Symmetry of the Neutron and Proton Superfluidity Effects in Cooling Neutron Stars

We investigate the combined effect of neutron and proton superfluidities on the cooling of neutron stars whose cores consist of nucleons and electrons. We consider singlet-state pairing of protons and triplet-state pairing of neutrons in the cores of neutron stars. The critical superfluid temperatures T_c are assumed to depend on the density of matter. We study two types of neutron pairing with different components of the total angular momentum of Cooper pairs along the quantization axis (|m_J| =0 or 2). Our calculations are compared with observations of thermal emission from isolated neutron stars. We show that the observations can be interpreted by using two classes of superfluidity models: (1) strong proton superfluidity with a maximum critical temperature in the stellar core T_c^{max} > 4 \times 10^9 K and weak neutron superfluidity of any type (T_c^{max} < 2 \times 10^8 K); (2) strong neutron superfluidity (pairing with |m_J|=0) and weak proton superfluidity. The two types of models reflect an approximate symmetry with respect to an interchange of the critical temperatures of neutron and proton pairing.Comment: 20 pages, 8 figure

Simultaneous IR and optical light curves of 2A0311−227

Original article can be found at: http://www.nature.com/nature/index.html Copyright Nature Publishing Group. DOI: 10.1038/301223a0 [Full text of this article is not available in the UHRA]The complex wavelength dependence shown by the light curves of the AM Herculis type binaries such as 2A0311−227 (EFERI) and AM Her itself has led to suggestions that accretion occurs onto both magnetic poles of the white dwarf. The field strengths of the two poles being sufficiently different that one pole dominates at optical wavelengths, while the other produces most of the emission in the IR. Other authors have argued for a single pole model explaining the wavelength dependence of the light curves in terms of the rapidly changing cyclotron opacity with wavelength. An observational method of distinguishing between these two models is provided by the rapid flickering, which is a characteristic property of the light curves at both optical and IR wavelengths. We report here that the optical and IR flickering of 2A0311−227 are highly correlated indicating that in this object the dominant source of cyclotron radiation at both wavelengths is the same accretion column.Peer reviewe