26,901 research outputs found
Dwarf Novae in the Shortest Orbital Period Regime: II. WZ Sge Stars as the Missing Population near the Period Minimum
WZ Sge-type dwarf novae are characterized by long recurrence times of
outbursts (~10 yr) and short orbital periods (<~ 85 min). A significant part of
WZ Sge stars may remain undiscovered because of low outburst activity.
Recently, the observed orbital period distribution of cataclysmic variables
(CVs) has changed partly because outbursts of new WZ Sge stars have been
discovered routinely. Hence, the estimation of the intrinsic population of WZ
Sge stars is important for the study of the population and evolution of CVs. In
this paper, we present a Bayesian approach to estimate the intrinsic period
distribution of dwarf novae from observed samples. In this Bayesian model, we
assumed a simple relationship between the recurrence time and the orbital
period which is consistent with observations of WZ Sge stars and other dwarf
novae. As a result, the minimum orbital period was estimated to be ~70 min. The
population of WZ Sge stars exhibited a spike-like feature at the shortest
period regime in the orbital period distribution. These features are consistent
with the orbital period distribution previously predicted by population
synthesis studies. We propose that WZ Sge stars and CVs with a low
mass-transfer rate are excellent candidates for the missing population
predicted by the evolution theory of CVs.Comment: 9 pages, 5 figures, accepted for publication in PAS
Spontaneously generated atomic entanglement in free space: reinforced by incoherent pumping
We study spontaneously generated entanglement (SGE) between two identical
multilevel atoms in free space via vacuum-induced radiative coupling. We show
that the SGE in two-atom systems may initially increase with time but
eventually vanishes in the time scale determined by the excited state lifetime
and radiative coupling strength between the two atoms. We demonstrate that a
steady-state SGE can be established by incoherently pumping the excited states
of the two-atom system. We have shown that an appropriate rate of incoherent
pump can help producing optimal SGE. The multilevel systems offer us more
chanel to establish entanglement. The system under consideration could be
realized in a tight trap or atoms/ions doped in a solid substrate.Comment: have some difference with published version (please see PRA
The Stern-Gerlach Experiment Revisited
The Stern-Gerlach-Experiment (SGE) of 1922 is a seminal benchmark experiment
of quantum physics providing evidence for several fundamental properties of
quantum systems. Based on today's knowledge we illustrate the different
benchmark results of the SGE for the development of modern quantum physics and
chemistry.
The SGE provided the first direct experimental evidence for angular momentum
quantization in the quantum world and thus also for the existence of
directional quantization of all angular momenta in the process of measurement.
It measured for the first time a ground state property of an atom, it produced
for the first time a `spin-polarized' atomic beam, it almost revealed the
electron spin. The SGE was the first fully successful molecular beam experiment
with high momentum-resolution by beam measurements in vacuum. This technique
provided a new kinematic microscope with which inner atomic or nuclear
properties could be investigated.
The original SGE is described together with early attempts by Einstein,
Ehrenfest, Heisenberg, and others to understand directional quantization in the
SGE. Heisenberg's and Einstein's proposals of an improved multi-stage SGE are
presented. The first realization of these proposals by Stern, Phipps, Frisch
and Segr\`e is described. The set-up suggested by Einstein can be considered an
anticipation of a Rabi-apparatus. Recent theoretical work is mentioned in which
the directional quantization process and possible interference effects of the
two different spin states are investigated.
In full agreement with the results of the new quantum theory directional
quantization appears as a general and universal feature of quantum
measurements. One experimental example for such directional quantization in
scattering processes is shown. Last not least, the early history of the
`almost' discovery of the electron spin in the SGE is revisited.Comment: 50pp, 17 fig
Superhumps and Repetitive Rebrightenings of the WZ Sge-Type Dwarf Nova, EG Cancri
We report on time-resolved photometric observations of the WZ Sge-type dwarf
nova, EG Cnc (Huruhata's variable, see also
http://www.kusastro.kyoto-u.ac.jp/vsnet/DNe/egcnc.html), during its
superoutburst in 1996-1997. EG Cnc, after the main superoutburst accompanied
with development of superhumps typical of a WZ Sge-type dwarf nova, exhibited a
series of six major rebrightenings. During these rebrightenings and the
following long fading tail, EG Cnc persistently showed superhumps having a
period equal to the superhump period observed during the main superoutburst.
The persistent superhumps had a constant superhump flux with respect to the
rebrightening phase. These findings suggest the superhumps observed during the
rebrightening stage and the fading tail are a "remnant" of usual superhumps,
and are not newly triggered by rebrightenings. By comparison with the 1977
outburst of this object and outbursts of other WZ Sge-type dwarf novae, we
propose an activity sequence of WZ Sge-type superoutbursts, in which the
current outburst of EG Cnc is placed between a single-rebrightening event and
distinct outbursts separated by a dip. The post-superoutburst behavior of WZ
Sge-type dwarf novae can be understood in the presence of considerable amount
of remnant matter behind the cooling front in the outer accretion disk, even
after the main superoutburst. We consider the premature quenching of the hot
state due to the weak tidal effect under the extreme mass ratio of the WZ
Sge-type binary is responsible for the origin of the remnant mass.Comment: 16 pages, 15 figures, to appear in PASJ (special issue on VSNET), for
more information, see http://www.kusastro.kyoto-u.ac.jp/vsnet
Transient jets in V617 Sagittarii
Some of the luminous Compact Binary Supersoft X-Ray sources (CBSS) have shown
indications of jets, also called satellites due to their appearance in the
spectra. In V Sagittae (V Sge) stars, the galactic counterparts of the CBSS,
such features have been reported only for WX Cen. If V Sge stars are indeed the
analogs of CBSS, one may expect transient jet emission in other objects of this
class. Spectroscopic observations of the V Sge star V617 Sgr have been made,
both at high photometric state and at decline. We show that V617 Sgr presents
Halpha satellites at high photometric state with velocities of +/-780 km/s.
This feature confirms, once more, the CBSS nature of the V Sge stars, however
the details of the spectral characteristics also suggest that the two groups of
stars display some intrinsic spectroscopic differences, which are likely to be
due to a selection effect related to chemical abundance.Comment: Four pages, accepted to be published as a Letter in A&
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