New uvby light curves of the overcontact eclipsing binary RZ Tauri have been analysed with the Wilson-Devinney computer model. The resulting orbital elements confirm that total eclipses occur in the system.

The gravity darkening is mid-way between the values expected for a fully-convective and a fully-radiative star. A new, quadratic ephemeris has been derived, based on the archival times of minima.

RT Lacertae is an eclipsing, double-lined spectroscopic binary with a beta Lyrae type light curve, which exhibits an appreciable and variable O'Connell effect. As a consequence, it has been considered an RS CVn type binary; Infrared and UV spectroscopy have also suggested the presence of a thick disk and a transient gas stream in the system.

Photometric data obtained at the Rothney Astrophysical Observatory with the RADS instrument on the 41 cm telescope in the summer of 1996 along with infrared and radial velocity data are analyzed. Initial solutions were determined by a preliminary parameter space search with the simplex algorithm. Final solutions and probable error calculations were performed with the Wilson-Devinney light curve analysis program. Spot-absence modelling cases will be presented, as will preliminary solutions for the spot-inclusive cases.

3C129 and 3C129.1 are a pair of 3C radio sources associated with a pair of galaxies with AGN (active galactic nuclei). 3C129 is the prototype for narrow-tailed radio galaxies, and both 3C129 and 3C129.1 are in rich a cluster of galaxies, also called 3C129. 3C129 has been detected by several non-imaging x-ray surveys but has not been previously studied with an imaging x-ray detector. Here we report ROSAT observations of the 3C129 region and show that the bright x-ray emission is from diffuse gas in the cluster and not from the AGN in the galaxies. We also derive some x-ray properties of the cluster.

Delta Scuti stars and their stellar cousins (dwarf Cepheids, SX Phoenicis stars, ...) are rapidly pulsating variable stars that are located at the bottom of the Cepheid instability strip on the Hertzsprung-Russell diagram.

They are dwarf or subgiant stars and so are not visible to as great distances as classical Cepheids, or even RR Lyrae stars, but they are very common. Therefore, an improvement in the determination of their luminosties will have useful consequences for distance determinations, especially in stellar ensembles that contain them. To that end, our program is aimed at refinement of the period-luminosity -- or the establishment of a P-L-metallicity relation -- for these objects.

As a first step we are determining the Baade-Wesselink radii of several of these objects; from these we are exploring period-radius relations from which P-L relations may be derived, thus providing a useful distance indicator. Work by other investigators, through various methods, confirms the likelihood of a P-R-metallicity relation for the family of these stars..

As a contribution towards the goal of establishing a P-R relation, we have obtained Baade-Wesselink radii for three such stars, EH Librae, DY Herculis, and DY Pegasi, and are observing (with optical and IR observations from RAO and RV data from DAO) several others of differing properties. Most recently we have been observing the multi-period system AI CVn = 4 CVn with the RADS photometer of the RAO.

We present a new model for pulsed emission from rotating neutron stars. This model considers asymmetrically-filled, offset emission regions extending above the neutron star surface as arising from variable accretion flow through its magnetosphere. The transient x-ray pulsar EXO 2030+375 exhibits strong luminosity-dependent changes in its pulse profile. Observations using the EXOSAT and BATSE satellites provide a basis for investigating how pulse formation varies with luminosity. Since the amount of matter available for 'loading' along the magnetic field lines is variable, and dependent on both the orbital phase of the neutron star, and the inclination of its rotation plane from the orbital plane, only certain magnetic field lines will be responsible for particle loading. With these considerations, the emission regions of a neutron star can be partially-filled, or asymmetric with respect to the magnetic axis. The boundaries of the emission regions are based on magnetic field geometry in flat space. Fan-beam emission is considered from the sides of the emission regions and use the results of magnetic radiative transfer calculations by Meszaros. The model considers shadowing by the neutron star on the emission regions. Magnetic dipole geometry in a Schwarzschild metric (gravitational- light bending of photon paths, and relativistic red-shifting) are currently being incorporated. Preliminary results from the flat-space model are presented.

In order to carry out quantitative investigations using satellite and airborne remote sensing images, atmospheric corrections must be applied to transform at-sensor radiances to surface radiance and reflectance. This is best accomplished through direct observations that characterize the optical properties of the atmosphere at the time and place that a remote sensing image is acquired. The resulting observational propoerties can then be applied to constrain a radiative transfer code providing the necessary calculations to convert radiances measured at the sensor to radiances upwelling from the Earth's surface. Our objective is to develop this type of atmospheric correction capability with hyperspectral resolution.

Here we present initial results working with ground truth data collected with the Portable Ground-based Atmospheric Monitoring System. PGAMS observations of atmospheric transmission & surface reflectance are used to calibrate Modtran3 and predict upwelling radiances from blue nylon tarp and grass targets. The resulting synthetic radiance spectra are compared to direct surface measurements obtained with PGAMS in order to evaluate the ability of the Modtran3 atmosphere to predict at-sensor radiances.

Observational Trials of New Passbands for Precision Infrared Photometry

--- E. F. Milone, K. Kijewski, F. M. Babott, L. Gallo, P. Langill, M. D. Williams, D. Alton, RAO; and A. T. Young, San Diego State University

The infrared passbands developed through synthetic extinction work and numerical simulations have been fabricated by Customs Scientific of Phoenix, Arizona, and are currently undergoing field trials at the Rothney Astrophysical Observatory. The underlying problems with conventional photometry and the simulations are shown. The new z, j, h, k, l, and l' filters are being tested along with three somewhat improved conventional JH & K filters. The results will be announced later this summer.