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An Infrared Census of R Coronae Borealis Stars II—Spectroscopic Classifications and Implications for the Rate of Low-mass White Dwarf Mergers

2024; Institute of Physics; Volume: 136; Issue: 8 Linguagem: Inglês

10.1088/1538-3873/ad6210

1538-3873

Viraj Karambelkar, M. M. Kasliwal, P. Tisserand, Shreya Anand, M. C. B. Ashley, Lars Bildsten, Geoffrey C. Clayton, Courtney C. Crawford, Kishalay De, Nicholas Earley, M. Hankins, Xander Hall, A. Lamberts, Ryan M. Lau, Dan McKenna, Anna Moore, E. O. Ofek, Roger M. Smith, Roberto Soria, Jamie Soon, Tony Travouillon,

Gamma-ray bursts and supernovae

Abstract We present results from a systematic infrared (IR) census of R Coronae Borealis (RCB) stars in the Milky Way, using data from the Palomar Gattini IR (PGIR) survey. RCB stars are dusty, erratic variable stars presumably formed from the merger of a He-core and a CO-core white dwarf (WD). PGIR is a 30 cm J -band telescope with a 25 deg 2 camera that surveys 18,000 deg 2 of the northern sky ( δ > −28°) at a cadence of 2 days. Using PGIR J- band lightcurves for ∼60 million stars together with mid-IR colors from WISE, we selected a sample of 530 candidate RCB stars. We obtained near-IR spectra for these candidates and identified 53 RCB stars in our sample. Accounting for our selection criteria, we find that there are a total of ≈ 350 − 100 + 150 RCB stars in the Milky Way. Assuming typical RCB lifetimes, this corresponds to an RCB formation rate of 0.8–5 × 10 −3 yr −1 , consistent with observational and theoretical estimates of the He-CO WD merger rate. We searched for quasi-periodic pulsations in the PGIR lightcurves of RCB stars and present pulsation periods for 16 RCB stars. We also examined high-cadenced TESS lightcurves for RCB and the chemically similar, but dustless hydrogen-deficient carbon (dLHdC) stars. We find that dLHdC stars show variations on timescales shorter than RCB stars, suggesting that they may have lower masses than RCB stars. Finally, we identified 3 new spectroscopically confirmed and 12 candidate Galactic DY Per type stars—believed to be colder cousins of RCB star—doubling the sample of Galactic DY Per type stars.