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Centro de Astrofísica da Universidade do Porto

A Hot Horizontal Branch Star with a Close K-type Main-sequence Companion

C. Moni-Bidin, Y. Momany, M. Montalto, M. Catelan, S. Villanova, G. Piotto, D. Geisler

Dynamical interactions in binary systems are thought to play a major role in the formation of extreme horizontal branch stars (EHBs) in the Galactic field. However, it is still unclear if the same mechanisms are at work in globular clusters (GCs), where EHBs are predominantly single stars. Here, we report on the discovery of a unique close binary system (period ~1.61 days) in the GC NGC 6752, comprising an EHB and a main-sequence companion of 0.63 ± 0.05 M Such a system has no counterpart among nearly 200 known EHB binaries in the Galactic field. Its discovery suggests that either field studies are incomplete, missing this type of system possibly because of selection effects, or that a particular EHB formation mechanism is active in clusters but not in the field.

binaries: close - stars: horizontal-branch - subdwarfs

The Astrophysical Journal Letters
Volume 812, Page L31
October 2015

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Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

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