31,628 research outputs found
A Modeling of the Super-Eddington Luminosity in Nova Outbursts: V1974 Cygni
We have modeled nova light curves exceeding the Eddington luminosity. It has
been suggested that a porous structure develops in nova envelopes during the
super Eddington phase and the effective opacity is much reduced for such a
porous atmosphere. Based on this reduced opacity model, we have calculated
envelope structures and light curves of novae. The optically thick wind model
is used to simulate nova winds. We find that the photospheric luminosity and
the wind mass-loss rate increase inversely proportional to the reducing factor
of opacities, but the wind velocity hardly changes. We also reproduce the
optical light curve of V1974 Cygni (Nova Cygni 1992) in the super-Eddington
phase, which lasts 13 days from the optical peak 1.7 mag above the Eddington
luminosity.Comment: 8 pages, 4 figures, to appear in ApJ
Toward a unified light curve model for multi-wavelength observations of V1974 Cygni (Nova Cygni 1992)
We present a unified model for optical, ultraviolet (UV), and X-ray light
curves of V1974 Cygni (Nova Cygni 1992). Based on an optically thick wind model
of nova outbursts, we have calculated light curves and searched for the best
fit model that is consistent with optical, UV, and X-ray observations. Our best
fit model is a white dwarf (WD) of mass 1.05 M_\sun with a chemical composition
of X=0.46, C+N+O=0.15, and Ne = 0.05 by mass weight. Both supersoft X-ray and
continuum UV 1455 \AA light curves are well reproduced. Supersoft X-rays
emerged on day ~ 250 after outburst, which is naturally explained by our model:
our optically thick winds cease on day 245 and supersoft X-rays emerge from
self-absorption by the winds. The X-ray flux keeps a constant peak value for ~
300 days followed by a quick decay on day ~ 600. The duration of X-ray flat
peak is well reproduced by a steady hydrogen shell burning on the WD. Optical
light curve is also explained by the same model if we introduce free-free
emission from optically thin ejecta. A t^{-1.5} slope of the observed optical
and infrared fluxes is very close to the slope of our modeled free-free light
curve during the optically thick wind phase. Once the wind stops, optical and
infrared fluxes should follow a t^{-3} slope, derived from a constant mass of
expanding ejecta. An abrupt transition from a t^{-1.5} slope to a t^{-3} slope
at day ~ 200 is naturally explained by the change from the wind phase to the
post-wind phase on day ~ 200. The development of hard X-ray flux is also
reasonably understood as shock-origin between the wind and the companion star.
The distance to V1974 Cyg is estimated to be ~ 1.7 kpc with E(B-V)= 0.32 from
the light curve fitting for the continuum UV 1455 \AA.Comment: 8 pages, 4 figures, to appear in the Astrophysical Journa
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
Antiferromagnetic Order in Pauli Limited Unconventional Superconductors
We develop a theory of the coexistence of superconductivity (SC) and
antiferromagnetism (AFM) in CeCoIn5. We show that in Pauli-limited nodal
superconductors the nesting of the quasi-particle pockets induced by Zeeman
pair-breaking leads to incommensurate AFM with the moment normal to the field.
We compute the phase diagram and find a first order transition to the normal
state at low temperatures, absence of normal state AFM, and coexistence of SC
and AFM at high fields, in agreement with experiments. We also predict the
existence of a new double-Q magnetic phase
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
Electron spin interferometry using a semiconductor ring structure
A ring structure fabricated from GaAs is used to achieve interference of the
net spin polarization of conduction band electrons. Optically polarized spins
are split into two packets by passing through two arms of the ring in the
diffusive transport regime. Optical pumping with circularly polarized light on
one arm establishes dynamic nuclear polarization which acts as a local
effective magnetic field on electron spins due to the hyperfine interaction.
This local field causes one spin packet to precess faster than the other,
thereby controlling the spin interference when the two packets are combined.Comment: 4 pages, 2 figure
Theoretical Sensitivity Analysis for Quantitative Operational Risk Management
We study the asymptotic behavior of the difference between the values at risk
VaR(L) and VaR(L+S) for heavy tailed random variables L and S for application
in sensitivity analysis of quantitative operational risk management within the
framework of the advanced measurement approach of Basel II (and III). Here L
describes the loss amount of the present risk profile and S describes the loss
amount caused by an additional loss factor. We obtain different types of
results according to the relative magnitudes of the thicknesses of the tails of
L and S. In particular, if the tail of S is sufficiently thinner than the tail
of L, then the difference between prior and posterior risk amounts VaR(L+S) -
VaR(L) is asymptotically equivalent to the expectation (expected loss) of S.Comment: 21 pages, 1 figure, 4 tables, forthcoming in International Journal of
Theoretical and Applied Finance (IJTAF
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&
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