Discovery of a nitrogen-enhanced mildly metal-poor binary system: Possible evidence for pollution from an extinct AGB star

José G. Fernández-Trincado, Ronald Mennickent, Mauricio Cabezas, Olga Zamora, Sarah L. Martell, Timothy C. Beers, Vinicius M. Placco, David M. Nataf, Szabolcs Mészáros, Dante Minniti, Dominik R.G. Schleicher, Baitian Tang, Angeles Pérez-Villegas, Annie C. Robin, Céline Reylé

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)

Abstract

We report the serendipitous discovery of a nitrogen-rich, mildly metal-poor ([Fe/H] = -1.08) giant star in a single-lined spectroscopic binary system found in the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) survey, Data Release 14 (DR14). Previous work has assumed that two percent of halo giants with unusual elemental abundances have been evaporated from globular clusters, but other origins for their abundance signatures, including binary mass transfer, must also be explored. We present the results of an abundance reanalysis of the APOGEE-2 high-resolution near-infrared spectrum of 2M12451043+1217401 with the Brussels Automatic Stellar Parameter (BACCHUS) automated spectral analysis code. We manually re-derive the main element families, namely light elements (C, N), elements (O, Mg, Si), the iron-peak element (Fe), s-process element (Ce), and light odd-Z element (Al). Our analysis confirms the N-rich nature of 2M12451043+1217401, which has a [N/Fe] ratio of +0.69, and shows that the abundances of C and Al are slightly discrepant from those of a typical mildly metal-poor red giant branch star, but exhibit Mg, Si, O and s-process abundances (Ce) of typical field stars. We also detect a particularly large variability in the radial velocity of this star over the period of the APOGEE-2 observations; the most likely orbit fit to the radial velocity data has a period of 730.89 ±106.86 days, a velocity semi-amplitude of 9.92 ±0.14 km s-1, and an eccentricity of ∼0.1276 ±0.1174. These data support the hypothesis of a binary companion, which has probably been polluted by a now-extinct asymptotic giant branch star.

Original languageEnglish
Article numberA97
JournalAstronomy and Astrophysics
Volume631
DOIs
Publication statusPublished - 1 Jan 2019

Keywords

  • Binaries: general
  • Stars: abundances
  • Stars: AGB and post-AGB
  • Stars: chemically peculiar
  • Stars: evolution
  • Techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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