J/ApJ/747/102 12C/13C ratio for 18 galactic R CrB stars (Hema+, 2012)
The galactic R Coronae Borealis stars: the C2 Swan bands, the carbon problem,
and the 12C/13C ratio.
Hema B.P., Pandey G., Lambert D.L.
<Astrophys. J., 747, 102 (2012)>
=2012ApJ...747..102H 2012ApJ...747..102H
ADC_Keywords: Abundances ; Atomic physics ; Stars, peculiar
Keywords: stars: abundances - stars: chemically peculiar - stars: evolution
Abstract:
Observed spectra of R Coronae Borealis (RCB) and hydrogen-deficient
carbon (HdC) stars are analyzed by synthesizing the C2 Swan bands
(1, 0), (0, 0), and (0, 1) using our detailed line list and the
Uppsala model atmospheres. The (0, 1) and (0, 0) C2 bands are used
to derive the 12C abundance, and the (1, 0) 12C13C band to
determine the 12C/13C ratios. The carbon abundance derived from
the C2 Swan bands is about the same for the adopted models
constructed with different carbon abundances over the range 8.5
(C/He=0.1%) to 10.5 (C/He=10%). Carbon abundances derived from C I
lines are about a factor of four lower than the carbon abundance of
the adopted model atmosphere over the same C/He interval, as reported
by Asplund et al., who dubbed the mismatch between adopted and derived
C abundance as the "carbon problem." In principle, the carbon
abundances obtained from C2 Swan bands and that assumed for the
model atmosphere can be equated for a particular choice of C/He that
varies from star to star. Then, the carbon problem for C2 bands is
eliminated. However, such C/He ratios are in general less than those
of the extreme helium stars, the seemingly natural relatives to the
RCB and HdC stars. A more likely solution to the C2 carbon problem
may lie in a modification of the model atmosphere's temperature
structure. The derived carbon abundances and the 12C/13C ratios
are discussed in light of the double degenerate and the final flash
scenarios.
Description:
High-resolution optical spectra of RCB/HdC stars at maximum light
were obtained from the W.J. McDonald Observatory and the Vainu
Bappu Observatory, from 1996 Jul 26 to 2010 May 27 (see table 1).
The spectra from the McDonald Observatory were obtained with the 2.7m
Harlan J. Smith Telescope and Tull coude cross-dispersed echelle
spectrograph at a resolving power of λ/dλ=60000. The
spectra from the Vainu Bappu Observatory were obtained with the 2.34m
Vainu Bappu Telescope (VBT) at a resolving power of about 30000.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 59 18 Log of the observations
table2.dat 43 1626 Sample lines for (1, 0) C2 Swan band
table4.dat 30 18 The Fe abundances for RCB and HdC stars
table7.dat 44 16 The adopted stellar parameters and the
12C/13C ratios for the analyzed stars
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See also:
J/ApJS/169/472 : Swan system of C2 (Tanabashi+, 2007)
J/AJ/134/1877 : Spectropolarimetry of R CrB in 1998-2003 (Kawabata+, 2007)
J/A+A/353/287 : The R CrB stars (Asplund+, 2000)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Star Star name
11- 21 A11 "YYYY/MMM/DD" Date Date of observation
22- 36 A15 --- ODate Other date(s) of observation
38- 42 F5.2 mag Vmag [6/12.8] Visual validated magnitude (AAVSO)
44- 55 A12 --- Obs Observatory
57- 59 I3 --- S/N [25/250] Signal to noise ratio per pixel of
the spectrum in the continuum near
the 4737Å 12C2 bandhead
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Band Band identification ((0,0), (0,1) or (1,0))
7- 16 A10 --- C2 The C2 identification (12C13C or 12C2)
18- 25 F8.3 0.1nm lambda [4692.34/5635.5] Wavelength λ in Å
27- 30 F4.1 --- J" [5/62] J value of lower level
32- 36 F5.3 eV chi [0.19/0.94] Lower excitation potential
38- 43 F6.3 [-] log(gf) [-0.985/0.474] Log of the oscillator strength
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Star Star name
11- 13 F3.1 [-] logE1 [5/7] logε(Fe) from the 4700Å region
15- 18 F4.2 [-] e_logE1 [0.1/0.3] Standard deviation
20- 21 I2 --- N1 [3/10] Number of lines used
23- 25 F3.1 [-] logE2 ? logε(Fe) from literature (1)
27 A1 --- l_logE3 Limit flag on logE3
28- 30 F3.1 [-] logE3 logε(Fe) from the 4744.4Å line,
assuming it to be entirely FeI
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Note (1): From Asplund et al. (2000, Cat. J/A+A/353/287) for RCB stars and from
Warner (1967MNRAS.137..119W 1967MNRAS.137..119W) for HdC stars.
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Star Star name
11- 14 I4 K Teff [5400/7000] Effective temperature
16- 18 F3.1 [cm/s2] logg Surface gravity
20- 22 F3.1 km/s Vt [4/8] Turbulence velocity
24 A1 --- l_Rat1 Limit flag on Rat1
25- 27 I3 --- Rat1 [3/400] 12C/13C ratio lower value
(or limit) from this work
28 A1 --- --- [-]
29- 31 I3 --- Rat1u ? 12C/13C ratio upper value
34 A1 --- l_Rat2 Limit flag on Rat2
35- 37 I3 --- Rat2 ? 12C/13C ratio lower value (or limit)
38 A1 --- --- [-]
39- 40 I2 --- Rat2u ? 12C/13C ratio upper value
42- 44 A3 --- r_Rat2 [bcde,] Reference(s) for Rat2 (2)
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Note (2): References as follows:
b = Cottrell & Lambert (1982ApJ...261..595C 1982ApJ...261..595C).
c = Rao & Lambert (2008MNRAS.384..477R 2008MNRAS.384..477R).
d = Climenhaga (1960AJ.....65Q..50C 1960AJ.....65Q..50C).
e = Fujita & Tsuji (1977PASJ...29..711F 1977PASJ...29..711F).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS), Emmanuelle Perret [CDS] 27-Sep-2013