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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
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 111 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) and van Bueren (VB, 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) and Cayrel, Cayrel de Strobel & Campbell (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) 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), 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). 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). 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). 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
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