On Echo Outbursts and ER UMa Supercycles in SU UMa-type Cataclysmic Variables

I present a variation on Osaki's tidal-thermal-instability model for SU UMa behavior. I suggest that in systems with the lowest mass ratios, the angular-momentum dissipation in an eccentric disk is unable to sustain the disk on the hot side of the thermal instability. This decoupling of the tidal and thermal instabilities in systems with q < 0.07 allows a better explanation of the `echo' outbursts of EG Cnc and the short supercycles of RZ LMi and DI UMa. The idea might also apply to the soft X-ray transients.Comment: To appear in PASP, April 2001 (6 pages, 4 figs

Enhanced mass transfer during dwarf nova outbursts by irradiation of the secondary?

One of the remaining issues in the problems of dwarf novae is whether or not enhanced mass transfer due to irradiation of the secondary stars could occur during outbursts. In a previous paper (Osaki and Meyer 2003), we presented a theoretical analysis that shows no appreciable enhancement of the mass outflow rate. This conclusion is challenged by Smak (2004) who claims that equations used in our analysis were incorrect and that in systems with short orbital periods substantial enhancement could occur. In this letter, we examine the origin of such divergent conclusions. We show that Smak's solutions are unacceptable from the standpoint of the equation of continuity and that our analysis is an appropriate one to treat this problem.Comment: 4 pages, accepted by Astronomy &.Astrophysics Letter

Superhumps in a Peculiar SU UMa-Type Dwarf Nova ER Ursae Majoris

We report the photometry of a peculiar SU UMa-type dwarf nova - ER UMa for ten nights during 1998 December and 1999 March covering a complete rise to the supermaximum and a normal outburst cycle. Superhumps have been found during the rise to the superoutburst. A negative superhump appeared in Dec.22 light curve, while the superhump on the next night became positive and had large amplitude and distinct waveform from that of the previous night. In the normal outburst we captured, superhumps with larger or smaller amplitudes seem to always exist, although it is not necessarily true for every normal outburst. These results show great resemblance with V1159 Ori (Patterson et al. 1995). It is more likely that superhumps occasionally exist at essentially all phases of the eruption cycles of ER UMa stars, which should be considered in modeling.Comment: 4 pages, 5 figures, Accepted by ApJ Letter

Evolution of Giant Planets in Eccentric Disks

We investigate the interaction between a giant planet and a viscous circumstellar disk by means of high-resolution, two-dimensional hydrodynamical simulations. We consider planet masses that range from 1 to 3 Jupiter masses (Mjup) and initial orbital eccentricities that range from 0 to 0.4. We find that a planet can cause eccentricity growth in a disk region adjacent to the planet's orbit, even if the planet's orbit is circular. Disk-planet interactions lead to growth in a planet's orbital eccentricity. The orbital eccentricities of a 2 Mjup and a 3 Mjup planet increase from 0 to 0.11 within about 3000 orbits. Over a similar time period, the orbital eccentricity of a 1 Mjup planet grows from 0 to 0.02. For a case of a 1 Mjup planet with an initial eccentricity of 0.01, the orbital eccentricity grows to 0.09 over 4000 orbits. Radial migration is directed inwards, but slows considerably as a planet's orbit becomes eccentric. If a planet's orbital eccentricity becomes sufficiently large, e > ~0.2, migration can reverse and so be directed outwards. The accretion rate towards a planet depends on both the disk and the planet orbital eccentricity and is pulsed over the orbital period. Planet mass growth rates increase with planet orbital eccentricity. For e~0.2 the mass growth rate of a planet increases by approximately 30% above the value for e=0. For e > ~0.1, most of the accretion within the planet's Roche lobe occurs when the planet is near the apocenter. Similar accretion modulation occurs for flow at the inner disk boundary which represents accretion toward the star.Comment: 20 pages 16 figures, 3 tables. To appear in The Astrophysical Journal vol.652 (December 1, 2006 issue

Lattice study on two-color QCD with six flavors of dynamical quarks

We study the dynamics of SU(2) gauge theory with NF=6 Dirac fermions by means of lattice simulation to investigate if they are appropriate to realization of electroweak symmetry breaking. The discrete analogue of beta function for the running coupling constant defined under the Schroedinger functional boundary condition are computed on the lattices up to linear size of L/a=24 and preclude the existence of infrared fixed point below 7.6. Gluonic observables such as heavy quark potential, string tension, Polyakov loop suggest that the target system is in the confining phase even in the massless quark limit.Comment: 7 pages, 9 figures, Proceedings of The 30th International Symposium on Lattice Field Theory, June 24-29, 2012, Cairns, Australi