- ID:
- ivo://CDS.VizieR/J/AJ/161/288
- Title:
- Stellar population in M53
- Short Name:
- J/AJ/161/288
- Date:
- 18 Jan 2022
- Publisher:
- CDS
- Description:
- We present results from a study of 94 red giant stars in the globular cluster M53. We use low-resolution spectra to measure the strength of CN and CH features at ~3800 and 4300{AA}, respectively. The strengths of these features are used to classify stars into a CN-enhanced and CN-normal population and to measure C and N abundances in all 94 stars. We find the red giant branch stars to be evenly split between the two populations identified, and observe the presence of CN-enhanced stars on the asymptotic giant branch. In addition, we identify five CH star candidates based on the strength of their CN and CH band features, and the presence of a P-branch in their CH band. We compare our identification of multiple populations to those based on the Na-O anticorrelation and pseudo-color indices in Hubble Space Telescope UV photometry, and find general agreement between all three methods. Our large sample size also allows us to study the radial distribution of each population, and we find that the CN-enhanced population is more centrally concentrated. We use our C and N measurements to compare the evolutionary changes in these elements as a function of magnitude between the two populations, and show that both populations experience similar evolutionary changes to the surface abundances of C and N. Finally, we calculate C+N+O abundances for each population and compare them to similar measurements made in M10; we find that in both clusters, CN-enhanced stars have a slightly enhanced C+N+O ({Delta}(C+N+O)~0.2dex).
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/438/813
- Title:
- Stellar population in {rho} Oph cloud core
- Short Name:
- J/ApJ/438/813
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This contribution reports the results of an infrared imaging survey aimed at characterizing the stellar populations associated with the three densest star-forming cores in the Ophiuchus molecular cloud complex. The survey has sufficient sensitivity at J, H, and K (at 5{sigma} limits of 16.5, 15.4 and 14.2) to provide a complete census of embedded young stellar objects (YSOs) with masses greater than the hydrogen-burning limit, provided that their ages are less than 3 Myr and that they are obscured by no more than ~18 mag of visual extinction. Our data suggest (1) a large fraction (>70%) of the sources located within the cores are still surrounded by circumstellar disks and/or envelopes; and (2) the shape of the initial mass function for masses, M<1M_sun_, appears to be consistent with that derived from the solar neighborhood. We also report the results of a deeper imaging survey of centimeter continuum sources (14 sources) in these star-forming cores and in the larger Ophiuchus complex (eight sources). A large fraction 11/14) of the radio sources associated with the cores appear to have infrared excesses diagnostic of circumstellar accretion disks and/or infalling circumstellar envelopes. In these cases, the centimeter continuum radiation most likely diagnoses the ionized component of energetic winds or jets which characterize YSOs during the disk accretion phase. By contrast, of the eight radio sources located outside dense cores, only two show infrared excesses. For the sources which lack infrared excesses, the centimeter continuum emission is probably produced by gyrosynchrotron radiation arising in the stellar magnetospheres of weak emission T Tauri stars. There is some evidence that the frequency of binary companions among the sample of centimeter continuum sources in the molecular cores may be higher (by as much as a factor of 3-4) than that among the older, distributed population of young stars in the larger Ophiuchus cloud complex.
- ID:
- ivo://CDS.VizieR/J/A+A/617/A65
- Title:
- Stellar population of the Arches cluster
- Short Name:
- J/A+A/617/A65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Located within the central region of the Galaxy, the Arches cluster appears to be one of the youngest, densest, and most massive stellar aggregates within the Milky Way. As such, it has the potential to be uniquely instructive laboratory for the study of star formation in extreme environments and the physics of very massive stars. To realise this possibility, the fundamental physical properties of both cluster and constituent stars need to be robustly determined; tasks we attempt here. Methods. In order to accomplish these goals we provide and analyse new multi-epoch near-IR spectroscopic data obtained with the VLT/SINFONI and photometry from the HST/WFC3. We are able to stack multiple epochs of spectroscopy for individual stars in order to obtain the deepest view of the cluster members ever obtained. We present spectral classifications for 88 cluster members, all of which are WNLh or O stars: a factor of three increase over previous studies. We find no further examples of Wolf-Rayet stars within the cluster; importantly no H-free examples were identified. The smooth and continuous progression in spectral morphologies from O super/hypergiants through to the WNLh cohort implies a direct evolutionary connection. We identify candidate giant and main sequence O stars spectroscopically for the first time. No products of binary evolution may be unambiguously identified despite the presence of massive binaries within the Arches. Notwithstanding difficulties imposed by the highly uncertain (differential) reddening to the Arches, we infer a main sequence/luminosity class V turn-off mass of ~30-38M_{sun}_ via the distribution of spectral types. Analysis of the eclipsing binary F2 suggests current masses of ~80M_{sun}_ and ~60M_{sun}_ for the WNLh and O hypergiant cohorts, respectively; we conclude that all classified stars have masses >20M_{sun}_. An age of ~2.0-3.3Myr is suggested by the turn-off between ~O4-5 V; constraints imposed by the supergiant population and the lack of H-free WRs are consistent with this estimate. While the absence of highly evolved WC stars strongly argues against the prior occurrence of SNe within the Arches, the derived age does accommodate such events for exceptionally massive stars. Further progress will require quantitative analysis of multiple individual cluster members in addition to further spectroscopic observations to better constrain the binary and main sequence populations; nevertheless it is abundantly clear that the Arches offers an unprecedented insight into the formation, evolution and death of the most massive stars nature allows to form.
- ID:
- ivo://CDS.VizieR/J/AJ/154/87
- Title:
- Stellar population of the young star cluster NGC 6231
- Short Name:
- J/AJ/154/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6231 is a young cluster (age ~2-7 Myr) dominating the Sco OB1 association (distance ~1.59 kpc) with ~100 O and B stars and a large pre-main-sequence stellar population. We combine a reanalysis of archival Chandra X-ray data with multiepoch near-infrared (NIR) photometry from the VISTA Variables in the Via Lactea (VVV) survey and published optical catalogs to obtain a catalog of 2148 probable cluster members. This catalog is 70% larger than previous censuses of probable cluster members in NGC 6231. It includes many low-mass stars detected in the NIR but not in the optical and some B stars without previously noted X-ray counterparts. In addition, we identify 295 NIR variables, about half of which are expected to be pre-main-sequence stars. With the more complete sample, we estimate a total population in the Chandra field of 5700-7500 cluster members down to 0.08 M_{sun}_ (assuming a universal initial mass function) with a completeness limit at 0.5 M_{sun}_. A decrease in stellar X-ray luminosities is noted relative to other younger clusters. However, within the cluster, there is little variation in the distribution of X-ray luminosities for ages less than 5 Myr. The X-ray spectral hardness for B stars may be useful for distinguishing between early-B stars with X-rays generated in stellar winds and B-star systems with X-rays from a pre-main-sequence companion (>35% of B stars). A small fraction of catalog members have unusually high X-ray median energies or reddened NIR colors, which might be explained by absorption from thick or edge-on disks or being background field stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/409/1455
- Title:
- Stellar populations of early-type galaxies
- Short Name:
- J/MNRAS/409/1455
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The influence of environment on the formation and evolution of early-type galaxies is, as yet, an unresolved issue. Constraints can be placed on models of early-type galaxy formation and evolution by examining their stellar populations as a function of environment. We present a catalogue of galaxies well suited to such an investigation. The magnitude-limited (b_J_<=19.45) sample was drawn from four clusters (Coma, A1139, A3558 and A930 at <z>=0.04) and their surrounds. The catalogue contains luminosities, redshifts, velocity dispersions and Lick line strengths for 416 galaxies, of which 245 are classified as early types. Luminosity-weighted ages, metallicities and {alpha}-element abundance ratios have been estimated for 219 of these early types. We also outline the steps necessary for measuring fully calibrated Lick indices and estimating the associated stellar population parameters using up-to-date methods and stellar population models. In a subsequent paper we perform a detailed study of the stellar populations of early-type galaxies in clusters and investigate the effects of environment.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A156
- Title:
- Stellar populations of quiescent galaxies
- Short Name:
- J/A+A/631/A156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our aim is to determine the distribution of stellar population parameters (extinction, age, metallicity, and star formation rates) of quiescent galaxies within the rest-frame stellar mass-colour diagrams and UVJ colour-colour diagrams corrected for extinction up to z~1. These novel diagrams reduce the contamination in samples of quiescent galaxies owing to dust-reddened galaxies, and they provide useful constraints on stellar population parameters only using rest-frame colours and stellar mass. We set constraints on the stellar population parameters of quiescent galaxies combining the ALHAMBRA multi-filter photo-spectra with our fitting code for spectral energy distribution, MUlti-Filter FITting (MUFFIT), making use of composite stellar population models based on two independent sets of simple stellar population (SSP) models. The extinction obtained by MUFFIT allowed us to remove dusty star-forming (DSF) galaxies from the sample of red UVJ galaxies. The distributions of stellar population parameters across these rest-frame diagrams are revealed after the dust correction and are fitted by LOESS, a bi-dimensional and locally weighted regression method, to reduce uncertainty effects. Quiescent galaxy samples defined via classical UVJ diagrams are typically contaminated by a 20% fraction of DSF galaxies. A significant part of the galaxies in the green valley are actually obscured star-forming galaxies (30-65%). Consequently, the transition of galaxies from the blue cloud to the red sequence, and hence the related mechanisms for quenching, seems to be much more efficient and faster than previously reported. The rest-frame stellar mass-colour and UVJ colour-colour diagrams are useful for constraining the age, metallicity, extinction, and star formation rate of quiescent galaxies by only their redshift, rest-frame colours, and/or stellar mass. Dust correction plays an important role in understanding how quiescent galaxies are distributed in these diagrams and is key to performing a pure selection of quiescent galaxies via intrinsic colours.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A148
- Title:
- Stellar populations towards Orion with Gaia DR1
- Short Name:
- J/A+A/608/A148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work we use the first data release of the Gaia mission to explore the three-dimensional arrangement and age ordering of the many stellar groups toward the Orion OB association, aiming at a new classification and characterization of the stellar population not embedded in the Orion A and B molecular clouds. We make use of the parallaxes and proper motions provided in the Tycho Gaia Astrometric Solution (TGAS) subset of the Gaia Data Release 1 (DR1) catalog and of the combination of Gaia DR1 and 2MASS photometry. In TGAS, we find evidence for the presence of a young population at a parallax {varpi}~2.65mas, which is loosely distributed around the following known clusters: 25 Ori, {epsilon} Ori, and {sigma} Ori, and NGC 1980 ({iota} Ori) and the Orion Nebula Cluster (ONC). The low mass counterpart of this population is visible in the color magnitude diagrams constructed by combining Gaia DR1 G-band photometry and 2MASS. We study the density distribution of the young sources in the sky using a kernel density estimation (KDE). We find the same groups as in TGAS and also some other density enhancements that might be related to the recently discovered Orion X group, Orion dust ring, and {lambda} Ori complex. The maps also suggest that the 25 Ori group presents a northern elongation.We estimated the ages of this population using a Bayesian isochronal fitting procedure assuming a unique parallax value for all the sources, and we inferred the presence of an age gradient going from 25 Ori (13-15Myr) to the ONC (1-2Myr). We confirmed this age ordering by repeating the Bayesian fit using the Pan-STARRS1 data. Intriguingly, the estimated ages toward the NGC 1980 cluster span a broad range of values. This can either be due to the presence of two populations coming from two different episodes of star formation or to a large spread along the line of sight of the same population. Some confusion might arise from the presence of unresolved binaries, which are not modeled in the fit, and usually mimic a younger population. Finally, we provisionally relate the stellar groups to the gas and dust features in Orion. Our results form the first step toward using Gaia data to unravel the complex star formation history of the Orion region in terms of the various star formation episodes, their duration, and their effects on the surrounding interstellar medium.
- ID:
- ivo://CDS.VizieR/J/ApJS/234/35
- Title:
- Stellar population synthesis of clumps
- Short Name:
- J/ApJS/234/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have identified 1027 star-forming complexes in a sample of 46 galaxies from the Spirals, Bridges, and Tails (SB&T) sample of interacting galaxies, and 693 star-forming complexes in a sample of 38 non-interacting spiral (NIS) galaxies in 8{mu}m observations from the Spitzer Infrared Array Camera. We have used archival multi-wavelength UV-to IR observations to fit the observed spectral energy distribution of our clumps with the Code Investigating GALaxy Emission using a double exponentially declined star formation history. We derive the star formation rates (SFRs), stellar masses, ages and fractions of the most recent burst, dust attenuation, and fractional emission due to an active galactic nucleus for these clumps. The resolved star formation main sequence holds on 2.5kpc scales, although it does not hold on 1kpc scales. We analyzed the relation between SFR, stellar mass, and age of the recent burst in the SB&T and NIS samples, and we found that the SFR per stellar mass is higher in the SB&T galaxies, and the clumps are younger in the galaxy pairs. We analyzed the SFR radial profile and found that the SFR is enhanced through the disk and in the tidal features relative to normal spirals.
- ID:
- ivo://CDS.VizieR/J/MNRAS/412/423
- Title:
- Stellar population trends in S0 galaxies
- Short Name:
- J/MNRAS/412/423
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present stellar population age and metallicity trends for a sample of 59 S0 galaxies based on optical Sloan Digital Sky Survey (SDSS) and near-infrared (NIR) J and H photometry. When combined with optical g and r passband imaging data from the SDSS archive and stellar population models, we obtain radial age and metallicity trends out to at least five effective radii for most of the galaxies in our sample. The sample covers a range in stellar mass and light concentration.
- ID:
- ivo://CDS.VizieR/J/AJ/157/109
- Title:
- Stellar proper motions in the Orion Nebula Cluster
- Short Name:
- J/AJ/157/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Orion Nebula Cluster (ONC) is the nearest site of ongoing massive star formation, which allows us to study the kinematics and dynamics of the region in detail and constrain star formation theories. Using HST ACS/WFPC2/WFC3IR and Keck II NIRC2 data, we have measured the proper motions of 701 stars within an ~6'x6' field of view around the center of the ONC. We have found more than 10 escaping star candidates, concentrated predominantly at the core of the cluster. The proper motions of the bound stars are consistent with a normal distribution, albeit elongated north-south along the Orion filament, with proper-motion dispersions of ({sigma}_{mu},{alpha}_*, {sigma}_{mu},{delta}_)=(0.83+/-0.02, 1.12+/-0.03) mas/yr or intrinsic velocity dispersions of ({sigma}_v,{alpha}_*, {sigma}_v,{delta}_)=(1.57+/-0.04, 2.12+/-0.06) km/s assuming a distance of 400 pc to the ONC. The cluster shows no evidence for tangential-to-radial anisotropy. Our velocity dispersion profile agrees with the prediction from the observed stellar + gas density profile from Da Rio et al. (2014ApJ...795...55D, 2017ApJ...845..105D), indicating that the ONC is in virial equilibrium. This finding suggests that the cluster was formed with a low star formation efficiency per dynamical timescale based on comparisons with current star formation theories. Our survey also recovered high-velocity IR sources BN, x and n in the BN/KL region. The estimated location of the first two sources ~500 yr ago agrees with that of the radio source I, consistent with their proposed common origin from a multistellar disintegration. However, source n appears to have a small proper motion and is unlikely to have been involved in the event.
