B. The Solar Atmospheric Convection Zone

1967 ◽  
Vol 28 ◽  
pp. 347-404 ◽  
Author(s):  
Edward A. Spiegel ◽  
Karl-Heinz Böhm
Keyword(s):  
Convective Instability ◽  
Convection Zone ◽  
Physical Structure ◽  
Velocity Fields ◽  
Stellar Atmospheres ◽  
Solar Photosphere ◽  
Theoretical Problem ◽  
General Area ◽  
Physical Insight ◽  
Made In

Observational progress has, in the last decade, greatly surpassed theoretical progress in our study of the non-thermal velocity fields in the solar photosphere and chromosphere. This differential progress has not been simply a matter of filling in details. Attempted formulation of the theoretical problem of the velocity fields arising from convective instability in stellar atmospheres has resulted in no really new conceptual developments, nor large clarifications in approach, to match the observational ones just summarized by Noyes. Discussion of the problem at Varenna consisted mainly in the expression by aerodynamicists of severe reservations on the likelihood of gaining deep physical insight, or reliable numerical results, from the mixing-length approach generally used in astrophysics, with essentially no suggestions of a better approach. What progress that has been made in the general area of convective problems similar to those of interest in stellar atmospheres lies in the exploration of the physical structure of simplified convective configurations, often by exploration of various intuitive approaches.

scholarly journals The Solar Hydrogen Convection Zone and its Direct Influence on the Photosphere

1966 ◽  
Vol 12 (2) ◽  
pp. 539-542
Author(s):  
E. A. Spiegel
Keyword(s):  
Solar Atmosphere ◽  
Convection Zone ◽  
Stellar Atmospheres ◽  
Oscillatory Motion ◽  
Solar Photosphere ◽  
The Sun ◽  
Direct Influence ◽  
Solar Hydrogen

The discovery of oscillatory motion in the solar photosphere and of the ‘super-granulation’ in the chromosphere has changed our ideas about the hydrodynamics of the solar atmosphere considerably. In this Joint Discussion we shall mainly consider the theoretical implications of this change. As the ultimate aim is an understanding of the hydrodynamics in all stellar atmospheres—not only in the Sun, some discussion of other stellar atmospheres will be included.

scholarly journals The Magnetic and Velocity Fields and Brightness in the Solar Atmosphere

1971 ◽  
Vol 43 ◽  
pp. 274-278 ◽  
Author(s):  
S. I. Gopasyuk ◽  
T. T. Tsap
Keyword(s):  
Active Regions ◽  
Velocity Fields ◽  
Spectral Lines ◽  
Line Of Sight ◽  
Solar Photosphere ◽  
Zero Line ◽  
Isotropic Distribution ◽  
The Mean ◽  
Different Levels ◽  
Made In

Simultaneous observations of the magnetic fields, the line-of-sight velocities and brightness were made in active and quiet regions with the Crimean double-magnetograph in the following lines: Hα, K3 Ca II, Hβ, Hγ, Hδ, MgI λ 5184 Å, CaI λ 4227 Å, D1 NaI, BaII λ 4554 Å, CaI λ 6103 Å, FeI λ 5250 Å.It is shown, that in the active regions the horizontal velocity is larger than the vertical one.The mean velocities in the quiet solar photosphere have an isotropic distribution (Gopasyuk and Kalman, 1971).The mean vertical velocities increase exponentially with height in active and quiet regions.The correlation between velocities at different levels in active and quiet regions decreases with the distance between the levels of the formation of spectral lines, and it disappears for the velocities recorded in λ 6103 Å and Hβ, for λ 5184 and Hα lines in active regions and for the velocities recorded in λ 5250 Å and Hα lines in quiet regions.The position of the maximal field strength within a magnetic hill coincides statistically with the zero line of the line-of-sight velocities for active as well as for quiet regions.

Velocity fields in stellar atmospheres and the concept of microturbulence

1973 ◽  
Vol 15 ◽  
pp. 39-60 ◽  
Author(s):  
Gordon Worrall ◽  
Alistair M. Wilson
Keyword(s):  
Velocity Fields ◽  
Stellar Atmospheres

scholarly journals FBILI method for the two-level atom line formation in media with low velocity fields

2014 ◽  
pp. 53-67
Author(s):  
I. Pirkovic ◽  
O. Atanackovic
Keyword(s):  
Finite Thickness ◽  
Velocity Fields ◽  
Stellar Atmospheres ◽  
Benchmark Problems ◽  
Line Formation ◽  
Convergence Properties ◽  
Low Velocity ◽  
Level Atom ◽  
Line Transfer ◽  
Transfer Problems

In this paper we generalized the fast convergent Forth-and-Back Implicit Lambda Iteration (FBILI) method to the solution of the two-level atom line transfer problems in media with low velocity fields using the observer?s reference frame. In order to test the accuracy and the convergence properties of the method we solved several astrophysically important benchmark problems of the NLTE line formation: in a plan-parallel differentially expanding medium of finite thickness, and in spherically symmetric stellar atmospheres, both static and expanding. We compared our solutions with those obtained by other authors using different numerical methods.

ADDITIONAL HEAT FLOW DETERMINATIONS IN THE AREA OF MOULD BAY, ARCTIC CANADA

1966 ◽  
Vol 3 (2) ◽  
pp. 237-246 ◽  
Author(s):  
W. S. B. Paterson ◽  
L. K. Law
Keyword(s):  
Heat Flow ◽  
Canadian Arctic ◽  
The Arctic ◽  
Canadian Arctic Archipelago ◽  
General Area ◽  
Geothermal Heat ◽  
Field Methods ◽  
The Mean ◽  
Water Depths ◽  
Made In

Seven determinations of geothermal heat flow were made in the general area of southern Prince Patrick Island in the Canadian Arctic Archipelago. Measurements were made from sea ice in water depths of between 200 and 600 m. The mean heat flow for the two stations on the continental shelf in the Arctic Ocean was 0.46 ± 0.08 μcal cm−2 s−1. The mean heat flow for the five stations in the channels to the east of Mould Bay was 1.46 ± 0.16 μcal cm−2 s−1. The instrument and field methods are described. Errors due to the instrument and to the environment are discussed.

Asymptotic Methods in the Theory of Non-linear Convection

1971 ◽  
Vol 2 (1) ◽  
pp. 45-46
Author(s):  
R. Van Der Borght
Keyword(s):  
Rayleigh Number ◽  
Numerical Integration ◽  
Convection Zone ◽  
Asymptotic Methods ◽  
Basic System ◽  
System Of Differential Equations ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
A Value ◽  
Made In

The effective Rayleigh number, in the solar convection zone, soon reaches a value of the order of 106 and, although considerable progress has been made in the numerical integration of the basic system of differential equations at high Rayleigh number, it is of interest to investigate more fully the application of asymptotic methods to such a problem.

scholarly journals Nucleation and Grain Growth in Interstellar Space

1965 ◽  
Vol 7 ◽  
pp. 191-206
Author(s):  
Bertram Donn
Keyword(s):  
Grain Growth ◽  
Chemical Reactions ◽  
Low Temperatures ◽  
Stellar Atmospheres ◽  
Interstellar Space ◽  
Considerable Influence ◽  
Direct Bearing ◽  
Interstellar Grains ◽  
Made In

The First Detailed Studies to determine the processes by which interstellar grains may form were made by a group of Dutch astronomers in the 1940's. (See refs. 1 to 5.) Since that time very little systematic work on this problem has been done until very recently when Hoyle and Wickramasinghe (ref. 6) investigated graphite formation in cool stellar atmospheres. Van de Hulst's paper in 1949 (ref. 5) represents the culmination of an intensive attack which had considerable influence on astronomical thought about interstellar grains.Somewhat ironically, beginning about 1949 many significant advances in physics and chemistry having a direct bearing on this problem were made. In 1949, Frank in reference 7 presented a theory which explained how real crystals tend to grow, and much work, both theoretical and experimental, has been done since then. (See ref. 8.) Recent extensive research in chemical reactions at low temperatures both in solids and on surfaces is reported in reference 9.

scholarly journals 3D non-LTE line formation of neutral carbon in the Sun

2019 ◽  
Vol 624 ◽  
pp. A111 ◽  
Author(s):  
A. M. Amarsi ◽  
P. S. Barklem ◽  
R. Collet ◽  
N. Grevesse ◽  
M. Asplund
Keyword(s):  
Three Dimensional ◽  
Solar Spectrum ◽  
Neutral Hydrogen ◽  
Stellar Atmospheres ◽  
Impact Excitation ◽  
Solar Photosphere ◽  
Late Type ◽  
Current Standard ◽  
Standard Value ◽  
Good Agreement

Carbon abundances in late-type stars are important in a variety of astrophysical contexts. However C I lines, one of the main abundance diagnostics, are sensitive to departures from local thermodynamic equilibrium (LTE). We present a model atom for non-LTE analyses of C I lines, that uses a new, physically-motivated recipe for the rates of neutral hydrogen impact excitation. We analyse C I lines in the solar spectrum, employing a three-dimensional (3D) hydrodynamic model solar atmosphere and 3D non-LTE radiative transfer. We find negative non-LTE abundance corrections for C I lines in the solar photosphere, in accordance with previous studies, reaching up to around 0.1 dex in the disk-integrated flux. We also present the first fully consistent 3D non-LTE solar carbon abundance determination: we infer log ɛC = 8.44 ± 0.02, in good agreement with the current standard value. Our models reproduce the observed solar centre-to-limb variations of various C I lines, without any adjustments to the rates of neutral hydrogen impact excitation, suggesting that the proposed recipe may be a solution to the long-standing problem of how to reliably model inelastic collisions with neutral hydrogen in late-type stellar atmospheres.

scholarly journals Working Group on Infrared Astronomy: (Groupe de Travail Pour L’Astronomie Infrarouge)

2000 ◽  
Vol 24 (1) ◽  
pp. 336-337
Author(s):  
Eugene F. Milone ◽  
Roger A. Bell ◽  
Michael Bessell ◽  
Robert Garrison ◽  
Martin Cohen ◽  
...  
Keyword(s):  
Water Vapor ◽  
Working Group ◽  
Infrared Astronomy ◽  
Stellar Atmospheres ◽  
Maximum Throughput ◽  
Small Subgroup ◽  
Infrared Measurements ◽  
Group A ◽  
Atmospheric Windows ◽  
Made In

In 1988, a Joint Commission (9 and 25) meeting on the causes of the well-known limitations on the precision of infrared astronomy led to several suggestions to improve matters (see Milone 1989). These included better reporting of the photometric systems in use by practitioners, redesign of the infrared passbands to be more optimally placed inside the atmospheric windows, and development of a method to ascertain the water vapor content of the atmosphere when the astronomical infrared measurements were being made. An Infrared Astronomy Working Group was formed to look into the matter. Advice and suggestions were solicited from the community at large. All who volunteered information became, de facto, members of the Working Group. A small subgroup composed of Andrew Young, Chris Stagg, and Milone set to work on the central of the recommendations: improvement of the passbands. Young, Milone, k Stagg (1994) (hereafter YMS) summarized the work: existing JHKLMN and Q infrared passbands were found to be both far from standardized, and all too frequently defined, to various degrees, by the water vapor and other components of the terrestrial atmosphere. Following extensive numerical simulations with a MODTRAN 3 terrestrial-atmospheres model package, and Kurucz stellar atmospheres, we suggested a set of improved infrared passbands designed explicitly to fit within, and not be defined by, the terrestrial atmospheric windows; however, we sought to optimize them so as to get the maximum throughput consistent with plausible limitations on precision of manufacture of the filters. In 1995 and again in 1997, a number of improvements were made in the code with which the improved passbands were designed. While they do not much affect the optimization trials and thus the passband recommendations, they have been used to extend the modeling.

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