More Like this

1. Two new double-lined spectroscopic binary white dwarfs

   https://doi.org/10.1093/mnras/staa466  

   Kilic, Mukremin; Bédard, A; Bergeron, P; Kosakowski, Alekzander (April 2020, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present radial velocity observations of four binary white dwarf candidates identified through their overluminosity. We identify two new double-lined spectroscopic binary systems, WD 0311–649 and WD 1606+422, and constrain their orbital parameters. WD 0311–649 is a 17.7 h period system with a mass ratio of 1.44 ± 0.06 and WD 1606+422 is a 20.1 h period system with a mass ratio of 1.33 ± 0.03. An additional object, WD 1447–190, is a 43 h period single-lined white dwarf binary, whereas WD 1418–088 does not show any significant velocity variations over time-scales ranging from minutes to decades. We present an overview of the 14 overluminous white dwarfs that were identified by Bédard et al., and find the fraction of double- and single-lined systems to be both 31 per cent. However, an additional 31 per cent of these overluminous white dwarfs do not show any significant radial velocity variations. We demonstrate that these must be in long-period binaries that may be resolved by Gaia astrometry. We also discuss the overabundance of single low-mass white dwarfs identified in the SPY survey, and suggest that some of those systems are also likely long-period binary systems of more massive white dwarfs. 

   more » « less
2. The ELM Survey South. II. Two Dozen New Low-mass White Dwarf Binaries

   https://doi.org/10.3847/1538-4357/acd187  

   Kosakowski, Alekzander; Brown, Warren_R; Kilic, Mukremin; Kupfer, Thomas; Bédard, Antoine; Gianninas, A.; Agüeros, Marcel_A; Barrientos, Manuel (June 2023, The Astrophysical Journal)

   Abstract We present the results from our ongoing spectroscopic survey targeting low-mass white dwarf binaries, focusing on the southern sky. We used a Gaia DR2- and eDR3-based selection and identified 28 new binaries, including 19 new extremely low-mass (ELM) white dwarfs, one short period, likely eclipsing, DABZ, and two potential LISA binaries. We present the orbital and atmospheric parameters for each new binary based on our spectroscopic follow up. Four of our new binaries show periodic photometric variability in TESS 2 minutes cadence data, including one new eclipsing double-lined spectroscopic binary. Three others show periodic photometric variability in ZTF, including one new eclipsing binary. We provide estimates for the inclinations and scaled component radii for these ZTF variables, based on light-curve modeling of our high-speed photometric follow-up observations. Our observations have increased the sample of ELM Survey binaries identified in the southern sky to 41, an increase of 64%. Future time domain surveys, such as BlackGEM and the Vera C. Rubin Observatory Legacy Survey of Space and Time, will efficiently identify photometric variables in the southern sky and significantly increase the population of southern sky low-mass white dwarf binaries, leading to a more complete all-sky population of these systems. 

   more » « less
3. A hidden population of massive white dwarfs: two spotted K + WD binaries

   https://doi.org/10.1093/mnras/stae517  

   Rowan, Dominick M; Jayasinghe, Tharindu; Tucker, Michael A; Lam, Casey Y; Thompson, Todd A; Kochanek, Christopher S; Abrams, Natasha S; Fulton, Benjamin J; Ilyin, Ilya; Isaacson, Howard; et al (February 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The identification and characterization of massive (≳ 0.8 M⊙) white dwarfs is challenging in part due to their low luminosity. Here, we present two candidate single-lined spectroscopic binaries, Gaia DR3 4014708864481651840 and 5811237403155163520, with K-dwarf primaries and optically dark companions. Both have orbital periods of P ∼ 0.45 d and show rotational variability, ellipsoidal modulations, and high-amplitude radial velocity variations. Using light curves from the Transiting Exoplanet Survey Satellite (TESS), radial velocities from ground-based spectrographs, and spectral energy distributions, we characterize these binaries to describe the nature of the unseen companion. We find that both systems are consistent with a massive white dwarf companion. Unlike simple ellipsoidal variables, star-spots cause the light-curve morphology to change between TESS sectors. We attempt to constrain the orbital inclination using phoebe binary light-curve models, but degeneracies in the light curves of spotted stars prevent a precise determination. Finally, we search for similar objects using Gaia DR3 and TESS, and comment on these systems in the context of recently claimed compact object binaries. 

   more » « less
4. Electromagnetic Characterization of the LISA Verification Binary ZTF J0526+5934

   https://doi.org/10.3847/1538-4357/ad0ce9  

   Kosakowski, Alekzander; Kupfer, Thomas; Bergeron, P.; Littenberg, Tyson B. (December 2023, The Astrophysical Journal)

   Abstract We present an analysis of new and archival data to the 20.506 minute LISA verification binary J052610.42+593445.32 (J0526+5934). Our joint spectroscopic and photometric analysis finds that the binary contains an unseenM₁= 0.89 ± 0.11M_⊙CO-core white dwarf primary with anM₂= 0.38 ± 0.07M_⊙post-core-burning subdwarf, or low-mass white dwarf, companion. Given the short orbital period and relatively large total binary mass, we find that LISA will detect this binary with signal-to-noise ratio 44 after 4 yr of observations. J0526+5934 is expected to merge within 1.8 ± 0.3 Myr and likely result in a D⁶scenario Type Ia supernova or form a He-rich star that will evolve into a massive single white dwarf. 

   more » « less
5. A Gravitational-wave-detectable Candidate Type Ia Supernova Progenitor

   https://doi.org/10.3847/1538-4357/add34c  

   Chickles, Emma T; Burdge, Kevin B; Chakraborty, Joheen; Dhillon, Vik S; Draghis, Paul; Munday, James; Rappaport, Saul A; Tonry, John; Bauer, Evan B; Brown, Alex J; et al (July 2025, The Astrophysical Journal)

   Abstract Type Ia supernovae (SNe Ia), critical for studying cosmic expansion, arise from thermonuclear explosions of white dwarfs, but their precise progenitor pathways remain unclear. Growing evidence supports the “double-degenerate scenario,” where two white dwarfs interact. The absence of nondegenerate companions capable of explaining the observed SN Ia rate, along with observations of hypervelocity white dwarfs, interpreted as surviving companions of such systems, provide compelling evidence for this scenario. Upcoming millihertz gravitational-wave observatories like the Laser Interferometer Space Antenna (LISA) are expected to detect thousands of double-degenerate systems, though the most compact known candidate SN Ia progenitors produce marginally detectable signals. Here, we report observations of ATLAS J1138-5139, a binary white dwarf system with an orbital period of just 28 minutes. Our analysis reveals a 1M_☉carbon–oxygen white dwarf accreting from a high-entropy helium-core white dwarf. Given its mass, the accreting carbon–oxygen white dwarf is poised to trigger a typical-luminosity SN Ia within a few million years, to evolve into a stably transferring AM Canum Venaticorum (or AM CVn) system, or undergo a merger into a massive white dwarf. ATLAS J1138-5139 provides a rare opportunity to calibrate binary evolution models by directly comparing observed orbital parameters and mass-transfer rates closer to merger than any known SN Ia progenitor. Its compact orbit ensures detectability by LISA, demonstrating the potential of millihertz gravitational-wave observatories to reveal a population of SN Ia progenitors on a Galactic scale, paving the way for multimessenger studies offering insights into the origins of these cosmologically significant explosions. 

   more » « less