J/PASP/136/H4201 R CrB stars spectroscopic classifications (Karambelkar+, 2024)
An infrared census of R Coronae Borealis stars.
II. Spectroscopic classifications
and Implications for the Rate of Low-mass White Dwarf Mergers.
Karambelkar V.R., Kasliwal M.M., Tisserand P., Anand S., Ashley M.C.B.,
Bildsten L., Clayton G.C., Crawford C.C., De K., Earley N.
<Publ. Astron. Soc. Pac. 136, 084201 (2024)>
=2024PASP..136h4201K 2024PASP..136h4201K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Photometry, infrared ; Spectra, infrared
Keywords: variable stars - R Coronae Borealis variable stars -
near infrared astronomy - white dwarf stars
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 30cm J-band telescope with a 25deg2 camera
that surveys 18000deg2 of the northern sky (DE>-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
RCB stars in the Milky Way. Assuming typical RCB lifetimes, this
corresponds to an RCB formation rate of 0.8-5x103yr-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.
Description:
In this paper, we presented results from a systematic infrared census
for RCB stars in the Milky Way. We selected RCB candidates using NIR
J-band lightcurves from PGIR, mid-IR colors from WISE and obtained
medium resolution NIR spectra for them. We identified 53 RCB stars
from our candidates.
We re-prioritize the WISE color-selected catalog of 2194 RCB
candidates from Tisserand et al. (2020A&A...635A..14T 2020A&A...635A..14T, Cat.
J/A+A/635/A14) using PGIR light-curves. First, we exclude 304
candidates that show large-amplitude periodic variations resembling
AGB stars and 23 candidates whose lightcurves resemble those of
RV-Tauri stars. Of the remaining candidates, we identify 177
candidates that show significant, non-periodic variations in their
lightcurves, 230 candidates that show no significant variations and
253 candidates where the lightcurve is ambiguous (i.e., shows some
variations that are not obviously periodic or large-amplitude). Using
the location of known RCBs and LPVs in the WISE and 2MASS color
diagrams, we further sub-divide Priorities A, B, C, and D into seven
color-based sub-categories. We prioritize categories A, 1-a, 2-a, and
3-a comprising 383 candidates in total for spectroscopic follow-up.
Table 1 lists the lightcurve and color priorities of all 2194
candidates. The classifications of all sources are listed in Table 2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table12.dat 40 2194 Classification table (table 1 and 2 of the paper)
lc/* . 1030 Individual light curves
sp/* . 456 Individual fits spectra
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See also:
IV/39 : TESS Input Catalog version 8.2 (TIC v8.2) (Paegert+, 2021)
J/A+A/635/A14 : New R Coronae Borealis stars (Tisserand+, 2020)
Byte-by-byte Description of file: table12.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- TOI [1/4175] TOI identifier
6- 16 F11.7 deg RAdeg Right ascension (J2000)
18- 28 F11.7 deg DEdeg Declination (J2000)
30 A1 --- lc-pri [A-G] Updated priorities of WISE-selected
candidates based on PGIR lightcurves
32- 34 A3 --- col-pri Spectroscopic classification of candidates
selected for followup (1)
36- 37 A2 --- LC [lc ] indicates light curve in lc subdirectory
39- 40 A2 --- SP [sp ] indicates fits spectrum in sp subdirectory
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Note (1): As discussed in Karambelkar et al. (2021ApJ...910..132K 2021ApJ...910..132K), RCB stars
are characterised by the following NIR spectral features:
1 : RCB stars show HeI (λ10830) emission or absorption. The RCB stars
undergoing a photometric minimum usually show HeI emission, however this
can be suppressed by the circumstellar dust. The stars at or rising to
maximum light show either a P-cygni profile or strong blueshifted
absorption (1-a, 1-b, 1-c).
2 : RCB stars in a minimum exhibit a mostly featureless, reddened spectrum with
emission lines of HeI, and sometimes Si i and C2 (2-a, 2-b)
3 : At maximum light, the spectra of RCB stars resemble F-G type supergiants,
with the absence or significantly weak hydrogen lines. Prominent features
include absorption lines of CI (most prominently at 1.0686 and 1.0688um),
FeI, SiI, and KI. Stars with cold effective (Teff≤6800K) temperatures
show molecular absorption features due to CN (1.0875, 1.0929, 1.0966, and
1.0999um), 12C16O (2.2935, 2.3227, 2.3525, 2.3829, 2.4141um) and
12C18O (3-a, 3-b).
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Byte-by-byte Description of file: lc/*
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Bytes Format Units Label Explanations
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1- 17 F17.9 d JD Julian date
19- 37 F19.16 mag mag Magnitude
39- 59 F21.19 mag e_mag Magnitude error
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History:
Copied at https://zenodo.org/records/12683155
References:
Karambelkar et al., Paper I 2021ApJ...910..132K 2021ApJ...910..132K
(End) Patricia Vannier [CDS] 04-Jun-2025