4,114 research outputs found
Discovery of Crystallized Water Ice in a Silhouette Disk in the M43 Region
We present the 1.9--4.2um spectra of the five bright (L<11.2) young stars
associated with silhouette disks with moderate to high inclination angle of
39--80deg in the M42 and M43 regions. The water ice absorption is seen toward
d121-1925 and d216-0939, while the spectra of d182-316, d183-405, and d218-354
show no water ice feature around 3.1um within the detection limits. By
comparing the water ice features toward nearby stars, we find that the water
ice absorption toward d121-1925 and d216-0939 most likely originates from the
foreground material and the surrounding disk, respectively. The angle of the
disk inclination is found to be mainly responsible for the difference of the
optical depth of the water ice among the five young stars. Our results suggest
that there is a critical inclination angle between 65deg and 75deg for the
circumstellar disk where the water ice absorption becomes strong. The average
density at the disk surface of d216-0939 was found to be 6.38x10^(-18) g
cm^(-3). The water ice absorption band in the d216-0939 disk is remarkable in
that the maximum optical depth of the water ice band is at a longer wavelength
than detected before. It indicates that the primary carrier of the feature is
purely crystallized water ice at the surface of the d216-0939 disk with
characteristic size of ~0.8um, which suggests grain growth. This is the first
direct detection of purely crystallized water ice in a silhouette disk.Comment: 28 pages, 8 figures, Accepted by Ap
Multivalued memory effects in electronic phase-change manganites controlled by Joule heating
Non-volatile multivalued memory effects caused by magnetic fields, currents,
and voltage pulses are studied in Nd_{0.65}Ca_{0.35}MnO_3 and
(Nd_{1-y}Sm_{y})_{0.5}Sr_{0.5}MnO_3 (y=0.75) single crystals in the hysteretic
region between ferromagnetic metallic and charge-ordered insulating states. The
current/voltage effects observed in this study are explained by the
self-heating effect, which enable us to control the colossal electroresistance
effects. This thermal-cycle induced switching between electronic solid and
liquid states can be regarded as electronic version of atomic crystal/amorphous
transitions in phase-change chalcogenides.Comment: 5 pages, 4 figures. to appear in Phys. Rev.
Infrared observations of the dust coma
The main infrared observational results were briefly reviewed at the start of this session. The new results are summarized. All of these results have yet to be synthesized into a self-consistent picture of the dust grain composition, dust production history, outburst mechanisms, and composition of the nucleus. The workshop discussion was helpful in pointing out problems faced by theorists, such as data quality, the lack of the proper theory for computing the scattering and emission of irregular particles, and in some cases the lack of optical constants of realistic materials. It is expected that the gross spectral and dynamical properties of Halley's Comet can be understood in time, even if the details of the observations and the theoretical calculations continue to vex us in the future
Comparison of the 3.36 micrometer feature to the ISM
It has been noted that the 3.36 micrometer emission feature is not the same as that of any ISM band at 3.4 micrometer. This is documented herein. There is no convincing analog to the cometary 3.36 micrometer emission feature seen in the Interstellar Matter band. This fact suggests that if the carbonaceous material in comets came from the ISM, it was either further processed in the solar nebula or has a different appearance because of the different excitation environment of the sun and ISM
Moderate spectral resolution observations of 3 micron absorption features in highly obscured objects
The 3 micron absorption spectra of sources seen in or behind molecular clouds generally show a variety of absorption features. Three separate absorptions are used to explain these features. The cooled-grating array spectrometer (CGAS) at the NASA Infrared Telescope Facility was used to obtain spectra of the late-type mass-loss star OH 0739-12 and the protostars MonR2 IRS-2 and IRS-3 (solid circles). The differences between the spectra are discussed
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