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

Brogaard, K. ; Christiansen, S. M. ; Grundahl, F. ; Miglio, A. ; Izzard, R. G. ; Tauris, T. M. ; Sandquist, E. L. ; Vanden Berg, D. A. ; Jessen-Hansen, J. and Arentoft, T. , et al. (2018) In Monthly Notices of the Royal Astronomical Society 481(4). p.5062-5072
Abstract

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... (More)

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.

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keywords
Binaries: close, Blue stragglers, Stars: fundamental parameters, Stars: individual: V106, White dwarfs
in
Monthly Notices of the Royal Astronomical Society
volume
481
issue
4
pages
11 pages
publisher
Oxford University Press
external identifiers
  • scopus:85059612803
ISSN
0035-8711
DOI
10.1093/MNRAS/STY2504
language
English
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yes
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aa197dba-0e92-493f-a464-8faada673cbb
date added to LUP
2019-05-13 16:18:59
date last changed
2020-03-24 06:49:39
@article{aa197dba-0e92-493f-a464-8faada673cbb,
  abstract     = {<p>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 M<sub>p</sub> ~ 1.67M<sub>⊙</sub>, more massive than the cluster turn-off, with R<sub>p</sub> ~ 1.91R<sub>⊙</sub> and T<sub>eff</sub> = 7110 ± 100 K. The secondary component is highly oversized and overluminous for its low mass with M<sub>s</sub> ~ 0.182M<sub>⊙</sub>, R<sub>⊙</sub> ~ 0.864R<sub>⊙</sub>, and T<sub>⊙</sub> =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.</p>},
  author       = {Brogaard, K. and Christiansen, S. M. and Grundahl, F. and Miglio, A. and Izzard, R. G. and Tauris, T. M. and Sandquist, E. L. and Vanden Berg, D. A. and Jessen-Hansen, J. and Arentoft, T. and Bruntt, H. and Frandsen, S. and Orosz, J. A. and Feiden, G. A. and Mathieu, R. and Geller, A. and Shetrone, M. and Ryde, N. and Stello, D. and Platais, I. and Meibom, S.},
  issn         = {0035-8711},
  language     = {eng},
  month        = {12},
  number       = {4},
  pages        = {5062--5072},
  publisher    = {Oxford University Press},
  series       = {Monthly Notices of the Royal Astronomical Society},
  title        = {The blue straggler V106 in NGC6791 : A prototype progenitor of old single giants masquerading as young},
  url          = {http://dx.doi.org/10.1093/MNRAS/STY2504},
  doi          = {10.1093/MNRAS/STY2504},
  volume       = {481},
  year         = {2018},
}