35,249 research outputs found
Search for brown-dwarf like secondaries in cataclysmic variables II
We have examined VTL/ISAAC 1-2.5 \umum spectroscopy of a sample of short
orbital period cataclysmic variables which are candidates for harboring
substellar companions. We provide descriptions of the infrared spectrum of
\hbox{EI Psc}, \hbox{V834 Cen}, \hbox{WX Cet}, \hbox{VW Hyi}, \hbox{TY PsA} and
\hbox{BW Scl}. Fitting of the IR spectral energy distribution (SED) was
performed by comparing the observed spectrum with late-type templates.
Absorption features of the secondary star were detected in \hbox{EI Psc} and
\hbox{V834 Cen}, consistent with dwarf secondaries of spectral type K 5 1
and M 8 0.5, respectively. In addition, we report the first detection of
the secondary star in \hbox{VW Hyi}. The SED in this case is well matched by an
L 0 2 type secondary contributing 23 per cent to the overall flux at
= 1.15 \umum. This is a surprising result for a system with a
relatively high mass transfer rate. We discuss the implication of our findings
on the current scenarios for cataclysmic variable star evolution.Comment: accepted for publication in MNRA
Spontaneous patterns in coherently driven polariton microcavities
We consider a polariton microcavity resonantly driven by two external lasers
which simultaneously pump both lower and upper polariton branches at normal
incidence. In this setup, we study the occurrence of instabilities of the
pump-only solutions towards the spontaneous formation of patterns. Their
appearance is a consequence of the spontaneous symmetry breaking of
translational and rotational invariance due to interaction induced parametric
scattering. We observe the evolution between diverse patterns which can be
classified as single-pump, where parametric scattering occurs at the same
energy as one of the pumps, and as two-pump, where scattering occurs at a
different energy. For two-pump instabilities, stripe and chequerboard patterns
become the dominant steady-state solutions because cubic parametric scattering
processes are forbidden. This contrasts with the single-pump case, where
hexagonal patterns are the most common arrangements. We study the possibility
of controlling the evolution between different patterns. Our results are
obtained within a linear stability analysis and are confirmed by finite size
full numerical calculations.Comment: 15 pages, 9 figure
How does breakup influence the total fusion of Li at the Coulomb barrier?
Total (complete + incomplete) fusion excitation functions of Li on
Co and Bi targets around the Coulomb barrier are obtained using
a new continuum discretized coupled channel (CDCC) method of calculating
fusion. The relative importance of breakup and bound-state structure effects on
total fusion is particularly investigated. The effect of breakup on fusion can
be observed in the total fusion excitation function. The breakup enhances the
total fusion at energies just around the barrier, whereas it hardly affects the
total fusion at energies well above the barrier. The difference between the
experimental total fusion cross sections for Li on Co is notably
caused by breakup, but this is not the case for the Bi target.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.
Effects of Bulk Viscosity on Cosmological Evolution
The effect of bulk viscisity on the evolution of the homogeneous and
isotropic cosmological models is considered. Solutions are found, with a
barotropic equation of state, and a viscosity coefficient that is proportional
to a power of the energy density of the universe. For flat space, power law
expansions, related to extended inflation are found as well as exponential
solutions, related to old inflation; also a solution with expansion that is an
exponential of an exponential of the time is found.Comment: 8 pages, latex, no figure
- …