A strange dwarf scenario for the formation of the peculiar double white dwarf binary SDSS J125733.63+542850.5. Issue 1 (29th January 2018)

• Record Type: Journal Article
• Authors: Jiang, Long; Chen, Wen-Cong; Li, Xiang-Dong
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 476:Issue 1(2018)
• Page Start: 109
• Page End: 113
• Publication Date: 2018-01-29
• Subjects: binaries: close -- stars: evolution -- stars: individual: SDSS J125733.63+542850.5 -- white dwarfs; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty238
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: The Hubble Space Telescope observation of the double white dwarf (WD) binary SDSS J125733.63+542850.5 reveals that the massive WD has a surface gravity log g 1 ∼ 8.7 (which implies a mass of M 1 ∼ 1.06 M⊙ ) and an effective temperature T 1 ∼ 13 000 K, while the effective temperature of the low-mass WD ( M 2 < 0.24 M⊙ ) is T 2 ∼ 6400 K . Therefore, the massive and the low-mass WDs have a cooling age τ1 ∼ 1 Gyr and τ2 ≥ 5 Gyr, respectively. This is in contradiction with traditional binary evolution theory. In this paper, we propose a strange dwarf (SD) scenario to explain the formation of this double WD binary. We assume that the massive WD is a SD originating from a phase transition (PT) in a ∼1.1 M⊙ WD, which has experienced accretion and spin-down processes. Its high effective temperature could arise from the heating process during the PT. Our simulations suggest that the progenitor of SDSS J125733.63+542850.5 can be a binary system consisting of a 0.65 M⊙ WD and a 1.5 M⊙ main-sequence star in a 1.492 d orbit. Especially, the secondary star (i.e. the progenitor of the low-mass WD) is likely to have an ultra-low metallicity of Z = 0.0001.