Census of R Coronae Borealis stars I: Infrared light curves from Palomar Gattini IR

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Viraj R. Karambelkar (1), Mansi M. Kasliwal (1), Patrick Tisserand (2), Kishalay De (1), Shreya Anand (1), Michael C. B. Ashley (3), Alex Delacroix (4), Matthew Hankins (5), Jacob E. Jencson (6), Ryan M. Lau (7), Dan McKenna (4), Anna Moore (8), Eran O. Ofek (9), Roger M. Smith (4), Roberto Soria (10, 11), Jamie Soon (8), Samaporn Tinyanont (12), Tony Travouillon (8), Yuhan Yao (1) ((1) California Institute of Technology, (2) Institut d'Astrophysique de Paris (3) University of New South Wales, (4) Caltech Optical Observatories, (5) Arkansas Tech University, (6) University of Arizona, (7) Japan Aerospace Exploration Agency, (8) Australian National University, (9) Weizmann Institute of Science, (10) University of the Chinese Academy of Sciences, (11) The University of Sydney, (12) University of California Santa Cruz)

We are undertaking the first systematic infrared (IR) census of R Coronae Borealis (RCB) stars in the Milky Way, beginning with IR light curves from the Palomar Gattini IR (PGIR) survey. PGIR is a 30 cm J-band telescope with a 25 deg2 camera that is surveying 18000 deg2 of the northern sky (δ>−28o) at a cadence of 2 days. We present PGIR light curves for 922 RCB candidates selected from a mid-IR color-based catalog (Tisserand et al. 2020). Of these 922, 149 are promising RCB candidates as they show pulsations or declines similar to RCB stars. Majority of the candidates that are not RCB stars are either long period variables (LPVs) or RV-Tauri stars. We identify IR color-based criteria to better distinguish between RCB stars and LPVs. As part of a pilot spectroscopic run, we obtained NIR spectra for 26 out of the 149 promising candidates and spectroscopically confirm 11 new RCB stars. We detect strong He I λ10830 features in spectra of all RCB stars, likely originating within high velocity (200-400 km-s−1) winds in their atmospheres. 9 of these RCB stars show 12C16O and 12C18O molecular absorption features, suggesting that they are formed through a white dwarf merger. We detect quasi-periodic pulsations in the light curves of 5 RCB stars. The periods range between 30-125 days and likely originate from the strange-mode instability in these stars. Our pilot run results motivate a dedicated IR spectroscopic campaign to classify all RCB candidates.


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