- ID:
- ivo://CDS.VizieR/J/A+A/437/61
- Title:
- Near-IR photometry of AGB stars in NGC 185
- Short Name:
- J/A+A/437/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- J, H and K' images obtained with the Canada-France-Hawaii Telescope were used to investigate the stellar contents of asymptotic giant branch (AGB) in the dwarf elliptical galaxy NGC 185. The bright parts of (K, J-K) and (K, H-K) color-magnitude diagrams consist of a group of brights blue stars, a dominant populations of M-giants, and a red C star population. There were 73 C stars with a mean magnitude of <K>=16.26+/-0.38, corresponding to <M_K_>=-7.93 and mean colors of <(J-k)_0_>=2.253 and <(H-K)_0_>=0.865. The number ratio of C stars to M-giants was estimated to be 0.11+/-0.04 without any radial gradient from the center of NGC 185. The (J-K) and (H-K) color distributions of AGB stars showed an M-giant pick, blue and red tails, where the latter two correspond to AGB stars younger than those along M-giant peak and C stars. The bolometric luminosity functions of M-giants and C stars indicated that the M-giant AGB sequence has terminated at M_bol_=-6.2, while the most luminous C star very similar to that of Nowotny et al. (2003, Cat. <J/A+A/403/93>) which was derived from VI band photometry. The logarithmic slope of the luminosity function for bright M-giant stars was estimated to be 0.83+/-0.02 in K band. Theoritical isochrone models, compared with the observed near-infrared photometric properties of AGB stars, indicated that the star formation in NGC 185 has a wide range of age span with possibly two different epochs of star formation.
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- ID:
- ivo://CDS.VizieR/J/A+A/454/717
- Title:
- Near-IR photometry of C and AGB stars in NGC 6822
- Short Name:
- J/A+A/454/717
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Images of JHK and gi obtained with the Canada-France-Hawaii Telescope are used to investigate the stellar contents of the resolved asymptotic giant branch (AGB) population in the area of 3.6'x6.3' on the central bar of the dwarf irregular galaxy NGC 6822. The upper envelope of near-infrared (J-K, K) and (H-K, K) color-magnitude diagrams (CMDs) shows four components of main-sequence stars, foreground stars, massive supergiants, and AGB stars. These components are also noticeable in the bright part of (g-i, g) CMD. We select AGB stars in NGC 6822 from the (g-K, g) CMD, which has a long spectral wavelength base line in the color index. There are 141 C stars with a mean absolute magnitude of <M_K_>=-7.60+/-0.50, and with mean colors of <(J-K)_o_>=1.77+/-0.41, and <(H-K)_o_>=0.75+/-0.28. The number ratio of C stars to M-giants (C/M) is estimated as 0.27+/-0.03, while the northern part of the bar has a somewhat lower C/M ratio than the southern part. The (J-K) and (H-K) color distributions of AGB stars contain a main peak of M-giant stars and a red tail of C stars. The broad color distributions for M-giants indicate that NGC 6822 has a wide range of intermediate ages with a peak at log(t_yr_)~9.0. The M_K_ luminosity function (LF) for C stars in the central bar of NGC 6822 is likely to be a Gaussian distribution, while the LF of C stars in the southern part is slightly skewed to the brighter side than in northern part. The mean bolometric magnitude of 141 C stars in NGC 6822 is <M_bol_>=-4.36+/-0.54. The bolometric LF for M-giants extends up to M_bol_=-6.5, while the one for C stars spans -5.8<M_bol_<-3.5.
- ID:
- ivo://CDS.VizieR/J/A+A/543/A35
- Title:
- Near-IR photometry of C stars in NGC 205
- Short Name:
- J/A+A/543/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigated the distribution of resolved asymptotic giant branch (AGB) stars over a much larger area than covered by previous near-infrared studies in the nearby dwarf elliptical galaxy NGC 205. Using data obtained with the WIRCam near-infrared imager of the CFHT, we selected the AGB stars in the JHKs color - magnitude diagrams, and separated the C stars from M-giant stars in the JHKs color - color diagram. We identified 1,550 C stars in NGC 205 with a mean absolute magnitude of <M_Ks>=-7.49+/-0.54, and colors of <(J-K)_0>=1.81+/-0.41 and <(H-Ks)_0>=0.76+/-0.24. The ratio of C stars to M-giant stars was estimated to be 0.15+/-0.01 in NGC 205, and the local C/M ratios for the southern region are somewhat lower than those for the northern region. The (J-K) color distributions of AGB stars contain the main peak of the M-giant stars and the red tail of the C stars. A comparison of the theoretical isochrone models with the observed color distribution indicates that most of the bright M-giant stars in NGC 205 were formed at log(t_yr_)~9.0-9.7. The logarithmic slope of the M_Ks_ luminosity function for M-giant stars was estimated to be 0.84+/-0.01, which is comparable with dwarf elliptical galaxies NGC 147 and NGC 185. Furthermore, we found that the logarithmic slopes of the M_Ks_ luminosity function for C and M-giant stars are different to places, implying a different star formation history within NGC 205. The bolometric luminosity function for M-giant stars extends to M_bol_=-6.0mag, and that for C stars spans -5.6<M_bol_<-3.0. The bolometric luminosity function of C stars is unlikely to be a Gaussian distribution and the mean bolometric magnitude of C stars is estimated to be M_bol_=-4.24+/-0.55, which is consistent with our results for dwarf elliptical galaxies NGC 147 and NGC 185.
- ID:
- ivo://CDS.VizieR/J/MNRAS/400/1413
- Title:
- Near-IR spectra of extremely red AGB stars
- Short Name:
- J/MNRAS/400/1413
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a library of 139 near-IR spectra of cool asymptotic giant branch stars that will be useful for comparison with theoretical model atmosphere calculations and for modelling the integrated emission from intermediate-age stellar populations. The source list was selected from the 'extremely red' region of the Isaac Newton Telescope (INT) Photometric H{alpha} Survey (IPHAS) colour-colour plane that is overwhelmingly dominated by very late-type stars. The spectral library also includes a large fraction of S-type and carbon stars. We present a number of spectral classification sequences highlighting the various molecular features identified and discuss a number of rare features with uncertain identifications in the literature. With its focus on particularly cool photospheres, this catalogue serves as a companion to recent spectroscopic atlases of MK standards in the near-IR. Finally, the relationship between IPHAS (r'-i') and (r'-H{alpha}) colours and spectroscopically determined properties is discussed and a strong correlation between the (r'-H{alpha}) colour and the C/O abundance index for S-type and carbon stars is noted. This relation has the potential to separate O-rich, S-type and carbon stars in the Galaxy based on their photometry alone.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A135
- Title:
- NGC 104, 6121 & 6809 AGB and RGB stars Na abundance
- Short Name:
- J/A+A/607/A135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze high-resolution spectra of a large sample of asymptotic giant branch AGB and red giant branch (RGB) stars in the Galactic GCs NGC 104, NGC 6121, and NGC 6809 obtained with FLAMES/GIRAFFE at ESO/VLT, and determine their Na abundances. This is the first time that the AGB stars in NGC 6809 are targeted. We find that NGC 104 and NG 6809 have comparable AGB and RGB Na abundance distributions, while NGC 6121 shows a lack of very Na-rich AGB stars. Moreover, to investigate the dependence of AGB Na abundance dispersion on GC parameters, we compare the AGB [Na/H] distributions of a total of nine GCs, with five determined by ourselves with homogeneous method and four from literature, covering a wide range of GC parameters. Their Na abundances and multiple populations of AGB stars form complex picture. In some GCs, AGB stars have similar Na abundances and/or second-population fractions as their RGB counterparts, while some GCs do not have Na-rich second-population AGB stars, and various cases exist between the two extremes. In addition, the fitted relations between fractions of the AGB second population and GC global parameters show that the AGB second-population fraction slightly anticorrelates with GC central concentration, while no robust dependency can be confirmed with other GC parameters.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A66
- Title:
- NGC 2808 AGB and RGB stars Na abundance
- Short Name:
- J/A+A/592/A66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic globular clusters (GC) are known to have multiple stellar populations and be characterised by similar chemical features, e.g., O-Na anti-correlation. While second-population stars, identified by their Na overabundance, have been found from the main sequence turnoff up to the tip of the red giant branch in various Galactic GCs, asymptotic giant branch stars have rarely been targeted. Here we present the results of our high-resolution spectroscopic study of a sample of AGB and RGB stars in the Galactic globular cluster NGC 2808. We derived accurate Na abundances for 31 AGB and 40 RGB stars in this cluster. Comparable Na abundance dispersions are found for our AGB and RGB samples, and we conclude that NGC 2808 has Na-rich second-population AGB stars, which turn out to be even more numerous - in relative terms - than their Na-poor counterparts (on the AGB) and the Na-rich stars on the RGB.
- ID:
- ivo://CDS.VizieR/J/A+A/537/A108
- Title:
- NGC 6822 AGB spectroscopic catalogue
- Short Name:
- J/A+A/537/A108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We calibrate spectroscopically the C- versus (vs.) M-type asymptotic giant branch (AGB) star selection made using near-IR photometry, and investigate the spatial distribution of the C/M ratio in NGC 6822, based on low resolution spectroscopy and near-IR photometry.
- ID:
- ivo://CDS.VizieR/J/ApJ/791/39
- Title:
- NGC 6218 and NGC 5904 lithium abundances
- Short Name:
- J/ApJ/791/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Convergent lines of evidence suggest that globular clusters host multiple stellar populations. It appears that they experience at least two episodes of star formation whereby a fraction of first-generation stars contribute astrated ejecta to form the second generation(s). To identify the polluting progenitors, we require distinguishing chemical signatures such as that provided by lithium. Theoretical models predict that lithium can be synthesized in AGB stars, whereas no net Li production is expected from other candidates. It has been shown that in order to reproduce the abundance pattern found in M4, Li production must occur within the polluters, favoring the AGB scenario. Here, we present Li and Al abundances for a large sample of RGB stars in M12 and M5. These clusters have a very similar metallicity, while demonstrating differences in several cluster properties. Our results indicate that the first-generation and second-generation stars share the same Li content in M12; we recover an abundance pattern similar to that observed in M4. In M5, we find a higher degree of complexity, and a simple dilution model fails in reproducing the majority of the stellar population. In both clusters, we require Li production across the different stellar generations, but production seems to have occurred to different extents. We suggest that such a difference might be related to the cluster mass with the Li production being more efficient in less-massive clusters. This is the first time a statistically significant correlation between the Li spread within a GC and its luminosity has been demonstrated. Finally, although Li-producing polluters are required to account for the observed pattern, other mechanisms, such as MS depletion, might have played a role in contributing to the Li internal variation, though at a relatively low level.
- ID:
- ivo://CDS.VizieR/J/AJ/141/58
- Title:
- NGC 2204 and NGC 2243 red giant abundances
- Short Name:
- J/AJ/141/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detailed element abundances have been determined for 10-13 stars each in the open clusters (OCs) NGC 2204 and NGC 2243 based on Hydra multi-object echelle spectra obtained with the CTIO 4m telescope. We have found average cluster metallicities of [Fe/H]=-0.23+/-0.04 and -0.42+/-0.05 for NGC 2204 and NGC 2243, respectively, from an equivalent width analysis.
- ID:
- ivo://CDS.VizieR/J/ApJ/859/75
- Title:
- NGC 5824 giant star members from VLT obs.
- Short Name:
- J/ApJ/859/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 5824 is a massive Galactic globular cluster suspected to have an intrinsic spread in its iron content, according to the strength of the calcium triplet lines. We present chemical abundances of 117 cluster giant stars using high-resolution spectra acquired with the multi-object spectrograph FLAMES. The metallicity distribution of 87 red giant branch stars is peaked at [Fe/H]=-2.11+/-0.01dex, while that derived from 30 asymptotic giant branch stars is peaked at [Fe/H]=-2.20+/-0.01dex. Both the distributions are compatible with a null spread, indicating that this cluster did not retain the ejecta of supernovae. The small iron abundance offset between the two groups of stars is similar to the abundances already observed among red and asymptotic giant branch stars in other clusters. The lack of intrinsic iron spread rules out the possibility that NGC 5824 is the remnant of a disrupted dwarf galaxy, as previously suggested. We also find evidence of the chemical anomalies usually observed in globular clusters, namely the Na-O and the Mg-Al anticorrelations. In particular, NGC 5824 exhibits a huge range of [Mg/Fe] abundance, observed in only a few metal-poor and/or massive clusters. We conclude that NGC 5824 is a normal globular cluster, without spread in [Fe/H] but with an unusually large spread in [Mg/Fe], possibly due to an efficient self-enrichment driven by massive asymptotic giant branch stars.
