%R 1994PASP..106.1113V %J-1119 %T The Hubble Parameter Revisited %A SIDNEY VAN DEN BERGH %B Observations obtained during the last two years are reviewed, and are summarized in Table 1. These new data appear to have slightly shifted the balance of evidence towards larger values of the Hubble Parameter. In particular it is argued that supernovae of Type Ia have a large luminosity dispersion at maximum light, and may therefore not be good standard candles. Furthermore spiral galaxies of a given Hubble type and luminosity class have too large a range in diameters to be useful as standard meter sticks. On balance available evidence suggests that Hubble paramter >= 75 km s^-1 Mpc^-1. %R 1994PASP..106.1120M %J-1133 %T Studies of Large-Amplitude Delta Scuti Variables. II. DY Herculis %A E. F. MILONE, W. J. F. WILSON, D. J. I. FRY, and S. J. SCHILLER %B This is the second paper in a series on large-amplitude delta Scuti stars intended to determine Baade-Wesselink radii and luminosities with precision. The first paper discussed our method of analysis and its application to EH Librae; in this paper we discuss the observations and analysis of DY Herculis. Optical and infrared photometry and cross-correlated radial velocity data have been obtained and analyzed. Fourier representations for the UBVRIJHK light curves and for the radial velocity curves were used to derive a value for the minimum radius for each of sixty combinations of flux and color index. From these we adopt a mean value for the minimum radius of R_min = 2.77 +- 0.20 R_sun. When combined with effective temperatures from Breger et al. (1978), we find a mean bolometric luminosity of = 21.70 L_sun and a mean absolute magnitude of = 1.41. The radial excursion is 0.149 R_sun. \par We use the same procedure to improve our results fro EH Librae, deriving R_min for each of 42 combinations of flux and color index, and obtain mean values of R_min = 2.62 +- 0.19 R_sun, = 24.56 L_sun and = 1.27. \par ** Tabular material from this article will appear in Vol. 3 of the AAS CD-ROM Series. \par %R 1994PASP..106.1134D %J-1137 %T Positions and Proper Motions of Dwarf Carbon Stars %A ERIC W. DEUTSCH %B Recent-epoch positions and proper motions of nine dwarf carbon star candidates are presented along with finding charts for each object. Measurements are obtained from digitized POSS and Quick V plate archives at the Space Telescope Science Institute, and from recent CCD images. %R 1994PASP..106.1138F %J-1140 %T R Coronae Borealis in 1992 and 1993 %A J. D. FERNIE and S. SEAGER %B Two hundred and three nights of UBV APT data are reported for R CrB in the years 1992 and 1993. An additional twenty-one nights of photometry from this observatory are also reported, and previously reported visual estimates are included to sketch the early stages of a deep decline at the end of the 1993 season. Through most of these two seasons R CrB reached peak brightness and showed well-developed pulsations of 0.25 mag amplitude and period 35.3 +- 0.2 days. To within the observational errors these maintained phase-coherence across the two seasons. The deep decline began near the minimum phase of pulsation, whereas in 1985 the deep decline began nearer to the maximum phase of pulsation, casting some doubt on the role of pulsation in triggering deep declines. %R 1994PASP..106.1141P %J-1150 %T Superhumps in Cataclysmic Binaries. III. V795 Herculis %A JOSEPH PATTERSON and DAVID R. SKILLMAN %B We report photometry of the cataclysmic variabla V795 Herculis during 1990-94. Comparison of recent with previously published data shows that the 2.78 hr periodicity has essentially disappeared; the amplitude has diminished by a factor of at least 10. In its place, there is a low-amplitude signal near the radial-velocity (orbital?) period of 2.60 hr. \par During 1983-89, the star did show an obvious 2.78 hr signal. We study the published data on this signal, together with our own data under the (questionable) assumption that the signal still exists with an amplitude too small to survive the rigors of unbiased period detection. The data are really too sparse and too poorly distributed to decide the issue of phase stability. But since the photometric signal is transient and exceeds the likely orbital period by ~8%, the photometric waves are likely to be yet another example of "superhumps," the phenomenon made famous by dwarf novae in superoutburst. \par At high frequencies, the star shows a quasi-periodic signal with P ~1160 s, and possibly also a stable signal with P = 1310.2 s (or 1330.4 s, the one-day alias). The beat period between these signals could be the orbital period, or that of the vanished superhump. %R 1994PASP..106.1151G %J-1156 %T Correcting the Distortion of Images Taken with the Ultraviolet Imaging Telescope %A MICHAEL R. GREASON, JOEL D. OFFENBERG, ROBERT H. CORNETT, ROBERT S. HILL, and THEODORE P. STECHER %B The Ultraviolet Imaging Telescope cameras include two-stage magnetically focussed image intensifiers that introduce small but significant geometrical distortions to the data. These distortions, which create positional offsets as large as 25 arcseconds at the field edges, are corrected by the procedure described here to 2-3 arcseconds, approximately the resolution of the images. The distortion is measured by comparing and correcting UIT images to digitized Guidestar survey plates of the same fields. Two-dimensional third-order polynomials are used to model the distortion. The models assume that the distortion is an instrumental effect, independent of mission elapsed time and target, and that the effect of distortion in the center of each field is minimal. The models are used to improve computed astrometric plate solutions and to remove the geometric distortion while transforming the image to a standard north-up, east-left orientation. %R 1994PASP..106.1157L %J-1164 %T Sky Subtraction with Fiber-Spectrographs %A C. LISSANDRINI, S. CRISTIANI, and F. LA FRANCA %B The sky subtraction performance of multi-fiber spectrographs are discussed, analyzing in detail the case of the OPTOPUS system at the 3.6 meter ESO telescope at La Silla. A standard technique, based on flat-fields obtained with a uniformly illuminated screen on the dome, provides poor results. A new method has been developed, using the [O I] emission line at 5577 A as a calibrator of the fiber transmittance, taking into account the diffuse light and the influence of each fiber on the adjacent ones, and correcting for the effects of the image distortions on the sky sampling. In this way the accuracy of the sky subtraction improves from 2-8% to 1.3-1.6%. %R 1994PASP..106.1165S %J-1171 %T Application of the TDI Method in Observations of Lunar Occultations %A LASZLO STURMANN %B In this paper, we discuss how the Time Delay and Integration (TDI) method can be applied to observations of lunar occultations. The TDI method allows us to track the diffraction pattern of an occulted star by stepping the photon generated charge packages in a CCD array synchronously with the moving diffraction pattern. The use of TDI should considerably improve the signal-to-noise ratio that can be reached in occultation observations compared with that which can be obtained currently using conventional high speed photometers. The TDI method could extend lunar occultation studies to faint stars and telescopes with large apertures without sacrificing angular resolution. We show that observers can achieve 1 mas angular resolution in observations of stars as faint as m_V~8 with a 5-m class telescope. %R 1994PASP..106.1172J %J-1183 %T Calibration of the UBVRI High-Speed Photometer of Laboratorio Nacional de Astrofisica Brazil %A F. JABLONSKI, R. BAPTISTA, J. BARROSO, JR., C. D. GNEIDING, F. RODRIGUES, and R. P. CAMPOS %B We describe the characteristics and performance of a high-speed multicolor photometer, FOTRAP, which has been used since 1988 at LNA, Laboratorio Nacional de Astrofisicas/CNPq, Brazil. The opto-mechanical concepts, electronics and software are outlined. We discuss the quality and consistency of the transformations from the natural system to the UBVRI standard system. We give particular attention to the problem of transforming to the standard system observations of objects with blue spectra, like cataclysmic variables. We compare the results of our UBVRI measurements for a few spectrophotometric standards with the values published in the literature. %R 1994PASP..106.1184G %J-1189 %T Second Order UV Contamination in Astronomical Spectra %A A. GUTIERREZ-MORENO, S. HEATHCOTE, H. MORENO, and M. HAMUY %B Observations of the planetary nebula Me 2-1 are used to discuss some effects of contamination produced by the second order ultraviolet spectrum in the first order red, longer than approximately 6200 A. It is found that this contamination is present with some instrument set-ups, and that the contaminating lines are displaced in wavelength with respect to the predictions from diffraction theory by an amount which varies slightly for different set-ups. From the theoretical and empirical analysis of these displacements, it is concluded that the shift in wavelength is due to the presence of chromatic difference in magnification in spectrograph cameras including any transmission element, as is the case in teh semi-solid Schmidt-Cassegrain cameras used in our observations. %R 1994PASP..106.1190H %J-1216 %T Network Resources for Astronomers %A HEINZ ANDERNACH, ROBERT J. HANISCH, and FIONN MURTAGH %B The amount of data produced by large observational facilities and space missions has led to the archiving and on-line accessibility of much of this data, available to the entire astronomical community. This allows a much wider multi-frequency approach to astronomical research than previously possible. Here we provide an overview of these services, and give a basic description of their contents and possibilities for accessing them. Apart from services providing observational data, many of those providing general information, e.g., on addresses, bibliographies, software etc. are also described. The field is rapidly growing with improved network technology, and our attempt to keep the report as complete and up-to-date as possible will inevitably be outdated shortly. We will endeavor to maintain an updated version of this document on-line. %R 1994PASP..106.1217M %J-1221 %T 2.4 micron Sky Brightness at Balloon Altitude %A T. MATSUMOTO, S. MATSUURA, and M. NODA %B The atmospheric airglow is thought to have a narrow window at 2.4 micron, which corresponds to the wavelength gap between the fundamental and the first overtone of the OH vibration bands. In order to confirm this window, we analyzed data of past balloon experiments, and found that the sky brightness, labmda*I_lambda, at 2.4 micron amounted to (7 +- 2)X10^-10 W*cm^-2*sr^-1 or ~15.5 mag*arcsec^-2. This level is considerably higher than expected. It can be explained, however, by assuming the non-equilibrium and partially high rotation temperature for OH radicals. This mechanism suggests that the OH window is shifted to longer wavelengths if the emission of other molecules and telescope itself is taken into account. %R 1994PASP..106.1222T %J-1222 %T Soft X-ray Analysis and Multiwavelength Modeling of X-ray Selected Active Galactic Nuclei %A RICHARD J. THOMPSON %B We survey the broadband spectral properties of ~500 X-ray-selected Active Galactic Nuclei (AGN) observed with the Einstein X-ray Observatory in order to better understand the X-ray emission characteristics of this population as compared to previously studied optically- and radio-selected populations. We further select a subsample of X-ray-selected AGN which possess strong components of soft X-ray emission below ~0.5 keV. This sample is used to investigate in greater detail this ultrasoft emission and to search for possible correlations between it and emission at other wavelengths. These ultrasoft sources are used for multiwavelength accretion disk modeling in a test of the current black hole plus accretiondisk paradigm of AGN energy generation. \par We find the mean spectral index of the AGN between 0.1 and 0.6 keV to be softer, and the distributions of indices wider, than previous estimates based on analyses of the X-ray spectra of optically-selected AGN. We confirm a correlation between radio and hard X-ray luminosity, but find that the data do not support a correlation between radio and soft X-ray spectral slope. We report evidence for physically distinct soft and hard X-ray components. \par Imaging photometry in the J, H, and K infrared bands is carried out for a sample of eight AGN. The infrared images show the AGN to be primarily point sources, with little extended emission from the host galaxy. The photometric measurements represent part of a multiwavelength database to be used for accretion disk modeling. \par We report observations of six AGN in the ultraviolet region with the International Ultraviolet Explorer satellite. The ultraviolet spectra from these observations are used for measurement of the strengths of the emission lines present (e.g., Ly-alpha, CIV, and CIII]). The data also allow a measurement of the shape of the ultraviolet continua of these AGN to be used further in multiwavelength accretion disk modeling. \par Observations of a sample of six optically faint, X-ray-selected AGN with the ROSAT Position Sensitive Proportional Counter are reported. The spectra of the AGN are all fit satisfactorily with single power-law models and their spectral indices (with one exception) agree with those estimated from their Einstein IPC observations. Tests of short term variability are carried out, with all sources showing constant count rates over the period of their ROSAT observations. Some sources do show significant changes in count rate when compared to previous Einstein data taken a decade earlier. The measurements of the soft X-ray spectra of these objects are combined with the infrared and ultraviolet data discussed above to carry out multiwavelength accretion disk modeling. \par Accretion disk modeling is carried out on a sample of five Seyfert I galaxies possessing strong optical-ultraviolet-soft X-ray emission components. It is found that while bare accretion disk models cannot account for the soft X-ray emission observed in these objects, the addition of a hot (kTe~120 keV), Comptonizing component enables the soft X-ray emission to be accounted for within the black hole plus accretion disk paradigm.