%R 1997PASP..109..633D %J-638 %T A Photometric System for Detection of Embedded Wolf-Rayet Stars %A DAMINELI-NETO A., JABLONSKI F., DE FREITAS L.C., DE FREITAS-PACHECO J.A. %F contents_97_06 %K Stars %B We describe a photometric system designed for detection of WR stars in the near infrared region and based on a combination of narrow band filters and a CCD detector. The system is sensitive to Of and faint lined WN and WC stars and suitable for obscured regions of star formation in our Galaxy. %R 1997PASP..109..639H %J-642 %T Fourier Decomposition of the Light Curves of Three Dwarf Cepheids: CY Aquarii, XX Cygni and V798 Cygni %A HINTZ E.G., JONER M.D. %F contents_97_06 %K Stars %B The three dwarf Cepheid variable stars CY Aquarii, XX Cygni, and V798 Cygni were examined with CCD time series ensemble photometry. The Fourier decomposition of the light curves showed no evidence that any of the three stars was a double-mode variable. CY Aqr was fit with a nine term harmonic series with a residual error of 10 mmag. XX Cyg was fit with a ten term harmonic series with a residual error of 10 mmag. V798 Cyg was fit with a four term harmonic series with a residual error of 7 mmag. In addition, we examined a set of double-mode dwarf Cepheids with the same Fourier decomposition techniques. We present evidence that these double-mode dwarf Cepheids fill the gap in the amplitude ratio distribution reported by Antonello et al.(1986) and Poretti et al.(1990). %R 1997PASP..109..643P %J-644 %T Objective-Prism Spectral Types for 29 Late-Type Dwarfs %A PESCH P., BIDELMAN W. %F contents_97_06 %K Stars %B Spectral types, absolute magnitudes, and tangential velocities are given for 28 faint late-type dwarfs on the U.S. Naval Observatory parallax program. Also, the 8th-magnitude star BD+58 degrees 2455 is found to be a previously unrecognized nearby K5 dwarf. %R 1997PASP..109..645B %J-658 %T BVRIJHK Photometry of Cepheid Variables %A BARNES III T.G., FERNLEY J.A., FRUEH M.L., NAVAS J.G., MOFFETT T.J., SKILLEN I. %F contents_97_06 %K Stars %B Contemporaneous BVRI and JHK photometry are presented for twenty-two Cepheid variables. Nineteen of these variables also have uvby photometry available, making them excellent candidates for application of the Infrared Flux Method of distance determination. We are in the process of acquiring high precision radial velocities of sixteen of these variables in anticipation of conducting that analysis. %R 1997PASP..109..659F %J-666 %T The IUE Spectrum of the Binary Nucleus of the Planetary Nebula NGC 1514 %A FEIBELMAN W.A. %F contents_97_06 %K Stars %B Archival IUE low-dispersion spectra and the first ultraviolet high-dispersion spectrum of the binary nucleus of NGC 1514 have been analyzed. Both SWP and LWR low-dispersion spectra show variability by as much as a factor of two in the continuum level between the years 1978 and 1989. Weak P Cygni features for OV lambda 1371 and C IV lambda 1549 yield terminal wind velocities of -105 plus or minus 25 and -960 plus or minus 150 km s-1, respectively. No nebular emission lines were detected, but several photospheric and interstellar absorption features were observed. Absorption lines of Fe VII are suspected. The He II lambda 1640 absorption line has a radial velocity of +49 plus or minus 3 km s-1 and is in good agreement with optical data. The peculiar energy distribution of the SWP continuum for NGC 1514 can be synthesized by the coaddition of spectral type A0 - A3 III plus hot subdwarf IUE spectra. %R 1997PASP..109..667H %J-672 %T Near Infrared Imaging of the Proposed z=2 Cluster Behind CL 0939+4713 (Abell 851) %A HUTCHINGS J.B., DAVIDGE T.J. %F contents_97_06 %K Galaxies %B We have obtained deep J and K' images of a 90 arcsec square field containing the z=2.0 QSO that is viewed through the z=0.4 rich cluster A851. Brightnesses of individual galaxies are measured from these data, and archival F702W WFPC2 images from HST. The results are used to construct 2-colour diagrams, colour-magnitude diagrams, and luminosity functions of galaxies in A851 and the faint objects discovered by Dressler et al (1993) near the QSO. The QSO faint companions appear to form a separate population from other faint galaxies in the field. Comparisons with the GISSEL models covering redshifts from 0 to 3 indicate that (1) the A851 galaxies have ages between 3 and 10 Gyr, and (2) if they are at the QSO redshift, the QSO companion galaxies are within 1Gyr of cessation of star-formation. %R 1997PASP..109..673M %J-675 %T CC Bootis: QSO, Not Variable Halo Giant %A MARGON B., DEUTSCH E.W. %F contents_97_06 %K Quasars and Active Galactic Nuclei %B The poorly-studied, faint 18 less than m_pg_ less than 19.5) variable star CC~Bootis has been noted in the literature as a candidate for a halo red giant. It proves instead to be a quasi-stellar object of redshift z=0.172, and is detected as an X-ray source by ROSAT. In addition to its odd heritage, CC~Boo exhibits unusually high amplitude optical variability for an optically-selected QSO. %R 1997PASP..109..676M %J-681 %T High-Resolution Optical Spectra of the Head of the Comet C/1996 B2 (Hyakutake) %A MORRISON N.D., KNAUTH C.D., MULLISS C.L., LEE W. %F contents_97_06 %K The Solar System %B \begin{tex}On 23 and 27 March 1996, we obtained high-resolution ($R \simeq 26,000$) \'echelle spectra by manually guiding on the head of Comet C/1996 B2 (Hyakutake). The two spectra cover different but slightly overlapping sets of 9 disjoint 70-\AA\ regions of the green, yellow, and red. The continuum signal-to-noise ratio is in the range 40--100 per spectral resolution element. We used line lists from the standard astronomical literature to identify lines of [O~I], Na I, C2, NH2, CN, and H2O, we unsuccessfully sought evidence for CO$^+$, and we obtained upper limits on HCO line strengths. In addition, we used laboratory data to make new identifications, by wavelength coincidence only, of lines of NH$_2$. For the lines that remain unidentified, we have listed measured wavelengths and relative fluxes, in order to aid future efforts at identification. Our spectra include the green and one of the red lines of [\ion{O}{1}], and the indicated photon flux ratio of \lam 5577 / (\lam 6300 + \lam 6364) is in the range 0.12 to 0.16, consistent with formation of the excited O atoms from photodissociation of H2O. \end{tex} %R 1997PASP..109..682G %J-687 %T Relevant Parameters for Tip-Tilt Systems of Large Telescopes %A GLINDEMANN A. %F contents_97_06 %K Astronomical Instrumentation %B In order to provide criteria for the design of tip-tilt systems on large telescopes, we derive analytic formulae for the aberrations of the tip-tilt corrected wavefront as a function of the tracking algorithm and of the tracking frequency. We present a new definition for the required bandwidth of tip-tilt systems based upon the residual high order aberrations, and we suggest a new, simple method to eliminate the influence of coma on the image centroid measurement. The effect of the science camera pixel size on the image quality is investigated. A simple approximation is given for the power spectrum of the image motion, and measured power spectra are compared to this approximation. We show that in order to measure the rms image motion properly, it is important to run the measurement over a sufficient period of time (>10 min). In a second paper (Glindemann et al. 1997) in this journal, a tip-tilt system (CHARM) is presented where the parameters derived here are used to evaluate the system performance. %R 1997PASP..109..688G %J-696 %T CHARM - A Tip-Tilt Tertiary System for the Calar Alto 3.5m Telescope %A GLINDEMANN A., MCCAUGHREAN M.J., HIPPLER S., BIRK C., WAGNER K., ROHLOFF R-R %F contents_97_06 %K Astronomical Instrumentation %B \begin{tex}We discuss a tip-tilt tertiary mirror system developed for the Calar Alto 3.5m telescope in Spain, that corrects the rapid image motion caused by atmospheric turbulence. Using either a visible or an infrared tip-tilt sensor, the image motion is reduced typically to less than 0\farcs03 rms (corresponding to 0.29 rad$^2$ mean square wavefront tilt error) at 2.2\micron{} on a 3.5m telescope. The system is equipped with a CCD camera to measure the image motion in the visible. Alternatively, using a novel technique for reading out a subarray of an infrared detector, the infrared science camera can be used to measure the slope of the wavefront by taking short exposure images on a very small subarray while simultaneously taking long exposure images on the rest of the array. This enables the system to be used even in obscured regions where only infrared stars are available. Astronomical results from several observing runs with this system at the Calar Alto 3.5m telescope are presented. \end{tex} %R 1997PASP..109..697S %J-706 %T Wolfgang-Amadeus: The University of Vienna Twin Automatic Photoelectric Telescope %A STRASSMEIER K.G., BOYD L.J., EPAND D.H., GRANZER TH. %F contents_97_06 %K Astronomical Instrumentation %B We describe the University of Vienna twin automatic photoelectric telescope (APT) located at the new Fairborn Observatory at Washington Camp in southern Arizona. Not only are the telescopes fully automatic, also the observatory itself is automatic. A site-control computer monitors weather sensors and operates the roof while the telescope control computer operates the photometer and accepts input files from and provides nightly observations to the astronomer; no direct operating personnel is needed. Both telescopes have 0.75-m primary mirrors, a CCD finder camera, and an environmentally controlled single-channel photoelectric photometer with filter combinations optimized for use in the blue (Wolfgang) and in the red (Amadeus) wavelength for asteroseismology of non-radially pulsating variables, and for monitoring asymtotic-giant-branch stars. Some first results are presented. %R 1997PASP..109..707J %J-718 %T A Wide Bandwidth Digital Recording System for Radio Pulsar Astronomy %A JENET F.A., COOK W.R., PRINCE T.A., UNWIN S.C. %F contents_97_06 %K Astronomical Instrumentation %B The study of radio pulsars at the highest time resolution is currently limited by the capability of the signal detection system to accept a wide-bandwidth signal, and to sample the data rapidly enough. We describe a new instrument for pulsar research which utilizes baseband recording at 400 Mbit/s to achieve both a high bandwidth and a high sustained data rate. The Wide Bandwidth Digital Recording (WBDR) system is based on a custom analog/digital VLSI digitizer operating at 50 MHz, and a commercial digital cassette tape recorder. Signal analysis is performed entirely in software, using a massively parallel computer. Since we record a representation of the electric vector of the pulsar emission, the instrument is very flexible, and the data can be analyzed in several modes in software. We can synthesize the software equivalent of a conventional hardware filterbank, and we have implemented a 'coherent dedispersion' algorithm, which yields a sample time of 10~ns. The combination of wide bandwidth and sustained data rate make this instrument a unique and powerful tool for pulsar astronomy. Our instrument is particularly well-suited to searches for millisecond pulsars at low frequency, in directions where pulsed signals are strongly dispersed by the interstellar medium. We present results based on dual-polarization test observations in a 600 +/- 25 MHz band at the Owens Valley Radio Observatory 40-m Telescope. %R 1997PASP..109..719M %J-724 %T Determining Locations of Unknown Sites for Astronomical Purposes %A MALEY P.D., PALMER J.L., NUGENT R., ROSENZWEIG P., NARANJO O. %F contents_97_06 %K Computing and Data Analysis %B An important problem for an astronomical research program is examined for observers traveling to poorly mapped areas to monitor rare phenomena such as solar eclipses, lunar eclipses, and occultations but who require accurate knowledge of the geodetic coordinates of observing sites whose true locations are not known. This study uses commercial off-the-shelf (COTS) hardware and software to address the problem and provides guidelines for determination of ground truth by utilization of hand-held Global Positioning System (GPS) receivers. %R 1997PASP..109..725D %J-737 %T Atmospheric Intensity Scintillation of Stars. II. Dependence on Optical Wavelength %A DRAVINS D., LINDEGREN L., MEZEY E, YOUNG A.T. %F contents_97_06 %K Atmospheric Phenomena and Seeing %B \begin{tex}Atmospheric intensity scintillation of stars on milli- and microsecond time scales was extensively measured at the astronomical observatory on La Palma (Canary Island). Scintillation statistics and temporal changes were discussed in Paper I, while this paper shows how scintillation depends on optical wavelength. Such effects originate from the changing refractive index of air, and from wavelength-dependent diffraction in atmospheric inhomogeneities. The intensity variance \sigma2/I increases for shorter wavelengths, at small zenith distances approximately consistent with a theoretical \lambda $^{-7/6}$ slope, but with a tendency for a somewhat weaker dependence. Scintillation in the blue is more rapid than in the red. The increase with wavelength of autocorrelation time scales (roughly proportional to $sqrt{\lambda}$ is most pronounced in very small apertures, but was measured up to \o 20 cm. Scintillation at different wavelengths is not simultaneous: atmospheric chromatic dispersion stretches the atmospherically induced 'flying shadows' into 'flying spectra' on the ground. As the 'shadows' fly past the telescope aperture, a time delay appears between fluctuations at different wavelengths whenever the turbulence-carrying winds have components parallel to the direction of dispersion. These effects increase with zenith distance (reaching \approx 100 ms cross-correlation delay between blue and red at Z = 60\deg), and also with increased wavelength difference. This time delay between scintillation in different colors is a property of the atmospheric flying shadows, and thus a property that remains unchanged even in very large telescopes. However, the wavelength dependence of scintillation amplitude and time scale is 'fully' developed only in small telescope apertures (less than about 5 cm), the scales where the 'flying shadows' on the Earth's surface become resolved. Although these dependences rapidly vanish after averaging in larger apertures, an understanding of chromatic effects may still be needed for the most accurate photometric measurements. These will probably require a sampling of the [stellar] signal with full spatial, temporal and chromatic resolution to segregate the scintillation signatures from those of astrophysical variability. \end{tex} %R 1997PASP..109..738C %J-738 %T The Low-Ionization Gaseous Content in Intermediate-Redshift Galaxies %A CHURCHILL C.W. %F contents_97_06 %K Dissertation Summaries %B \begin{tex}The kinematic, chemical, and ionization conditions and spatial distributions of low ionization gas associated with early epoch ($0.3 \leq z \leq 1.7$) galaxies have been studied using high resolution (6.6~{\kms}) absorption line spectra. The absorption profiles for a total of 48 {\MgII} selected systems were obtained from 25 quasar (QSO) spectra observed with the HIRES spectrograph on the Keck~I telescope. In addition to the {\MgIIwaves} doublet, the {\MgI}~$\lambda 2853$ transition and multiple transitions of {\FeII} were also studied. In some cases, {\MnII} and {\CaII} were observed. The absorption profiles were objectively searched for weak absorbing ``subsystems'' in line--of--sight velocity space. For each overall system, and their multiple subsystems, absorption properties were measured directly from the flux values in the spectra. Additionally, the absorption profiles were modeled by Voigt Profile (VP) decomposition using an algorithm written for this work. Extensive simulations of the VP decomposition were performed in order to establish confidence levels on inferences based upon VP profile fits. \end{tex} %R 1997PASP..109..739M %J-739 %T Search for Periodicity in Image Sequences from the Yokoh Soft X-Ray Telescope %A MCKENZIE D.E. %F contents_97_06 %K Dissertation Summaries %B \begin{tex}The process by which the Sun's corona is heated is not well known. A leading model is the resonant absorption of Alfv\'enic surface waves. In order to be efficient as a heating mechanism, this process depends on the surface waves being well matched ot the length of the coronal loop through the condition of global-mode resonance: $v_{Alfv\acute{e}n}$ = 2L/period (Davila, 1987). The Yohkoh Soft X-Ray Telescope (SXT) provides a means of recording the behavior and evolution of structures in the solar corona. Relatively fast-cadence sequences of CCD images become movies depicting the changing conditions in the X-ray emitting regions. By using software provided by the Yohkoh science team to measure the brightness of a selected subset of pixels in all the images of a movie, we can generate an X-ray light curve of a small portion of a given coronal structure. For the present dissertation, a number of SXT image sequences were selected from the Yohkoh archives. Light curves were generated in the manner outlined above, and these light curves were then examined for periodic modulations. It is shown that periodic modulations of X-ray brightness were detected with amplitudes of nearly 1\%, and that the speeds inferred from interpreting these oscillations as global-mode resonance are in the neighborhood of 1800 -- 14000 km/s, consistent with Alfv\'en wave speeds but much higher than sound speeds implied by the temperatures measured from the images. The wave speeds and the modulation amplitudes imply plasma beta values in the range $\beta_p \approx 10^{-3} -- 10^{-2}$. \end{tex} %R 1997PASP..109..740R %T H II Regions in the Disks of Spiral Galaxies %A ROZAS M. %F contents_97_06 %K Dissertation Summaries %B \begin{tex}The objective of the research presented in the thesis is to use photometrically calibrated high quality images in \ha\ of the disks of spiral galaxies to study their global star forming properties. In the first part of the study we catalog and study statistically the \hii\ regions in a set of spirals, imaged in \ha\ . The observed parameters of each region are its fluxes and diameters, from which we can also derive the mean surface brightness and its internal radial gradient (the latter for the largest most luminous regions). Plotting the luminosity function (LF) for a given galaxy (the number of regions versus \ha\ flux) we find a characteristic discontinuity: a peak accompanied by a change in gradient of the function, at a luminosity of 10$^{38.6}$ erg s$^{-1}$ per region. We attribute this to the change from ionization-bounded \hii\ regions, at luminosities below the transition, to density-bounded regions above the transition, and explain with a quantitative model based on this assumption why the transition takes place at a well-defined luminosity, and one which varies very little from galaxy to galaxy. In the six galaxies observed and analyzed in this way, the variance is 0.07 mag., making the transition a good prima facie candidate to be a powerful standard candle for accurate extragalactic distance measurements. Confirmation of the nature of the transition is provided by measurements of the internal brightness gradients, which show a jump from a constant value (predicted for ionization bounded regions) below the transition to a larger and increasing value above the transition. The theoretical model which can account for the transition was used to show how the gradients of the LF in the ionization bounded and the density bounded regimes can be used to derive the mass function of the ionizing stars in regions close to the transition luminosity, yielding a mean value for the slope of the MF in the galaxies observed of -2.4; the brightest stars in these regions are characteristically early O-types. Further evidence that the most luminous regions are density-bounded is provided by measuring the internal velocity dispersions of \hii\ regions across a galaxy, using the TAURUS Fabry-Perot spectral line imager. A plot of velocity dispersion v. luminosity in \ha\ is a scatter diagram in the log-log plane with a linear upper envelope having a slope of +2.6, on which lies the brightest regions: those above the transition. We explain these findings by assuming that a typical region does not show gas in virial equilibrium, since sporadic stellar events: winds and explosions, provide a non-negligible fraction of the \ha\ luminosity. However the locus of the upper envelope should correspond to a virial relation; the more massive regions show more rapid damping of impulsive energy input. The slope of the envelope is that predicted for regions whose mass rather than total luminosity is being sampled, i.e. density-bounded regions. The thesis is completed with a different application of our \ha\ observations: a technique to test the relation between the presence or absence of twofold symmetries in the star formation patterns of grand design spirals, and the strength of any bar which is present. We find that a strong bar inhibits the second degree of symmetry, implying more mixing in the disk. Finally we apply a dynamical model, using numerical simulations, to the spiral galaxy NGC 157, in order to determine its principal resonances. \end{tex}