The blue straggler V106 in NGC6791 : A prototype progenitor of old single giants masquerading as young

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We determine the properties of the binary star V106 in the old open cluster NGC6791. We identify the system to be a blue straggler cluster member by using a combination of groundbased and Kepler photometry and multi-epoch spectroscopy. The properties of the primary component are found to be Mp ~ 1.67M⊙, more massive than the cluster turn-off, with Rp ~ 1.91R⊙ and Teff = 7110 ± 100 K. The secondary component is highly oversized and overluminous for its low mass with Ms ~ 0.182M⊙, R⊙ ~ 0.864R⊙, and T⊙ =6875±200 K. We identify this secondary star as a bloated (proto) extremely low-mass helium white dwarf. These properties of V106 suggest that it represents a typical Algol-paradox system and that it evolved through a mass-transfer phase, which provides insight into its past evolution. We present a detailed binary stellar evolution model for the formation of V106 using the MESA code and find that the mass-transfer phase only ceased about 40 Myr ago. Due to the short orbital period (P = 1.4463 d), another mass-transfer phase is unavoidable once the current primary star evolves towards the red giant phase. We argue that V106 will evolve through a common-envelope phase within the next 100 Myr and merge to become a single overmassive giant. The high mass will make it appear young for its true age, which is revealed by the cluster properties. Therefore, V106 is potentially a prototype progenitor of old field giants masquerading as young.

Christiansen, S. M.Aarhus University (author)
Grundahl, F.Aarhus University (author)
Miglio, A.University of Birmingham,Aarhus University (author)
Izzard, R. G.University of Surrey (author)
Tauris, T. M.University of Bonn,Max Planck Institute for Radio Astronomy,Aarhus University (author)
Sandquist, E. L.San Diego State University (author)
Vanden Berg, D. A.University of Victoria (author)
Jessen-Hansen, J.Aarhus University (author)
Arentoft, T.Aarhus University (author)
Bruntt, H.Aarhus University (author)
Frandsen, S.Aarhus University (author)
Orosz, J. A.San Diego State University (author)
Feiden, G. A.Uppsala University (author)
Mathieu, R.University of Wisconsin-Madison (author)
Geller, A.University of Wisconsin-Madison (author)
Shetrone, M.University of Texas System (author)
Ryde, N.Lund University,Lunds universitet,Astronomi - Genomgår omorganisation,Institutionen för astronomi och teoretisk fysik - Genomgår omorganisation,Naturvetenskapliga fakulteten,Lund Observatory - Undergoing reorganization,Department of Astronomy and Theoretical Physics - Undergoing reorganization,Faculty of Science(Swepub:lu)astr-nlr (author)
Stello, D.University of New South Wales,University of Sydney,Aarhus University (author)
Platais, I.Johns Hopkins University (author)
Meibom, S.Harvard–Smithsonian Center for Astrophysics (author)
Aarhus UniversityUniversity of Birmingham (creator_code:org_t)

In:Monthly Notices of the Royal Astronomical Society481:4, s. 5062-50720035-8711

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NATURAL SCIENCES: NATURAL SCIENCES; and Physical Science ...; and Astronomy Astrop ...

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