J/A+A/423/677 Oxygen abundances in chromospherically active stars (Morel+, 2004)
On the determination of oxygen abundances in chromospherically active stars.
Morel T., Micela G.
<Astron. Astrophys. 423, 677 (2004)>
=2004A&A...423..677M 2004A&A...423..677M
ADC_Keywords: Stars, variable ; Abundances
Keywords: stars: abundances - stars: activity - line: formation
Abstract:
We discuss oxygen abundances derived from [O I] 6300 and the
O I triplet in stars spanning a wide range in chromospheric activity
level, and show that these two indicators yield increasingly
discrepant results with higher chromospheric/coronal activity
measures. While the forbidden and permitted lines give fairly
consistent results for solar-type disk dwarfs, spuriously high
O I triplet abundances are observed in young Hyades and Pleiades
stars, as well as in individual components of RS CVn binaries (up to
1.8dex). The distinct behaviour of the [O I]-based abundances which
consistently remain near-solar suggests that this phenomenon mostly
results from large departures from LTE affecting the O I triplet at
high activity level that are currently unaccounted for, but also
possibly from a failure to adequately model the atmospheres of K-type
stars. These results suggest that some caution should be exercised
when interpreting oxygen abundances in active binaries or young open
cluster stars.
Description:
Table 2 presents the oxygen abundances derived for a sample of RS CVn
binaries and field subgiants from a curve-of-growth analysis using
FEROS spectra and plane-parallel, line-blanketed LTE Kurucz
atmospheric models. These observations are supplemented by literature
data for Pleiades, Hyades and field FG dwarfs. Two activity indices
derived from the Ca II H+K lines and the X-ray emission are also
given.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 101 100 Oxygen abundances and activity indices
refs.dat 108 26 References
--------------------------------------------------------------------------------
See also:
J/A+A/412/495 : Equivalent widths for 6 RS CVn systems (Morel+, 2003)
J/A+A/426/1007 : Abundances of 8 single-lined active binaries (Morel+, 2004)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Star Star name (1)
11- 14 I4 K Teff Effective temperature
16- 20 F5.2 [Sun] [Fe/H] Iron abundance (2)
22- 25 F4.2 [Sun] e_[Fe/H] Iron abundance uncertainty (2)
27- 31 F5.2 [Sun] [O/Fe]6300 ? Oxygen abundance yielded by [O I] 6300 (3)
33- 36 F4.2 [Sun] e_[O/Fe]6300 ? Uncertainty for the oxygen abundance
yielded by [O I] 6300 (3)
38- 42 F5.2 [Sun] [O/Fe]trip ? Oxygen abundance yielded by the O I-7774
triplet (3)
44- 47 F4.2 [Sun] e_[O/Fe]trip ? Uncertainty for the oxygen abundance
yielded by the O I-7774 triplet (3)
49 I1 --- r_[O/Fe]trip Reference code for the oxygen abundance data
(in refs.dat file)
51- 55 F5.2 [---] log(R'HK) ? Activity index derived from the Ca II H+K
lines (4)
57- 60 F4.2 [---] e_log(R'HK) ? Uncertainty for the activity index derived
from the Ca II H+K lines (4)
62- 63 I2 --- r_log(R'HK) ? Reference code for the R'HK data
(in refs.dat file)
65- 69 F5.2 [10-7W] logLX ? ROSAT X-ray luminosity (5)
71- 74 F4.2 [10-7W] e_logLX ? ROSAT X-ray luminosity uncertainty (5)
76- 80 F5.2 [---] logRX ? Activity index derived from the X-ray
data (5)
82- 85 F4.2 [---] e_logRX ? Uncertainty for the activity index derived
from the X-ray data (5)
87 I1 --- f_logRX ? X-ray detection flag (6)
89- 90 I2 --- r_logRX ? Reference code for the RX data
(in refs.dat file)
--------------------------------------------------------------------------------
Note (1): Identification for Pleiades and Hyades stars from Hertzsprung
(HII, 1947AnLei..19a...1H 1947AnLei..19a...1H) and van Bueren (VB, 1952BAN....11..385V 1952BAN....11..385V),
respectively.
Note (2): We quote the mean cluster metallicity of the Pleiades and Hyades
determined by King et al. (2000AJ....119..859K 2000AJ....119..859K) and Cayrel, Cayrel de
Strobel & Campbell (1985A&A...146..249C 1985A&A...146..249C), respectively.
Note (3): The [O/Fe] data from the literature were rescaled to our
adopted iron and oxygen solar abundances (log(εsolarFe)=7.67
and log(εsolarO)=8.93), and corrected for departures from
LTE in the case of the O I triplet (Gratton et al., 1999, Cat.
J/A+A/350/955). The EWs of [O I] 6300 have been corrected for the
contribution of Ni I 6300.339. We use the values of Schuler et al.
(2004ApJ...602L.117S 2004ApJ...602L.117S) derived without convective overshoot ('NOVER').
Note (4): For the RS CVn binaries and field subgiants, a blank indicates
that the Ca II H+K profiles were not filled in by emission. The errors
take into account the uncertainties in (V-R)0 and Teff.
Note (5): Except for the open cluster stars and HD 118238 (130pc;
Strassmeier et al., 1993A&A...268..671S 1993A&A...268..671S), all luminosities were
rescaled to the Hipparcos distances. For consistency with previous
X-ray observations, the bolometric luminosities were computed adopting
a mean distance to the Pleiades of 127pc (Crawford & Perry,
1976AJ.....81..419C 1976AJ.....81..419C). For the Hyades, we used the individual distances
of Schwan (1991, Cat. J/A+A/243/386). No reddening and a mean
extinction A(V)=0.12mag were assumed for the Hyades and Pleiades,
respectively (Nissen, 1988A&A...199..146N 1988A&A...199..146N). We used A(V)=0.26mag for
HII 676 (Stauffer et al., 1994, Cat. J/ApJS/91/625). The bolometric
corrections are taken from Flower (1996ApJ...469..355F 1996ApJ...469..355F). The errors
take into account the uncertainties in the X-ray counts and in the
distances.
Note (6): X-ray detection flags.
0 = X-ray detected, 1 = upper limit.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: refs.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Ref Reference code
4- 22 A19 --- BibCode BibCode
24- 51 A28 --- Aut Author's name
52-111 A60 --- Com Comments
--------------------------------------------------------------------------------
Acknowledgements: Thierry Morel
(End) Patricia Vannier [CDS] 17-Jun-2004