K. T. Korista
A5025741144- Galaxies: Formation, Evolution, Phenomena
- Astrophysical Phenomena and Observations
- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Atomic and Molecular Physics
- Astrophysics and Cosmic Phenomena
- Adaptive optics and wavefront sensing
- Plasma Diagnostics and Applications
- Laser-induced spectroscopy and plasma
- Spectroscopy and Laser Applications
- X-ray Spectroscopy and Fluorescence Analysis
- Atmospheric Ozone and Climate
- Pulsars and Gravitational Waves Research
- Advanced Chemical Physics Studies
- Ionosphere and magnetosphere dynamics
- Calibration and Measurement Techniques
- Particle Accelerators and Free-Electron Lasers
- Magnetic confinement fusion research
- Scientific Research and Discoveries
- Solar and Space Plasma Dynamics
- History and Developments in Astronomy
- Radio Astronomy Observations and Technology
Western Michigan University
2015-2024
Western University
2017
University of Kentucky
1995-2000
University of St Andrews
2000
Johns Hopkins University
1996
Carnegie Observatories
1991-1996
The Ohio State University
1989-1996
Space Telescope Science Institute
1993-1995
Carnegie Institution for Science
1990-1994
University of Illinois System
1988
ABSTRACT CLOUDY is a large‐scale spectral synthesis code designed to simulate fully physical conditions within an astronomical plasma and then predict the emitted spectrum. Here we describe version 90 (C90) of code, paying particular attention changes in atomic database numerical methods that have affected predictions since last publicly available version, C84. The computational uncertainties are outlined together with direction future development will take. freely widely used analysis...
view Abstract Citations (1439) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Atomic Data for Astrophysics. II. New Analytic FITS Photoionization Cross Sections of Atoms and Ions Verner, D. A. ; Ferland, G. J. Korista, K. T. Yakovlev, We present a complete set analytic fits to the nonrelativistic photoionization cross sections ground states atoms ions elements from H through Si, S, Ar, Ca, Fe. Near ionization thresholds, are based on Opacity...
view Abstract Citations (502) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Steps toward Determination of the Size and Structure Broad-Line Region in Active Galactic Nuclei. I. an 8 Month Campaign Monitoring NGC 5548 with IUE Clavel, J. ; Reichert, G. A. Alloin, D. Crenshaw, M. Kriss, Krolik, H. Malkan, Netzer, Peterson, B. Wamsteker, W. Altamore, Baribaud, T. Barr, P. Beck, S. Binette, L. Bromage, E. Brosch, N. Diaz, Filippenko, V. Fricke,...
The similarity of quasar line spectra has been taken as an indication that the emission clouds have preferred parameters, suggesting environment is subject to a fine tuning process. We show here observed spectrum natural consequence powerful selection effects. computed large grid photoionization models covering widest possible range cloud gas density and distance from central continuum source. For each only narrow source results in maximum reprocessing efficiency, corresponding ``locally...
view Abstract Citations (284) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Steps toward Determination of the Size and Structure Broad-Line Region in Active Galactic Nuclei. VIII. an Intensive HST, IUE, Ground-based Study NGC 5548 Korista, K. T. ; Alloin, D. Barr, P. Clavel, J. Cohen, R. Crenshaw, M. Evans, I. N. Horne, Koratkar, A. Kriss, G. Krolik, H. Malkan, Morris, S. L. Netzer, O'Brien, Peterson, B. Reichert, Rodriguez-Pascual,...
view Abstract Citations (302) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Steps toward Determination of the Size and Structure Broad-Line Region in Active Galactic Nuclei. II. an Intensive Study NGC 5548 at Optical Wavelengths Peterson, B. M. ; Balonek, T. J. Barker, E. S. Bechtold, Bertram, R. Bochkarev, N. G. Bolte, Bond, D. Boroson, A. Carini, Carone, Christensen, Clements, Cochran, L. Cohen, Crampton, Dietrich, Elvis, Ferguson,...
We present graphically the results of several thousand photoionization calculations broad emission-line clouds in quasars, spanning 7 orders magnitude hydrogen ionizing flux and particle density. The equivalent widths 42 quasar emission lines are presented as contours density-ionizing plane for a typical incident continuum shape, solar chemical abundances, cloud column density N(H) = 1023 cm-2. Results similarly given small subset two other densities (1022 1024 cm-2), five shapes, gas...
We present high spectral resolution Very Large Telescope observations of the broad absorption line quasar SDSS J0318 − 0600. This high-quality data set allows us to extract accurate ionic column densities and determine an electron number density ne = 103.3±0.2 cm−3 for main outflow component. The heavily reddened spectrum J0318-0600 requires purely silicate dust with a reddening curve characteristic predominately large grains, from which we estimate bolometric luminosity. carry out...
We present a detailed analysis of the Astrophysical Research Consortium 3.5 m telescope spectrum QSO SDSS J0838+2955. The object shows three broad absorption line (BAL) systems at 22,000, 13,000, and 4900 km s^-1 blueshifted from systemic redshift z=2.043. Of particular interest is lowest velocity system that displays low-ionization species such as Mg II, Al Si II*, Fe II II*. Accurate column densities were measured for all transitions in this BAL using an inhomogeneous absorber model. ratio...
Recent intensive Swift monitoring of the Seyfert 1 galaxy NGC 5548 yielded 282 usable epochs over 125 days across six UV/optical bands and X-rays. This is densest extended AGN continuum sampling ever obtained, with a mean rate <0.5 day. Approximately daily HST UV was also obtained. The light curves show strong correlations (r_max = 0.57 - 0.90) clearest measurement to date interband lags. These lags are well-fit by \tau propto \lambda^4/3 wavelength dependence, normalization that indicates...
Abstract Swift intensive accretion disk reverberation mapping of four AGN yielded light curves sampled ∼200–350 times in 0.3–10 keV X-ray and six UV/optical bands. Uniform reduction cross-correlation analysis these data sets yields three main results: (1) The X-ray/UV correlations are much weaker than those within the UV/optical, posing severe problems for lamp-post reprocessing model which variations a central corona drive power surrounding disk. (2) interband lags generally consistent with...
ABSTRACT We present ground-based optical photometric monitoring data for NGC 5548, part of an extended multiwavelength reverberation mapping campaign. The light curves have nearly daily cadence from 2014 January to July in nine filters ( BVRI and ugriz ). Combined with ultraviolet the Hubble Space Telescope Swift , we confirm significant time delays between continuum bands as a function wavelength, extending wavelength coverage 1158 Å z band (~9160 Å). find that lags at wavelengths longer...
We describe the first results from a six-month long reverberation-mapping experiment in ultraviolet based on 170 observations of Seyfert 1 galaxy NGC 5548 with Cosmic Origins Spectrograph Hubble Space Telescope. Significant correlated variability is found continuum and broad emission lines, amplitudes ranging ~30% to factor two lines three continuum. The variations all strong lag behind those continuum, He II 1640 lagging by ~2.5 days Lyman alpha 1215, C IV 1550, Si 1400 ~5-6 days....
We report the results of intensive X-ray, UV, and optical monitoring Seyfert 1 galaxy NGC 4593 with Swift. There is no intrinsic flux-related spectral change in any variable component small apparent variations being due to contamination by a constant hard (reflection) X-rays red host UV/optical. Relative shortest wavelength band, UVW2, lags other UV/optical bands mostly agree predictions reprocessing high energy emission an accretion disc. The U-band lag is, however, larger than expected,...
We present the first results from ongoing, intensive, multi-wavelength monitoring program of luminous Seyfert 1 galaxy Mrk 817. While this AGN was, in part, selected for its historically unobscured nature, we discovered that X-ray spectrum is highly absorbed, and there are new blueshifted, broad narrow UV absorption lines, which suggest a dust-free, ionized obscurer located at inner line region partially covers central source. Despite obscuration, measure optical continuum reverberation lags...
An 8 month monitoring campaign on the Seyfert 1 galaxy Fairall 9 has been conducted with International Ultraviolet Explorer in an attempt to obtain reliable estimates of continuum-continuum and continuum-emission-line delays for a high-luminosity active galactic nucleus (AGN). While results this are more ambiguous than those previous campaigns lower luminosity sources, we find general agreement earlier results: (1) there is no measurable lag between ultraviolet continuum bands, (2) measured...
view Abstract Citations (194) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Low-Ionization Broad Absorption Lines in Quasars Voit, G. M. ; Weymann, Ray J. Korista, Kirk T. About 10% of optically selected radio-quiet quasars have broad high- ionization absorption lines and are known as line quasars, or BALQSOs. 15% these BALQSOs also low-ionization Mg II Although uncommon surveys, appear to be much more common IR-selected samples might...
view Abstract Citations (180) References (64) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multiwavelength Observations of Short-Timescale Variability in NGC 4151. IV. Analysis Continuum Edelson, R. A. ; Alexander, T. Crenshaw, D. M. Kaspi, S. Malkan, Peterson, B. Warwick, Clavel, J. Filippenko, V. Horne, K. Korista, Kriss, G. Krolik, H. Maoz, Nandra, O'Brien, P. Penton, Yaqoob, Albrecht, Alloin, Ayres, Balonek, Barr, Barth, Bertram, Bromage, E. Carini,...
From 1996 June 10 to July 29, the International Ultraviolet Explorer monitored Seyfert 1 galaxy NGC 7469 continuously in an attempt measure time delays between continuum and emission-line fluxes. delays, one can estimate size of region dominating production UV emission lines this source. We find strong respond variations with about 23-31 for Lyα, 27 C IV λ1549, 19-24 N V λ1240, 17-18 Si λ1400, 07-10 He II λ1640. The most remarkable result, however, is detection apparent different bands. With...
The broad emission lines (BELs) of quasars and active galactic nuclei (AGNs) are important diagnostics the relative abundances overall metallicity in gas. Here we present new theoretical predictions for several UV BELs. We focus specifically on nitrogen abundance as a indicator, based expected secondary enrichment at metallicities Z ≳ 0.2 Z☉. Among consider, N III] λ1750/O λ1664, V λ1240/(C IV λ1549 + O VI λ1034), V/He II λ1640 most robust diagnostics. argue, particular, that average BEL is...
We investigate the effect of a global change in ionizing continuum level on behavior strong optical broad emission lines seen spectra nuclear emission-line regions active galactic nuclei (AGNs), including Balmer lines, He I λ5876, and II λ4686. Unlike most prominent heavy-element found UV, hydrogen helium recombination lines' emissivities are strongly dependent incident flux, since these arise out excited states whose depths depend flux photons. Using photoionization calculations, we...
This paper describes the techniques that we have used to incorporate a large-scale model of Feì on and resulting Fe II emission into CLOUDY, spectral synthesis code designed simulate conditions within plasma spectrum.We describe numerical methods use determine level populations, mutual line overlap Ñuorescence, collisional e †ects, heatingcooling †ects atom its environment.As currently implemented, includes lowest 371 levels (up 11.6 eV) predicts intensities 68,635 lines.We our data sources,...
We used a very large set of models broad emission line region (BELR) clouds in active galactic nuclei to investigate the formation observed Fe II lines. show that photoionized BELR cannot produce both shape and equivalent width 2200-2800 Å UV bump unless there is considerable velocity structure corresponding microturbulent parameter vturb ≥ 100 km s-1 for locally optimally emitting cloud here. This could be either microturbulence gas confined by some phenomenon such as MHD waves or shear...
We present high quality (high signal-to-noise ratio and moderate spectral resolution) near-infrared (near-IR) spectroscopic observations of 23 well-known broad-emission line active galactic nuclei (AGN). Additionally, we obtained simultaneous (within two months) optical spectroscopy similar quality. The near-IR broad emission spectrum AGN is dominated by permitted transitions hydrogen, helium, oxygen, calcium, the rich singly-ionized iron. In this paper spectra, identifications measurements,...
We investigate the contribution of reprocessed continuum emission (1000A - 10,000A) originating in broad line region (BLR) gas, diffuse (DC), to wavelength-dependent delays measured AGN disk reverberation mapping experiments. Assuming a spherical BLR geometry, we adopt Local Optimally-emitting Cloud (LOC) model for that approximately reproduces emission-line strengths strongest UV lines (Ly-alpha and C IV) NGC 5548. Within this LOC framework, explore how assumptions about gas hydrogen...