Details

Autor(en) / Beteiligte

• Brogaard, K
• Christiansen, S M
• Grundahl, F
• Miglio, A
• Izzard, R G
• 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

Titel

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

Ist Teil von

• Monthly notices of the Royal Astronomical Society, 2018-12, Vol.481 (4), p.5062-5072

Erscheinungsjahr

2018

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• 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 M-p similar to 1.67 M-circle dot, more massive than the cluster turn-off, with R-p similar to 1.91 R-circle dot and T-eff = 7110 +/- 100 K. The secondary component is highly oversized and overluminous for its low mass with M-s similar to 0.182 M-circle dot, R-s similar to 0.864 R-circle dot, and T-eff = 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.