778 research outputs found
An evolutionary model for the gamma-ray system PSR J1311-3430 and its companion
The most recent member of the millisecond pulsar with very low-mass
companions and short orbital periods class, PSR J1311-3430 (Pletsch et al.
2012) is a remarkable object in various senses. Besides being the first
discovered in gamma-rays, its measured features include the very low or absent
hydrogen content. We show in this Letter that this important piece of
information leads to a very restricted range of initial periods for a given
donor mass. For that purpose, we calculate in detail the evolution of the
binary system self-consistently, including mass transfer and evaporation,
finding the features of the new evolutionary path leading to the observed
configuration. It is also important to remark that the detailed evolutionary
history of the system naturally leads to a high final pulsar mass, as it seems
to be demanded by observations.Comment: 5 pages, 5 figures, 1 table. Accepted for publication in MNRAS
Letter
The Quasi-Roche lobe overflow state in the evolution of Close Binary Systems containing a radio pulsar
We study the evolution of close binary systems formed by a normal (solar
composition), intermediate mass donor star together with a neutron star. We
consider models including irradiation feedback and evaporation. These
non-standard ingredients deeply modify the mass transfer stages of these
binaries. While models that neglect irradiation feedback undergo continuous,
long standing mass transfer episodes, models including these effect suffer a
number cycles of mass transfer and detachment. During mass transfer the systems
should reveal themselves as low-mass X-ray binaries (LMXBs), whereas when
detached they behave as a binary radio pulsars. We show that at these stages
irradiated models are in a Roche lobe overflow (RLOF) state or in a quasi-RLOF
state. Quasi-RLOF stars have a radius slightly smaller than its Roche lobe.
Remarkably, these conditions are attained for orbital period and donor mass
values in the range corresponding to a family of binary radio pulsars known as
"redbacks". Thus, redback companions should be quasi-RLOF stars. We show that
the characteristics of the redback system PSR J1723-2837 are accounted for by
these models.
In each mass transfer cycle these systems should switch from LMXB to binary
radio pulsar states with a timescale of \sim million years. However, there is
recent and fast growing evidence of systems switching on far shorter, human
timescales. This should be related to instabilities in the accretion disc
surrounding the neutron star and/or radio ejection, still to be included in the
model having the quasi-RLOF state as a general condition.Comment: 27 pages, 7 figures. Accepted for publication in The Astrophysical
Journa
Apsidal motion in massive close binary systems. I. HD 165052 an extreme case?
We present a new set of radial-velocity measurements of the spectroscopic
binary HD 165052 obtained by disentangling of high-resolution optical spectra.
The longitude of the periastron (60 +- 2 degrees) shows a variation with
respect to previous studies. We have determined the apsidal motion rate of the
system (12.1 +- 0.3 degree/yr), which was used to calculate the absolute masses
of the binary components: M_1 = 22.5 +- 1.0 and M_2 = 20.5 +- 0.9 solar masses.
Analysing the separated spectra we have re-classified the components as O7Vz
and O7.5Vz stars
Strangelet spectra from type II supernovae
We study in this work the fate of strangelets injected as a contamination in
the tail of a "strange matter-driven" supernova shock. A simple model for the
fragmentation and braking of the strangelets when they pass through the
expanding oxygen shell is presented and solved to understand the reprocessing
of this component. We find that the escaping spectrum is a scaled-down version
of the one injected at the base of the oxygen shell. The supernova source is
likely to produce low-energy particles of quite independently
of the initial conditions. However, it is difficult that ultrarrelativistic
strangelets (such as the hypothetical Centauro primaries) can have an origin in
those explosive events.Comment: RevTex file, 5 pp., no figure
Self-bound models of compact stars and recent mass-radius measurements
The exact composition of a specific class of compact stars, historically
referred to as "neutron stars", is still quite unknown. Possibilities ranging
from hadronic to quark degrees of freedom, including self-bound versions of the
latter have been proposed. We specifically address the suitability of strange
star models (including pairing interactions) in this work, in the light of new
measurements available for four compact stars. The analysis shows that these
data might be explained by such an exotic equation of state, actually selecting
a small window in parameter space, but still new precise measurements and also
further theoretical developments are needed to settle the subject.Comment: To appear in PR
The potential of the variable DA white dwarf G117-B15A as a tool for Fundamental Physics
White dwarfs are well studied objects. The relative simplicity of their
physics allows to obtain very detailed models which can be ultimately compared
with their observed properties. Among white dwarfs there is a specific class of
stars, known as ZZ-Ceti objects, which have a hydrogen-rich envelope and show
periodic variations in their light curves. G117-B15A belongs to this particular
set of stars. The luminosity variations have been successfully explained as due
to g-mode pulsations. G117-B15A has been recently claimed to be the most stable
optical clock ever found, being the rate of change of its 215.2 s period very
small: \dot{P}= (2.3 +- 1.4)x10^{-15} s s^-1, with a stability comparable to
that of the most stable millisecond pulsars. The rate of change of the period
is closely related to its cooling timescale, which can be accurately computed.
In this paper we study the pulsational properties of G117-B15A and we use the
observed rate of change of the period to impose constraints on the axion
emissivity and, thus, to obtain a preliminary upper bound to the mass of the
axion. This upper bound turns out to be 4cos^{2}{\beta} meV at the 95%
confidence level. Although there are still several observational and
theoretical uncertainties, we conclude that G117-B15A is a very promising
stellar object to set up constraints on particle physics.Comment: 32 pages, 14 figures, accepted for publication in New Astronom
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