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Title:
GRACES observations of young [alpha/Fe]-rich stars
Authors:
Yong, David; Casagrande, Luca; Venn, Kim A.; Chené, André-Nicolas; Keown, Jared; Malo, Lison; Martioli, Eder; Alves-Brito, Alan; Asplund, Martin; Dotter, Aaron; Martell, Sarah L.; Meléndez, Jorge; Schlesinger, Katharine J.
Affiliation:
AA(Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia ), AB(Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia), AC(Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 3P2, Canada), AD(Gemini Observatory, Northern Operations Centre, 670 North A'ohoku Place, Hilo, HI 96720, USA), AE(Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 3P2, Canada), AF(Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Highway, Kamuela, HI 96743, USA), AG(Laboratório Nacional de Astrofísica (LNA/MCTI), Rua Estados Unidos, 154, Itajubá, MG, Brazil), AH(Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, Porto Alegre, RS, Brazil), AI(Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia), AJ(Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia), AK(School of Physics, University of New South Wales, Sydney, NSW 2052, Australia), AL(Departamento de Astronomia do IAG/USP, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo, SP, Brazil), AM(Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 459, Issue 1, p.487-495 (MNRAS Homepage)
Publication Date:
06/2016
Origin:
OUP
Astronomy Keywords:
techniques: radial velocities, stars: abundances
Abstract Copyright:
2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
DOI:
10.1093/mnras/stw676
Bibliographic Code:
2016MNRAS.459..487Y

Abstract

We measure chemical abundance ratios and radial velocities in four massive (i.e. young) [alpha/Fe]-rich red giant stars using high-resolution high-S/N spectra from ESPaDOnS fed by Gemini-GRACES. Our differential analysis ensures that our chemical abundances are on the same scale as the Alves-Brito et al. (2010) study of bulge, thin, and thick disc red giants. We confirm that the program stars have enhanced [alpha/Fe] ratios and are slightly metal poor. Aside from lithium enrichment in one object, the program stars exhibit no chemical abundance anomalies when compared to giant stars of similar metallicity throughout the Galaxy. This includes the elements Li, O, Si, Ca, Ti, Cr, Ni, Cu, Ba, La, and Eu. Therefore, there are no obvious chemical signatures that can help to reveal the origin of these unusual stars. While our new observations show that only one star (not the Li-rich object) exhibits a radial velocity variation, simulations indicate that we cannot exclude the possibility that all four could be binaries. In addition, we find that two (possibly three) stars show evidence for an infrared excess, indicative of a debris disc. This is consistent with these young [alpha/Fe]-rich stars being evolved blue stragglers, suggesting their apparent young age is a consequence of a merger or mass transfer. We would expect a binary fraction of ˜50 per cent or greater for the entire sample of these stars, but the signs of the circumbinary disc may have been lost since these features can have short time-scales. Radial velocity monitoring is needed to confirm the blue straggler origin.
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