Atmosphere In Radiative Equilibrium Research Articles

Model Atmospheres for 05 V and BO V Stars with Line Blanketing

view Abstract Citations (87) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Model Atmospheres for 05 V and BO V Stars with Line Blanketing Hickok, Frederick R. ; Morton, Donald C. Abstract Two model atmospheres in radiative equilibrium have been computed for log g = 4.0, T~ = 374500 K (O~ = 0.1346) and T6 = 286400 K (Oe = 0.176) incorporating the detailed blanketing of the strongest lines in the ultraviolet (911.6 «= X «= 1700 A), where the majority of the flux emerges. The visible spectra closely resemble those of unbianketed models with log g = 40, T6 = 381800 K (06 = 0.132) and Te = 303600 K (Oe = 0.166), respectively. The corresponding models are classified as 05 and BO Von the basis of the Balmer discontinuities. The bolometric corrections are estimated to he -3.23 and -2 57 for the blanketed models compared with -3 31 and -2 82 for the unbianketed ones. The strongest ultraviolet lines and detai]~s of the models are tabulated while the emergent flux distributions are shown graphically for X > 911.6 A and tabulated for shorter wavelengths Publication: The Astrophysical Journal Pub Date: April 1968 DOI: 10.1086/149537 Bibcode: 1968ApJ...152..203H full text sources ADS | data products SIMBAD (4)

Non-LTE line formation with spatial variations in the Doppler width

Spatial variations of the Doppler width resulting from temperature gradients are shown to play an important role in determining the sensitivity of the radiation field in strong, non-LTE lines to the local kinetic temperature. The consequences of this effect are discussed in connection with: (1) the temperature structure of an atmosphere in radiative equilibrium; and (2) the problem of inferring from line observations the temperature distribution in the surface layers of a star. Large increases in temperature near the surface are shown to lead to substantial non-local effects which depend critically on variations in Doppler width.

Approximate Integral Equations for the Temperature in Non-Gray Model Atmospheres.

view Abstract Citations (1) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Approximate Integral Equations for the Temperature in Non-Gray Model Atmospheres. Stone, Peter H. Abstract Approximate integral equations for the temperature distribution in non-gray model atmospheres in radiative equilibrium are derived and compared with the equations derived by using standard approximations. Use of the approximate equations greatly facilitates the numerical solution for the temperature distribution. Iteration procedures, implemented by an IBM 7090, are two approximate forms of the temperature equation for the special case where the monochromatic absorption coefficient is a step function of frequency, with the step's size independent of depth. Solutions for 56 representative models of this type are attempted and the convergence properties of the equations determined. The results show the effect of absorption discontinuities on atmospheric temperatures and thus indicate those spectral features that may be expected to have an important influence on atmospheric temperatures. Publication: The Astrophysical Journal Pub Date: February 1963 DOI: 10.1086/147537 Bibcode: 1963ApJ...137..628S full text sources ADS |

Iterative Solution for the Source Function in the Grey Atmosphere in Radiative Equilibrium.

Iterative Solution for the Source Function in the Grey Atmosphere in Radiative Equilibrium.

Hydrogen-Helium Adiabats for Late-Type Stars.

For late-type main-sequence stars, the earlier models that consisted of convective cores and radiative envelopes have been superseded by models with radiative cores and convective envelopes, topped by an atmosphere in radiative equilibrium. But in the available models of the latter type, the representation of the convective zone has been rather schematic, in so far as the adiabats used would apply only if the gas were completely ionized. Accordingly, an expression for the adiabatic gradient of hydrogen-helium mixtures has been derived from thermodynamics. This derivation takes account of the interlocking ionization of hydrogen and helium and of its coupling with the association of hydrogen into molecules. Adiabats have been computed with three values of hydrogen to helium ratio (by number), 8/1, 16/1, and . Moreover, an expression for the adiabatic gradient, in which the effect of pressure ionization has been included in an approximate way, has been given for the special case of pure hydrogen.

The Temperature of the Lower Atmosphere of the Earth

From the known amounts of the various gases of the atmosphere from sea level to about 20 km, from the observed light absorption coefficients of the gases and from the albedo of the earth's surface the temperature of the atmosphere in radiative equilibrium is calculated on the assumption that the sunlight is the only source of energy. The calculation is perhaps more rigorous than has hitherto been attempted, although it contains a number of approximations. The sea level temperature comes out to be about 19\ifmmode^\circ\else\textdegree\fi{} above the observed world-wide average value 287\ifmmode^\circ\else\textdegree\fi{}K, and the temperature above about 3 km falls many degrees below the observed temperatures. The temperature gradient in levels from 3 to 6 km is greater than that of convective equilibrium and hence the atmosphere would not be dynamically stable if radiation equilibrium prevailed. Therefore air currents take place to bring about convective equilibrium. Continuing the calculation it is found that only when the convective region extends to about 12 km (as is observed), with radiative equilibrium above 12 km (as is observed), does the atmosphere satisfy the conditions of dynamic stability and thermal equilibrium with the received solar energy. For this case the calculated sea level temperature is 290\ifmmode^\circ\else\textdegree\fi{}K in good agreement with the observed value 287\ifmmode^\circ\else\textdegree\fi{}K. Calculation shows that doubling or tripling the amount of the carbon dioxide of the atmosphere increases the average sea level temperature by about 4\ifmmode^\circ\else\textdegree\fi{} and 7\ifmmode^\circ\else\textdegree\fi{}K, respectively; halving or reducing to zero the carbon dioxide decreases the temperature by similar amounts. Such changes in temperature are about the same as those which occur when the earth passes from an ice age to a warm age, or vice versa. Thus the calculation indicates that the carbon dioxide theory of the ice ages, originally proposed by Tyndall, is a possible theory.