Engineering topics

Gudmundsson, E. H.

Publications and source records attributed to Gudmundsson, E. H..

4 records

NASA NTRS1989

Surface structure of neutron stars with high magnetic fields

The equation of state of cold dense matter in strong magnetic fields is calculated in the Thomas-Fermi and Thomas-Fermi-Dirac approximations. For use in the latter calculation, a new expression is derived for the exchange energy of the uniform electron gas in a strong magnetic field. Detailed calculations of the density profile in the surface region of a neutron star are described for a variety of equations of state, and these show that the surface density profile is strongly affected by the magnetic field, irrespective of whether or not matter in a magnetic field has a condensed state bound with respect to isolated atoms. It is also shown that, as a consequence of the field dependence of the screening potential, magnetic fields can significantly increase nuclear reaction rates.

Fushiki, I.↗

NASA NTRS1983

Structure of neutron star envelopes

The envelopes of nonmagnetic neutron stars are studied using the best available opacities and equation of state. The general relativistic equations of the structure and evolution of nonmagnetic neutron stars are discussed, and it is shown that they can be reduced to a single equation for calculating the thermal structure of neutron star envelopes. The physical input needed to solve the thermal structure equation is investigated and the numerical results of envelope model calculations are presented. It is shown that the thermal structure of neutron star envelopes is determined by the single parameter T(s) to the 4th/g(s), where T(s) is the effective surface temperature and g(s) the surface gravity of the star. This result is used to derive a number of other scaling relations, and the effects of general relativity on the envelope thermal structure are examined in detail. The results of a sensitivity analysis of the regional opacity needed to obtain a reliable relationship between the temperatures of the inner and outer boundaries of the envelope is presented.

Gudmundsson, E. H.↗

NASA NTRS1983

Sensitivity of model calculations to uncertain inputs, with an application to neutron star envelopes

A method is given for determining the sensitivity of certain types of calculations to the uncertainties in the input physics or model parameters; this method is applicable to problems that involve solutions to coupled, ordinary differential equations. In particular the sensitivity of calculations of the thermal structure of neutron star envelopes to uncertainties in the opacity and equation of state is examined. It is found that the uncertainties in the relationship between the surface and interior temperatures of a neutron star are due almost entirely to the imprecision in the values of the conductive opacity in the region where the ions form a liquid; here the conductive opacity is, for the most part, due to the scattering of electrons from ions.

Epstein, R. I.↗

NASA NTRS1982

Neutron star envelopes

It is pointed out that the separate study of neutron star envelopes is a valuable technique for gaining insights into neutron star cooling calculations. It is shown that, to an excellent approximation, the temperature at the inner boundary of the envelope, T sub b, is a function only of T sub s to the 4th power over g sub s, where T sub s is the effective temperature and g sub s is the surface gravity. This result makes it possible to investigate very simply the effects of general relativity and of opacity changes on the T sub b - T sub s relation and to compare calculations by different workers, even though they use different neutron star models. It is also shown that the most important opacity source for obtaining a reliable T sub b - T sub s relation is the conductive opacity of matter when the ions are liquid. Calculations are presented in which particular attention is given to this region and the best available opacities are used.

Gudmundsson, E. H.↗