J/A+A/667/A83 Hydrogen-deficient Carbon stars spectra (Tisserand+, 2022)
The dawn of a new era for dustless HdC stars with GAIA eDR3.
Tisserand P., Crawford C.L., Clayton G.C., Ruiter A.J., Karambelkar V.,
Bessell M.S., Seitenzahl I.R., Kasliwal M.M., Soon J., Travouillon T.
<Astron. Astrophys. 667, A83 (2022)>
=2022A&A...667A..83T 2022A&A...667A..83T (SIMBAD/NED BibCode)
ADC_Keywords: Infrared sources ; Stars, late-type ; Stars, carbon ;
Stars, peculiar
Keywords: methods: observational - stars: carbon - stars: chemically peculiar -
supergiants - stars: evolution - white dwarfs
Abstract:
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, that is 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.
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 (EHe) stars, the final phase of HdC stars.
We primarily used 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
Hertzsprung-Russell diagram.
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 exhibits a
bulge-like distribution, like the RCB stars, but show multiple
differences from RCB stars that indicate that they are a different
population of HdC stars. This population follows its own evolutionary
sequence with a fainter luminosity and also a narrow range of
effective temperatures, between 5000 and 8000K. Not all the new dLHdC
stars belong to this new population, as we found an indication of a
current low dust production activity around 4 of them: the warm F75,
F152, and C526, and the cold A166. They might be typical RCB stars
passing through a transition time, entering or leaving the RCB phase.
For the first time, we have evidence of a wide range of absolute
magnitudes in the overall population of HdC stars, spanning more than
3mag. In the favoured formation framework, this is explained by a
wide 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 RCB stars, possibly due to a difference in
metallicity between the original population of stars, resulting in a
different WD mass ratio. The unveiled population of dLHdC stars
indicates that the ability to create dust might be linked to the
initial total mass. In our Galaxy, there could be as many dLHdC stars
as RCB stars.
Description:
The visible spectra of hydrogen-deficient carbon rich stars (HdC)
presented in figures 5, 6, 7 and 9 of the paper are available in FITS
format. It corresponds to 32 dustless HdC (dLHdC) stars, 4 R Coronae
Borealis (RCB) and 3 extreme helium (eHe) stars. Their name and
coordinates are listed in table 2.
All spectra were taken with the Wide Field Spectrograph (WiFeS)
instrument (Dopita et al., 2007Ap&SS.310..255D 2007Ap&SS.310..255D) attached to the 2.3m
telescope of the Australian National University at Siding Spring
Observatory (SSO). The visible wavelength interval is divided by a
dichroic at around 600nm, feeding two essentially similar
spectrographs. The spectra have a two-pixel resolution of 2 angstroms
(R∼3000) and wide wavelength coverage, from 340 to 960nm. The
provided spectra are in FITS format. There are two per stars,
respectively for the blue and the red parts, expect for the 5 HD stars
and PV Tel, whose spectra are divided in four parts as they were
observed in 2010, when four distinct amplifiers composed the reading
electronic assembly. The spectra of all newly discovered HdC stars
were observed in 2021 and were reduced using the PyWiFeS data
reduction pipeline (Childress et al., 2014Ap&SS.349..617C 2014Ap&SS.349..617C). The oxygen
telluric lines around 687 and 760nm are not well removed for these
spectra and some emissions like features are visible instead. The
corresponding wavelength range should not be consider.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 116 39 Newly discovered HdC and EHe stars and
other stars with spectra
list.dat 153 90 List of fits spectra
fits/* . 90 Individual fits spectra
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See also:
J/A+A/667/A83 : Peculiar Hydrogen-deficient Carbon stars (Crawford +, 2022)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 A1 --- Type [ABCDE] Type of stars (1)
3- 7 A5 --- Star New star name
9- 24 A16 --- 2MASS 2MASS name
26- 37 A12 --- OName Other name
38- 39 I2 --- r_OName ? Reference for OName (2)
41- 42 I2 h RAh Right ascension (J2000)
44- 45 I2 min RAm Right ascension (J2000)
47- 51 F5.2 s RAs Right ascension (J2000)
53 A1 --- DE- Declination sign (J2000)
54- 55 I2 deg DEd Declination (J2000)
57- 58 I2 arcmin DEm Declination (J2000)
60- 64 F5.2 arcsec DEs Declination (J2000)
66- 70 F5.2 --- S/N ? Gaia parallax S/N
72- 76 F5.2 kpc Dist Distance From Bailer-Jones et al.
(2021AJ....161..147B 2021AJ....161..147B, Cat. I/352)
78- 82 F5.2 kpc E_Dist Distance error (upper value)
83- 87 F5.2 kpc e_Dist Distance error (lower value)
89- 93 F5.2 mag Gmag Gaia G magnitude
95- 98 F4.2 mag BP-RP Gaia BP-RP colour index
100-103 F4.2 mag E(B-V) ? Reddening from Schlafly & Finkbeiner
(2011ApJ...737..103S 2011ApJ...737..103S)
105-116 A12 --- Name Name as in list.dat file
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Note (1): Types as follows:
A = Known Galactic dLHdC stars
B = New Galactic dLHdC stars
C = New Galactic RCB star
D = New Galactic EHe stars
E = Stars with spectra, not in original table2
Note (2): References as follows:
1 = Stephenson (1973, Cat. III/43),
Alksnis et al. (2001BaltA..10....1A 2001BaltA..10....1A, Cat. III/227);
2 = Stock & Wroblewski (1972POAN....2...59S 1972POAN....2...59S)
3 = The "Cordoba Durchmusterung" catalogue (1932, Cat. I/114/)
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Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Name Star name
16- 19 I4 --- Nx Number of pixels along X-axis
21- 41 A21 "datime" Obs.date Observation date
43- 49 F7.2 0.1nm blambda Lower value of wavelength interval
51- 57 F7.2 0.1nm Blambda Upper value of wavelength interval
59- 66 F8.6 0.1nm dlambda Wavelength resolution
68- 69 I2 Kibyte size Size of FITS file
71-122 A52 --- FileName Name of FITS file, in subdirectory fits
124-153 A30 --- Title Title of the FITS file
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Acknowledgements:
Patrick Tisserand, tisserand(at)iap.fr
References:
Dopita et al., 2007Ap&SS.310..255D 2007Ap&SS.310..255D (The Wide Field Spectrograph (WiFeS))
Childress et al., 2014Ap&SS.349..617C 2014Ap&SS.349..617C (PyWiFeS: a rapid data reduction
pipeline for the Wide Field Spectrograph (WiFeS))
(End) Patricia Vannier [CDS] 13-May-2022