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The merger of close double white dwarfs (CDWDs) is one of the favourite evolutionary channels for producing Type Ia supernovae (SN Ia). Unfortunately, current theories of the evolution and formation of CDWDs are still poorly constrained and have several serious uncertainties, which affect the predicted SN Ia rates. Moreover, current observational constraints on this evolutionary pathway for SN Ia mainly rely on only 18 double-lined and/or eclipsing CDWDs with measured orbital and stellar parameters for both white dwarfs. In this paper we present the orbital periods and the individual masses of three new double-lined CDWDs, derived using a new method. This method employs mass ratios, the Halpha core ratios and spectral model-fitting to constrain the masses of the components of the pair. The three CDWDs are WD0028-474 (Porb=9.350 +- 0.007 hours, M1=0.60 +- 0.06 Msun, M2=0.45 +- 0.04 Msun), HE0410-1137 (Porb = 12.208 +- 0.008 hours, M1= 0.51 +- 0.04 Msun, M2= 0.39 +- 0.03 Msun) and SDSSJ031813.25-010711.7 (Porb = 45.908 +- 0.006 hours, among the longest period systems, M1= 0.40 +- 0.05 Msun, M2= 0.49 +- 0.05 Msun). While the three systems studied here will merge in timescales longer than the Hubble time and are expected to become single massive (>~0.9 Msun) white dwarfs rather than exploding as SN Ia, increasing the small sample of CDWDs with determined stellar parameters is crucial for a better overall understanding of their evolution.
Axions are the natural consequence of the introduction of the Peccei-Quinn symmetry to solve the strong CP problem. All the efforts to detect such elusive particles have failed up to now. Nevertheless, it has been recently shown that the luminosity f
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Double white dwarf (double-WD) binaries may merge within a Hubble time and produce high-mass WDs. Compared to other high-mass WDs, the double-WD merger products have higher velocity dispersion because they are older. With the power of Gaia data, we s
We present Chandra and Swift X-ray observations of four extremely low-mass (ELM) white dwarfs with massive companions. We place stringent limits on X-ray emission from all four systems, indicating that neutron star companions are extremely unlikely a
ASASSN-V J205543.90+240033.5 has been suggested to be a white dwarf pulsar by Kato (2021, arXiv:2108.09060). We obtained time-resolved photometry and identified the orbital and spin periods to be 0.523490(1) d and 0.00678591(1) d = 9.77 min, respecti