D. G. Yakovlev

Atomic data for astrophysics. II. New analytic fits for photoionization cross sections of atoms and ions

We present a complete set of analytic fits to the nonrelativistic photoionization cross sections for the ground states of atoms and ions of elements from H through Si, and S, Ar, Ca, and Fe. Near the ionization thresholds, the fits are based on the Opacity Project theoretical cross sections interpolated and smoothed over resonances. At higher energies, the fits reproduce calculated Hartree-Dirac-Slater photoionization cross sections. {copyright} {ital 1996 The American Astronomical Society.}

Neutron star cooling after deep crustal heating in the X-ray transient KS 1731-260

We simulate the cooling of the neutron star in the X-ray transient KS 1731−260 after the source returned to quiescence in 2001 from a long (≳12.5 yr) outburst state. We show that the cooling can be explained assuming that the crust underwent deep heating during the outburst stage. In our best theoretical scenario the neutron star has no enhanced neutrino emission in the core, and its crust is thin, superfluid, and has the normal thermal conductivity. The thermal afterburst crust–core relaxation in the star may not be over.

Three types of cooling superfluid neutron stars: Theory and observations

Cooling of neutron stars (NSs) with the cores composed of neutrons, protons, and electrons is simulated assuming 1 S 0 pairing of neutrons in the NS crust, and also 1 S 0 pairing of protons and weak 3 P 2 pairing of neutrons in the NS core, and using realistic density profiles of the superfluid critical temperatures

Nucleon superfluidity vs. observations of cooling neutron stars

T_{rm c}(rho)

The cooling of Akmal—Pandharipande—Ravenhall neutron star models

. The theoretical cooling models of isolated middle-aged NSs can be divided into three main types. (I) Low-mass , slowly cooling NSs where the direct Urca process of neutrino emission is either forbidden or almost fully suppressed by the proton superfluidity. (II) Medium-mass NSs which show moderate cooling via the direct Urca process suppressed by the proton superfluidity. (III) Massive NSs which show fast cooling via the direct Urca process weakly suppressed by superfluidity. Confronting the theory with observations we treat RX J0822–43, PSR 1055–52 and RX J1856–3754 as slowly cooling NSs. To explain these sufficiently warm sources we need a density profile

Thermal state of transiently accreting neutron stars

T_{rm c}(rho)

The neutron star in HESS J1731−347: Central compact objects as laboratories to study the equation of state of superdense matter

in the crust with a rather high and flat maximum and sharp wings. We treat 1E 1207–52, RX J0002+62, PSR 0656+14, Vela, and Geminga as moderately cooling NSs. We can determine their masses for a given model of proton superfluidity,

Enhanced cooling of neutron stars via Cooper-pairing neutrino emission

T_{rm cp}(rho)

Magnetars as cooling neutron stars with internal heating

, and the equation of state in the NS core. No rapidly cooling NS has been observed so far.

Quantum effects in cyclotron plasma absorption

Cooling simulations of neutron stars (NSs) are performed assuming that stellar cores consist of neutrons, protons and electrons and using realistic density proles of superfluid critical temperatures Tcn( )a ndTcp( )o f neutrons and protons. Taking a suitable prole of Tcp( )w ith maximum5 10 9 K one can obtain smooth transition from slow to rapid cooling with increasing stellar mass. Adopting the same prole one can explain the majority of observations of thermal emission from isolated middle{aged NSs by cooling of NSs with dierent masses either with no neutron superfluidity in the cores or with a weak superfluidity, Tcn < 10 8 K. The required masses range from1:2 M for (young and hot) RX J0822{43 and (old and warm) PSR 1055{52 and RX J1856- 3754 to1:45 M for the (rather cold) Geminga and Vela pulsars. Observations constrain the Tcn( )a ndTcp() proles with respect to the threshold density of direct Urca process and maximum central density of NSs.