Search Publications
The Ultraviolet and Optical Continuum Emission in Active Galactic Nuclei: The Status of Accretion Disks
Koratkar, Anuradha; Blaes, Omer
A fundamental component of models of active galactic nuclei (AGNs) is an accretion disk around a supermassive black hole. However, the nature of this accretion disk is not well understood, and current models do not provide a satisfactory explanation of the optical/UV continuum observed in AGNs. In this paper we review the substantial theoretical a…
White Dwarfs in Cataclysmic Variables
Sion, E. M.
Prior to the last 15 years, the literature on cataclysmic variables (CVs) contained little on the properties of the underlying white dwarf accreter other than estimates of their masses. They were regarded simply as nondescript potential wells for studies of accretion disk structure and stability. Estimates of their masses and associated core compo…
Calibration of the MACHO Photometry Database
Alcock, C.; Allsman, R. A.; Alves, D. R. +22 more
The MACHO Project is a microlensing survey that monitors the brightnesses of ~60 million stars in the Large Magellanic Cloud (LMC), Small Magellanic Cloud, and Galactic bulge. Our database presently contains about 80 billion photometric measurements, a significant fraction of all astronomical photometry. We describe the calibration of MACHO two-co…
Charge-Transfer Efficiency of WFPC2
Casertano, Stefano; Heyer, Inge; Whitmore, Bradley
Observations of ω Centauri have been used to characterize the charge-transfer efficiency (CTE) of the Wide Field and Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope. A set of formulae has been developed to correct aperture photometry for CTE loss with dependencies on the X- and Y-positions, the background counts, the brightness of t…
The Detection and Photometric Redshift Determination of Distant Galaxies Using SIRTF's Infrared Array Camera
Simpson, Chris; Eisenhardt, Peter
We investigate the ability of the Space Infrared Telescope Facility's Infrared Array Camera to detect distant (z~3) galaxies and measure their photometric redshifts. Our analysis shows that changing the original long-wavelength filter specifications provides significant improvements in performance in this and other areas.
The Photometry of Undersampled Point-Spread Functions
Lauer, Tod R.
An undersampled point-spread function (PSF) may interact with the microstructure of a solid-state detector such that the total flux detected can depend sensitively on where the PSF center falls within a pixel. Such intrapixel sensitivity variations will not be corrected by flat-field calibration and may limit the accuracy of stellar photometry con…
The Nuclear Spectral Energy Distribution of NGC 4395, the Least Luminous Type 1 Seyfert Galaxy
Moran, Edward C.; Filippenko, Alexei V.; Ho, Luis C. +5 more
We present X-ray (ROSAT), infrared, and radio observations of NGC 4395, which harbors the optically least luminous type 1 Seyfert nucleus discovered thus far. In combination with published optical and ultraviolet spectra, we have used these data to assemble the broadband spectral energy distribution (SED) of the galaxy's nucleus. Interestingly, th…
The Age of the Sculptor Dwarf Spheroidal Galaxy from Imaging with WFPC2
Ballester, Gilda E.; Grillmair, Carl; Krist, John E. +17 more
From images taken with the Hubble Space Telescope's WFPC2, we have obtained photometry of a field in the Sculptor dwarf spheroidal galaxy to 3 mag below the main-sequence turnoff. We determine an age equal to that of the earliest globular clusters for the bulk of the stars in our field of view. We attempt to constrain the star formation history of…
The Orbit of 16 Cygni AB
Marcy, Geoffrey W.; Hauser, Heather M.
The high orbital eccentricity of the planet around 16 Cygni B may have been induced by the companion star, 16 Cygni A, but only if the stellar binary has sufficiently small periastron distance. The long period of the stellar binary, ~3x10^4 yr, implies that less than 1% of the orbit has transpired since its first astrometric measurements in 1830. …
Calibration of Hubble Space Telescope WFPC2 Emission-Line Filters
O'Dell, C. R.; Doi, Takao
The results of calibration of the primary emission-line filters of the Hubble Space Telescope WFPC2 are presented in a form which allows observers to easily calculate emission-line surface brightnesses for Hα, Hβ, [O III] λ5007, and [N II] λ6583. The Hα and [N II] filters pass both lines in such a way that observations in both are necessary to obt…