The search for DA double white dwarf binary candidates from SDSS DR14

¹ Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Shandong University at Weihai, Weihai 264209, PR China
e-mail: swb@sdu.edu.cn
² CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
³ Department of Scientific Research, Beijing Planetarium, Xizhimenwai Street, Beijing 100044, PR China
⁴ Yunnan Observatories, Chinese Academy of Sciences, Kunming, 650011, PR China
⁵ Key Laboratory of Stars and Interstellar Medium, Xiangtan University, Xiangtan 411105, PR China
⁶ School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, PR China

Received: 1 August 2023
Accepted: 31 January 2024

Abstract

Aims. Double white dwarf (DWD) binaries are one of the channels through which type Ia supernovae explosions occur. With the release of more and more sky survey data, the search for additional DWDs has become a possibility. We utilized the spectroscopic data from SDSS DR14 to search for DWD binaries based on variations in radial velocities (RVs).

Methods. We obtained a sample of 4089 DA white dwarfs (WDs) with two or more spectra from SDSS DR14, and their RVs were derived using the cross-correlation function. Using the chi-squared (χ²) distribution of RVs as a base, we calculated the corresponding logarithmic probabilities (log p) for different degrees of freedom.

Results. We selected the targets with log p < −3.0 and obtained 65 highly credible DWD candidates, of which 56 were newly discovered. We compared the distributions of the T_eff, log g, and mass of the DWD candidates and found that the mass distribution of DWDs has two peaks. The primary peak, located at 0.45 M_⊙, is lower than the peak of the total WD sample, while the secondary peak, located at 0.60 M_⊙, is similar to the peak of the total sample. Finally, we crossmatched our sample with Zwicky Transient Facility (ZTF) photometry data and identified two targets with clear periodic variability. Based on the shape of their light curve, we think both could be white dwarf main-sequence binary stars