Does the chemical signature of TYC 8442–1036–1 originate from a rotating massive star that died in a faint explosion?⋆
1 Centre for Astrophysics Research,
School of Physics, Astronomy and Mathematics, University of
Lane, Hatfield AL10
2 BRIDGCE UK Network (www.bridgce.net), UK
3 Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
4 GEPI – Observatoire de Paris, 64 avenue de l’Observatoire, 75014 Paris, France
5 Université de Picardie Jules Verne, 33 rue St-Leu, 80080 Amiens, France
6 South African Astronomical Observatory (SAAO), Observatory Road Observatory Cape Town, WC 7925, South Africa
7 Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, 69117 Heidelberg, Germany
8 Departamento de Física, Facultad de Ciencias Básicas, Universidad Metropolitana de la Educación, Av. José Pedro Alessandri 774, 7760197 Nuñoa, Santiago, Chile
9 Millennium Institute of Astrophysics (MAS), 7820436 Macul, Santiago, Chile
Accepted: 10 August 2016
Context. We have recently investigated the origin of chemical signatures observed in Galactic halo stars by means of a stochastic chemical evolution model. We found that rotating massive stars are a promising way to explain several signatures observed in these fossil stars.
Aims. We discuss how the extremely metal-poor halo star TYC 8442−1036−1, for which we have now obtained detailed abundances from VLT-UVES spectra, fits into the framework of our previous work.
Methods. We applied a standard one-dimensional (1D) LTE analysis to the spectrum of this star. We measured the abundances of 14 chemical elements; we computed the abundances for Na, Mg, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, and Zn using equivalent widths; we obtained the abundances for C, Sr, and Ba by means of synthetic spectra generated by MOOG.
Results. We find an abundance of [Fe/H] = −3.5 ±0.13 dex based on our high-resolution spectrum; this points to an iron content that is lower by a factor of three (0.5 dex) compared to that obtained by a low-resolution spectrum. The star has a [C/Fe] = 0.4 dex, and it is not carbon enhanced like most of the stars at this metallicity. Moreover, this star lies in the plane [Ba/Fe] versus [Fe/H] in a relatively unusual position, shared by a few other Galactic halo stars, which is only marginally explained by our past results.
Conclusions. The comparison of the model results with the chemical abundance characteristics of this group of stars can be improved if we consider in our model the presence of faint supernovae coupled with rotating massive stars. These results seem to imply that rotating massive stars and faint supernovae scenarios are complementary to each other, and are both required in order to match the observed chemistry of the earliest phases of the chemical enrichment of the Universe.
Key words: stars: rotation / stars: massive / Galaxy: evolution / Galaxy: halo / nuclear reactions, nucleosynthesis, abundances / stars: abundances
© ESO 2016