- ID:
- ivo://CDS.VizieR/J/AJ/142/22
- Title:
- Heavy-element dispersion in M92
- Short Name:
- J/AJ/142/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dispersion among the light elements is common in globular clusters (GCs), while dispersion among heavier elements is less common. We present detection of r-process dispersion relative to Fe in 19 red giants of the metal-poor GC M92. Using spectra obtained with the Hydra multi-object spectrograph on the WIYN Telescope at Kitt Peak National Observatory, we derive differential abundances for 21 species of 19 elements.
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- ID:
- ivo://CDS.VizieR/J/A+A/648/A108
- Title:
- Heavy-elements heritage of the falling sky
- Short Name:
- J/A+A/648/A108
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- A fundamental element of galaxy formation is the accretion of mass through mergers of satellites or gas. Recent dynamical analyses based on Gaia data have revealed major accretion events in the history of the Milky Way. Nevertheless, our understanding of the primordial Galaxy is hindered because the bona fide identification of the most metal-poor and correspondingly oldest accreted stars remains challenging. Galactic archaeology needs a new accretion diagnostic to understand primordial stellar populations. Contrary to {alpha}-elements, neutron-capture elements present unexplained large abundance spreads for low-metallicity stars, which could result from a mixture of formation sites. We analysed the abundances of yttrium, europium, magnesium, and iron in MilkyWay satellite galaxies, field halo stars, and globular clusters. The chemical information was complemented by orbital parameters based on Gaia data. In particular, we considered the average inclination of the orbits. The [Y/Eu] abundance behaviour with respect to the [Mg/Fe] turnovers for satellite galaxies of various masses reveals that higher-luminosity systems, for which the [Mg/Fe] abundance declines at higher metallicities, present enhanced [Y/Eu] abundances, particularly in the [Fe/H] regime between -2.25dex and -1.25dex. In addition, the analysis has uncovered a chemo-dynamical correlation for both globular clusters and field stars of the Galactic halo, accounting for about half of the [Y/Eu] abundance spread. In particular, [Y/Eu] under-abundances typical of protracted chemical evolutions are preferentially observed in polar-like orbits, pointing to a possible anisotropy in the accretion processes. Our results strongly suggest that the observed [Y/Eu] abundance spread in the Milky Way halo could result from a mixture of systems with different masses. They also highlight that both nature and nurture are relevant to the formation of the Milky Way since its primordial epochs, thereby opening new pathways for chemical diagnostics of the build-up of our Galaxy.
- ID:
- ivo://CDS.VizieR/IV/26
- Title:
- Hercules Messier 13 (M13) photometry
- Short Name:
- IV/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ludendorff's catalog of the M13 globular cluster results from observations made with the 32.5cm refractor of Potsdam Observatory, one on 17 July 1900 (plate A), and the second on June 1902 (plate B). Each plate was measured twice, in opposite position, to remove the possible errors. The catalog contains accurate positions on both plates, photographic magnitudes, and comparison with the previous results from Scheiner (1892). Number 1119 to 1127 where seen only in one position on plate A, and in two positions on plate B. Number 1128 to 1136 where seen only on plate A, and are not in Scheiner catalog.
- ID:
- ivo://CDS.VizieR/J/ApJ/834/105
- Title:
- High-resolution GC abundances. II.
- Short Name:
- J/ApJ/834/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present abundances of globular clusters (GCs) in the Milky Way and Fornax from integrated-light (IL) spectra. Our goal is to evaluate the consistency of the IL analysis relative to standard abundance analysis for individual stars in those same clusters. This sample includes an updated analysis of seven clusters from our previous publications and results for five new clusters that expand the metallicity range over which our technique has been tested. We find that the [Fe/H] measured from IL spectra agrees to ~0.1dex for GCs with metallicities as high as [Fe/H]=-0.3, but the abundances measured for more metal-rich clusters may be underestimated. In addition we systematically evaluate the accuracy of abundance ratios, [X/Fe], for Na I, Mg I, Al I, Si I, Ca I, Ti I, Ti II, Sc II, V I, Cr I, Mn I, Co I, Ni I, Cu I, Y II, Zr I, Ba II, La II, Nd II, and Eu II. The elements for which the IL analysis gives results that are most similar to analysis of individual stellar spectra are Fe I, Ca I, Si I, Ni I, and Ba II. The elements that show the greatest differences include Mg I and Zr I. Some elements show good agreement only over a limited range in metallicity. More stellar abundance data in these clusters would enable more complete evaluation of the IL results for other important elements.
- ID:
- ivo://CDS.VizieR/J/ApJ/746/29
- Title:
- High-resolution GC abundances. IV. 8 LMC GCs
- Short Name:
- J/ApJ/746/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present detailed chemical abundances in eight clusters in the Large Magellanic Cloud (LMC). We measure abundances of 22 elements for clusters spanning a range in age of 0.05-12 Gyr, providing a comprehensive picture of the chemical enrichment and star formation history of the LMC. The abundances were obtained from individual absorption lines using a new method for analysis of high-resolution (R~25000), integrated-light (IL) spectra of star clusters. This method was developed and presented in Papers I (2008ApJ...684..326M), II (2009PhDT........20C), and III (Cat. J/ApJ/735/55) of this series. In this paper, we develop an additional IL {chi}^2^-minimization spectral synthesis technique to facilitate measurement of weak (~15m{AA}) spectral lines and abundances in low signal-to-noise ratio data (S/N~30). Additionally, we supplement the IL abundance measurements with detailed abundances that we measure for individual stars in the youngest clusters (age<2Gyr) in our sample. In both the IL and stellar abundances we find evolution of [{alpha}/Fe] with [Fe/H] and age. Fe-peak abundance ratios are similar to those in the Milky Way (MW), with the exception of [Cu/Fe] and [Mn/Fe], which are sub-solar at high metallicities. The heavy elements Ba, La, Nd, Sm, and Eu are significantly enhanced in the youngest clusters. Also, the heavy to light s-process ratio is elevated relative to the MW ([Ba/Y]>+0.5) and increases with decreasing age, indicating a strong contribution of low-metallicity asymptotic giant branch star ejecta to the interstellar medium throughout the later history of the LMC. We also find a correlation of IL Na and Al abundances with cluster mass in the sense that more massive, older clusters are enriched in the light elements Na and Al with respect to Fe, which implies that these clusters harbor star-to-star abundance variations as is common in the MW. Lower mass, intermediate-age, and young clusters have Na and Al abundances that are lower and more consistent with LMC field stars. Our results can be used to constrain both future chemical evolution models for the LMC and theories of globular cluster formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/735/55
- Title:
- High-resolution GCs abundances. III. LMC
- Short Name:
- J/ApJ/735/55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we refine our method for the abundance analysis of high-resolution spectroscopy of the integrated light of unresolved globular clusters (GCs). This method was previously demonstrated for the analysis of old (>10Gyr) Milky Way (MW) GCs. Here, we extend the technique to young clusters using a training set of nine GCs in the Large Magellanic Cloud. Depending on the signal-to-noise ratio of the data, we use 20-100 Fe lines per cluster to successfully constrain the ages of old clusters to within a ~5Gyr range, the ages of ~2Gyr clusters to a 1-2Gyr range, and the ages of the youngest clusters (0.05-1Gyr) to a ~200Myr range. We also demonstrate that we can measure [Fe/H] in clusters with any age less than 12Gyr with similar or only slightly larger uncertainties (0.1-0.25dex) than those obtained for old MW GCs (0.1dex); the slightly larger uncertainties are due to the rapid evolution in stellar populations at these ages. In this paper, we present only Fe abundances and ages. For several of the clusters in this sample, there are no high-resolution abundances in the literature from individual member stars; our results are the first detailed chemical abundances available.
- ID:
- ivo://CDS.VizieR/J/ApJ/816/70
- Title:
- High resolution spectra of 3 NGC104 member stars
- Short Name:
- J/ApJ/816/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters are known to host peculiar objects named blue straggler stars (BSSs), significantly heavier than the normal stellar population. While these stars can be easily identified during their core hydrogen-burning phase, they are photometrically indistinguishable from their low-mass sisters in advanced stages of the subsequent evolution. A clear-cut identification of these objects would require the direct measurement of the stellar mass. We used the detailed comparison between chemical abundances derived from neutral and from ionized spectral lines as a powerful stellar "weighing device" to measure stellar mass and to identify an evolved BSS in 47Tucanae. In particular, high-resolution spectra of three bright stars, located slightly above the level of the "canonical" horizontal branch (HB) sequence in the color-magnitude diagram of 47 Tucanae, have been obtained with the UVES spectrograph. The measurements of iron and titanium abundances performed separately from neutral and ionized lines reveal that two targets have stellar parameters fully consistent with those expected for low-mass post-HB objects, while for the other target the elemental ionization balance is obtained only by assuming a mass of ~1.4M_{sun}_, which is significantly larger than the main sequence turn-off mass of the cluster (~0.85M_{sun}_). The comparison with theoretical stellar tracks suggests that this is a BSS descendant possibly experiencing its core helium-burning phase. The large applicability of the proposed method to most of the globular clusters in our Galaxy opens the possibility to initiate systematic searches for evolved BSSs, thus giving access to still unexplored phases of their evolution.
- ID:
- ivo://CDS.VizieR/J/ApJ/832/99
- Title:
- HK', CN & CH chemical indexes in NGC 362 & NGC 6723
- Short Name:
- J/ApJ/832/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most globular clusters (GCs) are now known to host multiple stellar populations with different abundances of light elements. Here we use narrow-band photometry and low-resolution spectroscopy for NGC 362 and NGC 6723 to investigate their chemical properties and radial distributions of subpopulations. We confirm that NGC 362 and NGC 6723 are among the GCs with multiple populations showing bimodal CN distribution and CN-CH anticorrelation without a significant spread in calcium abundance. These two GCs show more centrally concentrated CN-weak, earlier generation stars compared to the CN-strong, later generation stars. These trends are reversed with respect to those found in previous studies for many other GCs. Our findings, therefore, seem contradictory to the current scenario for the formation of multiple stellar populations, but mass segregation acting on the two subpopulations might be a possible solution to explain this reversed radial trend.
- ID:
- ivo://CDS.VizieR/J/A+A/563/A13
- Title:
- Horizontal branch stars in M22
- Short Name:
- J/A+A/563/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained high-resolution spectra for 94 candidate stars belonging to the HB of M 22 with FLAMES. Previous works have indicated that this cluster has split subgiant (SGB) and red giant branches (RGB) and hosts two different stellar populations, differing in overall metal abundance and both exhibiting a Na-O anti-correlation. The HB stars we observed span a restricted temperature range (7800<Teff<11000K), where about 60% of the HB stars of M 22 are. Within our sample, we can distinguish three groups of stars segregated (though contiguous) in colours: Group 1 (49 stars) is metal-poor, N-normal, Na-poor and O-rich: our abundances for this (cooler) group match very well those determined for the primordial group of RGB stars (a third of the total) from previous studies. Group 2 (23 stars) is still metal-poor, but it is N- and Na-rich, though only very mildly depleted in O. We can identify this intermediate group as the progeny of the metal-poor RGB stars that occupy an intermediate location along the Na-O anti-correlation and include about 10% of the RGB stars. The third group (20 stars) is metal-rich, Na-rich, and O-rich. This hotter group likely corresponds to the most O-rich component of the previously found metal-rich RGB population (a quarter of the total). We did not observe any severely O-depleted stars and we think that the progeny of these stars falls on the hotter part of the HB. Furthermore, we found that the metal-rich population is also over-abundant in Sr, in agreement with results for corresponding RGB and SGB stars. However, we do not find any significant variation in the ratio between the sum of N and O abundances to Fe. We do not have C abundances for our stars. There is some evidence of an enhancement of He content for Groups 2 and 3 stars (Y=0.338+/-0.014+/-0.05); the error bar due to systematics is large, but a consistent analysis of data for several GCs confirms that stars in these groups within M22 are likely overabundant in He. We conclude that on the whole, our results agree with the proposition that chemical composition drives the location of stars along the HB of a GC. Furthermore, we found a number of fast rotators. They are concentrated in a restricted temperature range along the HB of M22. Fast rotating stars might be slightly less massive and bluer than slowly rotating ones, but other interpretations are possible.
- ID:
- ivo://CDS.VizieR/J/A+A/539/A19
- Title:
- Horizontal branch stars in NGC 1851
- Short Name:
- J/A+A/539/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical composition of horizontal branch (HB) stars might help to clarify the formation history of individual globular clusters (GCs). We studied the Na-O anti-correlation from moderately high resolution spectra for 91 stars on the bimodal HB of NGC 1851; in addition we observed 13 stars on the lower red giant branch (RGB). In our HB sample, 35 stars are on the blue HB (BHB), one is an RR Lyrae, and 55 stars are on the red HB (RHB). The ratio of BHB to RHB stars is close to the total in the cluster (35 and 54%, respectively), while RR Lyrae variables are under-represented, (they are ~12% of the NGC 1851 stars). We also derived abundances for He and N in BHB stars.
