34,952 research outputs found
Outburst Photometry of the Eclipsing Dwarf Nova GY Cancri
We observed the ROSAT-selected eclipsing dwarf nova GY Cnc (=RX J0909.8+1849)
during the 2001 November outburst. We refined the orbital period to be
0.17544251(5) d. The fading portion of the outburst was indistinguishable from
those of typical dwarf novae with similar orbital periods. However, the
signature of orbital humps (or a hot spot) was far less prominently observed in
the orbital light curves and eclipse profiles than in usual dwarf novae with
similar orbital periods. The combination of low frequency of outbursts and the
apparent lack of slowly rising, long outbursts in GY Cnc is difficult to
reconcile within the standard framework of dwarf novae. We suspect that GY Cnc
may be the first above-the-gap counterpart of unusual eclipsing dwarf novae HT
Cas and IR Com.Comment: 6 pages, 7 figures, to appear in Publ. Astron. Soc. Japa
Particle Propagator of Spin Calogero-Sutherland Model
Explicit-exact expressions for the particle propagator of the spin 1/2
Calogero-Sutherland model are derived for the system of a finite number of
particles and for that in the thermodynamic limit. Derivation of the expression
in the thermodynamic limit is also presented in detail. Combining this result
with the hole propagator obtained in earlier studies, we calculate the spectral
function of the single particle Green's function in the full range of the
energy and momentum space. The resultant spectral function exhibits power-law
singularity characteristic to correlated particle systems in one dimension.Comment: 43 pages, 6 figure
Measuring spin of a supermassive black hole at the Galactic centre -- Implications for a unique spin
We determine the spin of a supermassive black hole in the context of
discseismology by comparing newly detected quasi-periodic oscillations (QPOs)
of radio emission in the Galactic centre, Sagittarius A* (Sgr A*), as well as
infrared and X-ray emissions with those of the Galactic black holes. We find
that the spin parameters of black holes in Sgr A* and in Galactic X-ray sources
have a unique value of which is smaller than the generally
accepted value for supermassive black holes, suggesting evidence for the
angular momentum extraction of black holes during the growth of supermassive
black holes. Our results demonstrate that the spin parameter approaches the
equilibrium value where spin-up via accretion is balanced by spin-down via the
Blandford-Znajek mechanism regardless of its initial spin. We anticipate that
measuring the spin of black holes by using QPOs will open a new window for
exploring the evolution of black holes in the Universe.Comment: 5 pages, 3 figures, accepted by MNRAS LETTE
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&
Currency Runs, International Reserves Management and Optimal Monetary Policy Rules
This paper studies the design of optimal monetary policy rules for emerging economies confronted to sharp capital outflows and speculative attacks. We extend Taylor type monetary policy rules by allowing the central bank to give some weight to the level of precautionary foreign reserve balances as one of its targets. We show that a currency crisis scenario can easily occur when the weight is zero, and that it can be avoided when the weight is positive. The impacts of the central bank's monetary control on the output level, the inflation rate, the exchange rate, and the foreign reserve level are investigated as well. By applying both the Hamiltonian as well as the Hamilton-Jacobi-Bellman (HJB) equation (the latter leading to a dynamic programming formulation of the problem), we can explore safe domains of attractions in a variety of complicated model variants. Given the uncertainties the central banks faces, we also show of how central banks can enlarge safe domains of attraction.Currency Crises, Capital Outflows, Monetary Policy Rules
On spectrum of a Schroedinger operator with a fast oscillating compactly supported potential
We study the phenomenon of an eigenvalue emerging from essential spectrum of
a Schroedinger operator perturbed by a fast oscillating compactly supported
potential. We prove the sufficient conditions for the existence and absence of
such eigenvalue. If exists, we obtain the leading term of its asymptotics
expansion.Comment: The article is originally written in Russian. The translation in
English is made by D. Boriso
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