Abundances of P, S, and K in 58 bulge spheroid stars from APOGEE

TL;DR

This study measures phosphorus, sulphur, and potassium abundances in 58 bulge spheroid stars using APOGEE data, confirming their behavior aligns with chemical evolution models and identifying phosphorus enhancement in old bulge stars.

Contribution

First derivation of P, S, and K abundances in bulge spheroid stars using H-band spectral synthesis and comparison with models and literature.

Findings

Moderately enhanced phosphorus observed in bulge stars.

Sulphur behaves as an alpha-element with expected trends.

Potassium and sulphur show star-to-star scatter consistent with models.

Abstract

We have previously studied several elements in 58 selected bulge spheroid stars, based on spectral lines in the H-band. We now derive the abundances of the less-studied elements phosphorus (P; Z=15), sulphur (S; Z=16), and potassium (K; Z=19). The abundances of P, S, and K in 58 bulge spheroid stars are compared both with the results of a previous analysis of the data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), and with a few available studies of these elements. We derive the individual abundances through spectral synthesis, using the stellar physical parameters available for our sample from the DR17 release of the APOGEE project. We provide recommendations for the best lines to be used for the studied elements among those in the H-band. We also compare the present results, together with literature data, with chemical-evolution models. Finally, the neutrino-process was taken into account for the suitable fit to the odd-Z elements P and K. We confirm that the H-band has useful lines for the derivation of the elements P, S, and K in moderately metal-poor stars. The abundances, plotted together with literature results from high-resolution spectroscopy, indicate that: moderately enhanced phosphorus stars are found, reminiscent results obtained for thick disk and halo stars of metallicity [Fe/H]~-1.0. Therefore, for the first time, we identify this effect to occur in the old stars from the bulge spheroid. Sulphur is an alpha-element and behaves as such. Potassium and sulphur both exhibit some star-to-star scatter, but fit within the expectations from chemical evolution models.