Dwarf Cepheids in the Carina Dwarf Spheroidal Galaxy

We have discovered 20 dwarf Cepheids (DC) in the Carina dSph galaxy from the analysis of individual CCD images obtained for a deep photometric study of the system. These short-period pulsating variable stars are by far the most distant (~100 kpc) and faintest (V ~ 23.0) DCs known. The Carina DCs obey a well-defined period-luminosity relation, allowing us to readily distinguish between overtone and fundamental pulsators in nearly every case. Unlike RR Lyr stars, the pulsation mode turns out to be uncorrelated with light-curve shape, nor do the overtone pulsators tend towards shorter periods compared to the fundamental pulsators. Using the period-luminosity (PL) relations from Nemec et al. (1994 AJ, 108, 222) and McNamara (1995, AJ, 109, 1751), we derive (m-M)_0 = 20.06 +/- 0.12, for E(B-V) = 0.025 and [Fe/H] = -2.0, in good agreement with recent, independent estimates of the distance/reddening of Carina. The error reflects the uncertainties in the DC distance scale, and in the metallicity and reddening of Carina. The frequency of DCs among upper main sequence stars in Carina is approximately 3%. The ratio of dwarf Cepheids to RR Lyr stars in Carina is 0.13 +/- 0.10, though this result is highly sensitive to the star-formation history of Carina and the evolution of the Horizontal Branch. We discuss how DCs may be useful to search effectively for substructure in the Galactic halo out to Galactocentric distances of ~100 kpc.Comment: 20 pages of text, 7 figure

Auditing practice, research, and education : a productive collaboration

https://egrove.olemiss.edu/aicpa_assoc/1506/thumbnail.jp

The Sphaleron Rate in SU(N) Gauge Theory

The sphaleron rate is defined as the diffusion constant for topological number NCS = int g^2 F Fdual/32 pi^2. It establishes the rate of equilibration of axial light quark number in QCD and is of interest both in electroweak baryogenesis and possibly in heavy ion collisions. We calculate the weak-coupling behavior of the SU(3) sphaleron rate, as well as making the most sensible extrapolation towards intermediate coupling which we can. We also study the behavior of the sphaleron rate at weak coupling at large Nc.Comment: 18 pages with 3 figure

Out-of-equilibrium states as statistical equilibria of an effective dynamics

We study the formation of coherent structures in a system with long-range interactions where particles moving on a circle interact through a repulsive cosine potential. Non equilibrium structures are shown to correspond to statistical equilibria of an effective dynamics, which is derived using averaging techniques. This simple behavior might be a prototype of others observed in more complicated systems with long-range interactions, like two-dimensional incompressible fluids or self-gravitating systems.Comment: 4 figure

Gravitational Mesoscopic Constraints in Cosmological Dark Matter Halos

We present an analysis of the behaviour of the `coarse-grained' (`mesoscopic') rank partitioning of the mean energy of collections of particles composing virialized dark matter halos in a Lambda-CDM cosmological simulation. We find evidence that rank preservation depends on halo mass, in the sense that more massive halos show more rank preservation than less massive ones. We find that the most massive halos obey Arnold's theorem (on the ordering of the characteristic frequencies of the system) more frequently than less massive halos. This method may be useful to evaluate the coarse-graining level (minimum number of particles per energy cell) necessary to reasonably measure signatures of `mesoscopic' rank orderings in a gravitational system.Comment: LaTeX, 15 pages, 3 figures. Accepted for publication in Celestial Mechanics and Dynamical Astronomy Journa

A Prescription for Building the Milky Way's Halo from Disrupted Satellites

We develop a semi-analytic method for determining the phase-space population of tidal debris along the orbit of a disrupting satellite galaxy and illustrate its use with a number of applications. We use this method to analyze Zhao's proposal that the microlensing events towards the Large Magellanic Cloud (LMC) might be explained by an appropriately placed tidal streamer, and find that his scenarios lead either to unacceptably high overdensities (10 -- 100%) in faint star counts (apparent magnitudes 17.5 -- 20.5) away from the Galactic plane or short timescales for the debris to disperse (10^8 years). We predict that the tidal streamers from the LMC and the Sagittarius dwarf galaxy currently extend over more than $2\pi$ in azimuth along their orbits. Assuming that each satellite has lost half of its primordial mass, we find that the streamers will have overdensities in faint star counts of 10 -- 100% and < 1% respectively, and conclude that this mass loss rate is unlikely for the LMC, but possible for Sagittarius. If the Galaxy has accreted one hundred $10^5-10^6 M_{\odot}$ objects (comparable to its current population of globular clusters) at distances of 20 -- 100 kpc during its lifetime then 10% of the sky will now be covered by tidal streamers.Comment: 35 pages, LaTeX, 12 postscript figures included. Submitted to Ap

Speech Communication

Contains reports on three research projects.U.S. Air Force (Air Force Cambridge Research Center, Air Research and Development Command) under Contract AF 19(604)-2061National Science Foundatio

A new variational approach to the stability of gravitational systems

We consider the three dimensional gravitational Vlasov Poisson system which describes the mechanical state of a stellar system subject to its own gravity. A well-known conjecture in astrophysics is that the steady state solutions which are nonincreasing functions of their microscopic energy are nonlinearly stable by the flow. This was proved at the linear level by several authors based on the pioneering work by Antonov in 1961. Since then, standard variational techniques based on concentration compactness methods as introduced by P.-L. Lions in 1983 have led to the nonlinear stability of subclasses of stationary solutions of ground state type. In this paper, inspired by pioneering works from the physics litterature (Lynden-Bell 94, Wiechen-Ziegler-Schindler MNRAS 88, Aly MNRAS 89), we use the monotonicity of the Hamiltonian under generalized symmetric rearrangement transformations to prove that non increasing steady solutions are local minimizer of the Hamiltonian under equimeasurable constraints, and extract compactness from suitable minimizing sequences. This implies the nonlinear stability of nonincreasing anisotropic steady states under radially symmetric perturbations

On the Global Existence of Bohmian Mechanics

We show that the particle motion in Bohmian mechanics, given by the solution of an ordinary differential equation, exists globally: For a large class of potentials the singularities of the velocity field and infinity will not be reached in finite time for typical initial values. A substantial part of the analysis is based on the probabilistic significance of the quantum flux. We elucidate the connection between the conditions necessary for global existence and the self-adjointness of the Schr\"odinger Hamiltonian.Comment: 35 pages, LaTe

A tidal extension in the Ursa Minor dwarf spheroidal galaxy

We report the detection of main-sequence and blue horizontal-branch stars of the Ursa Minor dwarf spheroidal galaxy beyond its tidal radius, indicating the existence of a possible tidal extension in this satellite of the Milky Way. This tidal extension could spread out well beyond the area covered in our survey (R>80 arcmin),as suggested by the presence of a ``break'' to a shallower slope observed in its density profile. The V-band surface brightness for this possible tidal extension range from 29.8 to 31.5 mag arcsec^-2. The area covered in our survey (~1.65 deg^2) is not enough to discriminate if this extra-tidalpopulation is part of a tidal tail or an extended halo around the galaxy. The existence of this tidal extension in Ursa Minor indicates that this satellite is currently undergoing a tidal disruption process by the Milky Way. We discuss the possibility of a tidal origin for the high mass-to-light ratio observed in this galaxy on the basis on our result and recent theoretical simulations of the tidal disruption of dwarf satellites in the Galactic halo.Comment: 13 pages, 3 figures, accepted for publication in Astrophysical Journal Letter