LAMOST J113208.06-005052.3 and LAMOST J052957.56+344127.0: two new binaries with a hot white dwarf and a flaring companion star

TL;DR

Two new WD+flaring companion binaries, LAMOST J1132 and LAMOST J0529, are identified by integrating spectroscopy from LAMOST DR12 LRS with GAIA XP data, multi-band photometry, and time-domain light curves. Spectral fitting with the WDTOOLS GFP framework and random-forest regression yields hot WD primaries, with $T_{eff}=53728\pm2467$ K ($\log g=7.98\pm0.08$) for J1132 and $T_{eff}=47381\pm494$ K ($\log g=7.84\pm0.05$) for J0529, while GAIA XP mismatches and NIR/MIR colors indicate cool companions of spectral types K/M (J1132) and M (J0529). Time-domain data from ZTF and TESS reveal companion flare activity and a lack of eclipses, consistent with non-eclipsing WD+flaring companion binaries and complex multi-period variability. The study demonstrates the value of combining spectroscopy, multi-wavelength photometry, and time-domain analysis to uncover rare WD+flaring companion binaries and suggests future LAMOST MRS observations to probe WD magnetic fields.

Abstract

Binaries contain rich physical information, and the study of binaries has always been a hot topic in stellar physics research. The stars LAMOST J1132 and LAMOST J0529 have not yet been recorded in the SIMBAD astronomical database. We have investigated their physical properties via methods such as spectral analysis, photometric analysis, and light curve analysis. Based on comprehensive analysis, we conclude that they are two newly discovered binary systems, each consisting of a hot white dwarf and a flaring companion star. Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectra indicate that both stars contain hot white dwarfs. The spectral fitting yields $T_{eff}$=53728$\pm$2467\,K, log$g$=7.98$\pm$0.08 for LAMOST J1132, and $T_{eff}$=47381$\pm$494\,K, log$g$=7.84$\pm$0.05 for LAMOST J0529. The weak neutral metal lines in the LAMOST spectra and the discrepancy between the Global Astrometric Interferometer for Astrophysics (GAIA) and LAMOST spectra both indicate that these two sources are likely binary systems. The relatively high flux values for both sources in the near-infrared and mid-infrared bands support our preliminary judgment. The color index in the near-infrared bands suggests that the companion star is K or M type for LAMOST J1132 and M type for LAMOST J0529. Light curve data from the Zwicky Transient Facility (ZTF) indicate that the companion stars of both sources are stars exhibiting flare activity. The eclipse probability is very low, indicating that these two sources are non-eclipsing binary systems. The physics of binaries is fascinating, and future data from LAMOST Medium Resolution Spectra are expected to enable the detection of magnetic fields in these two hot white dwarfs.

Figures (9)

• Figure 1: LAMOST DR12 LRS (lower panel) and GAIA DR3 XP (upper panel) spectra of LAMOST J1132. The GAIA source ID for LAMOST J1132 is 3797112657191340032, with GAIA g mean magnitude of 17.26 mag.
• Figure 2: LAMOST DR12 LRS (lower panel) and GAIA DR3 XP (upper panel) spectra of LAMOST J0529. The GAIA source ID for LAMOST J0529 is 182658435048551040, with GAIA g mean magnitude of 12.60 mag.
• Figure 3: The fitting corner figure for LAMOST J1132 (left) and LAMOST J0529 (right) generated by WDTOOLS using the GFP.
• Figure 4: Photometric observation images of LAMOST J1132 and LAMOST J0529 from the CDS portal. The two lower panels of LAMOST J1132 are from SDSS9 color (left) and 2MASS J, H, and Ks bands (right), respectively. The two upper panels of LAMOST J0529 are from Pan-STARRS DR1 g band (left) and 2MASS J, H, and Ks bands (right), respectively. Each panel covers a 1.11' field of view.
• Figure 5: Light curves of g, r, and i bands for LAMOST J1132 (lower panel) and g and r bands for LAMOST J0529 (upper panel) from ZTF telescope. The black arrows indicate the flares.