Universität zu Köln

Szecsi, Dorottya ORCID: 0000-0001-6473-7085, Mackey, Jonathan ORCID: 0000-0002-5449-6131 and Langer, Norbert (2018). Supergiants and their shells in young globular clusters. Astron. Astrophys., 612. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. Anomalous surface abundances are observed in a fraction of the low-mass stars of Galactic globular clusters, that may originate from hot-hydrogen-burning products ejected by a previous generation of massive stars.& para;& para;Aims. We aim to present and investigate a scenario in which the second generation of polluted low-mass stars can form in shells around cool supergiant stars within a young globular cluster.& para;& para;Methods. Simulations of low-metallicity massive stars (M-i similar to 150-600 M-circle dot) show that both core-hydrogen-burning cool supergiants and hot ionizing stellar sources are expected to be present simulaneously in young globular clusters. Under these conditions, photoionization-confined shells form around the supergiants. We have simulated such a shell, investigated its stability and analysed its composition.& para;& para;Results. We find that the shell is gravitationally unstable on a timescale that is shorter than the lifetime of the supergiant, and the Bonnor-Ebert mass of the overdense regions is low enough to allow star formation. Since the low-mass stellar generation formed in this shell is made up of the material lost from the supergiant, its composition necessarily reflects the composition of the supergiant wind. We show that the wind contains hot-hydrogen-burning products, and that the shell-stars therefore have very similar abundance anomalies that are observed in the second generation stars of globular clusters. Considering the mass-budget required for the second generation star-formation, we offer two solutions. Either a top-heavy initial mass function is needed with an index of -1.71 to -2.07. Alternatively, we suggest the shell-stars to have a truncated mass distribution, and solve the mass budget problem by justifiably accounting for only a fraction of the first generation.& para;& para;Conclusions. Star-forming shells around cool supergiants could form the second generation of low-mass stars in Galactic globular clusters. Even without forming a photoionizaton-confined shell, the cool supergiant stars predicted at low-metallicity could contribute to the pollution of the interstellar medium of the cluster from which the second generation was born. Thus, the cool supergiant stars should be regarded as important contributors to the evolution of globular clusters.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Szecsi, Dorottya UNSPECIFIED orcid.org/0000-0001-6473-7085 UNSPECIFIED Mackey, Jonathan UNSPECIFIED orcid.org/0000-0002-5449-6131 UNSPECIFIED Langer, Norbert UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-189151
DOI:	10.1051/0004-6361/201731500
Journal or Publication Title:	Astron. Astrophys.
Volume:	612
Date:	2018
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language MASS-LOSS; MULTIPLE POPULATIONS; SELF-POLLUTION; MAIN-SEQUENCE; GIANT STARS; EVOLUTION; SUPERNOVAE; ORIGIN; RATIOS; PREDICTIONS Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/18915