J/A+A/667/A84 R CrB and hydrogen-deficient carbon stars (Karambelkar+, 2022)
R Coronae Borealis and dustless hydrogen-deficient carbon stars likely have
different oxygen isotope ratios.
Karambelkar V., Kasliwal M.M., Tisserand P., Clayton G.C., Crawford C.L.,
Anand S.G., Geballe T.R., Montiel E.
<Astron. Astrophys. 667, A84 (2022)>
=2022A&A...667A..84K 2022A&A...667A..84K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, carbon ; Spectra, infrared
Keywords: stars: AGB and post-AGB - stars: carbon - circumstellar matter -
stars: late-type - supergiants - infrared: stars
Abstract:
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 18O. 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.
It has been suggested that dLHdC stars have lower 16O/18O than RCB
stars. We aim to compare the 16O/18O ratios for a large sample of
dLHdC and RCB stars to conclusively examine this claim.
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
16O/18O ratios of 7 dLHdC and 31 RCB stars that show 12C16O
and 12C18O absorption bands, and present the largest sample of
values of 16O/18O for dLHdC and RCB stars to date.
We find that six of the seven dLHdC stars have 16O/18O<0.5, while
26 of the 31 RCB stars have 16O/18O>1. We also confirm that unlike
RCB stars, dLHdC stars do not show strong blueshifted (>200km/s) HeI
10833Å absorption, suggesting the absence of strong, dust-driven
winds around them.
We conclude that most dLHdC stars have lower 16O/18O 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.
Description:
We present near-infrared spectra for 20 newly identified dustless
Hydrogen- deficient Carbon (dLHdC) stars, 4 previously known dLHdC
stars and 49 R Coronae Borealis (RCB) stars. The spectra suggest that
RCB and dLHdC stars have distinct oxygen isotope ratios.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
objects.dat 99 73 Names and coordinates of RCB and dLHdC star
sp/* . 73 *Individual spectra
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Note on sp/*: The lines prefaced with # specify the name and instrument
with which the spectra were collected.
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Byte-by-byte Description of file: objects.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name Name of star
25- 26 I2 h RAh Right Ascension (J2000)
28- 29 I2 min RAm Right Ascension (J2000)
31- 35 F5.2 s RAs Right Ascension (J2000)
37 A1 --- DE- Declination sign (J2000)
38- 39 I2 deg DEd Declination (J2000)
41- 42 I2 arcmin DEm Declination (J2000)
44- 48 F5.2 arcsec DEs Declination (J2000)
50- 54 A5 --- Class Classification (RCB or dLHdC)
56- 75 A20 --- Inst Name and instrument with which the spectra
were collected
77- 99 A23 --- FileName Name of the spectrum file in subdirectory sp
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Byte-by-byte Description of file (#): sp/*
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Bytes Format Units Label Explanations
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1- 8 F8.6 um lambda Observed wavelength in microns
10- 22 F13.7 --- Flux Normalized flux
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Acknowledgements:
Viraj Karambelkar, viraj(at)astro.caltech.edu
(End) Viraj Karambelkar [Caltech USA], Patricia Vannier [CDS] 24-Aug-2022