- ID:
- ivo://CDS.VizieR/J/MNRAS/476/1213
- Title:
- Ages for stars in 19 clusters
- Short Name:
- J/MNRAS/476/1213
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The pace and pattern of star formation leading to rich young stellar clusters is quite uncertain. In this context, we analyse the spatial distribution of ages within 19 young (median t<=3Myr on the Siess et al. time-scale), morphologically simple, isolated, and relatively rich stellar clusters. Our analysis is based on young stellar object (YSO) samples from the Massive Young Star-Forming Complex Study in Infrared and X-ray and Star Formation in Nearby Clouds surveys, and a new estimator of pre-main sequence (PMS) stellar ages, Age_JX_, derived from X-ray and near-infrared photometric data. Median cluster ages are computed within four annular subregions of the clusters. We confirm and extend the earlier result of Getman et al. (2014ApJ...787..108G, Cat. J/ApJ/787/108; 2014ApJ...787..109G. Cat. J/ApJ/787/109): 80 per cent of the clusters show age trends where stars in cluster cores are younger than in outer regions. Our cluster stacking analyses establish the existence of an age gradient to high statistical significance in several ways. Time-scales vary with the choice of PMS evolutionary model; the inferred median age gradient across the studied clusters ranges from 0.75 to 1.5Myr/pc. The empirical finding reported in the present study - late or continuing formation of stars in the cores of star clusters with older stars dispersed in the outer regions - has a strong foundation with other observational studies and with the astrophysical models like the global hierarchical collapse model of Vazquez-Semadeni et al. (2017MNRAS.467.1313V).
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/415/1883
- Title:
- AGES HI sources in NGC 7448
- Short Name:
- J/MNRAS/415/1883
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we describe results from the Arecibo Galaxy Environments Survey (AGES). The survey reaches column densities of ~3x10^18^cm^-2^ and masses of ~10^7^M_{sun}_, over individual regions of order 10deg^2^ in size, out to a maximum velocity of 18000km/s. Each surveyed region is centred on a nearby galaxy, group or cluster, in this instance the NGC 7448 group. Galaxy interactions in the NGC 7448 group reveal themselves through the identification of tidal tails and bridges. We find ~2.5 times more atomic gas in the intergalactic medium than in the group galaxies. We identify five new dwarf galaxies, two of which appear to be members of the NGC 7448 group. This is too small, by roughly an order of magnitude, a number of dwarf galaxies to reconcile observation with theoretical predictions of galaxy formation models. If they had observed this region of the sky in previous wide-area blind HI surveys, HIPASS and ALFALFA, they would have detected only 5 and 43 per cent, respectively, of the galaxies we have detected, missing a large fraction of the atomic gas in this volume.
- ID:
- ivo://CDS.VizieR/J/MNRAS/443/2634
- Title:
- AGES HI sources in NGC 7448 field
- Short Name:
- J/MNRAS/443/2634
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present completed observations of the NGC 7448 galaxy group and background volume as part of the blind neutral hydrogen Arecibo Galaxy Environment Survey. Our observations cover a region spanning 5{deg}x4{deg}, over a redshift range of approximately -2000<cz<20000km/s. A total of 334 objects are detected, mostly in three overdensities at cz~7500, cz~9600 and cz~11400km/s. The galaxy density is extremely high (15deg^-2^) and many (~24%) show signs of extended HI emission, including some features as much as 800kpc in projected length. We describe the overall characteristics of this environment: kinematics, typical galaxy colours and mass-to-light ratios, and substructure. To aid in the cataloguing of this data set, we present a new fits viewer (FRELLED: fits Realtime Explorer of Low Latency in Every Dimension). This incorporates interactive source cataloguing tools which increase our source extraction speed by approximately a factor of 50.
- ID:
- ivo://CDS.VizieR/J/A+A/517/A50
- Title:
- Ages & luminosities of young SMC/LMC star clusters
- Short Name:
- J/A+A/517/A50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we discuss the age and spatial distribution of young (age<1Gyr) SMC and LMC clusters using data from the Magellanic Cloud Photometric Surveys. Luminosities are calculated for all age-dated clusters. Ages of 324 and 1193 populous star clusters in the Small and the Large Magellanic Cloud have been determined fitting Padova and Geneva isochrone models to their resolved color-magnitude diagrams. The clusters cover an age range between 10Myr and 1Gyr in each galaxy. For the SMC a constant distance modulus of (m-M)_0_=18.90 and a metallicity of Z=0.004 were adopted. For the LMC, we used a constant distance modulus of (m-M)_0_=18.50 and a metallicity of Z=0.008. For both galaxies, we used a variable color excess to derive the cluster ages. We find two periods of enhanced cluster formation in both galaxies at 160Myr and 630Myr (SMC) and at 125Myr and 800Myr (LMC). We present the spatially resolved recent star formation history of both Clouds based on young star clusters. The first peak may have been triggered by a close encounter between the SMC and the LMC. In both galaxies the youngest clusters reside in the supergiant shells, giant shells, the inter-shell regions, and toward regions with a high H\alpha content, suggesting that their formation is related to expansion and shell-shell interaction. Most of the clusters are older than the dynamical age of the supergiant shells. No evidence for cluster dissolution was found. Computed V band luminosities show a trend for fainter magnitudes with increasing age as well as a trend for brighter magnitudes with increasing apparent cluster radii.
- ID:
- ivo://CDS.VizieR/J/ApJ/870/9
- Title:
- Ages & masses for GPS1 WD-MS binary systems
- Short Name:
- J/ApJ/870/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observational tests of stellar and Galactic chemical evolution call for the joint knowledge of a star's physical parameters, detailed element abundances, and precise age. For cool main-sequence (MS) stars the abundances of many elements can be measured from spectroscopy, but ages are very hard to determine. The situation is different if the MS star has a white dwarf (WD) companion and a known distance, as the age of such a binary system can then be determined precisely from the photometric properties of the cooling WD. As a pilot study for obtaining precise age determinations of field MS stars, we identify nearly 100 candidates for such wide binary systems: a faint WD whose Gaia-PS1-SDSS (GPS1) proper motion (Tian+ 2017, I/343) matches that of a brighter MS star in Gaia/TGAS (Gaia Collaboration 2016, I/337) with a good parallax ({sigma}_{rho}_/{rho}=<0.05). We model the WD's multi-band photometry with the BASE-9 code using this precise distance (assumed to be common for the pair) and infer ages for each binary system. The resulting age estimates are precise to =<10% (=<20%) for 42 (67) MS-WD systems. Our analysis more than doubles the number of MS-WD systems with precise distances known to date, and it boosts the number of such systems with precise age determination by an order of magnitude. With the advent of the Gaia DR2 (Gaia Collaboration, 2018, I/345) data, this approach will be applicable to a far larger sample, providing ages for many MS stars (that can yield detailed abundances for over 20 elements), especially in the age range of 2-8Gyr, where there are only few known star clusters.
- ID:
- ivo://CDS.VizieR/V/89
- Title:
- Ages, Metallicities, Galactic Orbit of F stars
- Short Name:
- V/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Absolute magnitudes, metallicities, effective temperatures, surface gravities, distances, and tangential velocities are calculated for 5498 F stars with homogeneous data on uvby photometry and proper motion, and placed within 80 pc from the Sun. Components of space velocities, eccentricities of galactic orbits, perigalactic and apogalactic distances, and maximal remotness from galactic plane are presented for 1787 stars. Isochrone ages are determined for 3405 slightly evolved stars proceeding from Revised Yale isochrones.
- ID:
- ivo://CDS.VizieR/J/AJ/143/135
- Title:
- Ages of A-K type stars in DEBRIS survey
- Short Name:
- J/AJ/143/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- DEBRIS is a flux-limited survey of nearby stars (spectral types A-M) for evidence of debris disks with the Herschel Space Observatory. One goal of the survey is to determine disk incidence as a function of various stellar parameters. Understanding debris disk evolution depends on knowledge of the precise age of stars around which these debris disks are found. However, finding ages for field stars is notoriously difficult. Furthermore, in an unbiased sample like DEBRIS, one is working with stars across many spectral types. This requires a multi-method approach to age determination. In this paper, we outline several methods of age determination broken down by spectral type, including some strengths and limitations of each method. In total, we were able to calculate ages for 263 of 274 F-, G-, and K-type stars, and all 83 A-type stars in the DEBRIS sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/157
- Title:
- Ages of FGK stars considering C and O abundances
- Short Name:
- J/ApJ/889/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Precise stellar ages of stars are necessary to study the evolution of the Milky Way. The age determination is significantly affected by C and O abundances of stars due to their contribution to the overall metallicity and opacity. On the basis of C and O abundances derived from high-resolution observations, we determine the ages of 148 FGK-type dwarfs in the solar neighborhood by considering C and O enhancements individually. Our results show that using C and O enhancements individually could affect the age determination of the high-{alpha} population, especially for stars with [O/{alpha}]>0.2dex, making them about 1Gyr younger compared to the results using traditional {alpha}-enhanced models. This results in a steeper slope in the age-[{alpha}/Fe] relation for the high-{alpha} population (changes from 0.0339+/-0.0075 to 0.0436+/-0.0086), indicating a higher formation rate. We find no tight relation between age and [{alpha}/Fe] or [O/Fe] in the high-{alpha} populations. The distribution of space velocity for young {alpha}-rich stars shows that they are more likely characterized to the low-{alpha} populations.
- ID:
- ivo://CDS.VizieR/J/ApJS/253/58
- Title:
- Ages of field stars from white dwarf comp. in Gaia
- Short Name:
- J/ApJS/253/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze 4050 wide binary star systems involving a white dwarf (WD) and usually a main-sequence (MS) star, drawn from the large sample assembled by Tian+ (2020, J/ApJS/246/4). Using the modeling code BASE-9, we determine the system's ages, the WD progenitors' zero-age MS masses, the extinction values (AV), and the distance moduli. Discarding the cases with poor age convergences, we obtain ages for 3551 WDs, with a median age precision of {sigma}{tau}/{tau}=20%, and system ages typically in the range of 1-6Gyr. We validated these ages against the very few known clusters and through cross validation of 236 WD-WD binaries. Under the assumption that the components are coeval in a binary system, this provides precise age constraints on the usually low-mass MS companions, mostly inaccessible by any other means.
- ID:
- ivo://CDS.VizieR/J/A+A/348/897
- Title:
- Ages of main-sequence stars
- Short Name:
- J/A+A/348/897
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have determined the age of a sample of nearby main-sequence stars with spectral types B9-K9. We have derived the stellar ages from five different age estimators: the location in the HR diagram compared to theoretical isochrones, the rotational velocity, the strength of chromospheric calcium emission lines, the stellar metallicity, and their space velocity. New calibrations consistent with recent theoretical isochrones are provided for the last four indicators. For hot stars, isochrones are the best indicator, while stellar rotation is best for cool stars. However, many stars require in fact a combination of different methods to properly bracket their actual age. We also discuss the uncertainties involved, in particular those in using isochrones, and we find that these uncertainties are often underestimated in the literature.
