894 research outputs found
Unusual Phase Reversal of Superhumps in ER Ursae Majoris
We studied the evolution of superhumps in the peculiar SU UMa-type dwarf
nova, ER UMa. Contrary to the canonical picture of the SU UMa-type superhump
phenomena, the superhumps of ER UMa show an unexpected phase reversal during
the very early stage (~5 d after the superoutburst maximum). We interpret that
a sudden switch to so-called late superhumps occurs during the very early stage
of a superoutburst. What had been believed to be (ordinary) superhumps during
the superoutburst plateau of ER UMa were actually late superhumps. The
implication of this discovery is briefly discussed.Comment: 4 pages, 5 figures, submitted to Publ. Astron. Soc. Japa
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
Dirac's hole theory versus quantum field theory
Dirac's hole theory and quantum field theory are usually considered
equivalent to each other. For models of a certain type, however, the
equivalence may not hold as we discuss in this Letter. This problem is closely
related to the validity of the Pauli principle in intermediate states of
perturbation theory.Comment: No figure
In-the-Gap SU UMa-Type Dwarf Nova, Var73 Dra with a Supercycle of about 60 Days
An intensive photometric-observation campaign of the recently discovered SU
UMa-type dwarf nova, Var73 Dra was conducted from 2002 August to 2003 February.
We caught three superoutbursts in 2002 October, December and 2003 February. The
recurrence cycle of the superoutburst (supercycle) is indicated to be 60
d, the shortest among the values known so far in SU UMa stars and close to
those of ER UMa stars. The superhump periods measured during the first two
superoutbursts were 0.104885(93) d, and 0.10623(16) d, respectively. A
0.10424(3)-d periodicity was detected in quiescence. The change rate of the
superhump period during the second superoutburst was , which
is an order of magnitude larger than the largest value ever known. Outburst
activity has changed from a phase of frequent normal outbursts and infrequent
superoutbursts in 2001 to a phase of infrequent normal outbursts and frequent
superoutbursts in 2002. Our observations are negative to an idea that this star
is an related object to ER UMa stars in terms of the duty cycle of the
superoutburst and the recurrence cycle of the normal outburst. However, to
trace the superhump evolution throughout a superoutburst, and from quiescence
more effectively, may give a fruitful result on this matter.Comment: 9 pages, 8 figures, submitted to A&
The Extended Deep Minimum and the Subsequent Brightening of RX And in 1996-1997
We discovered that RX And, one of prototypical Z Cam-type dwarf novae,
underwent a deep, extended faint state in 1996-1997. Time-resolved photometry
at the bottom of the fading revealed the presence of strong flickering, and the
absence of detectable orbital modulation. This finding indicates that the
mass-transfer remained even at the deepest minimum of the fading, contrary to
what was observed in a deep minimum of a VY Scl-type star, MV Lyr. RX And
subsequently underwent a brightening (outburst) during its recovery stage. The
photometric and spectroscopic characteristics of the brightening significantly
differed from those of ordinary outbursts of RX And, and are considered to
resemble an inside-out type outburst of a long-period dwarf nova. An
examination of historical visual observations revealed the possible presence of
\~10-yr periodicity, which is close to what has been proposed for MV Lyr. The
common observed features between RX And and VY Scl-type stars may suggest a
common underlying mechanism for producing temporary deep fadings. The departure
from the disk instability model, as observed in VY Scl-type stars, was not
apparent in the present fading of RX And. In conjunction with the recently
published Hubble Space Telescope observation during the same fading, we can
conclude that the phenomenological difference from the VY Scl-type fading is
understood as a smaller effect of irradiation on the accretion disk in RX And.Comment: 7 pages, 5 figures, accepted for publication in PAS
Application of Total Variation Minimization to Doppler Tomography
We have developed a new model of the Doppler tomography using total variation minimization (DTTVM). We demonstrated that this method can reconstruct localized and non-axisymmetric profiles possibly having sharp edges in the Doppler map. We apply this model to the real data of the dwarf nova, WZ Sge in superoutburst. DTTVM can reproduce the observed spectra with a high precision, while the previous models fail to reproduce localized sources
Dynamics of bright matter wave solitons in a quasi 1D Bose-Einstein condensate with a rapidly varying trap
The dynamics of a bright matter wave soliton in a quasi 1D Bose-Einstein
condensate with periodically rapidly varying trap is considered. The governing
equation is derived based on averaging over fast modulations of the
Gross-Pitaevskii (GP) equation. This equation has the form of GP equation with
effective potential of more complicated structure than unperturbed trap. For
the case of inverted (expulsive) quadratic trap corresponding to unstable GP
equation, the effective potential can be stable. For the bounded in space trap
potential it is showed that the bifurcation exists, i.e.,the single well
potential bifurcates to the triple well effective potential. Stabilization of
BEC cloud on-site state in the temporary modulated optical lattice is found.
(analogous to the Kapitza stabilization of the pendulum). The predictions of
the averaged GP equation are confirmed by the numerical simulations of GP
equation with rapid perturbations.Comment: 15 pages, 4 figure
Photometric Observations of an SU UMa-type Dwarf Nova VW Coronae Borealis during Outbursts
We report the photometric observations of an SU UMa-type dwarf nova VW CrB
during two superoutbursts in 2001 and 2003 and a normal outburst in 2003.
Superhumps with a period of 0.07287(1) d were observed during the 2003
superoutburst. The change rate of the superhump period was positive. During the
normal outburst, there are some hint of modulation up to a 0.2-mag amplitude.
However, any periodicity was not found. The recurrence cycles of the normal
outburst and the superoutburst, and the distance were estimated to be > ~50 d,
270-500 d, and 690(+230, -170) pc, respectively. These recurrence cycles are
usual values for an SU UMa-type dwarf nova having this superhump period. The
superhump period of VW CrB was the longest among those of the SU UMa stars with
positive derivatives of the superhump period. The coverage of our observations
was, however, not enough, and the variation of the Psh change rate of VW CrB is
still unknown. A superhump regrowth and a brightening were seen near the end of
the plateau phase. Measuring the deviation of the start timings of the
brightening and the superhump regrowth (>2 days in VW CrB) will be a key to
reveal the mechanism of these phenomena.Comment: 7 pages, 8 figures, to appear in PAS
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