Table of contents

We present absorption-line strengths on the Lick/IDS line-strength system of 381 galaxies and 38 globular clusters in the 4000-6400 Å region. All galaxies were observed at Lick Observatory between 1972 and 1984 with the Cassegrain Image Dissector Scanner spectrograph, which makes this study one of the largest homogeneous collections of galaxy spectral line data to date. We also present a catalog of nuclear velocity dispersions used to correct the absorption-line strengths onto the stellar Lick/IDS system. Extensive discussion of both random and systematic errors of the Lick/IDS system is provided. Indices are seen to fall into three families: α-element-like indices (including CN, Mg, Na D, and TiO₂) that correlate positively with velocity dispersion; Fe-like indices (including Ca, the G band, TiO₁, and all Fe indices) that correlate only weakly with velocity dispersion and the α indices; and Hβ that anticorrelates with both velocity dispersion and the α indices. C₂4668 seems to be intermediate between the α and Fe groups. These groupings probably represent different element abundance families with different nucleosynthesis histories.

This paper introduces a continuing survey of galaxies in the local universe. Consistent deep images are being acquired for a representative sample of 321 galaxies in the Uppsala General Catalogue down to 21.7 mag arcsec^-2 at Ks (2.16 μm) and 22.4 mag arcsec^-2 at J (1.25 μm) using a NICMOS camera with a 38 × 38 field of view attached to the 61 inch (1.5 m) telescope on Mount Bigelow. We provide some examples of the results being obtained by employing 64 deep images of a subset of 44 galaxies. Bulge-to-disk ratios are tabulated for 30 galaxies. The brightness of the central region of 44 galaxies declines approximately 5 mag from Hubble type S0 to Sm. An exponential vertical scale height at Ks is found to be 500 pc for the disk of UGC 5173. Arm amplitudes of four nearly face-on spiral galaxies are found to range between 11% and 88% compared to the interarm region. There is some evidence that the arm amplitude is larger at Ks than it is at J. Color gradients are measured for 15 galaxies with only one showing a significant nonzero result. A measurement of galactic symmetry applied to 64 deep images reveals an average asymmetry of 7.6% (σ = 4.6%) for these galaxies.

We are interested in examining different artificial intelligence techniques for classifying astronomical objects. In this study we use two different neural networks that utilize supervised learning: learning vector quantization and back-propagation. The networks are trained to distinguish stars and galaxies using an example base of 17 × 17 pixel images consisting of 60 galaxies and 27 stars extracted from the first-generation Digitized Sky Survey. For each neural network we use four different preprocessing methods to create input vectors from the pixelized images. We also use as input the "raw" image data consisting of a 289 (17 × 17) point vector. Our results show that both networks are capable of distinguishing stars and galaxies, with back-propagation working somewhat better in most cases. We discuss the details of the preprocessing methods and which methods work better in which cases.

This paper is a progress report on my efforts to develop a robust numerical scheme for computing eigenmodes of arbitrary order at arbitrary rotation rates. The slowly pulsating B stars and the line-profile variables on the upper main sequence provide the main impetus for the work. Consequently, the focus here is on the gravity modes responsible for these variables rather than on pressure modes. Unfortunately, the g-modes are harder to compute in general because their oscillation periods can be longer than the rotation periods of high-mass stars, which makes them more sensitive to the effects of inertial forces.

The standard technique for calculating the nonradial modes of spherical stellar models is generalized to two dimensions. The four dependent variables are the radial and latitudinal components of the Lagrangian displacement together with the Eulerian pressure and gravitational potential perturbations, all evaluated on level surfaces and normalized to have nonzero values on the boundaries. The integration in polar angle is replaced by numerical differentiation which is performed by various techniques involving Fourier, Legendre, or Chebyshev transforms. For the radial integrations, two numerical schemes are explored. One involves explicit Runge-Kutta integration inward and outward with fitting at an intermediate level surface. The other is an implicit, finite-difference method that does not require an initial trial solution. Each has advantages and disadvantages, but both ultimately fail for the same reason—small numerical errors in the θ-derivatives of eigenfunctions that are being distorted by growing high-order spherical harmonic components that are mixed in by rotation. Lack of convergence appears when the ratio Ω/σ of angular velocity and mode frequency exceeds about 0.5. This makes high-order g-modes (n > 15) in the presence of large rotation inaccessible with the methods proposed here. Nevertheless, it is possible to conclude that rapid rotation and large radial order suppress the pressure perturbations but enhance the horizontal motions especially near the surface and the equatorial plane. In fact, this trend is sufficiently clear and persistent that it should be possible to model the line profiles of the observationally relevant modes without actually computing them exactly.

This paper deals with the description and testing of the numerical methods employed in the construction of a new multidimensional, explicit, radiation hydrodynamic code for studying protostellar collapse and fragmentation. The code is written in Eulerian spherical coordinates, and the determining equations are solved using second-order-accurate, finite-difference (FD) methods on a radially moving, nonstaggered grid. The set of hydrodynamic equations is advanced using a multistep solution procedure along with either a first-order or a second-order time-integration scheme. On a fixed grid, the code is effectively second-order accurate as demonstrated through convergence testing. For advection on a moving orthogonal mesh, however, the use of standard FD methods results in systematic errors that progressively affect the accuracy of the solution. In order to minimize these errors, a new FD formulation has been derived for both the temporally first-order and second-order versions of the code that yields solutions for the pressureless collapse test case that are numerically invariant under grid motion. Results are also presented for a number of isothermal and nonisothermal protostellar collapse tests that validate this conclusion. Within this new formulation, the radial dependence of the fluid variables is exactly preserved near the origin of the coordinate system. This aspect results in improved local conservation of angular momentum during axisymmetric collapse and in a significant decrease of the level of nonaxisymmetric noise as compared with a previous version of the code. The reduction of systematic sources of error in the new schemes should then allow for a more precise evaluation of the importance of fragmentation during protostellar collapse.

Measurements of the mean magnetic field of the Sun (MMFS) seen as a star were regularly conducted at the Mount Wilson Observatory from 1970 October through 1982 December. A listing is presented of all these data (2457 daily values) suitable for comparison with similar data of other observatories and for studies of magnetic variability and rotation of the Sun. The scatter-plot diagrams and power spectra of the Mount Wilson data and also of the total data 1968-1991 (collected from three observatories: Crimean Astrophysical Observatory, Mount Wilson Observatory, and Wilcox Solar Observatory) are also presented. Time variations of the MMFS connected with solar rotation at periods ≈ 27-28 days and also an enigmatic 1 yr variation are briefly discussed.

The power spectrum of the 24 yr data set shows that the most significant and phase-coherent synodic periods of the MMFS variations are 26.92 ± 0.02 and 27.13 ± 0.02 days (both are thought to be associated with rotation of the large-scale surface magnetic field near equator of the Sun) and 28.13 ± 0.02 days. It is suggested that the latter period reflects "rigid" rotation of the global magnetic field concentrated under the bottom of the solar convection zone. The arguments are given in favor of reality and high confidence level of major periodicities exhibited by MMFS variations.

In this paper we present a linearized formulation of the Riemann problem for ideal adiabatic and isothermal magnetohydrodynamic (MHD). Roe's property U is obtained. This ensures good capturing of shocks of arbitrary strength. A parameter vector is found which gives an almost consistent mean state, where consistency is defined in the sense of Roe. The eigenvalues and eigenvectors for the linearized Riemann problem for MHD have been explicitly constructed further facilitating numerical implementation. The method has been tested in the author's RIEMANN code for numerical MHD. In a companion paper on TVD methods for MHD, where this Riemann solver was used, we have shown that excellent results can be obtained. The consistency for this formulation is illustrated by the fact that the eigenvalues have the same symmetrical distribution around the Roe-averaged x-component of the velocity that the eigenvalues for ideal MHD have around the physical x-component of the velocity. The accuracy, simplicity, and noniterative nature of the linearized formulation of the MHD Riemann problem presented here make it especially suitable for use on massively parallel processor machines.

In this paper a total variation diminishing (TVD) scheme is constructed for solving the equations of ideal adiabatic and isothermal MHD. It is based on an extremely efficient formulation of the MHD Riemann problems for either case. Piecewise linear interpolation is applied to the characteristic variables along with steepening of linearly degenerate characteristic fields. A predictor-corrector formulation is used to achieve second-order-accurate temporal update. An artificial viscosity and hyperviscosity are formulated using the characteristic variables. The viscosity and hyperviscosity are designed so that they never damage the TVD property. An accurate formulation of the divergence cleaning step is presented. This formulation is more accurate than the one that has been used so far. The scheme designed is second-order accurate in space and time. It has been implemented in the author's RIEMANN code for numerical MHD. A variety of test problems are presented. They test all aspects of numerical MHD including (1) handling of exotic wave structures that occur in MHD, (2) treatment of multiple discontinuities, (3) handling of very strong shocks, and (4) multidimensional problems. The scheme displays robust and accurate behavior in each case. An extremely efficient implementation has been achieved for massively parallel processor (MPP) machines displaying the ability of this scheme to sustain scalable, load-balanced performance in MPP environments.