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  • Astrophysics  (41)
  • 2000-2004  (41)
  • 1980-1984
  • 2004  (41)
  • 1
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    Extremely Red Objects in the Lockman Hole (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We investigate extremely red objects (EROs) using near- and mid-infrared observations in five passbands (3.6 to 24 microns) obtained from the Spitzer Space Telescope, and deep ground-based R and K imaging. The great sensitivity of the Infrared Array Camera (IRAC) camera allows us to detect 64 EROs (a surface density of 2.90 +/- 0.36 arcmin(exp -2); [3.6](sub AB) is less than 23.7) in only 12 minutes of IRAC exposure time, by means of an R - [3.6] color cut (analogous to the traditional red R - K cut). A pure infrared K - [3.6] red cut detects a somewhat different population and may be more effective at selecting z greater than 1.3 EROs. We find approximately 17% of all galaxies detected by IRAC at 3.6 or 4.5 microns to be EROs. These percentages rise to about 40% at 5.8 microns, and about 60% at 8.0 microns. We utilize the spectral bump at 1.6 microns to divide the EROs into broad redshift slices using only near-infrared colors (2.2/3.6/4.5 microns). We conclude that two-thirds of all EROs lie at redshift z greater than 1.3. Detections at 24 microns imply that at least 11% of 0.6 less than z and less than 1.3 EROs and at least 22% of z greater than 1.3 EROs are dusty star-forming galaxies.
    Keywords: Astrophysics
    Type: The Astrophysical Journal Supplement Series; 154; 107-111
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  • 2
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    Near-infrared integral field spectroscopy of star-forming galaxies (2004)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: The Palomar Integral Field Spectrograph was used to probe a variety of environments in nine nearby galaxies that span a range of morphological types, luminosities, metallicities, and infrared-to-blue ratios.
    Keywords: Astrophysics
    Type: Astrophysical Journal; Volume 601; 813-830
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  • 3
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    Laboratory Experiments on Rotation and Alignment of the Analogs of Interstellar Dust Grains by Radiation (2004)
    In:  Other Sources
    Details
    Publication Date: 2018-06-12
    Description: The processes and mechanisms involved in the rotation and alignment of interstellar dust grains have been of great interest in astrophysics ever since the surprising discovery of the polarization of starlight more than half a century ago. Numerous theories, detailed mathematical models, and numerical studies of grain rotation and alignment with respect to the Galactic magnetic field have been presented in the literature. In particular, the subject of grain rotation and alignment by radiative torques has been shown to be of particular interest in recent years. However, despite many investigations, a satisfactory theoretical understanding of the processes involved in subject, we have carried out some unique experiments to illuminate the processes involved in the rotation of dust grains in the interstellar medium. In this paper we present the results of some preliminary laboratory experiments on the rotation of individual micron/submicron-sized, nonspherical dust grains levitated in an electrodynamic balance evacuated to pressures of approximately 10(exp -3) to 10(exp -5) torr. The particles are illuminated by laser light at 5320 A, and the grain rotation rates are obtained by analyzing the low-frequency (approximately 0 - 100 kHz) signal of the scattered light detected by a photodiode detector. The rotation rates are compared with simple theoretical models to retrieve some basic rotational parameters. The results are examined in light of the current theories of alignment.
    Keywords: Astrophysics
    Type: The Astrophysical Journal; Volume 614; 781-795
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  • 4
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    Laboratory Experiments on Rotation of Micron Size Cosmic Dust Grains with Radiation (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The processes and mechanisms involved in the rotation and alignment of interstellar dust grains have been of great interest in astrophysics ever since the surprising discovery of the polarization of starlight more than half a century ago. Numerous theories, detailed mathematical models and numerical studies of grain rotation and alignment along the Galactic magnetic field have been presented in the literature. In particular, the subject of grain rotation and alignment by radiative torques has been shown to be of particular interest in recent years. However, despite many investigations, a satisfactory theoretical understanding of the processes involved in grain rotation and alignment has not been achieved. As there appears to be no experimental data available on this subject, we have carried out some unique experiments to illuminate the processes involved in rotation of dust grains in the interstellar medium. In this paper we present the results of some preliminary laboratory experiments on the rotation of individual micron/submicron size nonspherical dust grains levitated in an electrodynamic balance evacuated to pressures of approx. 10(exp -3) to 10(exp -5) torr. The particles are illuminated by laser light at 5320 A, and the grain rotation rates are obtained by analyzing the low frequency (approx. 0-100 kHz) signal of the scattered light detected by a photodiode detector. The rotation rates are compared with simple theoretical models to retrieve some basic rotational parameters. The results are examined in the light of the current theories of alignment.
    Keywords: Astrophysics
    Type: 35th COSPAR Scientific Assembly; Jul 18, 2004 - Jul 25, 2004; Paris; France
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  • 5
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    Laboratory Experiments on Rotation and Alignment of the Analogs of Interstellar Dust Grains by Radiation (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The processes and mechanisms involved in the rotation and alignment of interstellar dust grains have been of great interest in astrophysics ever since the surprising discovery of the polarization of starlight more than half a century ago. Numerous theories, detailed mathematical models and numerical studies of grain rotation and alignment with respect to the Galactic magnetic field have been presented in the literature. In particular, the subject of grain rotation and alignment by radiative torques has been shown to be of particular interest in recent years. However, despite many investigations, a satisfactory theoretical understanding of the processes involved in grain rotation and alignment has not been achieved. As there appears to be no experimental data available on this subject, we have carried out some unique experiments to illuminate the processes involved in rotation of dust grains in the interstellar medium. In this paper we present the results of some preliminary laboratory experiments on the rotation of individual micron/submicron size nonspherical dust grains levitated in an electrodynamic balance evacuated to pressures of approximately 10(exp -3) to 10(exp -5) torr. The particles are illuminated by laser light at 5320 Angstroms, and the grain rotation rates are obtained by analyzing the low frequency (approximately 0-100 kHz) signal of the scattered light detected by a photodiode detector. The rotation rates are compared with simple theoretical models to retrieve some basic rotational parameters. The results are examined in the light of the current theories of alignment.
    Keywords: Astrophysics
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  • 6
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    The Mineralogy and Grain Properties of the Disk Surfaces in Three Herbig Ae/Be Stars (2004)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The ubiquity of accretion disks around pre-main sequence and young main sequence stars having the potential to form planetary systems is now well established. However, unknown is an accurate estimate of the fraction of single stars with disks that have produced planetary systems. Theoretical models of particle aggregation show that if particles can grow from submicron to mm to cm in size, then the formation of planetesimals is possible in the time before the disk dissipates. The problem remains to understand how grains condense from nebular gases, and how relic interstellar grains survive and are modified by their transport in the disk. If grains are lofted above the disk photosphere by processes such as winds, turbulent convection, or changes in vertical structure, the evolution of dust can be investigated by observing the properties of the small (less than or = 1 micron) grains in the optically thin disk surface layer or atmosphere.
    Keywords: Astrophysics
    Type: Chondrites and the Protoplanetary Disk, Part 2; LPI-Contrib-1218-Pt-2
    Format: application/pdf
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  • 7
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    Submillimeter Emission from Type Ia Supernova Host Galaxies at z = 0.5 (2004)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: We present deep submillimeter observations of 17 galaxies at z = 0.5 that are hosts of a Type Ia supernova.
    Keywords: Astrophysics
    Type: Astrophysical Journal; Volume 603; 489-494
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  • 8
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    GLAST Burst Monitor Trigger Classification Algorithm (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The Gamma Ray Large Area Space Telescope (GLAST), currently set for launch in the first quarter of 2007, will consist of two instruments, the GLAST Burst Monitor (GBM) and the Large Area Telescope (LAT). One of the goals of the GBM is to identify and locate gamma-ray bursts using on-board software. The GLAST observatory can then be re-oriented to allow observations by the LAT. A Bayesian analysis will be used to distinguish gamma-ray bursts from other triggering events, such as solar flares, magnetospheric particle precipitation, soft gamma repeaters (SGRs), and Cygnus X-1 flaring. The trigger parameters used in the analysis are the burst celestial coordinates, angle from the Earth's horizon, spectral hardness, and the spacecraft geomagnetic latitude. The algorithm will be described and the results of testing will be presented.
    Keywords: Astrophysics
    Type: Meeting of the High Energy Astrophysics Division of the American Astronomical Society; Sep 08, 2004 - Sep 11, 2004; New Orleans, LA; United States
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  • 9
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    High Angular Resolution Mid-Infrared Imaging of Young Stars in Orion BN/KL (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-11
    Description: The authors present Keck LWS images of the Orion BN/KL star forming region obtained in the first multi-wavelength study to have 0.3--0.5 resolution from 4.7 (micro)m to 22 (micro)m. The young stellar objects designed infrared source n and radio source I are believed to dominate the BN/KL region. They have detected extended emission from a probable accretion disk around source n but infer a stellar luminosity on the order of only 2000 L(sub (center-dot)).
    Keywords: Astrophysics
    Type: DE2004-827014 , SLAC-PUB-10522
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  • 10
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    Experiments on Dust Grain Charging (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Dust particles in various astrophysical environments are charged by a variety of mechanisms generally involving collisional processes with other charged particles and photoelectric emission with UV radiation from nearby sources. The sign and the magnitude of the particle charge are determined by the competition between the charging processes by UV radiation and collisions with charged particles. Knowledge of the particle charges and equilibrium potentials is important for understanding of a number of physical processes. The charge of a dust grain is thus a fundamental parameter that influences the physics of dusty plasmas, processes in the interplanetary medium and interstellar medium, interstellar dust clouds, planetary rings, cometary and outer atmospheres of planets etc. In this paper we present some results of experiments on charging of dust grains carried out on a laboratory facility capable levitating micron size dust grains in an electrodynamic balance in simulated space environments. The charging/discharging experiments were carried out by exposing the dust grains to energetic electron beams and UV radiation. Photoelectric efficiencies and yields of micron size dust grains of SiO2, and lunar simulates obtained from NASA-JSC will be presented.
    Keywords: Astrophysics
    Type: American Geophysical Union 2004 Fall Annual Meeting; Dec 13, 2004 - Dec 17, 2004; San Francisco, CA; United States
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