• Infrared Radiation from the Seyfert Galaxy NGC 1068

      Pacholczyk, A. G.; Wisniewski, W. Z.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1966-11)
    • Infrared Speckle Observations of Binary Ross 614 AB: Combined Shift-and-Add and Zero-and-Add Analysis

      Davey, B. L. K.; Cocke, W. J.; Bates, R. H. T.; McCarthy, D. W., jr.; Christou, J. C.; Cobb, M. L.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1988-12)
      One -dimensional infrared speckle scans of Ross 614 AB were recorded at a wavelength of 2.2μm. For each scan an estimate of the instantaneous quality of the seeing was calculated and the scan was binned accordingly. The three bins corresponding to the three best seeing conditions were further processed by applying the shift -and -add algorithm to the set of images contained within each bin, thereby generating three shift- and -add images with differing shift -and -add point -spread- functions. After windowing the shift -and -add images (using edge -extension) to reduce the effect of contamination, we have obtained parameters corresponding to the separation and brightness ratio of a two component model of the double star Ross 614 AB by deconvolving the three shift -and -add images with the aid of the zero-and -add technique. Least squares analysis on the positions of the clusters of zeros found from zero- and -add yields a separation of 1.04 arcseconds and a brightness ratio of 4.3 for the binary system at this wavelength. An extension of the processing, which takes explicit account of the nonlinear motion of the scanning mechanism gives improved estimates of 1.04 arcseconds and 3.9 for the separation and brightness ratio, respectively.
    • Infrared Variability of the Seyfert Galaxy NGC 1068

      Pacholczyk, A. G.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1970-06)
      Observations of NGC 1068 at 2.2y indicate variability with a timescale of a few days, implying that the size of the infrared emitting region is not larger than a few times 1015 cm. This limit on size is incompatible with the interpretation of infrared radiation by remission from dust grains, by synchrotron emission in a uniform model, and by synchrotron emission from many compact sources within the same object ( "irtrons".). The infrared observations of NGC 1068 could be explained in terms of a nonuniform spherically symmetric synchrotron source with a radial dependence of the flux and of the frequency at which the source becomes optically thick.
    • Interstellar C2, CH, and CN in Translucent Molecular Clouds

      van Dishoeck, E. F.; Univ Arizona, Steward Observ; Black, J. H. (Steward Observatory, The University of Arizona (Tucson, Arizona), 1988-12)
      Optical absorption line techniques have been applied to the study of a number of translucent molecular clouds in which the total column densities are large enough that substantial molecular abundances can be maintained. Results are presented for a survey of absorption lines of interstellar C2, CH, and CN. Detections of CN through the A2II -X2E+ (1,0) and (2,0) bands of the red system are reported, and are compared with observations of the blue system for one line of sight. The population distributions in C2 provide diagnostic information on temperature and density. The measured column densities of the three species can be used to test details of the theory of molecule formation in clouds where photo -processes still play a significant role. The C2 and CH column densities are strongly correlated with each other and probably also with the H2 column density. In contrast, the CN column densities are found to vary greatly from cloud to cloud. The observations are discussed with reference to detailed theoretical models.
    • Investigation of the Cancer Cluster of Galaxies

      Tifft, W. G.; Jewsbury, C. P.; Sargent, T. A.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1973-04)
    • The Ionization and Thermal Equilibrium of a Gas Excited by Ultraviolet Synchrotron Radiation

      Williams, R. E.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1966-10)
      The ionization and thermal balances are considered for a gas that is ionized by a dilute radiation field, taking into account the diffuse ionizing radiation produced by the gas. A number of models are constructed in which the electron temperature and the ionization of the elements H, He, C, N, 0, Ne, and Mg are determined for optically thin and optically thick gases ionized by ultraviolet synchrotron radiation under different conditions. Conclusions are then drawn about the general characteristics of ionization by synchrotron radiation. It is shown that, in an optically thin gas, because of the insensitive frequency- dependence of synchrotron radiation each element occupies a number of different stages of ionization at any one point in the gas. It is also shown that in an optically thick gas the heavy elements remain ionized to much greater distances from the source than hydrogen and helium, and that the gas becomes thermally unstable when H and He have become almost completely neutral. In addition, observations of the emission -line intensities of the Crab Nebula are compared with a model of this object. Considerable disagreement exists between the observed and predicted intensities, and possible reasons for the discrepancy are discussed.
    • The Ionization of Planetary Nebulae : Proceedings of the 34th IAU Symposium

      Williams, R. E.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1967-08)
      The ionization of the most abundant elements in planetary nebulae has been determined for a number of models of nebulae at different epochs in their expansion. The values used for the temperatures and radii of the central stars and the sizes and densities of the shells have come from Seaton's evolutionary sequence. The ionizing radiation field has been taken from model atmosphere calculations of the central stars by Gebbie and Seaton, and Biihm and Deinzer. Emission -line fluxes have been calculated for the models and compared with observations of planetary nebulae by O'Dell, Osterbrock's group, and Aller and his collaborators. Results indicate that the central stars have strong He+ Lyman continuum excesses, similar to those predicted by Gebbie and Seaton. The mean abundance determinations for the nebulae made by Aller are confirmed, with the exception of nitrogen, which appears to be 3 or 4 times more abundant than his value. It is also seen that the electron temperatures of the nebulae are higher than previous theoretical determinations, providing better agreement with empirically derived values.
    • IRAS Observations of Dust Heating and Energy Balance in the FHO Ophiuchi Dark Cloud

      Greene, T. P.; Young, E. T.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1989-10)
      The total luminosity of the Rho Ophiuchi molecular cloud is derived from IRAS data and is found to match the luminosity of known embedded sources very closely. High resolution 60 and 100 micron band IRAS images have been reduced to yield equilibrium color temperature maps and 60 micron band dust optical depth maps for the region. These data along with optically thin C18O column density data are used to evaluate dust grain sizes and compositions via competing grain models. Radiative modeling shows that a standard power law distribution of graphite and silicate grains is responsible for IRAS 60 and 100 micron band emissions. These grains are heated to about one tenth of the cloud's depth in the core region. Their optical depths closely follow molecular column density structure, but these grains are considerably colder than the molecular gas. We also find that a 10 nm minimum particle radius cutoff is appropriate for the 60 and 100 micron band emissions while very small grains or PAH molecules dominate the cloud's 12 and 25 micron band emissions.
    • IRAS Observations of the Rho Ophiuchi Infrared Cluster: Spectral Energy Distributions and Luminosity Function

      Wilking, B. A.; Lada, C. J.; Young, E. R.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1988-12)
    • Is the Probability of Occurrence of Absorption Lines in QSOs a Function of Redshift?

      Weymann, R. J.; Wilcox, R. C. (Steward Observatory, The University of Arizona (Tucson, Arizona), 1968-07)
    • Large-Scale Galaxy Flow from a Nongravitational Impulse

      Hogan, C. J.; Kalser, N.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1988-12)
    • Light Variations of the Seyfert Galaxy NGC 4151

      Fitch, W. S.; Pacholczyk, A. G.; Weymann, R. J.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1967-09)
    • Light Variations of the Seyfert Galaxy NGC 4151. III. Long Term Photographic B Variations and Infrared K Data

      Pacholczyk, A. G.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1970-07)
    • Long Wavelength Radio Spectra of Seyfert Galaxies

      Pacholczyk, A. G.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1970-12)
    • Luminosity Function of White Dwarfs in the Local Disk and Halo

      Liebert, J.; Dahn, C. C.; Monet, D. G.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1988-10)
    • Magellanic Cloud Investigations. IV. The LMC Blue Globular Cluster NGC 1850

      Tifft, W. G.; Connolly, L. P.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1972-11)
    • Magellanic Cloud Investigations. III. The LMC Bar

      Tifft, W. G.; Snell, C. M.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1970-08)
      Three -color photographic photometry has been carried out for three small regions at the west end of the LMC bar. Photoelectric calibration observations by Bok and Tifft for 26 stars were utilized. Program stars were selected so that the photographic photometry is uniformly representative to V = 16.6 magnitude in one region and to V = 18.0 magnitude in two smaller ones. The results include more than 600 stars with B and V and more than 160 of the brighter stars with U. Contamination by foreground stars is minimal since the regions are small. Color- magnitude diagrams show a narrow vertical blue sequence 0.25 magnitude wide extending from V = 14.5 to V = 18. The location of this sequence indicates about 0.13 magnitude of uniform reddening in the area. Red supergiants are seen between magnitude 14 and 16. A strong component of fainter red giants indicative of an older population is seen below magnitude 16. The red giants extend to B -V = 1.9. After reddening corrections the reddest normal giants have B -V = 1.8. A few very red stars, B -V = 2.2 to 2.8, are seen near V = 16. Two bright Harvard Variable Cepheids fall within the region under study. Light curves and color curves for both of these stars were obtained. The Cepheids lie to the red of the instability strip consistent with other local reddening effects. Fainter bright giants of intermediate color, including possible Cepheids, have been isolated using the color -color diagram. A period and light curve for one star has been derived. Matching the old giant star population a differential true modulus of 0.65 ±0.1 is derived between the SMC and LMC. For an SMC modulus of 19.1, the LMC modulus is 18.45. The three Cepheids in the field yield a modulus of 18.45 ±0.1 when the P -L -C relationship calibration of Sandage and Tammann (1969) is used. Outlying Cepheids as studied by Gascoigne (1969) are approximately 0.2 magnitudes fainter. Real intrinsic variation in Cepheid luminosities outside of the P -L -C relationship is possible but not large. An overall mean LMC true modulus of 18.5 ±0.1 is indicated.
    • MALIN: A Quiescent Disk Galaxy|MALIN 1: A Quiescent Disk Galaxy

      Impey, C. D.; Bothun, G. D.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1988-11)
      We present new optical and radio spectroscopic observations of the remarkable galaxy Malin 1. This galaxy has unique features that include an extremely low surface brightness disk with an enormous mass of neutral hydrogen, and a low luminosity Seyfert nucleus. Malin 1 is exceptional in its values of MHO, LB, and MHI /Ln, and modest in its surface mass density of gas and stars. Spirals with large Min /LB tend to have low mean column densities of HI, and are close to the threshold for star formation due to instabilities in a rotating gas disk. In these terms, Malin 1 has a disk with extremely inefficient star formation. The bulge spectrum is dominated by the absorption features of an old, metal rich stellar population, although there is some evidence for hot (young) stars. The emission line excitations and widths in the nucleus are typical of a Seyfert galaxy; but Malin 1 is in the lowest 5% of the luminosity function of Seyferts, despite a copious fuel supply. Malin 1 is in a low density region of the universe. We propose it as an unevolving disk galaxy, where the surface mass density is so low that the chemical composition and mass fraction in gas change very slowly over a Hubble time. Its properties are similar to those of the damped Lyman -a absorption systems seen in the spectra of high redshift quasars. We emphasize that there are strong observational selection effects against finding gas -rich galaxies that are both massive and diffuse. Finally, we suggest that large and massive HI disks may have formed as early as z - 2, and remained quiescent to the present day. Subject headings : individual (Malin 1) - galaxies : photometry - galaxies : Seyfert - galaxies : stellar content - radio sources : 21 cm radiation - stars : formation
    • MALIN: A Quiescent Disk Galaxy|MALIN 1: A Quiescent Disk Galaxy

      Impey, C. D.; Bothun, G. D.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1988-11)
      A study of the Galactic Center stellar population is continuing with a sensitive 2μm CCD camera. Using a 64 x 64 detector array, background limited images are recorded with modest amounts of observing time (tob, 20 sec to reach K =13). Magnitudes have been extracted using DAOPHOT from repeated imaging of the central 5' x 5' to search among approximately 1500 stars for long period variables (LPV's, P > 200d), particularily Miras. Miras have a well defined period - luminosity relationship as well as one in period -mass. This program investigates the nature of highly luminous stars at the Galactic Center. Presently 12 variables have been found and have several characteristics consistant with Miras. They have a maximum bolometric luminosity of -4.4 mag which supports the case that high luminosity stars in the central 6 pc are young supergiants.
    • Microturbulence vs Metal Abundance: An Observational Test

      Barry, D. C.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1967-01)