Gallery of Planetary Nebula Spectra

We present the Gallery of Planetary Nebula Spectra now available at http://oit.williams.edu/nebulae The website offers high-quality, moderate resolution (~7-10 A FWHM) spectra of 128 Galactic planetary nebulae from 3600-9600 A, obtained by Kwitter, Henry, and colleagues with the Goldcam spectrograph at the KPNO 2.1-m or with the RC spectrograph at the CTIO 1.5-m. The master PN table contains atlas data and an image link. A selected object's spectrum is displayed in a zoomable window; line identification templates are provided. In addition to the spectra themselves, the website also contains a brief discussion of PNe as astronomical objects and as contributors to our understanding of stellar evolution. We envision that this website, which concentrates a large amount of data in one place, will be of interest to a variety of users: researchers might need to check the spectrum of a particular object of interest; the non-specialist astronomer might simply be interested in perusing such a collection of spectra; and finally, teachers of introductory astronomy can use this database to illustrate basic principles of atomic physics and radiation. To particularly encourage this last use, we have developed two paper-and-pencil exercises to introduce beginning astronomy students to the wealth of information that PN spectra contain.Comment: Two pages, two figures. Contributed paper to IAU Symp. 234, ``Planetary Nebulae in our Galaxy and Beyond.'

The hindered rotor density-of-states interpolation function

We construct an approximation to the partition function for hindered rotors based entirely on their asymptotic behavior and no fitting parameters. The approximant is shown to be quite accurate in all temperature ranges. Explicit auxiliary functions are derived for the Helmholtz free energy, internal energy, heat capacity, and entropy. We apply this function to estimating the heat capacity and unimolecular dissociation rate for ethane

Approximation Techniques for Planar Periodic Structures

The rigorous calculation of electromagnetic properties of periodic meshes using moment methods requires considerable algebraic work and computer resources. In this paper, a number of easy to use approximation techniques for analyzing thin structures with square, rectangular, and circular holes are presented. Formulas for the effective impedante of these meshes are described which can easily take into account oblique incidence and the presence of a dielectric substrate. In addition, techniques for analyzing more complex-shaped apertures such as a cross are discussed. These methods are more accurate than existing approximation techniques and can be applied to a wide range of situations that could not be handled before

Free energy and surface tension of arbitrarily large Mackay icosahedral clusters

We present a model for predicting the free energy of arbitrarily large Mackay icosahedral clusters. van der Waals clusters are experimentally observed to be particularly stable at magic numbers corresponding to these structures. Explicit calculations on the vibrational states were used to determine the spectrum of fundamental frequencies for smaller (~561 atoms). Combining these predictions with correlations for the moment of inertia and for the minimum potential energy of large clusters leads to free energies of arbitrary large clusters. The free energies are used to predict the chemical potential and surface tension as a function of size and temperature. This connects macroscopic properties to the microscopic atomic parameters

Thermodynamic properties and homogeneous nucleation rates for surface-melted physical clusters

We predict the free energy of van der Waals clusters (Fn) in the surface-melted temperature regime. These free energies are used to predict the bulk chemical potential, surface tension, Tolman length, and vapor pressure of noble gas crystals. Together, these estimates allow us to make definitive tests of the capillarity approximation in classical homogeneous nucleation theory. We find that the capillarity approximation underestimates the nucleation rate by thirty orders of magnitude for argon. The best available experiments are consistent with our calculation of nucleation rate as a function of temperature and pressure. We suggest experimental conditions appropriate for determining quantitative nucleation rates which would be invaluable in guiding further development of the theory. To make the predictions of Fn, we develop the Shellwise Lattice Search (SLS) algorithm to identify isomer fragments and the Linear Group Contribution (LGC) method to estimate the energy of isomers composed of those fragments. Together, SLS/LGC approximates the distribution of isomers which contribute to the configurational partition function (for up to 147-atom clusters). Estimates of the remaining free energy contributions come from a previous paper in this series

X ray microscope/telescope test and alignment

The tasks performed by the Center for Applied Optics (CAO) in support of the Normal Incidence Multilayer X-Ray Optics Program are detailed. The Multi-Spectral Solar Telescope Array (MSSTA) was launched on a Terrier-boosted Black Brant sounding rocket from White Sands Missile Range on 13 May 1991. High resolution images of the sun in the soft x ray to extreme ultraviolet (EUV) regime were obtained with normal-incidence Cassegrain, Ritchey-Chretien, and Herschelian telescopes mounted in the sounding rocket. MSSTA represents the first use of multilayer optics to study a very broad range of x ray and EUV solar emissions. Energy-selective properties of multilayer-coated optics allow distinct groups of emission lines to be isolated in the solar corona and transition region. Features of the near and far coronal structures including magnetic loops of plasmas, coronal plumes, coronal holes, faint structures, and cool prominences are visible in these images. MSSTA successfully obtained unprecedented information regarding the structure and dynamics of the solar atmosphere in the temperature range of 10(exp 4)-10(exp 7) K. The performance of the MSSTA has demonstrated a unique combination of ultra-high spatial resolution and spectral differentiation by use of multilayer optics

Muon Dynamics in a Toroidal Sector Magnet

We present a Hamiltonian formulation of muon dynamics in toroidal sector solenoids (bent solenoids)Comment: format aipproc.cls; aipproc.sty; 7 pages, two figures (*.ps). Submitted to the Proceedings of the 4th International Conference on Physics Potential and Development of mu-mu Colliders, San Francisco, Dec. 199

Hydrodynamic Simulations of the Bardeen-Petterson Effect

We present SPH simulations of accretion discs in orbit about rotating compact objects such as black holes and neutron stars, and study the structure of warped discs produced by the Bardeen-Petterson effect. We calculate the transition radius out to which the disc specific angular momentum vector is aligned with that of the black hole. We focus on the parameter regime where the warp dynamics are controlled by bending wave propagation, but also consider models in which warps are subject to diffusion rather than wave transport, and are able to consider the fully nonlinear regime. Because of hydrodynamic or pressure effects, for the parameter range investigated, the transition radius is always found to be much smaller than that obtained by Bardeen & Petterson (1975). For discs with midplane Mach numbers of about 10, the transition occurs between 10 - 16 gravitational radii, whereas for a Mach number of about 30 it occurs at around 30 gravitational radii. A thicker disc with a Mach number of 5 is found to produce no discernible warped structure. The rate of black hole - disc alignment is found to be consistent with the ideas of Ress (1978), with the alignment torque behaving as if it arises from the accreted material transferring its misaligned component of angular momentum at the larger transition radius of Bardeen & Petterson (1975). The inclusion of Einstein precession in the calculations modified both the warped disc structure and, consistent with linear analysis, produced an increased alignment rate by up to a factor of 4 because of the effect that a non Keplerian potential has on the propagation of warps.Comment: 18 pages, 14 figures. Accepted for publication in M.N.R.A.S. A version with posctcript figures included can be obtained from http://www.maths.qmw.ac.uk/~rp