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Dive into the research topics where William H. Waller is active.

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Featured researches published by William H. Waller.


The Astrophysical Journal | 1991

Relics of an eruptive starburst in NGC 1569

William H. Waller

H-alpha, R, and I band CCD images of the posteruptive irregular galaxy NGC 1569 are presented. The discovery of two archlike structures of diffuse H-alpha emission located more than 1 kpc beyond the star-forming bar is reported. These features are used to estimate an age for the near-nuclear starburst that created them along with other filamentary and armlike structures previously seen in H-alpha photographs. The gravitational and kinematic energies associated with the H-alpha arcs are estimated to be orders of magnitude higher than can be provided by a single supernova explosion. Coherent outbursts involving thousands of supernovae each could explain the diffuse H-alpha features without exceeding the starbirth rate inferred from the total H-alpha luminosity of the galaxy. 46 refs.


Astrophysical Journal Supplement Series | 2000

Comparing Galaxy Morphology at Ultraviolet and Optical Wavelengths

L. E. Kuchinski; Wendy L. Freedman; Barry F. Madore; M. Trewhella; Ralph C. Bohlin; Robert H. Cornett; Michael Nicholas Fanelli; Pamela Marie Marcum; Susan G. Neff; Robert W. O'Connell; Morton S. Roberts; Andrew M. Smith; Theodore P. Stecher; William H. Waller

We have undertaken an imaging survey of 34 nearby galaxies in far-ultraviolet (FUV, ~1500 A) and optical (UBVRI) passbands to characterize galaxy morphology as a function of wavelength. This sample, which includes a range of classical Hubble types from elliptical to irregular, with emphasis on spirals at low inclination angle, provides a valuable database for comparison with images of high-z galaxies whose FUV light is redshifted into the optical and near-infrared bands. Ultraviolet data are from the Ultraviolet Imaging Telescope (UIT) Astro-2 mission. We present images and surface brightness profiles for each galaxy, and we discuss the wavelength dependence of morphology for different Hubble types in the context of understanding high-z objects. In general, the dominance of young stars in the FUV produces the patchy appearance of a morphological type later than that inferred from optical images. Prominent rings and circumnuclear star formation regions are clearly evident in FUV images of spirals, while bulges, bars, and old, red stellar disks are faint to invisible at these short wavelengths. However, the magnitude of the change in apparent morphology ranges from dramatic in early-type spirals with prominent optical bulges to slight in late-type spirals and irregulars, in which young stars dominate both the UV and optical emission. Starburst galaxies with centrally concentrated, symmetric bursts display an apparent E/S0 structure in the FUV, while starbursts associated with rings or mergers produce a peculiar morphology. We briefly discuss the inadequacy of the optically defined Hubble sequence in describing FUV galaxy images and estimating morphological k-corrections, and we suggest some directions for future research with this data set.


Publications of the Astronomical Society of the Pacific | 1997

THE ULTRAVIOLET IMAGING TELESCOPE: INSTRUMENT AND DATA CHARACTERISTICS

Theodore P. Stecher; Robert H. Cornett; Michael R. Greason; Wayne B. Landsman; Jesse K. Hill; R. S. Hill; R. C. Bohlin; Peter C. Chen; Nicholas R. Collins; Michael Nicholas Fanelli; J. I. Hollis; Susan G. Neff; Robert W. O'Connell; Joel D. Offenberg; Ronald A. Parise; Joel Wm. Parker; Morton S. Roberts; Andrew M. Smith; William H. Waller

The Ultraviolet Imaging Telescope (\UIT) was flown as part of the \AstroMiss\ observatory on the Space Shuttle Columbia in December 1990 and again on the Space Shuttle Endeavor in March 1995. Ultraviolet (1200-3300A) images of a variety of astronomical objects, with a 40\arcmin\ field of view and a resolution of about 3\arcsec, were recorded on photographic film. The data recorded during the first flight is available to the astronomical community through the National Space Science Data Center (NSSDC); the data recorded during the second flight will soon be available as well. This paper discusses in detail the design, operation, data reduction, and calibration of \UIT, providing the user of the data with information for understanding and using the data. It also provides guidelines for analyzing other astronomical imagery made with image intensifiers and photographic film.


The Astrophysical Journal | 1991

Two micron morphology of candidate protostars

Motohide Tamura; Ian Gatley; William H. Waller; Michael W. Werner

Results of a deep near-infrared imaging survey of low-luminosity cold IRAS sources in the Taurus dark cloud are discussed. The images involved identify the compact sources energizing the IRAS sources, identify infrared nebulosity around numbers of the invisible sources, and reveal the large-scale (about 1000 to 10,000 AU) morphology of this nebulosity. Some of the invisible sources show a clear bipolar or monopolar morphology suggesting a close relation of the nebulosity with a bipolar mass outflow. It is concluded that the nebulosity is likely due to scattering of radiation from the central source by the dust associated with the mass outflow extending to the poles of a circumstellar dust disk. 28 refs.


The Astrophysical Journal | 1997

Ultraviolet Colors and Extinctions of H II Regions in the Whirlpool Galaxy (M51)

Jesse K. Hill; William H. Waller; Robert H. Cornett; Ralph C. Bohlin; Kwang-Ping Cheng; Susan G. Neff; Z Morton S. Roberts; Andrew M. Smith; Paul M. Hintzen; Eric P. Smith; Theodore P. Stecher

Far-UV (wavelength 1520 A), U, Hα, and R images of the interacting Sbc spiral galaxy M51 were obtained by the Ultraviolet Imaging Telescope (UIT) during the Astro-2 Spacelab mission of 1995 March and at Mount Laguna Observatory. The μ152 - μU radial gradient of over 1 mag, becoming bluer with increasing radius, is attributed primarily to a corresponding radial extinction gradient. Magnitudes in both UV bands and Hα fluxes are reported for 28 H II regions. Optical extinctions for the 28 corresponding UV sources are computed from the measured m152 - U colors by fitting to the optical extinctions of Nakai & Kuno. The estimated normalized far-UV extinction A152/E(B-V) increases with increasing Galactocentric distance (decreasing metallicity), from 5.99 to 6.54, compared with the Galactic value 8.33. The best-fit m152 - U color for no extinction, -3.07, is the color of a model solar metallicity starburst of age ~2.5 Myr with IMF slope -1.0. H II regions show decreasing observed Hα fluxes with decreasing radius, relative to the Hα fluxes predicted from the observed f152 for age 2.5 Myr, after the Hα and f152 are corrected for extinction. We attribute the increasing fraction of missing Hα flux with decreasing radius to increasing extinction in the Lyman continuum. The increasing extinction-corrected far-UV flux of the H II regions with decreasing distance to the nucleus is probably a result of the corresponding increasing column density of the interstellar gas resulting in larger mass OB associations. The estimated dust-absorbed Lyman continuum energy flux is ~0.6 times the far-infrared energy flux of M51 observed by IRAS.


Publications of the Astronomical Society of the Pacific | 1990

Emission-line and continuum fluxes from narrow- and broad-band imagery

William H. Waller

The isolation of emission-line and continuum components from narrow- and broad-band imagery is developed theoretically and then demonstrated using the Orion nebula as a test case. CCD images of M 42 taken through standard R-band and H-alpha band filters are processed according to the developed formulations. The processing results in an H-alpha emission-line image that is free of contamination by the stellar and nebular-continuum emission. A red-continuum image is also obtained, where the previously strong contamination by the H-alpha emission is eliminated. The resulting nebular H-alpha equivalent width for the 7.3 x 4.5-arcmin field of view is 5500 A, thus agreeing with expectations based on considerations of recombination-line, free-free continuum and 2-photon continuum emission from a gas at Te of about 7500 K.


Publications of the Astronomical Society of the Pacific | 1999

Emission-Line Properties of the Large Magellanic Cloud Bubble N70

Brooke P. Skelton; William H. Waller; Richard Fredrick Gelderman; L. W. Brown; Bruce E. Woodgate; Adeline Caulet; Robert A. Schommer

We present a spectrophotometric imaging study of the emission bubble N70 (DEM 301) in the Large Magellanic Cloud. N70 is approximately 100 pc in size with a nearly circular shell-like morphology. The nebular emission is powered by an uncertain combination of EUV photons, intense winds, and supernova shock waves from the central population of high-mass stars (the OB association LH 114). We have obtained narrowband images (FWHM ~ 6 A) of N70 in the light of Hα λ6563, [N ii] λ6584, [S ii] λλ6717, 6731, and [O iii] λ5007, along with the corresponding red and green continua. The resulting line fluxes and flux ratios are used to derive ionization rates, nebular densities, volume filling fractions, and excitation indices. The photoionizing luminosity inferred from the embedded stellar population is more than adequate to account for the observed hydrogen ionization rate.We compare the emission-line photometry with that derived from similar imaging of the Orion Nebula and with data collected from the literature on other emission-line regions in the LMC. Compared with the Orion Nebula, N70 shows much higher [S ii]/Hα intensity ratios that increase smoothly with radius—from less than 0.3 near the center to greater than 1.0 toward the outer filamentary shell. The measured intensity ratios in N70 more closely match the range of excitation spanned by giant and supergiant H ii shells and by some of the supernova remnants observed in the LMC. The contending ionization and excitation processes in the interior and outer shell of N70 are evaluated in terms of the available data. EUV photons probably contribute most of the inner nebulas ionization, whereas a combination of photoionization plus collisional ionization and excitation of sulfur atoms by low-velocity shocks seems to best fit the emission-line luminosities and intensity ratios observed in the outer shell. Considerations of the radiative and mechanical energetics that are involved may indicate the need for one or two supernova explosions having occurred during the last ~Myr.


The Astronomical Journal | 1992

Circumnuclear pileups of dust and gas in M82

William H. Waller; M. A. Gurwell; Motohide Tamura

Red Hα and R-band CCD images of the starburst galaxy M82 are compared with corresponding near-infrared [S III] and I-band images and with a smaller Brγ infrared-array image of the central 500 pc. Enhancements in the continuum-subtracted [S III]/Hα flux ratio are evident along a ∼ kpc-long arc that includes the nuclear dust lanes visible at Hα as well as two especially enhanced regions on opposite sides of the bursting nucleus. If interpreted as the consequences of reddening by dust, the [S III]/Hα flux enhancements indicate the presence of obscured ionized gas, much of which is distributed immediately beyond the nuclear 1 kpc


The Astronomical Journal | 1988

Obscuration and star formation in NGC 253 - H-alpha and near-infrared forbidden S III line imagery

William H. Waller; S. G. Kleinmann; George R. Ricker

H-alpha (6563 A) and near-infrared forbidden S III line (9532 A) data are presented for the Sc galaxy NGC 253. Anomalous enhancements in the forbidden S III/H-alpha emission ratio throughout the inner disk may indicate the presence of concealed H II regions. Visual extinctions range from 3-7 mag. The results suggest that within the inner 7 kpc of the disk roughly 95 percent of the ionized gas is obscured from view at H-alpha, and that on large scales the massive star formation depends linearly on the available molecular gas. NGC 253 differs from other Sc-type galaxies by the stronger concentration of star-forming activity toward the nucleus, the richer presence of massive star formation, and the higher overall star-forming efficiency. 50 references.


Journal of the Optical Society of America | 1980

Field-of-view constraints on actively controlled long-baseline stellar interferometry

William H. Waller

The field-of-view limitations to actively controlled long-baseline interferometry are investigated. Without resorting to any specific atmospheric model, it is shown that the deleterious effects of nonisoplanatism do not grow with further baseline separation (higher spatial frequency sampled). Numerical calculations, which assume an atmospheric model, plus recently acquired data on the vertical profile of turbulence [Cn2(s)], suggest that the atmosphere induced field-of-view limitation is about 2 arcsec at optical wavelengths and about 50 arcsec at infrared wavelengths.

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Morton S. Roberts

National Radio Astronomy Observatory

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Robert H. Cornett

Goddard Space Flight Center

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Andrew M. Smith

Goddard Space Flight Center

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Ralph C. Bohlin

Space Telescope Science Institute

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