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  • 1
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    Vorticity Transport and Wave Emission In A Protoplanetary Disk (2002)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-18
    Beschreibung: Higher order numerical algorithms (4th order in time, 3rd order in space) are applied to the Euler equations and are used to examine vorticity transport and wave motion in a non-self gravitating, initially isentropic Keplerian disk. In this talk we will examine the response of the disk to an isolated vortex with a circulation about equal to the rotation rate of Jupiter. The vortex is located on the 4 AU circle and the nebula is simulated from 1 to 24 AU. We show that the vortex emits pressure-supported density and Rossby-type wave packets before it decays within a few orbits. The acoustic density waves evolve into weak (non entropy preserving) shock waves that propagate over the entire disk. The Rossby waves remain in the vicinity of the initial vortex disturbance, but are rapidly damped. Temporal frequencies and spatial wavenumbers are derived from the nonlinear simulation data and correlated with analytical dispersion relations from the linearized Euler and energy equations.
    Schlagwort(e): Astrophysics
    Materialart: AGU Meeting; May 28, 2002 - May 31, 2002; Washington, DC; United States
    Format: text
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  • 2
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    Chandra Observations of Point Sources in Abell 2255 (2003)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-29
    Beschreibung: In our search for "hidden" AGN we present results from a Chandra observation of the nearby cluster Abell 2255. Eight cluster galaxies are associated with point-like X-ray emission, and we classify these galaxies based on their X-ray, radio, and optical properties. At least three are associated with active galactic nuclei (AGN) with no optical signatures of nuclear activity, with a further two being potential AGN. Of the potential AGN, one corresponds to a galaxy with a post-starburst optical spectrum. The remaining three X-ray detected cluster galaxies consist of two starbursts and an elliptical with luminous hot gas. Of the eight cluster galaxies five are associated with luminous (massive) galaxies and the remaining three lie in much lower luminosity systems. We note that the use of X-ray to optical flux ratios for classification of X-ray sources is often misleading, and strengthen the claim that the fraction of cluster galaxies hosting an AGN based on optical data is significantly lower than the fraction based on X-ray and radio data.
    Schlagwort(e): Astrophysics
    Format: application/pdf
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  • 3
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    XMM Observations of an IXO in NGC 2276 (2003)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-29
    Beschreibung: We present the results from a approx. 53 ksec XMM observation of NGC 2276. This galaxy has an unusual optical morphology with the disk of this spiral appearing to be truncated along the western edge. This XMM observation shows that the X-ray source at the western edge is a bright Intermediate X-ray Object (IXO). Its spectrum is well fit by a multi-color disk blackbody model used to fit optically thick standard accretion disks around black holes. The luminosity derived for this IXO is 1.1 x 10(exp 41) erg/s in the 0.5 - 10 keV band making it one of the most luminous discovered to date. The large source luminosity implies a large mass black hole if the source is radiating at the Eddington rate. On the other hand, the inner disk temperature determined here is too high for such a massive object given the standard accretion disk model. In addition to the IXO we find that the nuclear source in this galaxy has dimmed by at least a factor of several thousand in the eight years since the ROSAT HRI observations.
    Schlagwort(e): Astrophysics
    Format: application/pdf
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  • 4
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    A Cepheid Distance to NGC 4603 in the Centaurus Cluster (1999)
    In:  Other Sources
    Details
    Publikationsdatum: 2018-06-08
    Beschreibung: In an attempt to use Cepheid variables to determine the distance to the Centaurus cluster, we have obtained images of NGC 4603 with the Hubble Space Telescope for 9 epochs (totalling 24 orbits) over 14 months in the F555W filter and 2 epochs (totalling 6 orbits) in the F814W filter.
    Schlagwort(e): Astrophysics
    Materialart: The Astrophysical Journal
    Format: text
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  • 5
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    Tracking the moving photocenters of active galaxies: binary black holes, accretion disks, and relativistic jets (2003)
    In:  Other Sources
    Details
    Publikationsdatum: 2018-06-11
    Beschreibung: SIM Science Team Meeting #10 December 16-18, 2003 Pasadena, California, USA.
    Schlagwort(e): Astrophysics
    Format: text
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  • 6
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    Chandra Observations of Point Sources in A2255 (2003)
    In:  Other Sources
    Details
    Publikationsdatum: 2018-06-06
    Beschreibung: In our search for "hidden" active galactic nuclei (AGNs), we present results from a Chandra observation of the nearby cluster A2255. Eight cluster galaxies are associated with pointlike X-ray emission, and we classify these galaxies based on their X-ray, radio, and optical properties. At least three are associated with AGNs with no optical signatures of nuclear activity, with a further two being potential AGNs. Of the potential AGNs, one corresponds to a galaxy with a post-starburst optical spectrum. The remaining three X-ray-detected cluster galaxies consist of two starbursts and an elliptical with luminous hot gas. Of the eight cluster galaxies, five are associated with luminous (massive) galaxies, and the remaining three lie in much lower luminosity systems. We note that the use of X-ray-to-optical flux ratios for classification of X-ray sources is often misleading and strengthens the claim that the fraction of cluster galaxies hosting an AGN based on optical data is significantly lower than the fraction based on X-ray and radio data.
    Schlagwort(e): Astrophysics
    Materialart: Astrophysical Journal; Volume 597; 202-209
    Format: text
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  • 7
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    Creation and Distribution of CAIs in the Protoplanetary Nebula (2003)
    In:  CASI
    Details
    Publikationsdatum: 2017-10-02
    Beschreibung: CaAl rich refractory mineral inclusions (CAIs) found at 1 - 10% mass fraction in primitive chondrites appear to be several million years older than the dominant (chondrule) components in the same parent bodies. A prevalent concern is that it is difficult to retain CAIs for this long against gas-drag-induced radial drift into the sun. We assess a hot inner (turbulent) nebula context for CAI formation, using analytical models of nebula evolution and particle diffusion. We show that outward radial diffusion in a weakly turbulent nebula can prevent significant numbers of CAI-size particles from being lost into the sun for times of 1 - 3 x 10(exp 6) years. To match the CAI abundances quantitatively, we advocate an enhancement of the inner hot nebula in silicate-forming material, due to rapid inward migration of very primitive, silicate and carbon rich, meter-sized objects. 'Combustion' of the carbon into CO would make the CAI formation environment more reduced than solar, as certain observations imply. Abundant CO might also play a role in mass-independent chemical fractionation of oxygen isotopes as seen in CAIs and associated primitive, high-temperature condensates.
    Schlagwort(e): Astrophysics
    Materialart: Lunar and Planetary Science XXXIV; LPI-Contrib-1156
    Format: text
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  • 8
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    Consistency of time dilation in temporal profiles and spectra of gamma-ray bursts (1995)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-01-25
    Beschreibung: If gamma-ray bursters are at cosmological distances-a possibility suggested by their isotropic distribution and spatial inhomogeneity-then the temporal profiles and spectra of more distant sources will be time dilated compared to those of relatively nearby sources. Analyses of bright and dim Burst and Transient Source Experiment (BATSE) gamma-ray bursts yield a relative time-dilation factor of 2.3 on timescales of pulses and event durations. We redshift the spectra of time intervals near the intensity peaks of the bright sample on a trial grid and compare with spectra of the dim sample. A redshift factor of order two-with wide latitude permitted-brings the spectra of the two brightness groups into alignment. Thus there is coarse agreement with the time-dilation factor found in the temporal domain.
    Schlagwort(e): Astrophysics
    Materialart: Gamma ray astronomy; E2 Symposium of COSPAR Scientific Commission E, COSPAR Scientific Assembly, 30th, Hamburg, Germany, July 11-21, 1994 . (ISSN 0273-1177); 15; 5; p. (5)135-(5)138
    Format: text
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  • 9
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    A Simplified Model for an Evolving Protoplanetary Nebula (2002)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-18
    Beschreibung: The dynamical evolution of the protoplanetary nebula is investigated using analytical solutions of the surface density transport equations. Constant and beta viscosity turbulence models are compared with a functional analytical model and the well-known alpha viscosity formulation. The beta viscosity model, heretofore used for steady-state disks, is shown to be a viable tool for separating dynamic and thermodynamic properties of an evolving disk.
    Schlagwort(e): Astrophysics
    Format: text
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  • 10
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    Vorticity Transport and Wave Emission in the Protoplanetary Nebula (2001)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-18
    Beschreibung: Higher order numerical algorithms (4th order in time, 3rd order in space) are applied to the Euler/Energy equations and are used to examine vorticity transport and wave motion in a non-self gravitating, initially isentropic Keplerian disk. In this talk we will examine the response of the nebula to an isolated vortex with a circulation about equal to the rotation rate of Jupiter. The vortex is located on the 4 AU circle and the nebula is simulated from 1 to 24 AU. We show that the vortex emits pressure-supported density and Rossby-type wave packets before it decays within a few orbits. The acoustic density waves evolve into weak (non entropy preserving) shock waves that propagate over the entire disk. The Rossby waves remain in the vicinity of the initial vortex disturbance, but are rapidly damped. Temporal frequencies and spatial wavenumbers are derived using the simulation data and compared with analytical dispersion relations from the linearized Euler/Energy equations.
    Schlagwort(e): Astrophysics
    Materialart: DPS; Nov 27, 2001 - Dec 01, 2001; New Orleans, LA; United States
    Format: text
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