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The blue straggler V106 in NGC 6791: A prototype progenitor of old single giants masquerading as young.

Brogaard, K, Christiansen, S M, Grundahl, F, Miglio, A, Izzard, Robert, Tauris, T M, Sandquist, E L, VandenBerg, D A, Jessen-Hansen, J, Arentoft, T , Bruntt, H, Frandsen, S, Orosz, J A, Feiden, G A, Mathieu, R, Geller, A, Shetrone, M, Ryde, N, Stello, D, Platais, I and Meibom, S (2018) The blue straggler V106 in NGC 6791: A prototype progenitor of old single giants masquerading as young. Monthly Notices of the Royal Astronomical Society.

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We determine the properties of the binary star V106 in the old open cluster NGC 6791. We identify the system to be a blue straggler cluster member by using a combination of ground-based 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⊙ , Rs∼0.864R⊙ and Teff = 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 over-massive 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.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
Brogaard, K
Christiansen, S M
Grundahl, F
Miglio, A
Tauris, T M
Sandquist, E L
VandenBerg, D A
Jessen-Hansen, J
Arentoft, T
Bruntt, H
Frandsen, S
Orosz, J A
Feiden, G A
Mathieu, R
Geller, A
Shetrone, M
Ryde, N
Stello, D
Platais, I
Meibom, S
Date : 18 September 2018
DOI : 10.1093/mnras/sty2504
Depositing User : Karen Garland
Date Deposited : 04 Oct 2018 13:10
Last Modified : 04 Oct 2018 13:10

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