• 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)
    • NGC 2818, An Open Cluster containing a Planetary Nebulae

      Tifft, W. G.; Connolly, L. P.; Webb, D. F.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1971-12)
      Three color UBV photometry of the cluster NGC 2818 shows it to lie at a distance of 3.2 kpc. The cluster has a color excess E_(B-V)= 0.22 and an ultraviolet excess of 0.09. The evolutionary turnoff from the main sequence occurs in mid A. The faint main sequence in the cluster shows a distinct bend or discontinuity. Preliminary velocity measurements indicate that the high excitation planetary nebula NGC 2818 is probably associated with the cluster.
    • OB Stars Near the Supernova Remnant RCW 86

      Westerlund, B. E.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1969-05)
      The filamentary nebula RCW 86, identical with the non - thermal radio source MSH 14 - 63, is part of a supernova remnant. A group of OB stars is found near the radio source. The distance of the group is 2500 pc; this agrees well with the radio distance of the remnant. It is suggested that the remnant was formed by the explosion of a member of the group; the explosion occurred probably in 185 A. D.
    • Observable Signatures of Young Galaxies

      White, S. D. M.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1989-10)
      I review theoretical expectations for the probable appearance of galaxies during their formation phase, placing particular emphasis on the uncertainties in these ideas. Recent models suggest that formation may occur relatively recently, but that young galaxies are less spectacular than previously supposed. They may be analogous to recently discovered high red - shift radio galaxies, and indeed they may have been observed directly in faint galaxy counts. I summarise several other lines of evidence which suggest that galaxy formation may have been a recent process. Finally I give preliminary results from a detailed analytic study of the observable properties of young galaxies in a Cold Dark Matter universe. Predictions are given for faint galaxy counts and redshift distributions, and for the galaxy luminosity function.
    • Observational Evidence for Galactic Spiral Structure

      Bok, B. J.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1970-08)
    • Photoelectric Photometry of Some Galaxies in the Region of the Virgo Cluster

      Tifft, W. G.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1973-01)
      Four color photometry of 26 galaxies, mostly in the region of the Virgo Cluster, is presented.
    • Photometric Standards for the Southern Hemisphere

      Bok, B. J.; Bok, P. F.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1969-08)
    • Polarization and Structure of the Crab Nebula : Proceedings of the 23rd IAU Colloquium

      Felten, J. E.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1973-04-03)
      Present knowledge of the optical, radio and X -ray polarization of the Crab is reviewed and discussed as it bears on the structure of the magnetic field, time scales in the nebula, and relations between nebula and pulsar. Not as much high -resolution polarimetry has been done on the Crab as might have been expected. Loops of field and a large -scale structure can be recognized, but it is not known whether the fields generally are smooth or chaotic on a small scale. Field lines tend to curl around the filaments. The large angular size of the X -ray source poses a difficulty to conventional theory. The form of the nebula does not single out the pulsar as its source, and the exact relation between pulsar and nebula is uncertain. The wave -field or "synchro- Compton" interpretation of the continuum emission is erroneous but has led to interesting observations of circular polarization. Circular polarization of the ordinary synchrotron radiation might be observable in the radio band. Magnetic flux may have been generated in the nebula by winding of lines around the rotating pulsar. Polaroid photographs then suggest that the pulsar rotation axis is roughly NW -SE, but confirmation is lacking.
    • Polarization of Radio Sources. I. Transfer of synchrotron Radition through an Extended Radio Source with Faraday Rotation|Polarization of Radio Sources. I. Homogeneous Source of Arbitrary Optical Thickness

      Pacholczyk, A. G.; Swihart, T. L.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1966-11)
      The problem of transfer of radiation in a medium with polarized emission, polarized absorption and Faraday rotation of the plane of polarization is formulated. Solutions are obtained for the case of a homogeneous source. In the range of frequencies for which a medium is optically thick the degree of polarization of synchrotron radiation depends on the type of absorption process and is different for synchrotron absorption and for thermal absorption. It is therefore suggested that the low frequency polarization measurements of radio sources with curved spectra may determine whether synchrotron self -absorption or thermal absorption or another process is responsible for the low frequency curvature in spectra of certain radio sources.
    • Polarization of Radio Sources. II. Faraday Effect in the Case of Quasitransverse Propagation

      Pacholczyk, A. G.; Swihart, T. L.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1970)
      Under the conditions of quasitransverse propagation of electromagnetic waves in a magnetoionic plasma, the effect analogous to Faraday rotation in the quasilongítudinal case (which we will call Faraday pulsation) can produce a large elliptical polarization of originally linearly polarized radiation. Therefore, the presence of elliptical polarization in the radiation cannot serve as a means for distinguishing between a synchrotron mechanism with high energy electrons and any other type of emission process in radio sources in which conditions suggesting quasi - transverse propagation (large magnetic fields) may take place. The Faraday pulsation has a wavelength dependence through which it can be identified.
    • A Possible Rotation Chain of Galaxies|Possible Systematic Redshifts in a Chain of Galaxies

      Gregory, S. A.; Connolly, L. P.; Univ Arizona, Steward Observ (Steward Observatory, The University of Arizona (Tucson, Arizona), 1972-11)
      Redshifts are reported for two groups of galaxies. Although these two groups have previously been assigned to the same cluster, their redshifts indicate that they are not associated. A systematic variation of redshifts is found across the chain of one of these groups, Abell 2247, and three possible interpretations are discussed. It is concluded that rotation of the chain is the most likely explanation of the systematic motions.