Abstract: We report 15 new times of maximum light for the delta Scuti star IP Virginis (formerly known as SA 106-1024). An analysis of all times of maximum light indicates that IP Vir has been decreasing in period at a constant rate of -7.4 x 10(-9) days day(-1). Evidence is also presented that IP Vir is a double-mode variable with a period ratio of pi(1)/pi(0), = 0.774. This period ratio predicts a [Fe/H] value of -0.3. From photometric (uvby beta) observations, we find a foreground reddening of E(b - y) = 0.008 mag and a metallicity of [Fe/H] = +0.05. It is shown that [Fe/H] = -0.3 is most likely the correct value. Intrinsic (b - y)- and c(1)-values, plotted in a model atmosphere grid, indicate a mean effective temperature, [T-eff] = 7400 K, and a mean surface gravity, [log g] = 3.89. All of these physical parameters support Landolt's initial conclusion that IP Vir is an ordinary delta Sct star.

Abstract: We have embarked on a long term project to obtain high precision photometry on individual galaxies in 45 rich clusters of galaxies. Data from the first set of six clusters have yielded BVRI photometric information on 961 galaxies and 384 stars. These objects come from the central one Mpc of Abell 576, 957, 1185, 1377, 2063, and 2657, each of which is of richness class R greater than or equal to 1. Each object was examined with two radial surface brightness fitting functions, and an asymptotic magnitude was determined. One fitting function produced a shape parameter beta which, when taken in. combination with the color index (B-I), shows a breakdown of the three basic morphological types (E, S0, and S) into four beta types and a set of peculiar galaxies. Our results match previous studies well, and also provide some new insights into the clusters. In addition, we have examined the effects of plate scale on the determination of these photometric parameters. All parameters were found to repeat across plate scale differences. We also examined the effects of co-adding frames in an attempt to understand the degradation or improvement of the photometric parameters with increasing signal-to-noise. (C) 1997 American Astronomical Society.

Abstract:

We have examined the short-period, double-mode variable star AE Ursae Majoris. Using time-series ensemble photometry we have determined six new times of maximum light. We also applied a Fourier decomposition to the data to determine the component frequencies of the light curve. Using our data, along with archival data, we find that the period of AE UMa is continually decreasing at a rate of -1.14x10(-10) d d(-1). However, from the Fourier decomposition we find that the period ratio P-1/P-0 has remained constant at 0.773. We also find that AE UMa is incorrectly classified as a SX Phoenicis star.

Abstract:

We have measured M67 stars in a Stromgren-beta system based ultimately on data for the Hyades and Coma clusters. By comparing our results to previously published data, we have derived formal corrections required to put the other data on our system. Corrections which are Statistically significant by our criteria are found for Stromgren measurements made by Strom et al. (1971, PASP, 83, 768). Those corrections range between 36 and 61 mmag. In addition, corrections of 17 and 8 mmag, respectively,are found for beta measurements made by Eggen (1981, ApJ, 247, 503) and Nissen et al. (1987, AJ, 93, 634). In addition to considering M67, we have updated earlier work of ours which was done on Praesepe and NGC 752. After revising our criterion for statistical significance, we have changed our judgment about two corrections which we had derived for published data for those clusters. Further work will be required to verify the reality of those corrections. We have also compared our results to closely similar work which was done by Nissen (1988, A&A, 199, 146) and which had previously escaped our notice. Differences between our results and those of Nissen appear Is exist for beta in Praesepe and for c(1) in NGC 752. Independent measurements support our Praesepe result. but the problem for NGC 752 remains unresolved.

Abstract: Optical, near-infrared, and radio observations of the BL Lac object PKS 2155-304 were obtained simultaneously with a continuous UV/EUV/X-ray monitoring campaign in 1994 May. Further optical observations were gathered throughout most of 1994. The radio, millimeter, and near-infrared data show no strong correlations with the higher energies. The optical light curves exhibit flickering of 0.2-0.3 mag on timescales of 1-2 days, superposed on longer timescale variations. sapid variations of similar to 0.01 mag minute(-1), if real, are the fastest seen to date for any BL Lac object. Small (0.2-0.3 mag) increases in the V and R bands occur simultaneously with a flare seen at higher energies. All optical wave bands (UBVRI) track each other well over the period of observation, with no detectable delay. For most of the period the average colors remain relatively constant, although there is a tendency for the colors (in particular, B-V) to vary more when the source fades. In polarized light, PKS 2155-304 showed strong color dependence (polarization increases toward the blue, P-U/P-I = 1.31) and the highest optical polarization (U = 14.3%) ever observed for this source. The polarization variations trace the flares seen in the UV flux. For the fastest variability timescale observed, we estimate a central black hole mass of less than or similar to 1.5 x 10(9)(delta/10) M-., consistent with UV and X-ray constraints and smaller than previously calculated for this object.

Abstract:

New photometric (uvby beta) observations of the intrinsic variable star V798 Cyg have been secured and used to derive values of foreground reddening, E(b-y) = 0.117 mag, and metallicity, [Fe/H] = 0.64. Intrinsic (b-y) and c(1) values indicate a mean effective temperature, [T-eff] = 7150 K, and a mean surface gravity, [log g] = 3.39. Pulsation theory and theoretical evolutionary tracks yield a mass of 2.3 M. and an age of 0.63 Gyr. Although V798 Cyg has been described as being multiperiodic, this conclusion is not confirmed by our observations. V798 Cyg in most respects resembles a typical Population I dwarf Cepheid.