- ID:
- ivo://CDS.VizieR/J/A+A/419/1123
- Title:
- Equivalent widths of 3 post-AGB
- Short Name:
- J/A+A/419/1123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present model atmosphere analyses of high resolution Keck and VLT optical spectra for three evolved stars in globular clusters, viz. ZNG-1 in M10, ZNG-1 in M15 and ZNG-1 in NGC6712. The derived atmospheric parameters and chemical compositions confirm the programme stars to be in the post-Asymptotic Giant Branch (post-AGB) evolutionary phase.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/129/1607
- Title:
- Equivalent widths of 4 RGB in NGC 7492
- Short Name:
- J/AJ/129/1607
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a detailed abundance analysis for 21 elements in a sample of four RGB stars in the outer halo globular cluster NGC 7492 (R_GC_ 25kpc); we find [Fe/H]=-1.82dex inferred from Fe I lines (-1.79 from Fe II) using high-dispersion (R={lambda}/{Delta}{lambda}=35,000) spectra obtained with HIRES at the Keck Observatory.
- ID:
- ivo://CDS.VizieR/J/ApJ/804/109
- Title:
- Equivalent widths of RGB stars in NGC 5053
- Short Name:
- J/ApJ/804/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 5053 provides a rich environment to test our understanding of the complex evolution of globular clusters (GCs). Recent studies have found that this cluster has interesting morphological features beyond the typical spherical distribution of GCs, suggesting that external tidal effects have played an important role in its evolution and current properties. Additionally, simulations have shown that NGC 5053 could be a likely candidate to belong to the Sagittarius dwarf galaxy (Sgr dSph) stream. Using the Wisconsin-Indiana-Yale-NOAO-Hydra multi-object spectrograph, we have collected high quality (signal-to-noise ratio ~75-90), medium-resolution spectra for red giant branch stars in NGC 5053. Using these spectra we have measured the Fe, Ca, Ti, Ni, Ba, Na, and O abundances in the cluster. We measure an average cluster [Fe/H] abundance of -2.45 with a standard deviation of 0.04 dex, making NGC 5053 one of the most metal-poor GCs in the Milky Way (MW). The [Ca/Fe], [Ti/Fe], and [Ba/Fe] we measure are consistent with the abundances of MW halo stars at a similar metallicity, with alpha-enhanced ratios and slightly depleted [Ba/Fe]. The Na and O abundances show the Na-O anti-correlation found in most GCs. From our abundance analysis it appears that NGC 5053 is at least chemically similar to other GCs found in the MW. This does not, however, rule out NGC 5053 being associated with the Sgr dSph stream.
- ID:
- ivo://CDS.VizieR/J/A+A/534/A53
- Title:
- Equivalent widths of 18 subgiant of {omega} Cen
- Short Name:
- J/A+A/534/A53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze spectra of 18 stars belonging to the faintest subgiant branch in omega Centauri (the SGB-a), obtained with GIRAFFE@VLT at a resolution of R~=17000 and a S/N ratio between 25 and 50. We measure abundances of Al, Ba, Ca, Fe, Ni, Si, and Ti and we find that these stars have <[Fe/H]>=-0.73+/-0.14dex, similarly to the corresponding red giant branch population (the RGB-a). We also measure <[alpha/Fe]>=+0.40+/-0.16dex, and <[Ba/Fe]>=+0.87+/-0.23dex, in general agreement with past studies. It is very interesting to note that we found a uniform Al abundance, <[Al/Fe]>=+0.32+/-0.14dex, for all the 18 SGB-a stars analysed here, thus supporting past evidence that the usual (anti-)correlations are not present in this population, and suggesting a non globular cluster-like origin of this particular population. In the dwarf galaxy hypothesis for the formation of omega Cen, this population might be the best candidate for the field population of its putative parent galaxy, although some of its properties appear contradictory. It has also been suggested that the most metal-rich population in omega Cen is significantly enriched in helium. If this is true, the traditional abundance analysis techniques, based on model atmospheres with normal helium content, might lead to errors. We have computed helium enhanced atmospheres for three stars in our sample and verified that the abundance errors due to the use of non-enhanced atmospheres are negligible. Additional, indirect support to the enhanced helium content of the SGB-a population comes from our Li upper limits.
- ID:
- ivo://CDS.VizieR/J/A+A/604/A41
- Title:
- ESO452-SC11 Stellar parameters and abundances
- Short Name:
- J/A+A/604/A41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters (GCs) have long been recognized as being amongst the oldest objects in the Galaxy. As such, they have the potential of playing a pivotal role in deciphering the Milky Way's early history. Here we present the first spectroscopic study of the low-mass system ESO452-SC11 using the AAOmega multifibre spectrograph at medium resolution. Given the stellar sparsity of this object and the high degree of foreground contamination due to its location toward the Galactic bulge, very few details are known for this cluster - there is no consensus, for instance, about its age, metallicity, or its association with the disk or bulge. We identify five member candidates based on common radial velocity, calcium-triplet metallicity, and position within the GC. Using spectral synthesis, the measurement of accurate Fe-abundances from Fe-lines, and abundances of several {alpha}-, Fe-peak, and neutron-capture elements (Si, Ca, Ti,Cr, Co, Ni, Sr, and Eu) is carried out, albeit with large uncertainties. We find that two of the five cluster candidates are likely non-members, as they have deviating iron abundances and [alpha/Fe] ratios. The cluster mean heliocentric velocity is 19+/-2km/s with a velocity dispersion of 2.8+/-3.4km/s, a low value in line with its sparse nature and low mass. The mean Fe-abundance from spectral fitting is -0.88+/-0.03dex, where the spread is driven by observational errors. Furthermore, the alpha-elements of the GC candidates are marginally lower than expected for the bulge at similar metallicities. As spectra of hundreds of stars were collected in a 2-degree field centered on ESO452-SC11, a detailed abundance study of the surrounding field was also enabled. The majority of the non-members have slightly higher [Fe] ratios, in line with the typical nearby bulge population. A subset of the spectra with measured Fe-peak abundance ratios shows a large scatter around solar values, albeit with large uncertainties. Furthermore, our study provides the first systematic measurements of strontium abundances in a Galactic bulge GC. Here, the Eu and Sr abundances of the GC candidates are broadly consistent with a disk or bulge association. Recent proper motions and our orbital calculations place ESO452 on an elliptical orbit in the central 3kpc of the Milky Way, establishing a firm connection with the bulge. Finally, while the radial velocities and preferential position of a dozen of stars outside the GC radius appear to imply the presence of extra-tidal stars, their significantly different chemical composition refutes this hypothesis.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A111
- Title:
- Evolution of long-lived globular cluster stars
- Short Name:
- J/A+A/592/A111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters host multiple populations of long-lived low-mass stars whose origin remains an open question. Several scenarios have been proposed to explain the associated photometric and spectroscopic peculiarities. They differ, for instance, in the maximum helium enrichment they predict for stars of the second population, which these stars can inherit at birth as the result of the internal pollution of the cluster by different types of stars of the first population. We present the distribution of helium-rich stars in present-day globular clusters as it is expected in the original framework of the fast-rotating massive stars scenario (FRMS) as first-population polluters. We focus on NGC 6752. We completed a grid of 330 stellar evolution models for globular cluster low-mass stars computed with different initial chemical compositions corresponding to the predictions of the original FRMS scenario for [Fe/H]=-1.75. Starting from the initial helium-sodium relation that allows reproducing the currently observed distribution of sodium in NGC 6752, we deduce the helium distribution expected in that cluster at ages equal to 9 and 13Gyr. We distinguish the stars that are moderately enriched in helium from those that are very helium-rich (initial helium mass fraction below and above 0.4, respectively), and compare the predictions of the FRMS framework with other scenarios for globular cluster enrichment.
- ID:
- ivo://CDS.VizieR/J/A+A/512/A10
- Title:
- Evolution of massive AGB stars. III.
- Short Name:
- J/A+A/512/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first simulations of the full evolution of super-AGB stars through the entire thermally pulsing AGB phase. We analyse their structural and evolutionary properties and determine the first SAGB yields. Stellar models of various initial masses and metallicities were computed using standard physical assumptions which prevents the third dredge-up. A postprocessing nucleosynthesis code was used to compute the SAGB yields, to quantify the effect of the third dredge-up (3DUP) and to assess the uncertainties associated with the treatment of convection. Owing to their massive oxygen-neon core, SAGB stars suffer weak thermal pulses, have very short interpulse periods and develop very high temperatures at the base of their convective envelope (up to 140x10^8^K), leading to very efficient hot bottom burning. SAGB stars are consequently heavy manufacturers of ^4^He, ^13^C, and ^14^N. They are also able to inject significant amounts of ^7^Li, ^17^O, ^25^Mg, and ^26,27^Al in the interstellar medium. The 3DUP mainly affects the CNO yields, especially in the lower metallicity models. Our post-processing simulations also indicate that changes in the temperature at the base of the convective envelope, which would result from a change in the efficiency of convective energy transport, have a dramatic impact on the yields and represent another major source of uncertainty.
258. Evolved stars in M13
- ID:
- ivo://CDS.VizieR/J/AJ/139/2374
- Title:
- Evolved stars in M13
- Short Name:
- J/AJ/139/2374
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed photometry from space- and ground-based cameras to identify all bright red giant branch (RGB), horizontal branch (HB), and asymptotic giant branch (AGB) stars within 10' of the center of the globular cluster M13.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A114
- Title:
- EW and [Fe/H] for 30000 globular cluster RGB stars
- Short Name:
- J/A+A/635/A114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The CaII triplet in the near-infrared at 8498, 8542, and 8662{AA} is visible in stars with spectral types between F and M and can be used to determine their metallicities. We calibrated the relation using average cluster metallicities from literature and MUSE spectra, and extend it below the horizontal branch - a cutoff that has traditionally been made to avoid a non-linear relation - using a quadratic function. In addition to the classic relation based on V-\vhb$ we used calibrations based on absolute magnitude and luminosity and used it for those cluster, for which no HB brightness was available. The obtained relations are then used to calculate metallicities for all the stars in the sample.
- ID:
- ivo://CDS.VizieR/J/A+A/527/A18
- Title:
- EW of 6 subgiants of {omega} Cen
- Short Name:
- J/A+A/527/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analysed high-resolution UVES spectra of six stars belonging to the subgiant branch of {omega} Centauri, and derived abundance ratios of 19 chemical elements (namely Al, Ba, C, Ca, Co, Cr, Cu, Fe, La, Mg, Mn, N, Na, Ni, Sc, Si, Sr, Ti, and Y). A comparison with previous abundance determinations for red giants provided remarkable agreement and allowed us to identify the sub-populations to which our targets belong. We found that three targets belong to a low-metallicity population at [Fe/H]=-2.0dex, [alpha/Fe]=+0.4dex and [s/Fe]=0dex. Stars with similar characteristics were found in small amounts by past surveys of red giants. We discuss the possibility that they belong to a separate sub-population that we name VMP (very metal-poor, at most 5% of the total cluster population), which - in the self-enrichment hypothesis - is the best-candidate first stellar generation in {omega} Cen. Two of the remaining targets belong to the dominant metal-poor population (MP) at [Fe/H]=-1.7dex, and the last one to the metal-intermediate (MInt) one at [Fe/H]=-1.2dex. The existence of the newly defined VMP population could help to understand some puzzling results based on low-resolution spectroscopy (Sollima et al. 2005ApJ...634..332S , Villanova et al., 2007, Cat. J/ApJ/663/296) in their age differences determinations, because the metallicity resolution of these studies was probably not enough to detect the VMP population. The VMP could also correspond to some of the additional substructures of the subgiant-branch region found in the latest HST photometry (Bellini et al., 2010, Cat. J/AJ/140/631). After trying to correlate chemical abundances with substructures in the subgiant branch of {omega} Cen, we found that the age difference between the VMP and MP populations should be small (0+/-2Gyr), while the difference between the MP and MInt populations could be slightly larger (2+/-2Gyr).
