Asymmetry of Absorption Lines in the Solar and Procyon Sprecta

Atroshchenko, I. N.; Gadun, A. S.; Костик, Р. І.

doi:10.1007/978-94-009-0911-3_17

Cited by 7 publications

(6 citation statements)

References 3 publications

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“…2a) and those found by Steffen et al (1989 -their Fig. 2a) or between the present 2-D results and 3-D computations done by Atroshchenko & Gadun (1994 -their Fig. 1b); -Differences in the velocity may also result from different upper boundary conditions for velocities.…”

Section: Discussionsupporting

confidence: 75%

“…These models can be applied to the simulation of spectral lines and reproduce numerous observational properties of solar granulation such as spectral line widths, line shifts, and bisector shapes (Dravins et al 1981(Dravins et al , 1986Nordlund 1984;Steffen 1989Steffen , 1991Steffen & Freytag 1991;Gadun 1986;Atroshchenko & Gadun 1994;Gadun et al 1999;Asplund et al 2000b); the distribution of granule sizes (Wöhl & Nordlund 1985;Gadun & Vorob'yov 1996); the evolution of granules (Rast et al 1993;Rast 1995;Ploner et al 1998Ploner et al , 1999; the reversal of the thermal contrast between granules and intergranular lanes in the photosphere (Nordlund 1984;Steffen 1989;Gadun et al 1999); correlations between various atmospheric and spectral line parameters , and localized anomalies probably related to shocks (Solanki et al 1996;. They were used to determine abundance of chemical elements on the Sun (Atroshchenko & Gadun 1994;Gadun & Pavlenko 1997;Asplund et al 2000a;Asplund 2000).…”

Section: Introductionmentioning

confidence: 99%

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Size-dependent properties of simulated 2-D solar granulation

Gadun

Hanslmeier²,

Pikalov

et al. 2000

Astron. Astrophys. Suppl. Ser.

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Abstract. Two time-dependent sets of two-dimensional hydrodynamic models of solar granulation have been analyzed to obtain dependence of simulated thermal convection on the horizontal size of the convection cells. The two sets of models treat thermal convection either as fully non-stationary, multiscale convection (granular convection is a surface phenomenon) or as quasi-steadystate convection cells (they treat granular convection as a collection of deep-formed cells). The following results were obtained: 1) quasi-steady convection cells can be divided into 3 groups according to their properties and evolution, namely small-scale (up to L ∼ 900 km), intermediatescale (1000 − 1500 km) and large-scale (larger 1500 km) convection cells. For the first group thermal damping due to radiative exchange of energy, mostly in the horizontal direction, is very important. Large-scale cells build up a pressure excess, which can lead to their total fragmentation. Similar processes also acts on the fully non-stationary convection.2) The largest horizontal size of convection cells for which steady-state solutions can be obtained is about 1500 km. This corresponds to granules, i.e. the bright parts of the convection cells, with a diameter of about 1000 km.3) In addition to the zone of high convective instability associated with the partial ionization of hydrogen, we identify another layer harboring important dynamic processes in steady-state models. Just below the hydrogen-ionization layer pressure fluctuations and the acoustic flux are reduced. Steady-state models with reflecting lateral boundaries even exhibit an inversion of pressure fluctuations there. 4) From observational point of view the surface convection differs from steady-state deep treatment of thermal convection in the dependence of vertical granular velocities Send offprint requests to: A. Hanslmeier, e-mail: arnold.hanslmeier@kfunigraz.ac.at † deceased.on their sizes for small-scale inhomogeneous. However, they cannot be distinguished by the dependence of temperature or emergent intensity of brightness structures. 5) Both kinds of models demonstrate the inversion of density in subphotospheric layers. It is more pronounced in small-scale cells and inside hot upflows.6) The brightness of simulated granules linearly increases with their size for small granules and is approximately constant or even decreases slightly for larger granules. For intergranular lanes the simulations predict a decrease of their brightness with increasing size. It falls very rapidly for narrow lanes and remains unchanged for broader lanes. 7) A quantitative comparison of the brightness properties of simulated granulation with real observations shows that the strong size-dependence of the properties of the smallest simulated granules is not accessible to current observations due to their limited spatial resolution. The observed size dependences result rather from spatial smoothing and the granule-finding algorithm. We do not exclude, however, an influence of the limitations of the 2-D treatment...

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Section: Discussionsupporting

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Size-dependent properties of simulated 2-D solar granulation

Gadun

Hanslmeier²,

Pikalov

et al. 2000

Astron. Astrophys. Suppl. Ser.

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“…This difficulty is naturally avoided by numerical simulations which have come into use during the last decade as a tool to study stellar surface convection. Simulations in 3D have mostly been devoted to solar convection (Nordlund & Dravins 1990, Atroshchenko & Gadun 1994, Kim & Chan 1998, Stein & Nordlund 1998, while 2D simulations have been used for more extended computations over the HR diagram (cf. Freytag 1995 andFreytag et al 1996).…”

Section: Introductionmentioning

confidence: 99%

A-star envelopes: a test of local and non-local models of convection

Kupka

Montgomery

2002

Monthly Notices of the Royal Astronomical Society

110

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We present results of a fully non-local, compressible model of convection for A-star envelopes. This model quite naturally reproduces a variety of results from observations and numerical simulations which local models based on a mixing length do not. Our principal results, which are for models with Teff between 7200 K and 8500 K, are the following: First, the photospheric velocities and filling factors are in qualitative agreement with those derived from observations of line profiles of A-type stars. Second, the He II and H I convection zones are separated in terms of convective flux and thermal interaction, but joined in terms of the convective velocity field, in agreement with numerical simulations. In addition, we attempt to quantify the amount of overshooting in our models at the base of the He II convection zone.Comment: 5 pages with 4 figures (1a, 1b, 2 and 3), MNRAS (letter), in prin

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“…More recently, a new generation of time-dependent 2D and 3D hydrodynamical model atmospheres has become available and applied in stellar abundance analyses (e.g. Steffen et al 1995;Atroshchenko & Gadun 1994;Stein & Nordlund 1998;Asplund et al 1999Asplund et al , 2000aAsplund et al ,b, 2004aAsplund 2000Asplund , 2004Asplund & García Pérez 2001;Steffen & Holweger 2002;Vögler et al 2004). By simultaneously solving the standard hydrodynamical equations for conservation of mass, momentum and energy together with the 3D radiative transfer equation, both the radiative and convective energy transport are self-consistently computed.…”

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confidence: 99%

The solar chemical composition

2006

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Abstract.We review our current knowledge of the solar chemical composition as determined from photospheric absorption lines. In particular we describe the recent significant revisions of the solar abundances as a result of the application of a time-dependent, 3D hydrodynamical model of the solar atmosphere instead of 1D hydrostatic models. This has decreased the metal content in the solar convection zone by almost a factor of two compared with the widely used compilation by Anders & Grevesse (1989). While resolving a number of longstandings problems, the new 3D-based element abundances also pose serious challenges, most notably for helioseismology.

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Asymmetry of Absorption Lines in the Solar and Procyon Sprecta

Cited by 7 publications

References 3 publications

Size-dependent properties of simulated 2-D solar granulation

Size-dependent properties of simulated 2-D solar granulation

A-star envelopes: a test of local and non-local models of convection

The solar chemical composition

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