5,008 research outputs found
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
The 3.4 micron emission in comets
Emission features near 3.4 microns were detected in comet Bradfield (1987s) on 17 Nov. 1987 UT, and, marginally, on two earlier dates, with the Cooled Grating Array Spectrometer at the NASA Infrared Radio Telescope Facility (IRTF) (Brooke et al., 1988b). The central wavelength (3.36 microns) and width (approx. 0.15 microns) of the strongest feature coincide with those observed in comet Halley. A weaker emission feature at 3.52 microns and a strong feature extending shortward of 2.9 microns were also detected. This brings the number of comets in which these three features have been seen to three, two new (Bradfield, Wilson) and one old (Halley). It seems almost certain that the 3.4 micron features are emissions by C-H groups in complex molecules. Based on the similarity of the 3.4 micron features in comets Halley and Wilson, the authors suggest that a particular set of organic compounds may be common to all comets (Brooke et al. 1988a). The absence of the feature in some comets could then be due to photodestruction or evaporation of the organics when the comet approaches the sun, in combination with a predominance of thermal emission from non C-H emitting grains. Detection of the 3.4 micron emission feature in comet Bradfield at 4 = 0.9 AU provides support for this argument. Complex organics in comets could have been formed by particle irradiation of parent ices in the nucleus or been incorporated as grains at the time the comets formed. Since the most heavily irradiated layers of Halley would have been lost in its hundreds of perihelion passages, the authors believe the more likely explanation is that the 3.4 micron emitting material was incorporated in comet nuclei at the time of formation. The 3.4 micron comet feature resembles, but is not identical to, the interstellar 3.29 micron (and longer wavelength) emission features and the broad 3.4 micron feature seen in absorption toward the Galactic center. Detailed comparisons of cometary and interstellar organics will require comet spectra with signal-to-noise and spectral resolution comparable to that available in spectra of the interstellar medium. Such observations are currently being planned
Limit on the CH4/CO ratio in Comet Levy (1990c) and comparisons with other comets
Near-infrared observations of comet Levy (1900c) were made on UT 4.3 and 5.3 Sep. 1990 from the United Kingdom Infrared Telescope on Mauna Kea. A scanning Fabry-Perot interferometer in combination with a cooled grating spectrometer was used to make a sensitive search for fluorescent emission from the v zub 3 band of CH4 near lambda approx. 3.3 microns. If CH4 is a parent molecule released directly from the nucleus, then the 3 sigma limit on its abundance is CH4/H2O approx. less than 0.0031, assuming that the kinetic temperature of the inner coma is approx. 50 K and that the CH4 spin species are equilibrated at a temperature approx. greater than 50 K. Since International Ultraviolet Explorer (IUE) observations of CO in Levy indicate that CO/H2O approx. 0.04 (Feldman et al.), researchers find that CH4/CO approx. less than 0.1. Infrared spectroscopic searches for CH4 in Comet Halley also yielded no positive detections; the more sensitive upper limit from the latter observations is CH4/H2O approx. less than 0.002. Since CO/H2O approx. 0.05 in Halley (not including the extended source of CO), the upper limits on the CH4/CO ratios are almost identical for comets Levy and Halley. A marginal infrared detection of the CH4 v sub 3 band in comet Wilson yielded CH4/H2O approx. 0.01 to 0.05 (Larson et al.), but there was no positive detection of CO. If the identification of the feature in the infrared spectrum of comet Wilson is correct, then that would indicate a very high CH4/CO ratio in this comet
A Study of Absorption Features in the Three Micron Spectra of Molecular Cloud Sources with HO Ice Bands
New 3.3--3.6~m spectra were obtained of nine young stellar objects
embedded in molecular clouds. An absorption feature at 3.47~m
(2880~cm) with FWHM0.09 m (80 cm), first identified by
Allamandola et al. (1992), was definitively detected toward seven objects, and
marginally in the other two. The feature is better correlated with HO ice
than with the silicate dust optical depth in the data obtained to date.
Assuming the feature is due to a C--H stretch absorption, the abundance of the
C--H bonds averaged along the lines of sight is closely related to that of
HO ice. We interpret the correlation with HO ice as indicating that the
C--H bonds form together with HO ice on grain surfaces in the molecular
clouds, though other formation mechanisms are not ruled out. A second
absorption feature at 3.25 m (3080 cm) was detected toward
NGC7538/IRS 1 and S140/IRS 1; this feature was first detected in spectra of
MonR2/IRS 3 (Sellgren, Smith, \& Brooke 1994; Sellgren et al. 1995). There is
as yet insufficient data to tell whether this feature is better correlated with
HO ice or silicates.Comment: 20 pages (37 kb), AASTex format. Also 9 Postscript figures (388 kB),
tarred, compressed and uuencoded, added with 'figure' command. 9 figures
(compressed PostScript) available from anonymous ftp at
ftp://bessel.mps.ohio-state.edu/pub/sellgren/brookefig.tar.Z A complete
(text+figs) compressed PostScript preprint is also available at
ftp://bessel.mps.ohio-state.edu/pub/sellgren/brooke.ps.Z Hardcopy available
upon request to [email protected]. Accepted by ApJ (March 1996
History Dependent Phenomena in the Transverse Ising Ferroglass: the Free Energy Landscape
In this paper we investigate the relationship between glassy and
ferromagnetic phases in disordered Ising ferromagnets in the presence of
transverse magnetic fields, . Iterative mean field simulations probe
the free energy landscape and suggest the existence of a glass transition as a
function of which is distinct from the Curie temperature. New
experimental field-cooled and zero-field-cooled data on LiHoYF
provide support for our theoretical picture.Comment: 4 pages RevTex; 5 figure
Panchromatic observations and modeling of the HV Tau C edge-on disk
We present new high spatial resolution (<~ 0.1") 1-5 micron adaptive optics
images, interferometric 1.3 mm continuum and 12CO 2-1 maps, and 350 micron, 2.8
and 3.3 mm fluxes measurements of the HV Tau system. Our adaptive optics images
reveal an unusually slow orbital motion within the tight HV Tau AB pair that
suggests a highly eccentric orbit and/or a large deprojected physical
separation. Scattered light images of the HV Tau C edge-on protoplanetary disk
suggest that the anisotropy of the dust scattering phase function is almost
independent of wavelength from 0.8 to 5 micron, whereas the dust opacity
decreases significantly over the same range. The images further reveal a marked
lateral asymmetry in the disk that does not vary over a timescale of 2 years.
We further detect a radial velocity gradient in the disk in our 12CO map that
lies along the same position angle as the elongation of the continuum emission,
which is consistent with Keplerian rotation around an 0.5-1 Msun central star,
suggesting that it could be the most massive component in the triple system. We
use a powerful radiative transfer model to compute synthetic disk observations
and use a Bayesian inference method to extract constraints on the disk
properties. Each individual image, as well as the spectral energy distribution,
of HV Tau C can be well reproduced by our models with fully mixed dust provided
grain growth has already produced larger-than-interstellar dust grains.
However, no single model can satisfactorily simultaneously account for all
observations. We suggest that future attempts to model this source include more
complex dust properties and possibly vertical stratification. (Abridged)Comment: 26 pages, 11 figures, editorially accepted for publication in Ap
The Spitzer Gould Belt Survey of Large Nearby Interstellar Clouds: Discovery of A Dense Embedded Cluster in the Serpens-Aquila Rift
We report the discovery of a nearby, embedded cluster of young stellar objects, associated filamentary infrared dark cloud, and 4.5 mu m shock emission knots from outflows detected in Spitzer IRAC mid-infrared imaging of the Serpens-Aquila Rift obtained as part of the Spitzer Gould Belt Legacy Survey. We also present radial velocity measurements of the region from molecular line observations obtained with the Submillimeter Array (SMA) that suggest the cluster is comoving with the Serpens Main embedded cluster to the north. We therefore assign it 3 degrees the same distance, 260 pc. The core of the new cluster, which we call Serpens South, is composed of an unusually large fraction of protostars (77%) at high mean surface density (> 430 pc(-2)) and short median nearest neighbor spacing (3700 AU). We perform basic cluster structure characterization using nearest neighbor surface density mapping of the YSOs and compare our findings to other known clusters with equivalent analyses available in the literature.Astronom
Precise Measurements of Atmospheric Muon Fluxes with the BESS Spectrometer
The vertical absolute fluxes of atmospheric muons and muon charge ratio have
been measured precisely at different geomagnetic locations by using the BESS
spectrometer. The observations had been performed at sea level (30 m above sea
level) in Tsukuba, Japan, and at 360 m above sea level in Lynn Lake, Canada.
The vertical cutoff rigidities in Tsukuba (36.2 N, 140.1 E) and in Lynn Lake
(56.5 N, 101.0 W) are 11.4 GV and 0.4 GV, respectively. We have obtained
vertical fluxes of positive and negative muons in a momentum range from 0.6 to
20 GeV/c with systematic errors less than 3 % in both measurements. By
comparing the data collected at two different geomagnetic latitudes, we have
seen an effect of cutoff rigidity. The dependence on the atmospheric pressure
and temperature, and the solar modulation effect have been also clearly
observed. We also clearly observed the decrease of charge ratio of muons at low
momentum side with at higher cutoff rigidity region.Comment: 35 pages, 9 figures. Submitted to Astroparticle Physic
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