on Scientific Activity in 2001
Spectroscopy of Quasars and Physics of Neutron Stars
This report includes only a part of significant results
Department of Theoretical Astrophysics.
A more detailed descriptions
of the fields of activity resides here.
preprints and publications related to these and other projects
can be found here.
For the first time at large redshifts (z=2.3377)
molecules HD have been discovered. The relative abundance
of deuterium is one of the key parameters of the modern
observational cosmology, because the primordial deuterium
is the most sensitive indicator of the baryon content
in the Universe. Until recently, the primordial deuterium
was determined only by an analysis of Lyman-alpha systems,
from the atomic deuterium abundance. The discovery
of the HD molecules at large z opens a unique, independent
possibility of estimation of the deuterium abundance
at early cosmological epochs.
D. Varshalovich, A. Ivanchik, P. Petitjean, R. Srianand, C. Ledoux
"HD molecular lines in an absorption system at redshift 2.3377"
[astro-ph/0107310] Astronomy Letters (accepted)
A new, essentially updated package of computer programs
is developed for modeling of primordial nucleosynthesis processes,
which allows us to take into account specific models of
dependence of the fundamental constants on parameters
of scalar-tensor gravity theories, widely used in the
modern literature. Bounds of a possible variation of
the constants at the epoch of primordial nucleosynthesis
A.V. Ivanchik, A.V. Orlov, D.A. Varshalovich
"Effects of possible deviations of fundamental physical constants
on primordial nucleosynthesis" Astronomy Letters27, 615 (2001)
Basing on an analysis of absorption spectra of
quasars with high redshifts, the upper limits of
the possible variation of the fundamental physical constants
at the epoch of quasar spectra formation (i.e., ~ 10 billion
years ago) are determined more precisely.
A number of systematic effects, which can simulate
variation of the constants, is studied.
The expulsion of proton fluxoids along
neutron vortices from the superfluid/superconductive core
is considered for
neutron star with weak (B < 1010 G) magnetic field. The
velocity of fluxoids is calculated from the balance of buoyancy,
drag and crustal forces. We show, that the proton fluxoids can
leave the superfluid core sliding along the neutron
vortices on a timescale of about 107 years. An alternative
possibility is that fluxoids are aligned with the vortices on the
same timescale. As the result, non-aligned surface magnetic
fields of millisecond pulsars can be sustained for > 109
years only in case of a comparable dissipation timescale of the
currents in the neutron star crust. This defines upper limits of
the impurity concentration in the neutron star crust: Q < 0.1
if a stiff equation of state determines the density profile.
D. Konenkov, U. Geppert
"Expulsion of magnetic flux from the core and its dissipation in the crust of a neutron star" Astronomy Letters27, 163 (2001)
D. Konenkov, U. Geppert
"The evolution of core and surface magnetic field in isolated neutron stars" Mon. Not. Roy. astron. Soc.325, 426 (2001)
D. Konenkov, U. Geppert
"On the nature of the residual magnetic fields in millisecond pulsars" Astron. Astrophys.372, 583 (2001)
Distribution functions are constructed, which describe the orientation
of orbital moments of binary systems containing neutron stars, with respect
to the Galaxy rotation axis, for various Galactic altitudes.
The calculation is done for two cases:
the systems acquire additional velocities at the supernova bursts,
the systems are accelerated by their own X-ray emission
(the photon rocket effect) at the stage of accretion of matter on the neutron star
with nonsymmetric magnetic field.
The results are applicable also
for the binary millisecond radio pulsars under the assumption that
they underwent the accretion stage and were born in the Galactic plane.
V.D. Pal'shin, A.I. Tsygan
"On acceleration of close binaries during supernova explosions"
Astron. Zh. 78, 1099 [Engl. transl.: Astronomy Rep. 45, 967] (2001)
V.D. Pal'shin, A.I. Tsygan
"Alignment of orbital moments of binaries containing neutron stars along the spin axis of the Galaxy" Astron. Astrophys. (submitted)
The thermal structure of neutron stars with magnetized envelopes is studied
using modern physics input. The relation between the internal (Ti) and local
surface temperatures is calculated and fitted by analytic expressions for
magnetic field strengths B from 0 to 1016 G and arbitrary inclination of the
field lines to the surface. The luminosity of a neutron star with dipole
magnetic field is calculated and fitted as a function of B, Ti, stellar mass
and radius. In addition, cooling of neutron stars with magnetized
envelopesis anlyzed and
the effects of the magnetic field of the Vela pulsar on the determination
of critical temperatures of neutron and proton superfluids in its core are revealed.
A review the main neutrino emission mechanisms in neutron star crusts and cores is published. Recent theoretical achievements, for instance, band structure effects in neutrino emission due to
scattering of electrons in Coulomb crystals of atomic nuclei,
are taken into account. The standard composition of matter
in the core and the case of exotic constituents such as the
condensates and quark matter are considered. The reduction of the neutrino emissivities by nucleon superfluidity, as well as the
specific neutrino emission produced by Cooper pairing of the superfluid particles, are discussed. The effects of strong
magnetic fields on some reactions, such as the direct Urca process and the neutrino synchrotron emission of electrons, are also analyzed. The
results are presented in the form convenient for practical use.
The effects of various neutrino reactions on the
cooling of neutron stars are analyzed,
and the prospects of exploring the properties of supernuclear matter by
confronting cooling simulations with observations of the thermal radiation from isolated neutron stars are explored.
D.G. Yakovlev, A.D. Kaminker, O.Y. Gnedin, P. Haensel
"Neutrino emission from neutron stars"
[astro-ph/0012122] Physics Reports354, 1 (2001)
Cooling of neutron stars (NSs) with the cores composed of neutrons, protons,
and electrons is simulated assuming 1S0 pairing of neutrons in the NS
crust, and also 1S0 pairing of protons and weak 3P2 pairing of
neutrons in the NS core, and using realistic density profiles of the superfluid
critical temperatures Tc(\rho). The theoretical cooling models of
isolated middle-aged NSs can be divided into three main types.
Low-mass, slowly cooling NSs where the direct Urca process of neutrino
emission is either forbidden or almost fully suppressed by the proton
Medium-mass NSs which show moderate cooling via
the direct Urca process suppressed by the proton superfluidity.
Massive NSs which show fast cooling via the direct Urca process weakly
suppressed by superfluidity.
RX J0822-43, PSR 1055-52 and RX J1856-3754 are shown to be slowly cooling NSs. To explain
these sufficiently warm sources, a density profile Tc(\rho) in
the crust with a rather high and flat maximum and sharp wings
is needed. 1E
1207-52, RX J0002+62, PSR 0656+14, Vela, and Geminga are shown to be moderately cooling
NSs. Their masses are determined for a given model of proton superfluidity,
Tcp(\rho), and the equation of state in the NS core.
A.D. Kaminker, D.G. Yakovlev, O.Y. Gnedin
"Three types of cooling superfluid neutron stars: Theory and observations"
[astro-ph/0111429] Astron. Astrophys. (submitted)
With the VLT/UVES we have measured for the first time
the argon abundances in high-redshift objects.
It was found that the Ar/O ratios in damped Ly-alpha
systems are close to those measured in the extragalactic HII
regions and in blue compact galaxies in the local universe
where oxygen is at least one order of magnitude more abundant.
This strengthes the universality of the Ar/O ratio and lends
support to the existence of a universal IMF.
S.A. Levshakov, I.I. Agafonova, M. Centurion, I.E. Mazets
"Metal abundances and kinematics of quasar absorbers. I. Absorption systems toward J2233-606"
[astro-ph/0201101] Astron. Astrophys. (accepted)
For the first time optical observations of an old (17.3 billion years old) pulsar
B0950+08 have been performed.
A faint point-like object, B=27.04+-0.15, has been detected with coordinates
coinciding with the radio position of the pulsar with the accuracy better
than ~ 0.5". Based on our B and previous HST/FOC/F130LP
photometry the broad band spectrum of the pulsar is apparently flat and
likely to be of nonthermal origin as it is observed for the optical
emission of younger middle-aged pulsars PSR B0656+14 and Geminga.
S. Zharikov, Yu. Shibanov, A. Koptsevich, N. Kawai, Y. Urata, V Komarova, V. Sokolov, S. Shibata,
"Subaru optical observations of the PSR B0950+08" Astron. Astrophys. (submitted)