J/A+A/457/651 Abundance of nine beta Cephei stars (Morel+, 2006)
Abundance analysis of prime B-type targets for asteroseismology
I. Nitrogen excess in slowly-rotating beta Cephei stars.
Morel T., Butler K., Aerts C., Neiner C., Briquet M.
<Astron. Astrophys. 457, 651 (2006)>
=2006A&A...457..651M 2006A&A...457..651M
ADC_Keywords: Stars, early-type ; Abundances
Keywords: stars: early-type - stars: fundamental parameters -
stars: abundances - stars: atmospheres - stars: oscillations
Abstract:
Seismic modelling of the beta Cephei stars promises major advances in
our understanding of the physics of early B-type stars on (or close
to) the main sequence. However, a precise knowledge of their physical
parameters and metallicity is a prerequisite for correct mode
identification and inferences regarding their internal structure. Here
we present the results of a detailed NLTE abundance study of nine
prime targets for theoretical modelling: gamma Peg, delta Cet, nu Eri,
beta CMa, xi1 CMa, V836 Cen, V2052 Oph, beta Cep and DD (12) Lac. The
following chemical elements are considered: He, C, N, O, Mg, Al, Si, S
and Fe. Our abundance analysis is based on a large number of
time-resolved, high-resolution optical spectra covering in most cases
the entire oscillation cycle of the stars.
Description:
The equivalent widths (EWs) were measured on high-resolution spectra
obtained with various echelle spectrographs (see Table 2 of paper for
further details). Our EWs are systematically larger than the values
quoted by Gies & Lambert (1992ApJ...387..673G 1992ApJ...387..673G) for the seven stars in
common, but a similar trend is evident when comparing their values
with previous measurements in the literature (see their Fig.4). This
is likely to result from their use of Gaussian fitting instead of the
direct integration used in our case. The same conclusion holds for the
EWs of xi1 CMa presented by Hambly et al. (1996MNRAS.278..811H 1996MNRAS.278..811H).
Objects:
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RA (2000) DE Designation(s) (Column)
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00 13 14.2 +15 11 01 gam Peg = HD 886 (EWgamPeg)
02 39 29.0 +00 19 43 del Cet = HD 16582 (EWdelCet)
04 36 19.1 -03 21 09 nu Eri = HD 29248 (EWnuEri)
06 22 42.0 -17 57 21 bet CMa = HD 44743 (EWbetCMa)
06 31 51.4 -23 25 06 xi1 CMa = HD 46328 (EWxi1CMamax)
06 31 51.4 -23 25 06 xi1 CMa = HD 46328 (EWxi1CMamin)
14 46 25.8 -37 13 20 V836 Cen = HD 129929 (EWV836Cen)
17 56 18.4 +00 40 13 V2052 Oph = HD 163472 (EWV2052Oph)
21 28 39.6 +70 33 39 bet Cep = HD 205021 (EWbetCep)
22 41 28.7 +40 13 32 12 Lac = HD 214993 (EW12Lac)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 84 184 Equivalent width measurements
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Ion Ion designation
8- 14 F7.2 0.1nm Lambda Mean wavelength of the spectral feature
16- 21 F6.1 0.1pm EWgamPeg ? Equivalent width for gamma Peg (1)
23- 28 F6.1 0.1pm EWdelCet ? Equivalent width for delta Cet (1)
30- 35 F6.1 0.1pm EWnuEri ? Equivalent width for nu Eri (1)
37- 42 F6.1 0.1pm EWbetCMa ? Equivalent width for beta CMa (1)
44- 49 F6.1 0.1pm EWxi1CMamax ? Equivalent width for xi1 CMa,
maximum value (1)(2)
51- 56 F6.1 0.1pm EWxi1CMamin ? Equivalent width for xi1 CMa,
minimum value (1)(2)
58- 63 F6.1 0.1pm EWV836Cen ? Equivalent width for V836 Cen (1)
65- 70 F6.1 0.1pm EWV2052Oph ? Equivalent width for V2052 Oph (1)(3)
72- 77 F6.1 0.1pm EWbetCep ? Equivalent width for beta Cep (1)
79- 84 F6.1 0.1pm EW12Lac ? Equivalent width for DD (12) Lac (1)
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Note (1): A blank may have various causes: the equivalent width was not
reliably measurable (spectral features lying in the wings of the
Balmer and diffuse He I lines were avoided); the line fell into
echelle inter-order gaps; was considered blended for the relevant
temperature range; or yielded a discrepant abundance. The latter point
notably applies to the C II 4267 line which is notoriously known to
yield spuriously low abundances (e.g. Lennon et al.,
2003A&A...398..455L 2003A&A...398..455L, although Nieva & Przybilla (2006ApJ...639L..39N 2006ApJ...639L..39N)
appear to have recently solved this problem).
Note (2): EW(xi1Cma)max and EW(xi1Cma)min are measured in the mean
spectra calculated for two phase intervals of width Delta_phi=0.1
corresponding to maximum and minimum EWs of the Si III lines,
respectively.
Note (3): The EW of the Mg II 4481.20 line has been corrected for the
contribution of Al III 4479.93 estimated from spectral synthesis.
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Acknowledgements: Thierry Morel, thierry(at)ster.kuleuven.be
(End) Patricia Vannier [CDS] 13-Jul-2006