444 research outputs found
QU Carinae: Supernova Ia in the making?
Variable NaI absorption lines have been reported in a number of type Ia
supernovae (SNeIa). The presence of this circumstellar material suggests that
cataclysmic variables (CVs) with a giant donor star may be the progenitors of
these SNeIa (Patat et al. 2007). We present echelle spectra of the CV QU
Carinae which strengthen the connection between CVs of the V Sge class, the
Accretion Wind Evolution scenario, variable wind features, variable NaI
absorption, and SNIa. This thread not only provides insight into the spectral
peculiarities of QU Car, but also links SNeIa as a class with their parent
systems.Comment: Accepted for publication to MNRAS. 23 pages (4 figures, 3 tables
Five-Year Optical and Near Infrared Observations of the Extremely Slow Nova V1280 Scorpii
We present optical (, , , and ) and near
infrared (, and ) photometric and spectroscopic observations
of a classical nova V1280 Scorpii for five years from 2007 to 2011. Our
photometric observations show a declining event in optical bands shortly after
the maximum light which continues 250 days. The event is most probably
caused by a dust formation. The event is accompanied by a short ( 30
days) re-brightening episode ( 2.5 mag in ), which suggests a
re-ignition of the surface nuclear burning. After 2008, the band
observations show a very long plateau at around = 10.5 for more than 1000
days until April 2011 ( 1500 days after the maximum light). The nova had
taken a very long time ( 50 months) before entering the nebular phase
(clear detection of both [\ion{O}{iii}] 4959 and 5007) and is still continuing
to generate the wind caused by H-burning. The finding suggests that V1280 Sco
is going through the historically slowest evolution. The interval from the
maximum light (2007 February 16) to the beginning of the nebular phase is
longer than any previously known slow novae: V723 Cas (18 months), RR Pic (10
months), or HR Del (8 months). It suggests that the mass of a white dwarf in
the V1280 Sco system might be 0.6 M_\mathrm{\sun} or smaller. The distance,
based on our measurements of the expansion velocity combined with the directly
measured size of the dust shell, is estimated to be 1.1 0.5 kpc.Comment: 17 pages, 14 figures, accepted for publication in A&
Stationary structures of irrotational binary systems -- models for close binary systems of compact stars
We propose a new numerical method to calculate irrotational binary systems
composed of compressible gaseous stars in Newtonian gravity. Assuming
irrotationality, i.e. vanishing of the vorticity vector everywhere in the star
in the inertial frame, we can introduce the velocity potential for the flow
field. Using this velocity potential we can derive a set of basic equations for
stationary states which consist of (i) the generalized Bernoulli equation, (ii)
the Poisson equation for the Newtonian gravitational potential and (iii) the
equation for the velocity potential with the Neumann type boundary condition.
We succeeded in developing a new code to compute numerically exact solutions to
these equations for the first time. Such irrotational configurations of binary
systems are appropriate models for realistic neutron star binaries composed of
inviscid gases, just prior to coalescence of two stars caused by emission of
gravitational waves. Accuracies of our numerical solutions are so high that we
can compute reliable models for fully deformed final stationary configurations
and hence determine the inner most stable circular orbit of binary neutron star
systems under the approximations of weak gravity and inviscid limit.Comment: 32 pages, 25 bitmapped ps files, to appear in ApJ supplemen
An approximate solver for Riemann and Riemann-like Ellipsoidal Configurations
We introduce a new technique for constructing three-dimensional (3D) models
of incompressible Riemann S-type ellipsoids and compressible triaxial
configurations that share the same velocity field as that of
Riemann S-type ellipsoids. Our incompressible models are exact steady-state
configurations; our compressible models represent approximate steady-state
equilibrium configurations. Models built from this method can be used to study
a variety of relevant astrophysical and geophysical problems.Comment: 25 pages, 10 figures, ApJ accepted, refereed versio
Evolution of Rotating Accreting White Dwarfs and the Diversity of Type Ia Supernovae
Type Ia supernovae (SNe Ia) have relatively uniform light curves and spectral
evolution, which make SNe Ia useful standard candles to determine cosmological
parameters. However, the peak brightness is not completely uniform, and the
origin of the diversity has not been clear. We examine whether the rotation of
progenitor white dwarfs (WDs) can be the important source of the diversity of
the brightness of SNe Ia. We calculate the structure of rotating WDs with an
axisymmetric hydrostatic code. The diversity of the mass induced by the
rotation is ~0.08 Msun and is not enough to explain the diversity of
luminosity. However, we found the following relation between the initial mass
of the WDs and their final state; i.e., a WD of smaller initial mass will
rotate more rapidly before the supernova explosion than that of larger initial
mass. This result might explain the dependence of SNe Ia on their host
galaxies.Comment: 7 pages, 6 figure
Electrodynamic trapping of spinless neutral atoms with an atom chip
Three dimensional electrodynamic trapping of neutral atoms has been
demonstrated. By applying time-varying inhomogeneous electric fields with
micron-sized electrodes, nearly strontium atoms in the state
have been trapped with a lifetime of 80 ms. In order to design the electrodes,
we numerically analyzed the electric field and simulated atomic trajectories in
the trap, which showed reasonable agreement with the experiment.Comment: 4pages, 4figures, to appear in Phys. Rev. Let
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