Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 846, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.3847/2041-8213/aa8032
Keywords
Galaxy: structure; globular clusters: general; stars: abundances; stars: Population II
Categories
Funding
- Chilean BASAL Centro de Excelencia en Astrofisica y Tecnologias Afines (CATA) grant [PFB-06/2007]
- Fondecyt [1170518, 1170121]
- Ramon y Cajal fellowship [RYC-2013-14182]
- Spanish Ministry of Economy and Competitiveness (MINECO) [AYA-2014-58082-P]
- Premium Postdoctoral Research Program of the Hungarian Academy of Sciences
- Hungarian NKFI of the Hungarian National Research, Development and Innovation Office [K-119517]
- Ministry of Economy, Development, and Tourism's Millennium Science Initiative [IC120009]
- UNAM/PAPIIT [IN105916, IN114114]
- FONDECYT REGULAR project [1170476]
- Centre national d'etudes spatiales (CNES) [0101973]
- UTINAM Institute of the Universite de Franche-Comte - Region de Franche-Comte
- Institut des Sciences de l'Univers (INSU)
- Alfred P. Sloan Foundation
- U.S. Department of Energy Office of Science
- Center for High-Performance Computing at the University of Utah
- STFC [ST/F007159/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/F007159/1, ST/M000966/1] Funding Source: researchfish
- Division Of Physics
- Direct For Mathematical & Physical Scien [1430152] Funding Source: National Science Foundation
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We report the peculiar chemical abundance patterns of 11 atypical Milky Way (MW) field red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). These atypical giants exhibit strong Al and N enhancements accompanied by C and Mg depletions, strikingly similar to those observed in the so-called second-generation (SG) stars of globular clusters (GCs). Remarkably, we find low Mg abundances ([Mg/Fe]. < 0.0) together with strong Al and N overabundances in the majority (5/7) of the metal-rich ([Fe/H] greater than or similar to-1.0) sample stars, which is at odds with actual observations of SG stars in Galactic GCs of similar metallicities. This chemical pattern is unique and unprecedented among MW stars, posing urgent questions about its origin. These atypical stars could be former SG stars of dissolved GCs formed with intrinsically lower abundances of Mg and enriched Al (subsequently self-polluted by massive AGB stars) or the result of exotic binary systems. We speculate that the stars Mg-deficiency as well as the orbital properties suggest that they could have an extragalactic origin. This discovery should guide future dedicated spectroscopic searches of atypical stellar chemical patterns in our Galaxy, a fundamental step forward to understanding the Galactic formation and evolution.
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