26,643 research outputs found
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
A combinatorial Li-Yau inequality and rational points on curves
We present a method to control gonality of nonarchimedean curves based on graph theory. Let k denote a complete nonarchimedean valued field.We first prove a lower bound for the gonality of a curve over the algebraic closure of k in terms of the minimal degree of a class of graph maps, namely: one should minimize over all so-called finite harmonic graph morphisms to trees, that originate from any refinement of the dual graph of the stable model of the curve. Next comes our main result: we prove a lower bound for the degree of such a graph morphism in terms of the first eigenvalue of the Laplacian and some “volume” of the original graph; this can be seen as a substitute for graphs of the Li–Yau inequality from differential geometry, although we also prove that the strict analogue of the original inequality fails for general graphs. Finally,we apply the results to give a lower bound for the gonality of arbitraryDrinfeld modular curves over finite fields and for general congruence subgroups Γ of Γ (1) that is linear in the index [Γ (1) : Γ ], with a constant that only depends on the residue field degree and the degree of the chosen “infinite” place. This is a function field analogue of a theorem of Abramovich for classical modular curves. We present applications to uniform boundedness of torsion of rank two Drinfeld modules that improve upon existing results, and to lower bounds on the modular degree of certain elliptic curves over function fields that solve a problem of Papikian
Coulomb analogy for nonhermitian degeneracies near quantum phase transitions
Degeneracies near the real axis in a complex-extended parameter space of a
hermitian Hamiltonian are studied. We present a method to measure distributions
of such degeneracies on the Riemann sheet of a selected level and apply it in
classification of quantum phase transitions. The degeneracies are shown to
behave similarly as complex zeros of a partition function.Comment: 4 page
Norm kernels and the closeness relation for Pauli-allowed basis functions
The norm kernel of the generator-coordinate method is shown to be a symmetric
kernel of an integral equation with eigenfunctions defined in the
Fock--Bargmann space and forming a complete set of orthonormalized states
(classified with the use of SU(3) symmetry indices) satisfying the Pauli
exclusion principle. This interpretation allows to develop a method which, even
in the presence of the SU(3) degeneracy, provides for a consistent way to
introduce additional quantum numbers for the classification of the basis
states. In order to set the asymptotic boundary conditions for the expansion
coefficients of a wave function in the SU(3) basis, a complementary basis of
functions with partial angular momenta as good quantum numbers is needed. Norm
kernels of the binary systems 6He+p, 6He+n, 6He+4He, and 8He+4He are considered
in detail.Comment: 25 pages; submitted to Few-Body System
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