Homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code

Abstract

Aims. We aim at providing abundances of a large set of light and neutron-capture elements homogeneously analyzed and covering a wide range of metallicity to constrain globular cluster (GC) formation and evolution models. Methods. We analyze a large sample of 885 GCs giants from the APOGEE survey. We used the Cannon results to separate the red giant branch and the asymptotic giant branch stars, not only allowing for a refinement of surface gravity from isochrones, but also providing an independent H-band spectroscopic method to distinguish stellar evolutionary status in clusters. We then use the BACCHUS code to derive metallicity, microturbulence, macroturbulence and many light-element abundances as well as the neutron-capture elements Nd and Ce for the first time from the APOGEE GCs data. Results. Our independent analysis helped us to diagnose issues regarding the standard analysis of the APOGEE DR14 for lowmetallicity GC stars. Furthermore, while we confirm most of the known correlations and anti-correlation trends (Na-O, Mg-Al, C-N), we discover that some stars within our most metal-poor clusters show an extreme Mg depletion and some Si enhancement but at the same time show some relative Al depletion, displaying a turnover in the Mg-Al diagram. These stars suggest that Al has been partially depleted in their progenitors by very hot proton-capture nucleosynthetic processes. Furthermore, we attempted to quantitatively correlate the spread of Al abundances with the global properties of GCs. We find an anti-correlation of the Al spread against clusters metallicity and luminosity, but the data do not allow to find clear evidence of a dependence of N against metallicity in the more metal-poor clusters. Conclusions. Large and homogeneously analyzed samples from on-going spectroscopic surveys unveil unseen chemical details for many clusters, including a turnover in the Mg-Al anti-correlation, thus yielding new constrains for GCs formation/evolution models.

SPCANet: Stellar Parameters and Chemical Abundances Network for LAMOST-II Medium Resolution Survey

“…Same as Fig.10 but density distribution of elemental abundances for LAMOST MRS giants. The white scatters are values from the previous literature (Masseron et al 2019;Donor et al 2018;Kovalev et al 2019;Magrini et al 2017;Kılıçoglu et al 2016;Tautvaišienė et al 2015;Mishenina et al 2011;Bensby et al 2014;Zhao et al 2016;Nissen 2016). (Bensby et al 2014) studied 714 F and G dwarfs and subgiants in the Solar neighborhood and determined their stellar parameters and elemental abundances based on high-resolution spectra.…”

“…We cross-match our results with GALAH DR2 and get 396 common stars corresponding 1021 LAMOST-II MRS spectra after setting "flag cannon=0" in GALAH parameter catalog. (Masseron et al 2019;Donor et al 2018;Kovalev et al 2019;Magrini et al 2017;Kılıçoglu et al 2016;Tautvaišienė et al 2015;Mishenina et al 2011;Bensby et al 2014;Zhao et al 2016;Nissen 2016).…”

Homogeneous analysis of globular clusters from the APOGEE survey with the BACCHUS code – II. The Southern clusters and overview

“…With the appearance of high spectral resolution sky surveys some of these southern clusters were revisited by the Gaia-ESO survey (Gilmore et al 2012) focusing on the same two element pairs (Pancino et al 2017). The first homogeneous exploration of 10 northern clusters was carried out by Mészáros et al (2015), which was updated by Masseron et al (2019), both using data from the SDSS-III (Eisenstein et al 2011) Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Results for additional clusters observed by APOGEE were published by Schiavon et al (2017), Tang et al (2017), andFernández-Trincado et al (2019).…”

“…In this paper we discuss 21 new (mostly southern) clusters observed from both LCO and APO by following the same steps of atmospheric parameter and abundance determination as Masseron et al (2019) and combine them with the 10 northern clusters discussed by Masseron et al (2019). Because M12 was observed from both observatories, we use this cluster to check how homogeneous the abundances are from APO and LCO.…”

“…These two improvements were not adopted by Masseron et al (2019), but now we refine the list of stars presented in that study. While the selected members of those 10 northern clusters have only changed slightly, because some stars were added or deleted, we did not rederive atmospheric parameters and abundances for stars that remained members, as our analysis method has not changed.…”