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611. Ages of A-K type stars in DEBRIS survey
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.
612. Ages of FGK stars considering C and O abundances
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.
613. Ages of field stars from white dwarf comp. in Gaia
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.
614. Ages of main-sequence stars
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.
615. Ages of SMC young clusters and field stars
ID:
ivo://CDS.VizieR/J/A+A/452/179
Title:
Ages of SMC young clusters and field stars
Short Name:
J/A+A/452/179
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this paper we discuss the cluster and field star formation in the central part of the Small Magellanic Cloud. The main goal is to study the correlation between young objects and their interstellar environment. The ages of about 164 associations and 311 clusters younger than 1Gyr are determined using isochrone fitting. The spatial distribution of the clusters is compared with the HI maps, with the HI velocity dispersion field, with the location of the CO clouds and with the distribution of young field stars.
616. Ages of star clusters in M33
ID:
ivo://CDS.VizieR/J/ApJ/700/103
Title:
Ages of star clusters in M33
Short Name:
J/ApJ/700/103
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a result of age estimation for star clusters in M33. We obtain color-magnitude diagrams (CMDs) of resolved stars in 242 star clusters from the Hubble Space Telescope/Wide Field Planetary Camera 2 images. We estimate ages of 100 star clusters among these, by fitting the Padova theoretical isochrones to the observational CMDs. Age distribution of the star clusters shows a dominant peak at log(t)~7.8. Majority of star clusters are younger than log(t)=9.0, while 10 star clusters are older than log(t)~9.0. There is only one cluster younger than log(t)=7 in this study, which is in contrast with the results based on the integrated photometry of star clusters in the previous studies. Radial distribution of the cluster ages shows that young- to intermediate-age clusters are found from the center to the outer region, while old clusters are distributed farther from the M33 center. We briefly discuss the implication of the results with regard to the formation of the M33 cluster system.
617. Ages of star clusters in SMC
ID:
ivo://CDS.VizieR/J/ApJ/853/104
Title:
Ages of star clusters in SMC
Short Name:
J/ApJ/853/104
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new study of the spatial distribution and ages of the star clusters in the Small Magellanic Cloud (SMC). To detect and estimate the ages of the star clusters we rely on the new fully automated method developed by Bitsakis+ (2017, J/ApJ/845/56). Our code detects 1319 star clusters in the central 18deg^2^ of the SMC we surveyed (1108 of which have never been reported before). The age distribution of those clusters suggests enhanced cluster formation around 240Myr ago. It also implies significant differences in the cluster distribution of the bar with respect to the rest of the galaxy, with the younger clusters being predominantly located in the bar. Having used the same setup, and data from the same surveys as for our previous study of the LMC, we are able to robustly compare the cluster properties between the two galaxies. Our results suggest that the bulk of the clusters in both galaxies were formed approximately 300Myr ago, probably during a direct collision between the two galaxies. On the other hand, the locations of the young (<=50Myr) clusters in both Magellanic Clouds, found where their bars join the HI arms, suggest that cluster formation in those regions is a result of internal dynamical processes. Finally, we discuss the potential causes of the apparent outside-in quenching of cluster formation that we observe in the SMC. Our findings are consistent with an evolutionary scheme where the interactions between the Magellanic Clouds constitute the major mechanism driving their overall evolution.
618. Ages of star clusters in tidal tails of 3 galaxies
ID:
ivo://CDS.VizieR/J/ApJ/805/99
Title:
Ages of star clusters in tidal tails of 3 galaxies
Short Name:
J/ApJ/805/99
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the stellar content in the tidal tails of three nearby merging galaxies, NGC 520, NGC 2623, and NGC 3256, using BVI imaging taken with the Advanced Camera for Surveys on board the Hubble Space Telescope (HST). The tidal tails in all three systems contain compact and fairly massive young star clusters, embedded in a sea of diffuse, unresolved stellar light. We compare the measured colors and luminosities with predictions from population synthesis models to estimate cluster ages and find that clusters began forming in tidal tails during or shortly after the formation of the tails themselves. We find a lack of very young clusters (<=10Myr old), implying that eventually star formation shuts off in the tails as the gas is used up or dispersed. There are a few clusters in each tail with estimated ages that are older than the modeled tails themselves, suggesting that these may have been stripped out from the original galaxy disks. The luminosity function of the tail clusters can be described by a single power-law, dN/dL{propto}L^{alpha}^, with -2.6<{alpha}<-2.0. We find a stellar age gradient across some of the tidal tails, which we interpret as a superposition of (1) newly formed stars and clusters along the dense center of the tail and (2) a sea of broadly distributed, older stellar material ejected from the progenitor galaxies.
619. Ages of stars in dwarf galaxies
ID:
ivo://CDS.VizieR/J/MNRAS/412/1539
Title:
Ages of stars in dwarf galaxies
Short Name:
J/MNRAS/412/1539
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of the variation of spatial structure of stellar populations within dwarf galaxies as a function of the population age. We use deep Hubble Space Telescope/Advanced Camera for Surveys imaging of nearby dwarf galaxies in order to resolve individual stars and create composite colour-magnitude diagrams (CMDs) for each galaxy. Using the obtained CMDs, we select blue helium burning stars, which can be unambiguously age-dated by comparing the absolute magnitude of individual stars with stellar isochrones. Additionally, we select a very young (~<10Myr) population of OB stars for a subset of the galaxies based on the tip of the young main sequence. By selecting stars in different age ranges, we can then study how the spatial distribution of these stars evolves with time.
620. Ages of the planet host stars
ID:
ivo://CDS.VizieR/J/A+A/649/A111
Title:
Ages of the planet host stars
Short Name:
J/A+A/649/A111
Date:
22 Feb 2022
Publisher:
CDS
Description:
Revealing the mechanisms shaping the architecture of planetary systems is crucial for our understanding of their formation and evolution. In this context, it has been recently proposed that stellar clustering might be the key in shaping the orbital architecture of exoplanets. The main goal of this work is to explore the factors that shape the orbits of planets. We performed different statistical tests to compare the properties of planets and their host stars associated with different stellar environments. Results. We used a homogeneous sample of relatively young FGK dwarf stars with radial velocity detected planets and tested the hypothesis that their association to phase space (position-velocity) over-densities ("cluster" stars) and under-densities ("field" stars) impacts the orbital periods of planets. When controlling for the host star properties on a sample of 52 planets orbiting around cluster stars and 15 planets orbiting around field stars, we found no significant difference in the period distribution of planets orbiting these two populations of stars. By considering an extended sample of 73 planets orbiting around cluster stars and 25 planets orbiting field stars, a significant difference in the planetary period distributions emerged. However, the hosts associated with stellar under-densities appeared to be significantly older than their cluster counterparts. This does not allow us to conclude as to whether the planetary architecture is related to age, environment, or both. We further studied a sample of planets orbiting cluster stars to study the mechanism responsible for the shaping of orbits of planets in similar environments. We could not identify a parameter that can unambiguously be responsible for the orbital architecture of massive planets, perhaps, indicating the complexity of the issue. An increased number of planets in clusters and in over-density environments will help to build large and unbiased samples which will then allow to better understand the dominant processes shaping the orbits of planets.

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