also study the relevance of spectral resolution in this context by utilizing two different spectral libraries (BaSeL and BT-Settl). We highlight the power of the mid-IR regime in terms of identifying young massive clusters in dusty star forming regions in distant galaxies. The spectra of the simulated star clusters and SSPs are made available online to enable follow-up studies by the community.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/309/749
- Title:
- Fundamental plane of early type galaxies
- Short Name:
- J/A+A/309/749
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyse the residuals to the fundamental plane (FP) of elliptical galaxies as a function of stellar-population indicators; these are based on the line-strength parameter Mg2 and on UBVRI broad-band colors, and are partly derived from new observations. The effect of the stellar populations accounts for approximately half the observed variation of the mass-to-light ratio responsible for the FP tilt. The residual tilt can be explained by the contribution of two additional effects: the dependence of the rotational support, and possibly that of the spatial structure, on the luminosity. We conclude to a constancy of the dynamical-to-stellar mass ratio. This probably extends to globular clusters as well, but the dominant factor would be here the luminosity dependence of the structure rather than that of the stellar population. This result also implies a constancy of the fraction of dark matter over all the scalelength covered by stellar systems. Our compilation of internal stellar kinematics of galaxies is appended.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/99
- Title:
- Gaia DR2 Blanco 1 member candidates
- Short Name:
- J/ApJ/889/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the stellar population, using Gaia DR2 parallax, kinematics, and photometry, of the young (~100Myr), nearby (~230pc) open cluster, Blanco 1. A total of 644 member candidates are identified via the unsupervised machine learning method StarGO to find the clustering in the 5-dimensional position and proper motion parameter (X, Y, Z, {mu}{alpha}*cos{delta}, {mu}{delta}) space. Within the tidal radius of 10.0+/-0.3pc, there are 488 member candidates, 3 times more than those outside. A leading tail and a trailing tail, each of 50-60pc in the Galactic plane, are found for the first time for this cluster, with stars further from the cluster center streaming away faster, manifest stellar stripping. Blanco 1 has a total detected mass of 285+/-32M_{sun}_ with a mass function consistent with a slope of alpha=1.35+/-0.2 in the sense of dN/dm{prop.to}m^-alpha^, in the mass range of 0.25-2.51M_{sun}_, where N is the number of members and $m$ is stellar mass. A Minimum Spanning Tree ({LAMBDA}_MSR_) analysis shows the cluster to be moderately mass segregated among the most massive members (>~1.4M_{sun}_), suggesting an early stage of dynamical disintegration.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A34
- Title:
- GC hot UV-bright stars model spectra
- Short Name:
- J/A+A/627/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a census of the UV-bright population in 78 globular clusters using wide-field UV telescopes. This population includes a variety of phases of post-horizontal branch (HB) evolution, including hot post-asymptotic giant branch (AGB) stars, and post-early AGB stars. There are indications that old stellar systems like globular clusters produce fewer post-(early) AGB stars than currently predicted by evolutionary models, but observations are still scarce. We wish to derive effective temperatures, surface gravities, and helium abundances of the luminous hot UV-bright stars in these clusters to determine their evolutionary status and compare the observed numbers to predictions from evolutionary theory. We obtained FORS2 spectroscopy of 11 of these UV-selected objects (covering a range of -2.3<[Fe/H]<-1.0), which we (re-)analysed together with previously observed data. We used model atmospheres of different metallicities, including super-solar ones. Where possible, we verified our atmospheric parameters using UV spectrophotometry and searched for metal lines in the optical spectra. We calculated evolutionary sequences for four metallicity regimes and used them together with information about the HB morphology of the globular clusters to estimate the expected numbers of post-AGB stars. We find that metal-rich model spectra are required to analyse stars hotter than 40000 K. Seven of the eleven new luminous UV-bright stars are post-AGB or post-early AGB stars, two are evolving away from the HB, one is a foreground white dwarf, and another is a white dwarf merger. Taking into account published information on other hot UV-bright stars in globular clusters, we find that the number of observed hot post-AGB stars generally agrees with the predicted values, although the numbers are still low. Spectroscopy is clearly required to identify the evolutionary status of hot UV-bright stars. For hotter stars, metal-rich model spectra are required to reproduce their optical and UV spectra, which may affect the flux contribution of hot post-AGB stars to the UV spectra of evolved populations. Adding published information on other hot UV-bright stars in globular clusters, we find that the number of observed hot post-AGB stars generally agrees with the predicted values, although the numbers are still low.
- ID:
- ivo://CDS.VizieR/J/MNRAS/488/3024
- Title:
- Globular clusters members with Gaia DR2
- Short Name:
- J/MNRAS/488/3024
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we present a method to identify possible members of globular clusters using data from Gaia DR2. The method consists of two stages: the first one based on a clustering algorithm, and the second one based on the analysis of the projected spatial distribution of stars with different proper motions. In order to confirm that the clusters members extracted by the method correspond to actual globular clusters, the spatial distribution, the vector point diagram of the proper motions, and the colour-magnitude diagrams are analysed. We apply the developed method to eight clusters: NGC 1261, NGC 3201, NGC 6139, NGC 6205, NGC 6362, NGC 6397, NGC 6712, and Palomar 13; we show the number of members extracted, the mean proper motions derived from them and finally we compare our results with other authors. In order to analyse the efficiency of the extraction method, we perform an estimation of the completeness and the degree of contamination of the extracted members.
- ID:
- ivo://CDS.VizieR/J/ApJS/111/377
- Title:
- H{gamma} & H{delta} absorption features
- Short Name:
- J/ApJS/111/377
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The H{gamma} and H{delta} absorption features are measured in a sample of 455 (out of an original 460) Lick IDS stars with pseudo-equivalent width indices. For each Balmer feature, two definitions, involving a narrow (~20{AA}) and a wide (~40{AA}) central bandpass, were measured. These four new Balmer indices augment 21 indices previously determined by Worthey et al., and polynomial fitting functions that give index strengths as a function of stellar temperature, gravity, and [Fe/H] are provided. The new indices are folded into models for the integrated light of stellar populations, and predictions are given for single-burst stellar populations of a variety of ages and metallicities. Contrary to our initial hopes, the indices cannot break a degeneracy between burst age and burst strength in poststarbust objects, but they are successful mean-age indicators when used with sensitive metallicity indicators. An appendix gives data, advice, and examples of how to transform new spectra to the 25-index Lick IDS system.
- ID:
- ivo://CDS.VizieR/J/A+A/611/A38
- Title:
- Hints for a bar in M31 kinematics and morphology
- Short Name:
- J/A+A/611/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As the nearest large spiral galaxy, M 31 provides a unique opportunity to study the structure and evolutionary history of this galaxy type in great detail. Among the many observing programs aimed at M 31 are microlensing studies, which require good three-dimensional models of the stellar mass distribution. Possible non-axisymmetric structures like a bar need to be taken into account. Due to M 31's high inclination, the bar is difficult to detect in photometry alone. Therefore, detailed kinematic measurements are needed to constrain the possible existence and position of a bar in M 31. We obtained ~=220 separate fields with the optical integral-field unit spectrograph VIRUS-W, covering the whole bulge region of M 31 and parts of the disk. We derived stellar line-of-sight velocity distributions from the stellar absorption lines, as well as velocity distributions and line fluxes of the emission lines H{beta}, [OIII] and [NI]. Our data supersede any previous study in terms of spatial coverage and spectral resolution. We find several features that are indicative of a bar in the kinematics of the stars, we see intermediate plateaus in the velocity and the velocity dispersion, and correlation between the higher moment h3 and the velocity. The gas kinematics is highly irregular, but is consistent with non-triaxial streaming motions caused by a bar. The morphology of the gas shows a spiral pattern, with seemingly lower inclination than the stellar disk. We also look at the ionization mechanisms of the gas, which happens mostly through shocks and not through starbursts.
- ID:
- ivo://CDS.VizieR/J/AJ/136/2259
- Title:
- HST photometry of stars in NGC 2419
- Short Name:
- J/AJ/136/2259
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of optical and ultraviolet Hubble Space Telescope photometry for evolved stars in the core of the distant massive globular cluster NGC 2419. We characterize the horizontal branch (HB) population in detail including corrections for incompleteness on the long blue tail. The majority of the HB stars can be identified with two main groups (one slightly bluer than the instability strip, and the other at the extreme end of the HB). We present a method for removing (to first-order) lifetime effects from the distribution of HB stars to facilitate more accurate measurements of helium abundance for clusters with blue HBs and to clarify the distribution of stars reaching the zero-age HB.
- ID:
- ivo://CDS.VizieR/J/A+A/621/L2
- Title:
- Hyades tidal tails revealed by Gaia DR2
- Short Name:
- J/A+A/621/L2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Within a 200pc sphere around the Sun, we search for the Hyades tidal tails in the Gaia DR2 dataset. We used a modified convergent-point method to search for stars with space velocities close to the space velocity of the Hyades cluster. We find a clear indication for the existence of the Hyades tidal tails, a leading tail extending up to 170pc from the centre of the Hyades with 292 stars (36 contaminants), and a trailing tail up to 70pc with 237 stars (32 contaminants). A comparison with an N-body model of the cluster and its tails shows remarkably good coincidence. Five white dwarfs are found in the tails.
- ID:
- ivo://CDS.VizieR/J/A+AS/97/587
- Title:
- JHK photometry of Galactic center stars
- Short Name:
- J/A+AS/97/587
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present K-counts and JHK detailed photometry for a number of stars with K<=+9.0 in three clear regions near the galactic centre. These regions are all located approximately at l~0.0 and at latitudes b~-3.5,-4.0 and 4.5 respectively. Their Cumulative Counts Functions (CCF's) are formed, and with the aid of an exponential disk model for the Galaxy they are separated into disk and bulge CCF. As for the case in Baade's Window (BW) (Ruelas-Mayorga & Teague, 1992A&AS...95..379R) the disk is dominant at bright magnitudes whereas the bulge dominates at the faint end of the CCF. The slope of the bulge CCF is steeper than that for the disk in all three cases corroborating the result obtained for BW. The two colour JHK diagram and the K vs J-K diagram for the three regions show that the stellar population in these areas is similar to that studied in BW by us and by Frogel & Whitford (1987ApJ...320..199F). An average value of E(J-K)~0.42mag for the reddening is obtained, which is somewhat larger than that found for BW (0.27). Finally it is shown that at K<=+9.0, the disk population may be accounted for by those sources with J-K<=+1.6 whereas the bulge population presents values for J-K in excess of +1.6.
