Kinematic and morphological modeling of the bipolar nebula Sa2-237

We present [OIII]500.7nm and Halpha+[NII] images and long-slit, high resolution echelle spectra in the same spectral regions of Sa2--237, a possible bipolar planetary nebula. The image shows a bipolar nebula of about 34" extent, with a narrow waist, and showing strong point symmetry about the central object, indicating it's likely binary nature. The long slit spectra were taken over the long axis of the nebula, and show a distinct ``eight'' shaped pattern in the velocity--space plot, and a maximum projected outflow velocity of V=106km/s, both typical of expanding bipolar planetary nebulae. By model fitting the shape and spectrum of the nebula simultaneously, we derive the inclination of the long axis to be 70 degrees, and the maximum space velocity of expansion to be 308 km/s. Due to asymmetries in the velocities we adopt a new value for the system's heliocentric radial velocity of -30km/s. We use the IRAS and 21cm radio fluxes, the energy distribution, and the projected size of Sa2-237 to estimate it's distance to be 2.1+-0.37kpc. At this distance Sa2-237 has a luminosity of 340 Lsun, a size of 0.37pc, and -- assuming constant expansion velocity -- a nebular age of 624 years. The above radial velocity and distance place Sa2--237 in the disk of the Galaxy at z=255pc, albeit with somewhat peculiar kinematics.Comment: 10pp, 4 fig

Kaluza-Klein electrically charged black branes in M-theory

We present a class of Kaluza-Klein electrically charged black p-brane solutions of ten-dimensional, type IIA superstring theory. Uplifting to eleven dimensions these solutions are studied in the context of M-theory. They can be interpreted either as a p+1 extended object trapped around the eleventh dimension along which momentum is flowing or as a boost of the following backgrounds: the Schwarzschild black (p+1)-brane or the product of the (10-p)-dimensional Euclidean Schwarzschild manifold with the (p+1)-dimensional Minkowski spacetime.Comment: 16 pages, uses latex and epsf macro, figures include

Abelian Duality

We show that on three-dimensional Riemannian manifolds without boundaries and with trivial first real de Rham cohomology group (and in no other dimensions) scalar field theory and Maxwell theory are equivalent: the ratio of the partition functions is given by the Ray-Singer torsion of the manifold. On the level of interaction with external currents, the equivalence persists provided there is a fixed relation between the charges and the currents.Comment: 11 pages, LaTeX, no figures, a reference added, submitted to Phys. Rev.

Structural and Electronic Properties of the Interface between the High-k oxide LaAlO3 and Si(001)

The structural and electronic properties of the LaAlO3/Si(001) interface are determined using state-of-the-art electronic structure calculations. The atomic structure differs from previous proposals, but is reminiscent of La adsorption structures on silicon. A phase diagram of the interface stability is calculated as a function of oxygen and Al chemical potentials. We find that an electronically saturated interface is obtained only if dopant atoms segregate to the interface. These findings raise serious doubts whether LaAlO3 can be used as an epitaxial gate dielectric.Comment: 4 pages, 5 figure

Addenda and corrections to work done on the path-integral approach to classical mechanics

In this paper we continue the study of the path-integral formulation of classical mechanics and in particular we better clarify, with respect to previous papers, the geometrical meaning of the variables entering this formulation. With respect to the first paper with the same title, we {\it correct} here the set of transformations for the auxiliary variables $\lambda_{a}$. We prove that under this new set of transformations the Hamiltonian ${\widetilde{\cal H}}$, appearing in our path-integral, is an exact scalar and the same for the Lagrangian. Despite this different transformation, the variables $\lambda_{a}$ maintain the same operatorial meaning as before but on a different functional space. Cleared up this point we then show that the space spanned by the whole set of variables ($\phi, c, \lambda,\bar c$) of our path-integral is the cotangent bundle to the {\it reversed-parity} tangent bundle of the phase space ${\cal M}$ of our system and it is indicated as $T^{\star}(\Pi T{\cal M})$. In case the reader feel uneasy with this strange {\it Grassmannian} double bundle, we show in this paper that it is possible to build a different path-integral made only of {\it bosonic} variables. These turn out to be the coordinates of $T^{\star}(T^{\star}{\cal M})$ which is the double cotangent bundle of phase-space.Comment: Title changed, appendix expanded, few misprints fixe

High-velocity collimated outflows in planetary nebulae: NGC 6337, He 2-186, and K 4-47

We have obtained narrow-band images and high-resolution spectra of the planetary nebulae NGC 6337, He 2-186, and K 4-47, with the aim of investigating the relation between their main morphological components and several low-ionization features present in these nebulae. The data suggest that NGC 6337 is a bipolar PN seen almost pole on, with polar velocities higher than 200 km/s. The bright inner ring of the nebula is interpreted to be the "equatorial" density enhancement. It contains a number of low-ionization knots and outward tails that we ascribe to dynamical instabilities leading to fragmentation of the ring or transient density enhancements due to the interaction of the ionization front with previous density fluctuations in the ISM. The lobes show a pronounced point-symmetric morphology and two peculiar low-ionization filaments whose nature remains unclear. The most notable characteristic of He 2-186 is the presence of two high-velocity (higher than 135 km/s) knots from which an S-shaped lane of emission departs toward the central star. K 4-47 is composed of a compact core and two high-velocity, low-ionization blobs. We interpret the substantial broadening of line emission from the blobs as a signature of bow shocks, and using the modeling of Hartigan, Raymond, & Hartman (1987), we derive a shock velocity of 150 km/s and a mild inclination of the outflow on the plane of the sky. We discuss possible scenarios for the formation of these nebulae and their low-ionization features. In particular, the morphology of K 4-47 hardly fits into any of the usually adopted mass-loss geometries for single AGB stars. Finally, we discuss the possibility that point-symmetric morphologies in the lobes of NGC 6337 and the knots of He 2-186 are the result of precessing outflows from the central stars.Comment: 16 pages plus 7 figures, ApJ accepted. Also available at http://www.iac.es/publicaciones/preprints.htm

A Note on Marginally Stable Bound States in Type II String Theory

Spectrum of elementary string states in type II string theory contains ultra-short multiplets that are marginally stable. $U$-duality transformation converts these states into bound states at threshold of $p$-branes carrying Ramond-Ramond charges, and wrapped around $p$-cycles of a torus. We propose a test for the existence of these marginally stable bound states. Using the recent results of Polchinski and of Witten, we argue that the spectrum of bound states of $p$-branes is in agreement with the prediction of $U$-duality.Comment: LaTeX file, 6 page

Self-dual Yang-Mills fields in pseudoeuclidean spaces

The self-duality Yang-Mills equations in pseudoeuclidean spaces of dimensions $d\leq 8$ are investigated. New classes of solutions of the equations are found. Extended solutions to the D=10, N=1 supergravity and super Yang-Mills equations are constructed from these solutions.Comment: 9 pages, LaTeX, no figure