- ID:
- ivo://CDS.VizieR/J/ApJ/870/115
- Title:
- Reddening, distance modulus & Fe/H of RRLs in w Cen
- Short Name:
- J/ApJ/870/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We developed a new approach to provide accurate estimates of the metal content, reddening, and true distance modulus of RR Lyrae stars (RRLs). The method is based on homogeneous optical (BVI) and near-infrared (JHK) mean magnitudes and on predicted period-luminosity-metallicity relations (IJHK) and absolute mean magnitude-metallicity relations (BV). We obtained solutions for three different RRL samples in {omega}Cen: first overtone (RRc, 90), fundamental (RRab, 80), and global (RRc+RRab) in which the period of first overtones were fundamentalized. The metallicity distribution shows a well defined peak at [Fe/H]~-1.98 and a standard deviation of {sigma}=0.54dex. The spread is, as expected, metal-poor ([Fe/H]<=-2.3) objects. The current metallicity distribution is ~0.3dex more metal-poor than similar estimates for RRLs available in the literature. The difference vanishes if the true distance modulus we estimated is offset by -0.06/-0.07mag in true distance modulus. We also found a cluster true distance modulus of {mu}=13.720{+/-}0.002{+/-}0.030mag, where the former error is the error on the mean and the latter is the standard deviation. Moreover, we found a cluster reddening of E(B-V)=0.132{+/-}0.002{+/-}0.028mag and spatial variations of the order of a few arcmin across the body of the cluster. Both the true distance modulus and the reddening are slightly larger than similar estimates available in the literature, but the difference is within 1{sigma}. The metallicity dependence of distance diagnostics agrees with theory and observations, but firm constraints require accurate and homogeneous spectroscopic measurements.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/810/148
- Title:
- Red giant abundances in NGC 2808
- Short Name:
- J/ApJ/810/148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical composition of multiple populations in the massive globular cluster (GC) NGC 2808 is addressed with the homogeneous abundance reanalysis of 140 red giant branch stars. UVES spectra for 31 stars and GIRAFFE spectra for the other giants were analyzed with the same procedures used for about 2500 giants in 23 GCs in our FLAMES survey, deriving abundances of Fe, O, Na, Mg, Si, Ca, Ti, Sc, Cr, Mn, and Ni. Iron, elements from {alpha} capture, and those in the Fe group do not show intrinsic scatter. On our UVES scale, the metallicity of NGC 2808 is [Fe/H]=-1.29+/-0.005+/-0.034 (+/-statistical+/-systematic error) with {sigma}=0.030 (31 stars). The main features related to proton-capture elements are retrieved, but the improved statistics and the smaller associated internal errors allow us to uncover five distinct groups of stars along the Na-O anticorrelation. We observe large depletions in Mg, anticorrelated with enhancements of Na and also Si, suggestive of unusually high temperatures for proton captures. About 14% of our sample is formed by giants with solar or subsolar [Mg/Fe] ratios. Using the [Na/Mg] ratios, we confirm the presence of five populations with different chemical compositions that we call P1, P2, I1, I2, and E in order of decreasing Mg and increasing Na abundances. Statistical tests show that the mean ratios in any pair of groups cannot be extracted from the same parent distribution. The overlap with the five populations recently detected from UV photometry is good but not perfect, confirming that more distinct components probably exist in this complex GC.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A17
- Title:
- Red giant Aluminium abundances in NGC 2808
- Short Name:
- J/A+A/615/A17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observed a sample of 90 red giant branch (RGB) stars in NGC 2808 using FLAMES/GIRAFFE and the high resolution grating with the set up HR21. These stars have previous accurate atmospheric parameters and abundances of light elements. We derived aluminium abundances for them from the strong doublet AlI 8772-8773 Angstrom as in previous works of our group. In addition, we were able to estimate the relative CN abundances for 89 of the stars from the strength of a large number of CN features. When adding self consistent abundances from previous UVES spectra analysed by our team, we gathered [Al/Fe] ratios for a total of 108 RGB stars in NGC 2808. The full dataset of proton-capture elements is used to explore in details the five spectroscopically detected discrete components in this globular cluster. We found that different classes of polluters are required to reproduce the (anti)-correlations among all proton-capture elements in the populations P2, I1, and I2 with intermediate composition. This is in agreement with the detection of lithium in lower RGB second generation stars, requiring at least two kind of polluters. To have chemically homogeneous populations the best subdivision of our sample is into six components, as derived from statistical cluster analysis. By comparing different diagrams [element/Fe] vs [element/Fe] we show for the first time that a simple dilution model is not able to reproduce all the sub-populations in this cluster. Polluters of different masses are required. NGC 2808 is confirmed to be a tough challenge to any scenario for globular cluster formation.
1424. Red giants in NGC 5286
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/815
- Title:
- Red giants in NGC 5286
- Short Name:
- J/MNRAS/450/815
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a high-resolution spectroscopic analysis of 62 red giants in the Milky Way globular cluster (GC) NGC 5286. We have determined abundances of representative light proton-capture, {alpha}, Fe-peak and neutron-capture element groups, and combined them with photometry of multiple sequences observed along the colour-magnitude diagram. Our principal results are: (i) a broad, bimodal distribution in s-process element abundance ratios, with two main groups, the s-poor and s-rich groups; (ii) substantial star-to-star Fe variations, with the s-rich stars having higher Fe, e.g. <[Fe/H]_s-rich_-<[Fe/H]>_s-poor_~0.1dex; and (iii) the presence of O-Na-Al (anti)correlations in both stellar groups. We have defined a new photometric index, c_BVI_=(B-V)-(V-I), to maximize the separation in the colour-magnitude diagram between the two stellar groups with different Fe and s-element content, and this index is not significantly affected by variations in light elements (such as the O-Na anticorrelation). The variations in the overall metallicity present in NGC 5286 add this object to the class of anomalous GCs. Furthermore, the chemical abundance pattern of NGC 5286 resembles that observed in some of the anomalous GCs, e.g. M 22, NGC 1851, M 2, and the more extreme {omega} Centauri, that also show internal variations in s-elements, and in light elements within stars with different Fe and s-elements content. In view of the common variations in s-elements, we propose the term s-Fe-anomalous GCs to describe this sub-class of objects. The similarities in chemical abundance ratios between these objects strongly suggest similar formation and evolution histories, possibly associated with an origin in tidally disrupted dwarf satellites.
- ID:
- ivo://CDS.VizieR/J/MNRAS/442/1680
- Title:
- Red giants in SMC. Abundances
- Short Name:
- J/MNRAS/442/1680
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from the largest Caii triplet line metallicity study of Small Magellanic Cloud (SMC) field red giant stars to date, involving 3037 objects spread across approximately 37.5deg^2^, centred on this galaxy. We find a median metallicity of [Fe/H]=-0.99+/-0.01, with clear evidence for an abundance gradient of -0.075+/-0.011dex/deg over the inner 5{deg}. We interpret the abundance gradient to be the result of an increasing fraction of young stars with decreasing galactocentric radius, coupled with a uniform global age-metallicity relation. We also demonstrate that the age-metallicity relation for an intermediate-age population located 10kpc in front of the north-east of the cloud is indistinguishable from that of the main body of the galaxy, supporting a prior conjecture that this is a stellar analogue of the Magellanic Bridge. The metal-poor and metal-rich quartiles of our red giant branch star sample (with complementary optical photometry from the Magellanic Clouds Photometric Survey) are predominantly older and younger than approximately 6Gyr, respectively. Consequently, we draw a link between a kinematical signature, tentatively associated by us with a disc-like structure, and the upsurges in stellar genesis imprinted on the star formation history of the central regions of the SMC. We conclude that the increase in the star formation rate around 5-6Gyr ago was most likely triggered by an interaction between the SMC and Large Magellanic Cloud.
1426. Red giants of NGC 1851
- ID:
- ivo://CDS.VizieR/J/A+A/658/A80
- Title:
- Red giants of NGC 1851
- Short Name:
- J/A+A/658/A80
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- NGC 1851 is one of several globular clusters for which multiple stellar populations of the subgiant branch have been clearly identified and a difference in metallicity detected. A crucial piece of information on the formation history of this cluster can be provided by the sum of A(C+N+O) abundances. However, these values have lacked a general consensus thus far. The separation of the subgiant branch can be based on age and/or A(C+N+O) abundance differences. Our main aim was to determine carbon, nitrogen, and oxygen abundances for evolved giants in the globular cluster NGC 1851 in order to check whether or not the double populations of stars are coeval. High-resolution spectra, observed with the FLAMES-UVES spectrograph on the ESO VLT telescope, were analysed using a differential model atmosphere method. Abundances of carbon were derived using spectral synthesis of the C 2 band heads at 5135 and 5635.5{AA}. The wavelength interval 6470-6490{AA}, with CN features, was analysed to determine nitrogen abundances. Oxygen abundances were determined from the [OI] line at 6300{AA}. Abundances of other chemical elements were determined from equivalent widths or spectral syntheses of unblended spectral lines. We provide abundances of up to 29 chemical elements for a sample of 45 giants in NGC 1851. The investigated stars can be separated into two populations with a difference of 0.07dex in the mean metallicity, 0.3dex in the mean C/N, and 0.35 dex in the mean s-process dominated element-to-iron abundance ratios [s/Fe]. No significant difference was determined in the mean values of A(C+N+O) as well as in abundance to iron ratios of carbon, {alpha}- and iron-peak-elements, and of europium. As the averaged A(C+N+O) values between the two populations do not differ, additional evidence is given that NGC 1851 is composed of two clusters, the metal-rich cluster being by about 0.6Gyr older than the metal-poor one. A global overview of NGC 1851 properties and the detailed abundances of chemical elements favour its formation in a dwarf spheroidal galaxy that was accreted by the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/795/52
- Title:
- Red giant star sample from SDSS
- Short Name:
- J/ApJ/795/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained a sample of ~22000 red giant branch (RGB) stars based on stellar parameters, provided by the ninth data release of the Sloan Digital Sky Survey (Cat. V/139), and the CH(G)/MgH indices, measured from the included spectra. The Galactic rest-frame velocity of V_gsr_ versus longitude for the sample shows the existence of several groups of stars from globular clusters and known streams. Excluding these substructures, a sample of ~16000 RGB stars from the general field is used to investigate the properties of the thick disk, the inner halo, and the outer halo of our Galaxy. The metallicity and rotational velocity distributions are investigated for stars at 0 kpc<|Z|<10 kpc. It is found that the canonical thick disk dominates at 0 kpc<|Z|<2 kpc and its contribution becomes negligible at |Z|>3 kpc. The MWTD is present and overlaps with the inner halo at 1 kpc<|Z|<3 kpc. The inner halo starts at 2 kpc<|Z|<3 kpc and becomes the dominated population for 4 kpc<|Z|<10 kpc. For halo stars with |Z|>5 kpc, bimodal metallicity distributions are found for 20 kpc<|Z|<25 kpc and 35 kpc<RR<45 kpc, which suggests a dual halo, the inner and the outer halo, as reported in Carollo et al. (2007Natur.450.1020C) at low|Z| values. The peak of metallicity for the inner halo is at [Fe/H]~-1.6 and appears to be at [Fe/H]~-2.3 for the outer halo. The transition point from the inner to the outer halo is located at|Z|~20 kpc and RR~35 kpc.
- ID:
- ivo://CDS.VizieR/J/AJ/153/261
- Title:
- Red giant stellar parameters in the LMC bar
- Short Name:
- J/AJ/153/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report new spectroscopic observations obtained with the Michigan/Magellan Fiber System of 308 red giants (RGs) located in two fields near the photometric center of the bar of the Large Magellanic Cloud. This sample consists of 131 stars observed in previous studies (in one field) and 177 newly observed stars (in the second field) selected specifically to more reliably establish the metallicity and age distributions of the bar. For each star, we measure its heliocentric line-of-sight velocity, surface gravity, and metallicity from its high-resolution spectrum (effective temperatures come from photometric colors). The spectroscopic Hertzsprung-Russell diagrams- modulo small offsets in surface gravities-reveal good agreement with model isochrones. The mean metallicity of the 177-RG sample is [Fe/H]=-0.76+/-0.02 with a metallicity dispersion {sigma}=0.28+/-0.03. The corresponding metallicity distribution-corrected for selection effects-is well fitted by two Gaussian components: one metal-rich with a mean -0.66+/-0.02 and a standard deviation 0.17+/-0.01, and the other metal-poor with -1.20+/-0.24 and 0.41+/-0.06. The metal-rich and metal-poor populations contain approximately 85% and 15% of stars, respectively. We also confirm that the velocity dispersion in the bar center decreases significantly from 31.2+/-4.3 to 18.7+/-1.9km/s with increasing metallicity over the range -2.09 to -0.38. Individual stellar masses are estimated using the spectroscopic surface gravities and the known luminosities. We find that lower mass, hence older, RGs have larger metallicity dispersion and lower mean metallicity than the higher-mass, younger RGs. The estimated masses, however, extend to implausibly low values (~0.1M_{sun}_), making it impossible to obtain an absolute age-metallicity or age distribution of the bar.
- ID:
- ivo://CDS.VizieR/J/A+A/577/A18
- Title:
- Reduced CRIRES spectra around S multiplet 3
- Short Name:
- J/A+A/577/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Sulphur is an important, volatile alpha element but its role in the Galactic chemical evolution is still uncertain. We derive the S abundances in RGB stars in three Galactic globular clusters (GC) that cover a wide metallicity range (-2.3<[Fe/H]<-1.2): M4, M22, and M30. The halo field stars show a large scatter in the [S/Fe] ratio in this metallicity span, which is inconsistent with canonical chemical evolution models. To date, very few measurements of [S/Fe] exist for stars in GCs, which are good tracers of the chemical enrichment of their environment. However, some light and alpha elements show star-to-star variations within individual GCs and it is yet unclear whether sulphur also varies between GC stars. We used the the infrared spectrograph CRIRES to obtain high-resolution (R~50000), high signal-to-noise (SNR~200 per px) spectra in the region of the SI multiplet 3 at 1045nm for 15 GC stars selected from the literature (6 stars in M4, 6 stars in M22 and 3 stars in M30). Multiplet 3 is better suited for S abundance derivation than the more commonly used lines of multiplet 1 at 920nm, since its lines are not blended by telluric absorption or other stellar features at low metallicity. We used spectral synthesis to derive the [S/Fe] ratio of the stars assuming local thermodynamic equilibrium (LTE). We find mean [S/Fe]=0.58+/-0.01+/-0.20dex (statistical and systematic error) for M4, [S/Fe]=0.57+/-0.01+/-0.19dex for M22, and [S/Fe]=0.55+/-0.02+/-0.16dex for M30. The negative NLTE corrections are estimated to be in the order of the systematic uncertainties. With the tentative exception of two stars with measured high S abundances, we conclude that sulphur behaves like a typical alpha element in the studied Galactic GCs, showing enhanced abundances with respect to the solar value at metallicities below [Fe/H]=-1.0dex without a considerable spread.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A72
- Title:
- Resolved molecular line observations
- Short Name:
- J/A+A/646/A72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Physical processes that govern the star and planet formation sequence influence the chemical composition and evolution of protoplanetary disks. Recent studies allude to an early start to planet formation already ongoing during the formation of a disk. To understand the chemical composition of protoplanets, we need to constrain the composition and structure of the disks from whence they are formed. We aim to determine the molecular abundance structure of the young disk around the TMC1A protostar on au scales in order to understand its chemical structure and any possible implications for disk formation. We present spatially resolved Atacama Large Millimeter/submillimeter Array observations of CO, HCO^+^, HCN, DCN, and SO line emission, as well as dust continuum emission, in the vicinity of TMC1A. Molecular column densities are estimated both under the assumption of optically thin emission from molecules in local thermodynamical equilibrium (LTE) as well as through more detailed non-LTE radiative transfer calculations. From the derived HCO^+^ abundance, we estimate the ionization fraction of the disk surface and find values that imply that the accretion process is not driven by the magneto-rotational instability. The molecular abundances averaged over the TMC1A disk are similar to its protostellar envelope and other, older Class II disks. We meanwhile find a discrepancy between the young disk's molecular abundances relative to Solar System objects. Abundance comparisons between the disk and its surrounding envelope for several molecular species reveal that the bulk of planet-forming material enters the disk unaltered. Differences in HCN and H_2_O molecular abundances between the disk around TMC1A, Class II disks, and Solar System objects trace the chemical evolution during disk and planet formation.