Atmospheres and radiating surfaces of neutron stars

The early 21st century witnesses a dramatic rise in the study of thermal radiation of neutron stars. Modern space telescopes have provided a wealth of valuable information which, when properly interpreted, can elucidate the physics of superdense matter in the interior of these stars. This interpretation is necessarily based on the theory of formation of neutron star thermal spectra, which, in turn, is based on plasma physics and on the understanding of radiative processes in stellar photospheres. In this paper, the current status of the theory is reviewed with particular emphasis on neutron stars with strong magnetic fields. In addition to the conventional deep (semi-infinite) atmospheres, radiative condensed surfaces of neutron stars and "thin" (finite) atmospheres are considered.Comment: 43 pages, 13 figures, 1 table. In v.3, there are more than 50 minor corrections (typos, wording, style) and one important typo fix (the sign in Eq.(61)). In v.4, beside a few minor improvements, ionization equilibrium equation (58) is corrected. In v.5, a typo in Eq.(12) is fixe

Hydrogen atom in a magnetic field: The quadrupole moment

The quadrupole moment of a hydrogen atom in a magnetic field for field strengths from 0 to 4.414e13 G is calculated by two different methods. The first method is variational, and based on a single trial function. The second method deals with a solution of the Schroedinger equation in the form of a linear combination of Landau orbitals.Comment: 4 pages, 1 figure, 1 table; RevTeX. Final (proofs-stage) version of the text; corrected numbers in Table 1 and in Eq.(15

Comment on "On the ionization equilibrium of hot hydrogen plasma and thermodynamic consistency of formulating finite partition functions"

Zaghloul [Phys. Plasmas 17, 062701 (2010); arXiv:1010.1161v1] reconsiders the occupation probability formalism in plasma thermodynamics and claims inconsistencies in previous models. I show that the origin of this incorrect claim is an omission of the configurational factor from the partition function. This arXiv version is supplemented with two appendices, where I add remarks and comments on two more recent publications of the same author on the same subject: on his response to this Comment [Phys. Plasmas 17, 124705 (2010)] and on his criticism towards the Hummer and Mihalas's (1988) formalism [Phys. Plasmas 17, 122903 (2010); arXiv:1010.1102v1].Comment: 4 pages: 2 pages of the journal publication + 2 pages of the electronic supplemen

Evolution of Young Neutron Star Envelopes

We extend our initial study of diffusive nuclear burning (DNB) for neutron stars (NSs) with Hydrogen atmospheres and an underlying layer of proton capturing nuclei. Our initial study showed that DNB can alter the photospheric abundance of Hydrogen on surprisingly short timescales (10^{2-4}\yrs). Significant composition evolution impacts the radiated thermal spectrum from the NS as well as its overall cooling rate. In this paper, we consider the case when the rate limiting step for the H consumption is diffusion to the burning layer, rather than the local nuclear timescale. This is relevant for NSs with surface temperatures in excess of $10^6 {\rm K}$, such as young ($<10^5$ yr) radio pulsars and accreting NSs in quiescence. When downward diffusion is the limiting rate in DNB, the rate of H consumption is suppressed by 1-2 orders of magnitude compared to a DNB estimate that assumes diffusive equilibrium. In order to apply our ongoing study to young neutron stars, we also include the important effects of strong magnetic fields ($B \sim 10^{12} {\rm G}$). In this initial study of magnetic modifications to DNB, we find that the H burning time is lengthened by 2-3 orders of magnitude for a $10^{12} {\rm G}$ field. However, even for NSs with dipole field strengths of $10^{12}$ G, we find that all of the H can be burned before the pulsar reaches an age of $\sim 10^5 \ {\rm yr}$, thus potentially revealing the underlying proton-capturing elements. Finally, we conclude by providing an overview of what can be learned about fallback and pulsar winds from measuring the surface composition of a young NS.Comment: 10 pages, 8 figures, to appear in Ap

Dense astrophysical plasmas

We briefly examine the properties of dense plasmas characteristic of the atmospheres of neutron stars and of the interior of massive white dwarfs. These astrophysical bodies are natural laboratories to study respectively the problem of pressure ionization of hydrogen in a strong magnetic field and the crystallization of the quantum one-component-plasma at finite temperature.Comment: 8 pages, 3 figures, LaTeX using iopart.cls and iopart12.clo (included). In the special issue "Liquid State Theory: from White Dwarfs to Colloids" (International Conf. in the honor of Prof. J.-P. Hansen's 60th birthday, Les Houches, April 1-5, 2002

Testing cosmological variability of fundamental constants

One of the topical problems of contemporary physics is a possible variability of the fundamental constants. Here we consider possible variability of two dimensionless constants which are most important for calculation of atomic and molecular spectra (in particular, the X-ray ones): the fine-structure constant \alpha=e^2/\hbar c and the proton-to-electron mass ratio \mu=m_p/m_e. Values of the physical constants in the early epochs are estimated directly from observations of quasars - the most powerful sources of radiation, whose spectra were formed when the Universe was several times younger than now. A critical analysis of the available results leads to the conclusion that present-day data do not reveal any statistically significant evidence for variations of the fundamental constants under study. The most reliable upper limits to possible variation rates at the 95% confidence level, obtained in our work, read: |\dot\alpha/\alpha| < (1.4e-14)/yr, |\dot\mu/\mu| < (1.5e-14)/yr on the average over the last ten billion years.Comment: 9 pages, 2 figures, 2 tables, LaTeX using aipproc.sty (included). In: X-ray and Inner-Shell Processes, R.W. Dunford, D.S. Gemmel, E.P. Kanter, B. Kraessig, S.H. Southworth, L. Young (eds.), AIP Conf. Proc. (AIP, Melville, 2000) vol. 506, p. 50