Libraries of synthetic stellar spectra – or are we building palaces upon sand?

Gustafsson, B.; Heiter, U.; Edvardsson, B.

doi:10.1017/s1743921307007429

Cited by 2 publications

(3 citation statements)

References 37 publications

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“…The multi-group opacities used by CO 5 BOLD are based on monochromatic opacities stemming from the MARCS stellar atmosphere package (Gustafsson et al 2007(Gustafsson et al , 2003 provided as a function of gas pressure and temperature with high wavelength resolution. For the calculation of the opacities, solar elemental abundances according to Grevesse & Sauval (1998) are assumed, with the exception of CNO for which values close to the recommendation of Asplund et al (2005) are adopted (specifically, A(C) = 8.41, A(N) = 7.80, A(O) = 8.67).…”

Section: Codes and Atmospheric Modelsmentioning

confidence: 99%

“…an ATLAS model computed by Fiorella Castelli 3 with version 9 of the ATLAS code and the solar abundances of Asplund et al (2005). With respect to other ATLAS solar models, this has been computed with an opacity distribution function explicitly computed for the solar chemical composition of Asplund et al (2005), a micro-turbulent velocity of 1 km s −1 , and a mixing-length parameter α MLT = 1.25; 2. a solar MARCS model 4 , also computed for a micro-turbulent velocity of 1 km s −1 , but with α MLT = 1.5 (Gustafsson et al 2003(Gustafsson et al , 2007; 3. the Holweger-Müller semi-empirical solar model (Holweger 1967;Holweger & Müller 1974); 4. an average 3D model denoted by 3D , generated by…”

Section: Codes and Atmospheric Modelsmentioning

confidence: 99%

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The photospheric solar oxygen project

Caffau¹,

Ludwig

Steffen

et al. 2008

A&A

267

305

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Context. The solar oxygen abundance has undergone a major downward revision in the past decade, the most noticeable one being the update including 3D hydrodynamical simulations to model the solar photosphere. Up to now, such an analysis has only been carried out by one group using one radiation-hydrodynamics code. Aims. We investigate the photospheric oxygen abundance considering lines from atomic transitions. We also consider the relationship between the solar model used and the resulting solar oxygen abundance, to understand whether the downward abundance revision is specifically related to 3D hydrodynamical effects. Methods. We performed a new determination of the solar photospheric oxygen abundance by analysing different high-resolution high signal-to-noise ratio atlases of the solar flux and disc-centre intensity, making use of the latest generation of CO5BOLD 3D solar model atmospheres. Results. We find 8.73 ≤ log (N O /N H ) + 12 ≤ 8.79. The lower and upper values represent extreme assumptions on the role of collisional excitation and ionisation by neutral hydrogen for the NLTE level populations of neutral oxygen. The error of our analysis is ± (0.04± 0.03) dex, the last being related to NLTE corrections, the first error to any other effect. The 3D "granulation effects" do not play a decisive role in lowering the oxygen abundance. Conclusions. Our recommended value is log (N O /N H ) = 8.76 ± 0.07, considering our present ignorance of the role of collisions with hydrogen atoms on the NLTE level populations of oxygen. The reasons for lower O abundances in the past are identified as (1) the lower equivalent widths adopted and (2) the choice of neglecting collisions with hydrogen atoms in the statistical equilibrium calculations for oxygen.

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Section: Codes and Atmospheric Modelsmentioning

confidence: 99%

Section: Codes and Atmospheric Modelsmentioning

confidence: 99%

The photospheric solar oxygen project

Caffau¹,

Ludwig

Steffen

et al. 2008

A&A

267

305

View full text Add to dashboard Cite

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“…The equation of state now includes Coulomb corrections due to low masses of these stars and the corresponding high density. We used MARCS models (Gustafsson et al 2003(Gustafsson et al , 2007(Gustafsson et al , 2008 1 for the atmosphere description. The treatment of convection makes use of a new modified routine (conv_a0) based on the classical mixing length theory (hereafter MLT).…”

Section: Modeling With Cesam2kmentioning

confidence: 99%

The radii of the nearby K5V and K7V stars 61 Cygni A & B

Kervella¹,

Mérand

Pichon

et al. 2008

A&A

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Context. The main sequence binary star 61 Cyg (K5V+K7V) is our nearest stellar neighbour in the northern hemisphere. This proximity makes it a particularly well suited system for very high accuracy interferometric radius measurements. Aims. Our goal is to constrain the poorly known evolutionary status and age of this bright binary star. Methods. We obtained high accuracy interferometric observations in the infrared K band, using the CHARA/FLUOR instrument. We then computed evolutionary models of 61 Cyg A & B with the CESAM2k code. As model constraints, we used a combination of observational parameters from classical observation methods (photometry, spectroscopy) as well as our new interferometric radii. Results. The measured limb darkened disk angular diameters are θ LD (A) = 1.775 ± 0.013 mas and θ LD (B) = 1.581 ± 0.022 mas, respectively for 61 Cyg A and B. Considering the high accuracy parallaxes available, these values translate into photospheric radii of R(A) = 0.665 ± 0.005 R and R(B) = 0.595 ± 0.008 R . The new radii constrain efficiently the physical parameters adopted for the modeling of both stars, allowing us to predict asteroseismic frequencies based on our best-fit models. Conclusions. The CESAM2k evolutionary models indicate an age around 6 Gyr and are compatible with small values of the mixing length parameter. The measurement of asteroseismic oscillation frequencies in 61 Cyg A & B would be of great value to improve the modeling of this important fiducial stellar system, in particular to better constrain the masses.

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Libraries of synthetic stellar spectra – or are we building palaces upon sand?

Cited by 2 publications

References 37 publications

The photospheric solar oxygen project

The photospheric solar oxygen project

The radii of the nearby K5V and K7V stars 61 Cygni A & B

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