Kurt S. Anderson

Bulge-Disk Decomposition of 659 Spiral and Lenticular Galaxy Brightness Profiles

We present one of the largest homogeneous sets of spiral and lenticular galaxy brightness profile decompositions completed to date. The 659 galaxies in our sample have been fitted with a de Vaucouleurs law for the bulge component and an inner-truncated exponential for the disk component. Of the 659 galaxies in the sample, 620 were successfully fitted with the chosen fitting functions. The fits are generally well defined, with more than 90% having rms deviations from the observed profile of less than 0.35 mag. We find no correlations of fitting quality, as measured by these rms residuals, with either morphological type or inclination. Similarly, the estimated errors of the fitted coefficients show no significant trends with type or inclination. These decompositions form a useful basis for the study of the light distributions of spiral and lenticular galaxies. The object base is sufficiently large that well-defined samples of galaxies can be selected from it.

Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XIII. Ultraviolet Observations of the Broad-Line Radio Galaxy 3C 390.3

As part of an extensive multiwavelength monitoring campaign, the International Ultraviolet Explorer satellite was used to observe the broad-line radio galaxy 3C 390.3 during the period 1994 December 31E1996 March 5. Spectra were obtained every 6E10 days. The UV continuum varied by a factor of 7 through the campaign, while the broad emission lines varied by factors of 2E5. Unlike previously moni- tored Seyfert 1 galaxies, in which the X-ray continuum generally varies with a larger amplitude than the UV, in 3C 390.3 the UV continuum light curve is similar in both amplitude and shape to the X-ray light curve observed by ROSAT . The UV broad emission-line variability lags that of the UV continuum by 35E70 days for Lya and C IV, values larger than those found for Seyfert 1 galaxies of comparable UV luminosity. These lags are also larger than those found for the Balmer lines in 3C 390.3 over the same period. The red and blue wings of C IV and Lya vary in phase, suggesting that radial motion does not dominate the kinematics of the UV line-emitting gas. Comparison with archival data provides evidence for velocity-dependent changes in the Lya and C IV line pro-les, indicating evolution in the detailed properties and/or distribution of the broad-line emitting gas. Subject headings: galaxies: active E galaxies: individual (3C 390.3) E ultraviolet: galaxies

Initial mass function for early-type stars in starburst galaxies

The IMF slope of early-type stars in starburst galaxies is investigated using IUE observations and a technique that utilizes mass-linewidth relations for early-type stars. Fourteen low-resolution IUE spectra of eight starburst galaxies and three H II region galaxies are used to obtain line-strength ratios Si IV(1400 A)/C IV(1550 A). These are compared to model line ratios, and indicate that the average IMF slope for OB stars in these intense star-formation regions is appreciably flatter than that of the solar neighborhood. 46 references.

Inner-truncated Disks in Galaxies

We present an analysis of the disk brightness profiles of 218 spiral and lenticular galaxies. At least 28% of disk galaxies exhibit inner truncations in these profiles. There are no significant trends of truncation incidence with Hubble type, but the incidence among barred systems is 49%, more than 4 times that for nonbarred galaxies. However, not all barred systems have inner truncations, and not all inner-truncated systems are currently barred. Truncations represent a real dearth of disk stars in the inner regions and are not an artifact of our selection or fitting procedures nor the result of obscuration by dust. Disk surface brightness profiles in the outer regions are well represented by simple exponentials for both truncated and nontruncated disks. However, truncated and nontruncated systems have systematically different slopes and central surface brightness parameters for their disk brightness distributions. Truncation radii do not appear to correlate well with the sizes or brightnesses of the bulges. This suggests that the low angular momentum material apparently missing from the inner disk was not simply consumed in forming the bulge population. Disk parameters and the statistics of bar orientations in our sample indicate that the missing stars of the inner disk have not simply been redistributed azimuthally into bar structures. The sharpness of the brightness truncations and their locations with respect to other galactic structures suggest that resonances associated with disk kinematics, or tidal interactions with the mass of bulge stars, might be responsible for this phenomenon.

UNCONVENTIONAL AGN FROM THE SDSS

We discuss some of the most unusual active galactic nuclei (AGN) discovered to date by the Sloan Digital Sky Survey (SDSS): the first broad absorption line quasar seen to exhibit He II absorption, several quasars with extremely strong, narrow UV Fe II emission, and an AGN with an unexplained and very strange continuum shape.

PHOTOMETRIC ACCRETION SIGNATURES NEAR THE SUBSTELLAR BOUNDARY

Multiepoch imaging of the Orion equatorial region by the Sloan Digital Sky Survey has revealed that significant variability in the blue continuum persists into the late-M spectral types, indicating that magnetospheric accretion processes occur below the substellar boundary in the Orion OB1 association. We investigate the strength of the accretion-related continuum veiling by comparing the reddening-invariant colors of the most highly variable stars against those of main-sequence M dwarfs and evolutionary models. A gradual decrease in the g-band veiling is seen for the cooler and less massive members, as expected for a declining accretion rate with decreasing mass. We also see evidence that the temperature of the accretion shock decreases in the very low mass regime, reflecting a reduction in the energy flux carried by the accretion columns. We find that the near-IR excess attributed to circumstellar disk thermal emission drops rapidly for spectral types later than M4. This is likely due to the decrease in color contrast between the disk and the cooler stellar photosphere. Since accretion, which requires a substantial stellar magnetic field and the presence of a circumstellar disk, is inferred for masses down to 0.05 M⊙, we surmise that brown dwarfs and low-mass stars share a common mode of formation.

A study of environmental influences on the structure of spiral galaxy disks

The results of photographic surface photometry of late-type spiral galaxies in the clusters Abell 426, Abell 1367, and Abell 2151 are presented. U- and R-band surface brightness profile properties are analyzed in terms of the following environmental parameters : the projected distance from cluster center, the projected distance to the nearest neighbor, and the local projected galaxy density. No significant correlation are found between the structure of the galaxies and the projected distance from cluster center