NASA Scientific and Technical Aerospace Reports

models, coronal observations, and ion calculations in conjunction with the in situ observations.
Derived from text
Ion Charge; Mathematical Models; Solar Wind; Plasmas (Physics); Astrophysics
20040074247 Alabama Univ., Huntsville, AL, USA
Discovery of a Three-Layered Atmospheric Structure in Accretion Disks around Stellar-Mass Black Holes
Zhang, S. N.; Zhang, Xiaoling; Sun, Xuejun; Yao, Yangsen; Cui, Wei; Chen, Wan; Wu, Xuebing; Xu, Haiguang; Bulletin of
the American Astronomical Society; Dec. 1999; Volume 31, pp. 1555; In English
Contract(s)/Grant(s): NAG5-7927; Copyright; Avail: Other Sources; Abstract Only
We have carried out systematic modeling of the X-ray spectra of the Galactic superluminal jet sources GRS 1915+105
and GRO J1655-40, using our newly developed spectral fitting methods. Our results reveal, for the first time, a three-layered
structure of the atmosphere in the inner region of the accretion disks. Above the conanonly known, cold and optically thick
disk of a blackbody temperature 0.2-0.5 keV, there is a layer of warm gas with a temperature of 1.0-1.5 keV and an optical
depth of around 10. Compton scattering of the underlying disk blackbody photons produces the soft X-ray component we
comonly observe. Under certain conditions, there is also a much hotter, optically thin corona above the warm layer,
characterized by a temperature of 100 keV or higher and an optical depth of unity or less. The corona produces the hard X-ray
component typically seen in these sources. We emphasize that the existence of the warm layer seem to be independent of the
presence of the hot corona and, therefore, it is not due to irradiation of the disk by hard X-rays from the corona. Our results
suggest a striking structural similarity between the accretion disks and the solar atmosphere, which may provide a new
stimulus to study the common underlying physical processes operating in these vastly different systems. We also report the
first unambiguous detection of an emission line around 6.4 keV in GRO J1655-40, which may allow further constraining of
the accretion disk structure. We acknowledge NASA GSFC and MFC for partial financial support. (copyright) 1999: American
Astronomical Society. All rights reverved.
Author
Black Holes (Astronomy); Accretion Disks; X Ray Astronomy
20040074314 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Interstellar Dust Models Consistent with Extinction, Emission, and Abundance Constraints
Zubko, Viktor; Dwek, Eli; Arendt, Richard G.; New Concepts for Far-Infrared and Submillimeter Space Astronomy; April
2004, pp. 129-133; In English; See also 20040074260; No Copyright; Avail: CASI; A01, Hardcopy
We present new interstellar dust models which have been derived by simultaneously fitting the far ultraviolet to near
infrared extinction, the diffuse infrared emission, and, unlike previous models, the elemental abundances in dust for the diffuse
interstellar medium. We found that dust models consisting of a mixture of spherical graphite and silicate grains, polycyclic
aromatic hydrocarbon (PAH) molecules, in addition to porous composite particles containing silicate, organic refractory, and
water ice, provide an improved .t to the UV-to-infrared extinction and infrared emission measurements, while consuming the
amounts of elements well within the uncertainties of adopted interstellar abundances, including B star abundances. These
models are a signi.cant improvement over the recent Li & Draine (2001, ApJ, 554, 778) model which requires an
excessive amount of silicon to be locked up in dust: 48 ppm (atoms per million of H atoms), considerably more than the solar
abundance of 34 ppm or the B star abundance of 19 ppm.
Author
Cosmic Dust; Interstellar Chemistry
20040074327 NASA Glenn Research Center, Cleveland, OH, USA
Velocity and Temperature Measurement in Supersonic Free Jets Using Spectrally Resolved Rayleigh Scattering
Panda, J.; Seasholtz, R. G.; May 2004; 26 pp.; In English; 37th Aerospace Sciences Meeting and Exhibit, 11-14 Jan. 1999,
Reno, NV, USA
Contract(s)/Grant(s): WBS 714-08-14
Report No.(s): NASA/TM-2004-212391; AIAA Paper 99-0296; E-13968; No Copyright; Avail: CASI; A03, Hardcopy
The flow fields of unheated, supersonic free jets from convergent and convergent-divergent nozzles operating at M = 0.99,
1.4, and 1.6 were measured using spectrally resolved Rayleigh scattering technique. The axial component of velocity and
temperature data as well as density data obtained from a previous experiment are presented in a systematic way with the goal
of producing a database useful for validating computational fluid dynamics codes. The Rayleigh scattering process from air
molecules provides a fundamental means of measuring flow properties in a non-intrusive, particle free manner. In the
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