J/A+A/498/527 Calibration of Stromgren phot. for late-type stars (Onehag+, 2009)
Calibration of Stromgren uvby-Hbeta photometry for late-type stars -
a model atmosphere approach.
Onehag A., Gustafsson B., Eriksson K., Edvardsson B.
<Astron. Astrophys. 498, 527 (2009)>
=2009A&A...498..527O 2009A&A...498..527O
ADC_Keywords: Models, atmosphere ; Photometry, uvby, beta ; Abundances ;
Effective temperatures
Keywords: stars: fundamental parameters - techniques: photometric -
stars: atmospheres - stars: late-type
Abstract:
The use of model atmospheres for deriving stellar fundamental
parameters, such as Teff, log(g), and [Fe/H], will increase as we find
and explore extreme stellar populations where empirical calibrations
are not yet available. Moreover, calibrations for upcoming large
satellite missions of new spectrophotometric indices, similar to the
uvby-Hbeta system, will be needed. We aim to test the power of
theoretical calibrations based on a new generation of MARCS models
by comparisons with observational photometric data.
We calculated synthetic uvby-Hbeta colour indices from synthetic
spectra. A sample of 367 field stars, as well as stars in globular
clusters, is used for a direct comparison of the synthetic indices
versus empirical data and for scrutizing the possibilities of
theoretical calibrations for temperature, metallicity, and gravity.
We show that the temperature sensitivity of the synthetic (b-y) colour
is very close to its empirical counterpart, whereas the temperature
scale based upon Hbeta shows a slight offset. The theoretical
metallicity sensitivity of the m1 index (and for G-type stars its
combination with c1) is somewhat higher than the empirical one, based
upon spectroscopic determinations. The gravity sensitivity of the
synthetic c1 index shows satisfactory behaviour when compared to
observations of F stars. For stars cooler than the sun, a deviation is
significant in the c1-(b-y) diagram. The theoretical calibrations of
(b-y), (v-y), and c1 seem to work well for Pop II stars and lead to
effective temperatures for globular cluster stars supporting recent
claims that atomic diffusion occurs in stars near the turnoff point
of NGC 6397.
Synthetic colours of stellar atmospheres can indeed be used, in many
cases, to derive reliable fundamental stellar parameters. The
deviations seen when compared to observational data could be due to
incomplete linelists but are possibly also due to the effects of
assuming plane-parallel or spherical geometry and LTE.
Description:
The file "stellar.dat" contains coordinates (J2000) and identifiers of
the comparison stars. Furthermore the stellar parameters: effective
temperature (Teff), logarithmic surface gravity (logg), and
metallicity with respect to the sun ([Fe/H]) are listed. The reddening
corrected Stromgren indices c1 and m1 and the reddening corrected
Stromgren (b-y) colours are listed together with the Crawford/Mander
H-beta indices.
The file "model.dat" contains data calculated from the MARCS models.
The following model parameters are listed: effective temperature
(Teff), logarithmic surface gravity (logg), and metallicity with
respect to the sun ([Fe/H]). Synthetic Stromgren indices c1 and m1 and
synthetic Stromgren (b-y) colours are listed together with the
synthetic Crawford/Mander H-beta indices.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stellar.dat 119 367 The comparison samples
model.dat 50 168 The model colours
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Byte-by-byte Description of file: stellar.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 10 F4.1 s RAs [0/60] Right ascension (J2000)
12 A1 --- DE- Declination sign (J2000)
13- 14 I2 deg DEd Declination (J2000)
16- 17 I2 arcmin DEm Declination (J2000)
19- 20 I2 arcsec DEs [0/60] Declination (J2000)
23- 33 A11 --- Name Designation
35- 57 A23 --- OName Other designation
59- 62 I4 K Teff Effective temperature
66- 69 F4.2 [cm/s2] logg Logaritmic surface gravity
73- 77 F5.2 [-] [Fe/H] ? Metallicity
81- 85 F5.3 mag c0 Reddening corrected Stromgren c1 colour index
89- 93 F5.3 mag m0 Reddening corrected Stromgren m1 colour index
97-101 F5.3 mag (b-y)0 Reddening corrected Stromgren (b-y) colour index
105-109 F5.3 mag Hbeta ? Stromgren H-beta index
113-119 A7 --- Ref Source of reference from which photometric
and/or fundamental parameters were gathered (1)
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Note (1): References as follows:
1 = Schuster & Nissen, 1988A&AS...73..225S 1988A&AS...73..225S
2 = Hoffleit & Warren, 1991, Cat. V/50, Bright Star Catalogue
3 = Jonsell et al., 2005, Cat. J/A+A/440/321
4 = STIS
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Byte-by-byte Description of file: model.dat
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Bytes Format Units Label Explanations
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1- 4 I4 K Teff [4500,7000] Effective temperature
8- 11 F4.2 [cm/s2] logg [2.0,4.5] Logaritmic surface gravity
14- 18 F5.2 [-] [Fe/H] [-5.0,0.5] Metallicity
22- 26 F5.3 mag c1 Stromgren c1 colour index
30- 34 F5.3 mag m1 Stromgren m1 colour index
38- 42 F5.3 mag b-y Stromgren (b-y) colour index
46- 50 F5.3 mag Hbeta Stromgren H-beta colour index
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Acknowledgements:
Anna Onehag, annao(at)fysast.uu.se
(End) Anna Onehag [Uppsala University], Patricia Vannier [CDS] 09-Mar-2009