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

Nature of the Earth's Interior

n/

3-D Photoionization Structure and Distances of Planetary Nebulae II. Menzel 1

We present the results of a spatio-kinematic study of the planetary nebula Menzel 1 using spectro-photometric mapping and a 3-D photoionization code. We create several 2-D emission line images from our long-slit spectra, and use these to derive the line fluxes for 15 lines, the Halpha/Hbeta extinction map, and the [SII] line ratio density map of the nebula. We use our photoionization code constrained by these data to derive the three-dimensional nebular structure and ionizing star parameters of Menzel 1 by simultaneously fitting the integrated line intensities, the density map, and the observed morphologies in several lines, as well as the velocity structure. Using theoretical evolutionary tracks of intermediate and low mass stars, we derive a mass for the central star of 0.63+-0.05 Msolar. We also derive a distance of 1050+_150 pc to Menzel 1.Comment: To be published in ApJ of 10th February 2005. 12 figure

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

The "Twin Jet" Planetary Nebula M2-9

We present a model for the structure, temporal behavior, and evolutionary status of the bipolar nebula M2-9. According to this model the system consists of an AGB or post-AGB star and a hot white dwarf companion, with an orbital period of about 120 years. The white dwarf has undergone a symbiotic nova eruption about 1200 years ago, followed by a supersoft x-ray source phase. The positional shift of the bright knots in the inner nebular lobes is explained in terms of a revolving ionizing source. We show that the interaction between the slow, AGB star's wind, and a collimated fast wind from the white dwarf clears a path for the ionizing radiation in one direction, while the radiation is attenuated in others. This results in the mirror-symmetric (as opposed to the more common point-symmetric) shift in the knots. We show that M2-9 provides an important evolutionary link among planetary nebulae with binary central stars, symbiotic systems, and supersoft x-ray sources.Comment: 13 pages + 2 figures. Submitted to Ap

Optical Polarimetry, High–Resolution Spectroscopy and IR Analysis of the Chamaeleon I Dark Cloud

We present optical polarimetry and high resolution spectroscopy of a sample of stars toward the Chamaeleon I dark cloud. We use our polarimetry which includes 33 stars to study the wavelength dependence of the degree and position angle of polarization.From our data we found, by interpretation of the various correlations between the polarimetry, photometry and IRAS fluxes, the following:the probable presence of shocked molecular gas; a warm molecular CH component; small dust grains at the edges of the cloud, and larger grains in the central parts, which are causing the polarization.Our results provide a consistent picture of the gas and dust content in the Cha I region, where larger grains, responsible of the starlight polarization, exist in the center of the cloud, surrounded by envelopes of warmer molecular and atomic material

The large-scale ionised outflow of CH Cygni

HST and ground-based [OII} and [NII] images obtained from 1996 to 1999 reveal the existence of a ionised optical nebula around the symbiotic binary CH Cyg extending out to 5000 A.U. from the central stars. The observed velocity range of the nebula, derived from long-slit echelle spectra, is of 130 km/s. In spite of its complex appearence, the velocity data show that the basic morphology of the inner regions of the optical nebula is that of a bipolar (or conical) outflow extending nearly along the plane of the sky out to some 2000 A.U. from the centre. Even if the extension of this bipolar outflow and its position angle are consistent with those of the radio jet produced in 1984 (extrapolated to the time of our optical imagery), no obvious counterpart is visible of the original, dense radio bullets ejected by the system. We speculate that the optical bipolar outflow might be the remannt of the interaction of the bullets with a relatively dense circumstellar medium.Comment: 8 text pages + 3 figures (jpeg). ApJ in press. For a full PostScript version with figures inline see ftp://ftp.ll.iac.es/pub/research/preprints/PP252001.ps.g

Fibre Bundles and Generalised Dimensional Reduction

We study some geometrical and topological aspects of the generalised dimensional reduction of supergravities in D=11 and D=10 dimensions, which give rise to massive theories in lower dimensions. In these reductions, a global symmetry is used in order to allow some of the fields to have a non-trivial dependence on the compactifying coordinates. Global consistency in the internal space imposes topological restrictions on the parameters of the compactification as well as the structure of the space itself. Examples that we consider include the generalised reduction of the type IIA and type IIB theories on a circle, and also the massive ten-dimensional theory obtained by the generalised reduction of D=11 supergravity.Comment: 23 pages, Late