- ID:
- ivo://CDS.VizieR/J/MNRAS/475/257
- Title:
- AGB subpopulations in NGC 6397
- Short Name:
- J/MNRAS/475/257
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has been well established that Galactic Globular clusters (GCs) harbour more than one stellar population, distinguishable by the anticorrelations of light-element abundances (C-N, Na-O, and Mg-Al). These studies have been extended recently to the asymptotic giant branch (AGB). Here, we investigate the AGB of NGC 6397 for the first time. We have performed an abundance analysis of high-resolution spectra of 47 red giant branch (RGB) and eight AGB stars, deriving Fe, Na, O, Mg, and Al abundances. We find that NGC 6397 shows no evidence of a deficit in Na-rich AGB stars, as reported for some other GCs - the subpopulation ratios of the AGB and RGB in NGC 6397 are identical, within uncertainties. This agrees with expectations from stellar theory. This GC acts as a control for our earlier work on the AGB of M4 (with contrasting results), since the same tools and methods were used.
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- ID:
- ivo://CDS.VizieR/J/ApJ/647/1075
- Title:
- Age-metallicity relation of {omega} Cen
- Short Name:
- J/ApJ/647/1075
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a metallicity distribution based on photometry and spectra for 442 Omega Centauri cluster members that lie at the main-sequence turnoff region of the color-magnitude diagram. This distribution is similar to that found for the red giant branch. The distribution shows a sharp rise to a mean of [Fe/H]=-1.7 with a long tail to higher metallicities. Ages have then been determined for the stars using theoretical isochrones enabling the construction of an age-metallicity diagram. Interpretation of this diagram is complicated by the correlation of the errors in the metallicities and ages. Nevertheless, after extensive Monte Carlo simulations, we conclude that our data show that the formation of the cluster took place over an extended period of time: the most metal-rich stars in our sample ([Fe/H]~-0.6) are younger by 2-4Gyr than the most metal-poor population.
- ID:
- ivo://CDS.VizieR/J/ApJ/751/122
- Title:
- Ages and masses for 920 LMC clusters
- Short Name:
- J/ApJ/751/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new age and mass estimates for 920 stellar clusters in the Large Magellanic Cloud (LMC) based on previously published broadband photometry and the stellar cluster analysis package, MASSCLEANage. Expressed in the generic fitting formula, d^2^N/dMdt{prop.to}M^{alpha}^t^{beta}^, the distribution of observed clusters is described by {alpha}=-1.5 to -1.6 and {beta}=-2.1 to -2.2. For 288 of these clusters, ages have recently been determined based on stellar photometric color-magnitude diagrams, allowing us to gauge the confidence of our ages. The results look very promising, opening up the possibility that this sample of 920 clusters, with reliable and consistent age, mass, and photometric measures, might be used to constrain important characteristics about the stellar cluster population in the LMC. We also investigate a traditional age determination method that uses a {chi}^2^ minimization routine to fit observed cluster colors to standard infinite-mass limit simple stellar population models. This reveals serious defects in the derived cluster age distribution using this method. The traditional {chi}^2^ minimization method, due to the variation of U, B, V, R colors, will always produce an overdensity of younger and older clusters, with an underdensity of clusters in the log(age/yr)=[7.0,7.5] range. Finally, we present a unique simulation aimed at illustrating and constraining the fading limit in observed cluster distributions that includes the complex effects of stochastic variations in the observed properties of stellar clusters.
- 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/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/AJ/146/87
- Title:
- AGN photometry. II. A catalog from the CFHTLS
- Short Name:
- J/AJ/146/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second paper of the series Detecting Active Galactic Nuclei Using Multi-filter Imaging Data. In this paper we review shapelets, an image manipulation algorithm, which we employ to adjust the point-spread function (PSF) of galaxy images. This technique is used to ensure the image in each filter has the same and sharpest PSF, which is the preferred condition for detecting AGNs using multi-filter imaging data as we demonstrated in Paper I of this series. We apply shapelets on Canada-France-Hawaii Telescope Legacy Survey Wide Survey ugriz images. Photometric parameters such as effective radii, integrated fluxes within certain radii, and color gradients are measured on the shapelets-reconstructed images. These parameters are used by artificial neural networks (ANNs) which yield: photometric redshift with an rms of 0.026 and a regression R-value of 0.92; galaxy morphological types with an uncertainty less than 2 T types for z<=0.1; and identification of galaxies as AGNs with 70% confidence, star-forming/starburst (SF/SB) galaxies with 90% confidence, and passive galaxies with 70% confidence for z<=0.1. The incorporation of ANNs provides a more reliable technique for identifying AGN or SF/SB candidates, which could be very useful for large-scale multi-filter optical surveys that also include a modest set of spectroscopic data sufficient to train neural networks.
- ID:
- ivo://CDS.VizieR/J/A+A/601/A10
- Title:
- A grid of MARCS model atmospheres for S stars
- Short Name:
- J/A+A/601/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- S-type stars are late-type giants whose atmospheres are enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing asymptotic giant branch. A grid of MARCS model atmospheres has been computed for S stars, covering the range 2700<=Teff(K)<=4000, 0.50<=C/O<0.99, 0<=logg<=5, [Fe/H]=0., -0.5dex, and [s/Fe]= 0, 1, and 2 dex (where the latter quantity refers to the global overabundance of s-process elements). The MARCS models make use of a new ZrO line list. Synthetic spectra computed from these models are used to derive photometric indices in the Johnson and Geneva systems, as well as TiO and ZrO band strengths. A method is proposed to select the model best matching any given S star, a non-trivial operation since the grid contains more than 3500 models covering a five-dimensional parameter space. The method is based on the comparison between observed and synthetic photometric indices and spectral band strengths, and has been applied on a vast subsample of the Henize sample of S stars. Our results confirm the old claim by Piccirillo (1980MNRAS.190..441P) that ZrO bands in warm S stars (Teff > 3200K) are not caused by the C/O ratio being close to unity, as traditionally believed, but rather by some Zr overabundance. The TiO and ZrO band strengths, combined with V-K and J-K photometric indices, are used to select Teff, C/O, [Fe/H] and [s/Fe]. The Geneva U-B_1 and B_2-V_1 indices (or any equivalent) are good at selecting the gravity. The defining spectral features of dwarf S stars are outlined, but none is found among the Henize S stars. More generally, it is found that, at Teff=3200K, a change of C/O from 0.5 to 0.99 has a strong impact on V-K (2mag). Conversely, a range of 2 mag in V-K corresponds to a 200K shift along the (Teff, V-K) relationship (for a fixed C/O value). Hence, the use of a (Teff, V-K) calibration established for M stars will yield large errors for S stars, so that a specific calibration must be used, as provided in the present paper. Using the atmospheric parameters derived by our method for the sample of Henize S stars, we show that the extrinsic-intrinsic dichotomy among S stars reveals itself very clearly as a bimodal distribution in the effective temperatures. Moreover, the increase of s-process element abundances with increasing C/O ratios and decreasing temperatures is apparent among intrinsic stars, confirming theoretical expectations.
- ID:
- ivo://CDS.VizieR/J/ApJS/183/295
- Title:
- A K-selected catalog of the ECDFS from MUSYC
- Short Name:
- J/ApJS/183/295
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new, K-selected, optical-to-near infrared photometric catalog of the Extended Chandra Deep Field South (ECDFS), making it publicly available to the astronomical community. The data set is founded on publicly available imaging, supplemented by original z'JK imaging data collected as part of the MUltiwavelength Survey by Yale-Chile (MUSYC). The final photometric catalog consists of photometry derived from UU_38_BVRIz'JK imaging covering the full 1/2x1/2{deg} of the ECDFS, plus H-band photometry for approximately 80% of the field. The 5{sigma} flux limit for point sources is K^(AB)^_tot_=22.0. This is also the nominal completeness and reliability limit of the catalog: the empirical completeness for 21.75<K<22.00 is >~85%. We have verified the quality of the catalog through both internal consistency checks, and comparisons to other existing and publicly available catalogs. As well as the photometric catalog, we also present catalogs of photometric redshifts and rest-frame photometry derived from the 10-band photometry. We have collected robust spectroscopic redshift determinations from published sources for 1966 galaxies in the catalog. Based on these sources, we have achieved a (1{sigma}) photometric redshift accuracy of {Delta}z/(1+z)=0.036, with an outlier fraction of 7.8%. Most of these outliers are X-ray sources. Finally, we describe and release a utility for interpolating rest-frame photometry from observed spectral energy distributions, dubbed InterRest available via http://www.strw.leidenuniv.nl/~ent/InterRest
- ID:
- ivo://CDS.VizieR/J/AJ/145/149
- Title:
- ALFALFA discovery of Leo P. II. BVR photometry
- Short Name:
- J/AJ/145/149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from ground-based optical imaging of a low-mass dwarf galaxy discovered by the ALFALFA 21cm HI survey. Broadband (BVR) data obtained with the WIYN 3.5m telescope at Kitt Peak National Observatory (KPNO) are used to construct color-magnitude diagrams of the galaxy's stellar population down to V_o_~25. We also use narrowband H{alpha} imaging from the KPNO 2.1m telescope to identify a HII region in the galaxy. We use these data to constrain the distance to the galaxy to be between 1.5 and 2.0Mpc. This places Leo P within the Local Volume but beyond the Local Group. Its properties are extreme: it is the lowest-mass system known that contains significant amounts of gas and is currently forming stars.
- ID:
- ivo://CDS.VizieR/J/AJ/147/145
- Title:
- Algol-type binaries. VIII. DI Peg & AF Gem
- Short Name:
- J/AJ/147/145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New extensive photometry for two triple binary stars, DI Peg and AF Gem, was performed from 2012 October to 2013 January, with two small telescopes at Xinglong station (XLs) of NAOC. From new multi-color observations and previously published ones in literature, the photometric models were (re)deduced using the updated Wilson-Devinney code. The results indicated that the low third lights exist in two classic Algol-type binaries, whose fill-out factors for the more massive components are f_p_=78.2(+/-0.4)% for DI Peg, and f_p_=69.0(+/-0.3)% for AF Gem, respectively. Through analyzing the O-C curves, the orbital periods for two binaries change in the complicated mode. The period of DI Peg possibly appears to show two light-time orbits, whose modulated periods are P_3_=54.6(+/-0.5)yr and P_4_=23.0(+/-0.6)yr, respectively. The inferred minimum masses for the inner and outer sub-stellar companions are M_in_=0.095M_{sun}_ and M_out_=0.170M_{sun}_, respectively. Therefore, DI Peg may be a quadruple star. The orbital period of AF Gem appears to show a continuous period decrease or a cyclic variation; the latter may be preferable. The cyclic oscillation, with a period of 120.3(+/-2.5)yr, may be attributed to the light-time effect due to the third body. This kind of additional companion may extract angular momentum from the central system, which may play a key role in the evolution of the binary.
