| 1. |
- Kanai, M, et al.
(författare)
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- 2023
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swepub:Mat__t
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| 2. |
- Brogaard, K., et al.
(författare)
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The blue straggler V106 in NGC6791 : A prototype progenitor of old single giants masquerading as young
- 2018
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711. ; 481:4, s. 5062-5072
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Tidskriftsartikel (refereegranskat)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 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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| 3. |
- Maund, J. R., et al.
(författare)
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Did the progenitor of SN 2011dh have a binary companion?
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 454:3, s. 2580-2585
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Tidskriftsartikel (refereegranskat)abstract
- We present late-time Hubble Space Telescope ultraviolet (UV) and optical observations of the site of SN 2011dh in the galaxy M51, similar to 1164 days post-explosion. At the supernova (SN) location, we observe a point source that is visible at all wavelengths, which is significantly fainter than the spectral energy distribution (SED) of the yellow supergiant progenitor observed prior to explosion. The previously reported photometry of the progenitor is, therefore, completely unaffected by any sources that may persist at the SN location after explosion. In comparison with the previously reported late-time photometric evolution of SN 2011dh, we find that the light curve has plateaued at all wavelengths. The SED of the late-time source is clearly inconsistent with an SED of stellar origin. Although the SED is bright at UV wavelengths, there is no strong evidence that the late-time luminosity originates solely from a stellar source corresponding to the binary companion, although a partial contribution to the observed UV flux from a companion star cannot be ruled out.
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| 4. |
- Brogaard, K., et al.
(författare)
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The blue straggler V106 in NGC 6791 : a prototype progenitor of old single giants masquerading as young
- 2018
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 481:4, s. 5062-5072
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Izzard, R. G., et al.
(författare)
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White-dwarf kicks and implications for barium stars
- 2010
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 523
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Tidskriftsartikel (refereegranskat)abstract
- The formation mechanism of the barium stars is thought to be well understood. Barium-rich material, lost in a stellar wind from a thermally-pulsing asymptotic-giant branch star in a binary system, is accreted by its companion main-sequence star. Now, many millions of years later, the primary is an unseen white dwarf and the secondary has itself evolved into a giant which displays absorption lines of barium in its spectrum and is what we call a barium star. A similar wind-accretion mechanism is also thought to form the low-metallicity CH and carbon-enhanced metal-poor stars. Qualitatively the picture seems clear but quantitatively it is decidedly murky: several key outstanding problems remain which challenge our basic understanding of binary-star physics. Barium stars with orbital periods less than about 4000 days should - according to theory - be in circular orbits because of tidal dissipation, yet they are often observed to be eccentric. Only one barium-star period longer than 10(4) days has been published although such stars are predicted to exist in large numbers. In this paper we attempt to shed light on these problems. First, we consider the impact of kicking the white dwarf at its birth, a notion which is supported by independent evidence from studies of globular clusters. Second, we increase the amount of orbital angular momentum loss during wind mass transfer, which shrinks barium-star binaries to the required period range. We conclude with a discussion of possible physical mechanisms and implications of a kick, such as the break up of wide barium-star binaries and the limits imposed on our models by observations.
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