323 research outputs found
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
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
Nucleosynthesis and Clump Formation in a Core Collapse Supernova
High-resolution two-dimensional simulations were performed for the first five
minutes of the evolution of a core collapse supernova explosion in a 15 solar
mass blue supergiant progenitor. The computations start shortly after bounce
and include neutrino-matter interactions by using a light-bulb approximation
for the neutrinos, and a treatment of the nucleosynthesis due to explosive
silicon and oxygen burning. We find that newly formed iron-group elements are
distributed throughout the inner half of the helium core by Rayleigh-Taylor
instabilities at the Ni+Si/O and C+O/He interfaces, seeded by convective
overturn during the early stages of the explosion. Fast moving nickel mushrooms
with velocities up to about 4000 km/s are observed. This offers a natural
explanation for the mixing required in light curve and spectral synthesis
studies of Type Ib explosions. A continuation of the calculations to later
times, however, indicates that the iron velocities observed in SN 1987 A cannot
be reproduced because of a strong deceleration of the clumps in the dense shell
left behind by the shock at the He/H interface.Comment: 8 pages, LaTeX, 2 postscript figures, 2 gif figures, shortened and
slightly revised text and references, accepted by ApJ Letter
Trapping of Neutral Mercury Atoms and Prospects for Optical Lattice Clocks
We report a vapor-cell magneto-optical trapping of Hg isotopes on the
intercombination transition. Six abundant isotopes, including
four bosons and two fermions, were trapped. Hg is the heaviest non-radioactive
atom trapped so far, which enables sensitive atomic searches for ``new
physics'' beyond the standard model. We propose an accurate optical lattice
clock based on Hg and evaluate its systematic accuracy to be better than
. Highly accurate and stable Hg-based clocks will provide a new
avenue for the research of optical lattice clocks and the time variation of the
fine-structure constant.Comment: 4 pages, 3 figure
Nova M31N 2007-12b: Supersoft X-rays reveal an intermediate polar?
For the He/N nova M31N 2007-12b, we analyzed XMM-Newton EPIC and Chandra
HRC-I observations of our monitoring program performed at intervals of ten days
and added results of a XMM-Newton target of opportunity observation and Swift
XRT observations. The supersoft source (SSS) emission started between 21 and 30
d after the optical outburst and ended between 60 and 120 d after outburst,
making M31N 2007-12b one of the few novae with the shortest SSS phase known.
The X-ray spectrum was supersoft and can be fitted with a white dwarf (WD)
atmosphere model with solar abundances absorbed by the Galactic foreground. The
temperature of the WD atmosphere seems to increase at the beginning of the SSS
phase from ~70 to ~80 eV. The luminosity of M31N 2007-12b during maximum was at
the Eddington limit of a massive WD and dropped by ~30% in the observation 60 d
after outburst. The radius of the emission region is ~6x10^8 cm. In the four
bright state observations, we detected a stable 1110 s pulsation, which we
interpret as the WD rotation period. In addition, we detect dips in three
observations that might represent a 4.9 h or 9.8 h binary period of the system.
Nova envelope models with <50% mixing between solar-like accreted material and
the degenerate core of the WD can be used to describe the data. We derive a WD
mass of 1.2 Msun, as well as an ejected and burned mass of 2.0x10^{-6} Msun}
and 0.2x10^{-6} Msun, respectively. The observed periodicities indicate that
nova M31N 2007-12b erupted in an intermediate polar (IP) system. The WD
photospheric radius seems to be larger than expected for a non-magnetic WD but
in the range for magnetic WDs in an IP system. (abridged)Comment: 10 pages, 5 figures, A&A accepte
Helium Nova on a Very Massive White Dwarf -- A Light Curve Model of V445 Puppis (2000) Revised
V445 Pup (2000) is a unique object identified as a helium nova. Color indexes
during the outburst are consistent with those of free-free emission. We present
a free-free emission dominated light curve model of V445 Pup on the basis of
the optically thick wind theory. Our light curve fitting shows that (1) the
white dwarf (WD) mass is very massive (M_WD \gtrsim 1.35 M_\sun), and (2) a
half of the accreted matter remains on the WD, both of which suggest that the
increasing WD mass. Therefore, V445 Pup is a strong candidate of Type Ia
supernova progenitor. The estimated distance to V445 Pup is now consistent with
the recent observational suggestions, 3.5 < d < 6.5 kpc. A helium star
companion is consistent with the brightness of m_v=14.5 mag just before the
outburst, if it is a little bit evolved hot (\log T (K) \gtrsim 4.5) star with
the mass of M_He \gtrsim 0.8 M_\sun. We then emphasize importance of
observations in the near future quiescent phase after the thick circumstellar
dust dissipates away, especially its color and magnitude to specify the nature
of the companion star. We have also calculated helium ignition masses for
helium shell flashes against various helium accretion rates and discussed the
recurrence period of helium novae.Comment: 8 pages including 12 figures, to appear in Ap
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