Multiple stellar populations at less-evolved stages: detection of chemical variations among main-sequence dwarfs in NGC 1978

Chengyuan Li, Baitian Tang, Antonino P. Milone, Richard de Grijs, Jongsuk Hong, Yujiao Yang, Yue Wang

Research output: Contribution to journalArticlepeer-review

Abstract

Multiple stellar populations (MPs) with different chemical compositions are not exclusive features of old globular clusters (older than 10 Gyr). Indeed, recent studies reveal that younger clusters (~2–6 Gyr-old) in the Magellanic Clouds also exhibit star-to-star chemical variations among evolved stars. However, whether MPs are present among less-evolved dwarfs of these intermediate-age clusters is still unclear. In this work, we search for chemical variations among GK-type dwarfs in the ~2 Gyr old cluster NGC 1978, which is the youngest cluster with MPs. We exploit deep ultraviolet and visual observations from the Hubble Space Telescope to constrain the nitrogen (N) and oxygen (O) variations among main-sequence (MS) stars. To do this, we compare appropriate photometric diagrams that are sensitive to N and O with synthetic diagrams of simple stellar populations and MPs. We conclude that the G- and K-type MS stars in NGC 1978 host MPs. Our statistical analysis shows that the fraction of N-rich stars ranges from ~40% to ~80%, depending on the detailed distributions of N and O.
Original languageEnglish
Article number133
Number of pages13
JournalAstrophysical Journal
Volume906
Issue number2
DOIs
Publication statusPublished - 18 Jan 2021

Bibliographical note

Copyright © 2021. The American Astronomical Society. First published in the Astrophysical Journal, 906(2), 50, 2021, published by IOP Publishing. The original publication is available at https://doi.org/10.3847/1538-4357/abc8f2. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

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