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  • 1
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    Hydrodynamic effects in the atmosphere of variable stars (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Numerical models of variable stars are established, using a nonlinear radiative transfer coupled hydrodynamics code. The variable Eddington method of radiative transfer is used. Comparisons are for models of W Virginis, beta Doradus, and eta Aquilae. From these models it appears that shocks are formed in the atmospheres of classical Cepheids as well as W Virginis stars. In classical Cepheids, with periods from 7 to 10 days, the bumps occurring in the light and velocity curves appear as the result of a compression wave that reflects from the star's center. At the head of the outward going compression wave, shocks form in the atmosphere. Comparisons between the hydrodynamic motions in W Virginis and classical Cepheids are made. The strong shocks in W Virginis do not penetrate into the interior as do the compression waves formed in classical Cepheids. The shocks formed in W Virginis stars cause emission lines, while in classical Cepheids the shocks are weaker.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Cepheid Modeling; p 71-83
    Format: text
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  • 2
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    Mean colors of Cepheids (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Color observations of Cepheids can be interpreted by a color effective temperature relation to give different T sub e values for each kind of mean color. Here, theoretical colors from numerical integrations of Cepheid pulsations are used to determine the proper method of taking the color mean in order to get, by the color T sub e relation, the correct nonpulsating T sub e.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Cepheid Modeling; p 43-55
    Format: text
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  • 3
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    Theoretical mean colors for RR Lyrae variables (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A hydrodynamically pulsating 0.6 solar mass model of a typical RR Lyrae variable was studied with a radiation transport-hydrodynamic computer program to predict theoretical T sub 3 and colors at many phases and to find the proper methods for getting mean colors and the consequent mean effective temperatures. The variable Eddington radiation approximation method was used with gray and with multifrequency absorption coefficients to represent the radiation flow in the outer optically thin layers. Comparison between observed and computed B-V colors indicate that these low Z population 2 models are reasonably accurate using King 1A composition opacities. The well known Oke, Giver, and Searle relation between B-V and T sub e reproduced. Mean colors were found by four different averaging methods. The method that gives a mean color and the mean T sub e closest to the nonpulsating model was the separate intensity means of B and V.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Current Probl. in Stellar Pulsation Instabilities; p 293-310
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Light curves for bump Cepheids computed with a dynamically zoned pulsation code (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The dynamically zoned pulsation code developed by Castor, Davis, and Davison was used to recalculate the Goddard model and to calculate three other Cepheid models with the same period (9.8 days). This family of models shows how the bumps and other features of the light and velocity curves change as the mass is varied at constant period. The use of a code that is capable of producing reliable light curves demonstrates that the light and velocity curves for 9.8 day Cepheid models with standard homogeneous compositions do not show bumps like those that are observed unless the mass is significantly lower than the 'evolutionary mass.' The light and velocity curves for the Goddard model presented here are similar to those computed independently by Fischel, Sparks, and Karp. They should be useful as standards for future investigators.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Current Probl. in Stellar Pulsation Instabilities; p 175-186
    Format: application/pdf
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  • 5
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    On the mass of the Cepheid X Cygni (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Using a new non-Lagrangian hydrodynamic radiation transport code, models of the Cepheid X Cygni have been calculated and compared with new observations. Adopting an effective temperature of 5300 K, the luminosity was varied for stellar masses of 6, 8, and 9 solar masses in order to obtain a period of 16.4d. The results indicate that in order to find reasonable agreement between the light curves as calculated and observed, the mass used in the models must be nearly the evolutionary mass, not some 60% less as found in earlier work for Cepheids with periods from 7d to 10d. In addition, the new observations support the physical reality of the so-called 'artificial viscosity dip'.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 246
    Format: text
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