The solar ultraviolet continuum

Dragon, J. N.; Mutschlecner, J. P.

doi:10.1086/158194

Cited by 22 publications

(16 citation statements)

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“…Neutral metals C, N, O, Mg, Al, Si, Ca and Fe are included. While we use hydrogenic approximations following Dragon & Mutschlecner (1980) for the calculations of the bound-free cross-sections of the elements C, N, O, Mg, Al, Si and Ca, we use the more recent calculations of Bautista (1997) to account for Fe I. Figure 5 shows the differences of simple hydrogenic approximations with the detailed calculations of Bautista (1997) for 4 selected levels.…”

Section: Continuous Opacitymentioning

confidence: 99%

MAFAGS-OS: New opacity sampling model atmospheres for A, F and G stars

Grupp

2004

A&A

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Abstract. We present a new opacity sampling model atmosphere code, named MAFAGS-OS. This code, designed for stars reaching from A0 down to G9 on a solar and metal poor main sequence and up to an evolutionary stage represented by the turnoff is introduced in its basic input physics and modelling techniques. Fe I bound-free cross-sections of Bautista (1997) are used and convection is treated according to Canuto & Mazzitelli (1991). An α cm -parameter for the efficiency of convection of 0.82 is used as determined by Bernkopf (1998) from stellar evolution requirements. Within the process of opacity sampling, special attention is drawn to the matter of line selection. We show that a selection criterion, in which lines are chosen by their opacity weighted relative to the continuous background opacity, is useful and valid. The solar model calculated using this new code is shown to fit the measured solar flux distribution. It is also tested against the measured solar colours and leads to U − B = 0.21 and B − V = 0.64, in good agreement with observation. Comparison with measured centre-to-limb continuum data show only small improvement with respect to opacity-sampling type model atmospheres. This is the first of a series of 2 papers. Paper II will deal with the matter of temperature determination using Balmer lines and the infrared-flux method; furthermore it will present three "standard" stars analysed using this new model.

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Section: Continuous Opacitymentioning

confidence: 99%

MAFAGS-OS: New opacity sampling model atmospheres for A, F and G stars

Grupp

2004

A&A

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“…Houdashelt et al (2000) estimated that if Dragon & Mutschlecner (1980) Fe I cross sections used in the MARCS model atmospheres (Gustafsson et al 1975) were replaced by the Bautista (1997) cross sections the solar continuous flux would be reduced by 15% in the near ultraviolet. That would imply systematic errors in models for F, G, and K stars.…”

Section: Introductionmentioning

confidence: 99%

“…That would imply systematic errors in models for F, G, and K stars. As a consequence, since ATLAS9 (Kurucz 1993a) uses an approximation to the same Dragon & Mutschlecner (1980) opacities, there should also be similar systematic errors in ATLAS9 models that required this investigation. Bound-free Fe I cross sections computed by Bautista (1997) in the framework of the IRON Project were used to generate the continuous Fe I absorption coefficient.…”

Section: Introductionmentioning

confidence: 99%

“…Bautista (1997), in the framework of the Iron Project, performed large-scale close coupling calculations using the R-matrix method and obtained Fe I photoionization cross sections which incorporate numerous autoionization lines with complex structures. Houdashelt et al (2000) estimated that if the Fe I cross sections from Dragon & Mutschlecner (1980), included in the MARCS model atmospheres (Gustafsson et al 1975) were replaced by the Bautista (1997) cross sections, the solar continuous flux would be reduced by 15% in the near ultraviolet around 3100 Å. As a consequence, this would imply systematic errors in the current models for F, G, and K stars which could be removed once different Fe I photoionization cross section are used in the models.…”

Section: Introductionmentioning

confidence: 99%

“…We used in this study Kurucz's codes, but the results would be the same when other model atmospheres programs employing Fe I continuous opacity from Dragon & Mutschlecner (1980) and line opacity from Kurucz (1994) are used.…”

Section: Introductionmentioning

confidence: 99%

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Is missing Fe I opacity in stellar atmospheres a significant problem?

Castelli

Kurucz²

2004

A&A

782

951

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Abstract.We present an empirical model-atmosphere investigation of missing Fe I opacity. Houdashelt et al. (2000) estimated that if Dragon & Mutschlecner (1980) Fe I cross sections used in the MARCS model atmospheres (Gustafsson et al. 1975) were replaced by the Bautista (1997) cross sections the solar continuous flux would be reduced by 15% in the near ultraviolet. That would imply systematic errors in models for F, G, and K stars. As a consequence, since ATLAS9 (Kurucz 1993a) uses an approximation to the same Dragon & Mutschlecner (1980) opacities, there should also be similar systematic errors in ATLAS9 models that required this investigation. Bound-free Fe I cross sections computed by Bautista (1997) in the framework of the IRON Project were used to generate the continuous Fe I absorption coefficient. It was incorporated in the Kurucz (1993a) ATLAS9 code, in place of that currently used, which is based on approximate cross sections by Kurucz. By combining Opacity Distribution Functions (ODFs) computed without the contribution of Fe I autoionization lines with the new Fe I absorption coefficient which is crowded with autoionization resonances, we obtained solar metallicity model atmospheres and energy distributions for several combinations of T eff and log g. The comparison of these models with the standard ATLAS9 models has shown that there are no differences in the T -τ Ross relations, while there are some changes in the energy distributions for T eff ≤ 7000 K, but limited to small wavelength regions around 2150 Å, where Kurucz has less opacity, and 3350 Å, where Bautista has less opacity. The differences are of the order of 25% and less than 10%, respectively. That around 2150 Å disappears for T eff ≤ 5500 K owing to the fall of the emergent flux at these wavelengths in cool stars. This behaviour is independent of the gravity. The explanation is that our line list actually has more autoionizing opacity than Bautista's but it is treated as bound-bound line opacity rather than as bound-free opacity.

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4.3.4.8 Continuous opacity in stellar atmospheres

Baschek¹,

Scholz²

Stars and Star Clusters

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The solar ultraviolet continuum

Cited by 22 publications

References 0 publications

MAFAGS-OS: New opacity sampling model atmospheres for A, F and G stars

MAFAGS-OS: New opacity sampling model atmospheres for A, F and G stars

Is missing Fe I opacity in stellar atmospheres a significant problem?

4.3.4.8 Continuous opacity in stellar atmospheres

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