Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

the abundance pattern of the heavy (Z greater than or = 56) n-capture elements in most giants is well-matched to a scaled Solar
System tau-process nucleosynthesis pattern. The onset of the main tau-process can be seen at [Fe/H] approx. = -2.9; this onset
is consistent with the suggestion that low mass Type 2 supernovae are responsible for the tau-process. Contributions from the
s-process can first be seen in some stars with metallicities as low as [Fe/H] approx. -2.75, and are present in most stars with metallicities
[Fe/H] greater than -2.3. The appearance of s-process contributions as metallicity increases presumably reflects the longer
stellar evolutionary timescale of the (low-mass) s-process nucleosynthesis sites. The lighter n-capture elements (SR-Y-Zr) are
enhanced relative to the heavier tau-process element abundances. Their production cannot be attributed solely to any combination
of the Solar System tau- and main s-processes, but requires a mixture of material from the tau-process and from an additional
n-capture process which can operate at early Galactic time. This additional process could be the weak s-process in massive
(approx.25 Solar Mass) stars, or perhaps a second tau-process site, i.e. different than the site that produces the heavier (Z greater
than or = 56) n-capture elements.
Author
Neutrons; Capture Effect; Galaxies; Heavy Elements; Massive Stars; Metallicity; Nuclear Reactions; Solar System
20000067652 NASA Marshall Space Flight Center, Huntsville, AL USA
Laboratory Studies of Optical Characteristics and Condensation Processes of Cosmic Dust Particles
Spann, J. F., Jr., NASA Marshall Space Flight Center, USA; Abbas, M. M., NASA Marshall Space Flight Center, USA; Venturini,
C. C., Alabama Univ., USA; [2000]; 1p; In English; 8th; Physics of Dusty Plasma, 26-28 Apr. 2000, Santa Fe, NM, USA; No
Copyright; Avail: Issuing Activity; Abstract Only
Information about the optical characteristics and physical processes involving cosmic dust particles is vital for interpretation
of astronomical observations and an understanding of the formation and processing of dust in the evolutionary cycle of matter
in the interstellar medium. Cosmic dust particles are formed in a variety of astrophysical environments such as in cool stellar outflows
and circumstellar envelopes. Definitive knowledge of the nature, composition, and physical processes of cosmic dust grains,
however, can only be inferred from astronomical observations through laboratory experiments on the analogs of hypothesized
dust particles and with modeling calculations. Laboratory investigations of the nature, composition, and optical characteristics
of cosmic dust particles are being, carried out at many institutions with a variety of experimental techniques. Despite a wealth
of available data, however, many basic issues remain unresolved. An experimental facility based on suspension of dust particles
in electrodynamic balance in a pressure/temperature controlled environment in a cavity has been operational at the NASA Marshall
Space Flight Center, and is currently being employed for studies of dust particle charging mechanisms using electron beams
and with UV radiation. In this paper, we discuss two general classes of experiments under planning stages that may be simultaneously
carried out on this facility for cosmic dust investigations (i) Infrared optical characteristics (extinction coefficients and
scattering phase functions) of the analogs of hypothesized of cosmic dust particles, such as natural and synthetic amorphous silicates
with varying compositions, amorphous carbon grains, polycyclic aromatic hydrocarbons (PAHs), and icy core-mantle particles
etc. The initial spectral range under consideration is 1-25 micrometers, to be extended to the far infrared region in the future
(ii) Condensation of volatile gases on nucleus dust particles to be investigated for planetary and astrophysical environments.
Author
Condensing; Cosmic Dust; Optical Properties; Astrophysics; Particles
20000067677 California Inst. of Tech., Pasadena, CA USA
The ISO View of Star Forming Galaxies
Helou, George, California Inst. of Tech., USA; [1999]; 1p; In English; No Copyright; Avail: Issuing Activity; Abstract Only
ISO studies of normal galaxies in the local Universe have revealed basic new properties whose significant implications for
the star formation process and cosmology are only starting to be understood. This review will touch on the general results of a
statistical nature, and provide a quick summary of the profusion of exciting results on individual objects. In the mid-infrared, PHT-
S has established that the spectra of star forming galaxies between 6 and-13microns are dominated by the Aromatic Features in
Emission (AFE), and show little variation as a function of the heating intensity. The Carriers of the AFE (CAFE) are thus a universal
component of dust with standard properties, and contribute between 10 and 25% of the total dust luminosity. In addition to
AFE, the spectra show a low-level continuum detectable at wavelengths longer than 3.5microns whose origin is still under investigation.
The mid-infrared colors formed as the ratio of flux densities in the 6.75micron and the 15micron bands of ISO-CAM
remain essentially constant and near unity for quiescent and mildly active galaxies. As dust heating increases further, the 15micron
flux increases steeply compared to 6.75microns, indicating that dust heated to 100K