Census of R Coronae Borealis Stars. I. Infrared Light Curves from Palomar Gattini IR

Karambelkar, Viraj; Kasliwal, M. M.; Tisserand, Patrick; De, Kishalay; Anand, S.; Ashley, M. C. B.; Delacroix, Alex; Hankins, Matthew J.; Jencson, J.; Lau, Ryan M.; McKenna, Dan; Moore, Anna; Ofek, E. O.; Smith, Roger M.; Soria, Roberto; Soon, J.; Tinyanont, Samaporn; Travouillon, Tony; Yao, Yuhan

doi:10.3847/1538-4357/abe5aa

Cited by 13 publications

(40 citation statements)

References 64 publications

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“…In addition, we identified large amplitude regular/semi-regular variables using independent criteria based on known variable counterparts in archival Wide-field Infrared Survey Explorer (Mainzer et al 2011(Mainzer et al , 2014 images. These sources will be presented as separate publications focusing on R Coronae Borealis variables (Karambelkar et al 2021) and young stellar objects (Hankins et al 2020;M. Hankins et al 2021, in preparation).…”

Section: Confirmation and Follow-upmentioning

confidence: 99%

A Population of Heavily Reddened, Optically Missed Novae from Palomar Gattini-IR: Constraints on the Galactic Nova Rate

Kasliwal

Hankins

et al. 2021

ApJ

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The nova rate in the Milky Way remains largely uncertain, despite its vital importance in constraining models of Galactic chemical evolution as well as understanding progenitor channels for Type Ia supernovae. The rate has been previously estimated to be in the range of ≈10-300 yr −1 , either based on extrapolations from a handful of very bright optical novae or the nova rates in nearby galaxies; both methods are subject to debatable assumptions. The total discovery rate of optical novae remains much smaller (≈5-10 yr −1 ) than these estimates, even with the advent of all-sky optical time-domain surveys. Here, we present a systematic sample of 12 spectroscopically confirmed Galactic novae detected in the first 17 months of Palomar Gattini-IR (PGIR), a wide-field near-infrared time-domain survey. Operating in the J band (≈1.2 μm), which is significantly less affected by dust extinction compared to optical bands, the extinction distribution of the PGIR sample is highly skewed to a large extinction values (>50% of events obscured by A V  5 mag). Using recent estimates for the distribution of Galactic mass and dust, we show that the extinction distribution of the PGIR sample is commensurate with dust models. The PGIR extinction distribution is inconsistent with that reported in previous optical searches (null-hypothesis probability <0.01%), suggesting that a large population of highly obscured novae have been systematically missed in previous optical searches. We perform the first quantitative simulation of a 3π time-domain survey to estimate the Galactic nova rate using PGIR, and derive a rate of » -+ 43.7 8.719.5 yr −1 . Our results suggest that all-sky near-infrared timedomain surveys are well poised to uncover the Galactic nova population.

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Section: Confirmation and Follow-upmentioning

confidence: 99%

A Population of Heavily Reddened, Optically Missed Novae from Palomar Gattini-IR: Constraints on the Galactic Nova Rate

Kasliwal

Hankins

et al. 2021

ApJ

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“…The distances and G-band brightnesses reported by the GAIA survey (Gaia Collaboration et al 2016) for the first four dLHdC stars range respectively between 1 and 2 kpc, and between 6th and 9th magnitude. There was clearly room for progress in increasing their numbers, especially as an important successful effort has been made in the past 20 years to search for new RCB stars up to the distance of the Galactic Bulge (Zaniewski et al 2005;Tisserand et al 2008Tisserand et al , 2011Tisserand et al , 2013Shields et al 2019;Tisserand et al 2020;Karambelkar et al 2021) and in the Magellanic Clouds (Alcock et al 1996(Alcock et al , 2001Tisserand et al 2004Tisserand et al , 2009. The search for new dLHdC stars is motivated to understand their Galactic distribution and to test the first estimate of their total Galactic numbers made by (Tisserand et al 2020).…”

Section: Introductionmentioning

confidence: 99%

The dawn of a new era for dustless HdC stars withGaiaeDR3

Tisserand

Crawford

Clayton

et al. 2022

A&A

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Context. Decades after their discovery, only four hydrogen-deficient carbon (HdC) stars were known to have no circumstellar dust shell. This is in complete contrast to the ∼130 known Galactic HdC stars that are notorious for being heavy dust producers, i.e. the R Coronae Borealis (RCB) stars. Together they form a rare class of supergiant stars that are thought to originate from the merger of CO/He white dwarf (WD) binary systems, otherwise known as the double degenerate scenario. Aims. We searched for new dustless HdC (dLHdC) stars to understand their Galactic distribution, to estimate their total number in the Milky Way and to study their evolutionary link with RCB stars and extreme Helium stars, the final phase of HdC stars. Methods. We used primarily the 2MASS and GAIA eDR3 all-sky catalogues to select candidates that were then followed up spectroscopically. We studied the distribution of known and newly discovered stars in the HR diagram. Results. We discovered 27 new dLHdC stars, one new RCB star, and two new EHe stars. Surprisingly, 20 of the new dLHdC stars share a characteristic of the known dLHdC star HD 148839, having lower atmospheric hydrogen deficiencies. The uncovered population of dLHdC stars exhibit a Bulge-like distribution, like the RCB stars, but show multiple differences from those that indicate they are a different population of HdC stars following its own evolutionary sequence with a fainter luminosity and also a narrow range of effective temperatures, between 5000 and 8000 K. Not all the new dLHdC stars belong to that new population, as we found indication of a current low dust production activity around four of them: the warm F75, F152, C526 and the cold A166. Those could in fact be typical RCB stars passing through a transition time, going in or out of the RCB phase. Conclusions. For the first time we have evidence of a large range of absolute magnitude in the overall population of HdC stars, spanning more than 3 mag. In the favoured formation framework, this is explained by a large range in the initial total WD binary mass which leads to a series of evolutionary sequences with distinct maximum brightness and initial temperature. The cold Galactic RCB stars are also noticeably fainter than the Magellanic ones, possibly due to a difference in metallicity between the original population of stars resulting in different WD mass ratio. The unveiled population of dLHdC stars indicates that the ability to create dust could be linked to the initial total mass. In our Galaxy, there could be as many dLHdC stars as RCB stars.

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“…viraj@astro.caltech.edu 1 Historically, dLHdC stars were referred to as HdC stars. Here, we follow the updated nomenclature of Tisserand et al 2021. It has been relatively easier to identify RCB stars than dL-HdC stars owing to their spectacular photometric variations. There are 128 RCB stars known in the Milky Way, while only 5 Galactic dLHdC stars were known for the last four decades (Clayton 2012;Tisserand et al 2020;Karambelkar et al 2021).…”

Section: Introductionmentioning

confidence: 99%

“…Here, we follow the updated nomenclature of Tisserand et al 2021. It has been relatively easier to identify RCB stars than dL-HdC stars owing to their spectacular photometric variations. There are 128 RCB stars known in the Milky Way, while only 5 Galactic dLHdC stars were known for the last four decades (Clayton 2012;Tisserand et al 2020;Karambelkar et al 2021). However, the sample of Galactic dLHdC stars has more than quintupled in the last year with the discovery of 27 new dL-HdC stars (Tisserand et al 2021, submitted).…”

Section: Introductionmentioning

confidence: 99%

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R Coronae Borealis and dustless Hydrogen-deficient Carbon stars have different oxygen isotope ratios

Karambelkar¹,

Kasliwal²,

Tisserand³

et al. 2021

Preprint

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Context. R Coronae Borealis (RCB) and dustless Hydrogen-deficient Carbon (dLHdC) stars are believed to be remnants of low mass white dwarf mergers. These supergiant stars have peculiar hydrogen-deficient carbon-rich chemistries and stark overabundances of 18 O. RCB stars undergo dust formation episodes resulting in large-amplitude photometric variations that are not seen in dLHdC stars. Recently, the sample of known dLHdC stars in the Milky Way has more than quintupled with the discovery of 27 new dLHdC stars. Aims. It has been suggested that dLHdC stars have lower 16 O/ 18 O than RCB stars. We aim to compare the 16 O/ 18 O ratios for a large sample of dLHdC and RCB stars to conclusively examine this claim. Methods. We present medium resolution (R≈ 3000) near-infrared spectra of 20 newly discovered dLHdC stars. We also present medium resolution (R≈ 3000 − 8000) K-band spectra for 47 RCB stars. We measure the 16 O/ 18 O ratios of 7 dLHdC and 31 RCB stars that show 12 C 16 O and 12 C 18 O absorption bands, and present the largest sample of values of 16 O/ 18 O for dLHdC and RCB stars to date. Results. We find that six of the seven dLHdC stars have 16 O/ 18 O < 0.5, while 26 of the 31 RCB stars have 16 O/ 18 O > 1. We also confirm that unlike RCB stars, dLHdC stars do not show strong blueshifted (> 200 km s −1 ) He i 10833 Å absorption, suggesting the absence of strong, dust-driven winds around them. Conclusions. We conclude that most dLHdC stars have lower 16 O/ 18 O than most RCB stars. This confirms one of the first, longsuspected spectroscopic differences between RCB and dLHdC stars. Our results rule out the existing picture that RCB stars represent an evolved stage of dLHdC stars. Instead, we suggest that whether the white dwarf merger remnant is a dLHdC or RCB star depends on the mass ratios, masses and compositions of the merging white dwarfs.

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Census of R Coronae Borealis Stars. I. Infrared Light Curves from Palomar Gattini IR

Cited by 13 publications

References 64 publications

A Population of Heavily Reddened, Optically Missed Novae from Palomar Gattini-IR: Constraints on the Galactic Nova Rate

A Population of Heavily Reddened, Optically Missed Novae from Palomar Gattini-IR: Constraints on the Galactic Nova Rate

The dawn of a new era for dustless HdC stars withGaiaeDR3

R Coronae Borealis and dustless Hydrogen-deficient Carbon stars have different oxygen isotope ratios

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