114,672 research outputs found
Review of cometary spectra
The spectra of comet Kohoutek, comet Bradfield, and comet Mrkos are reviewed and compared in relation to stellar spectroscopy and evolution. The possibility of observing the absorption spectrum of a comet and direct measurement of Doppler shifts due to expansion or streaming motions in comets are considered along with the spectra of giant comets, such as, comet Minkowski, comet Baade, and comet Lovas. A speculative explanation for possible intrinsic abundance differences between comets is given
A Bima Array Survey of Molecules in Comets Linear (C/2002 T7) and Neat (C/2001 Q4)
We present an interferometric search for large molecules, including methanol,
methyl cyanide, ethyl cyanide, ethanol, and methyl formate in comets LINEAR
(C/2002 T7) and NEAT (C/2001 Q4) with the Berkeley-Illinois-Maryland
Association (BIMA) array. In addition, we also searched for transitions of the
simpler molecules CS, SiO, HNC, HN13C and 13CO . We detected transitions of
methanol and CS around Comet LINEAR and one transition of methanol around Comet
NEAT within a synthesized beam of ~20''. We calculated the total column density
and production rate of each molecular species using the variable temperature
and outflow velocity (VTOV) model described by Friedel et al.(2005).Considering
the molecular production rate ratios with respect to water, Comet T7 LINEAR is
more similar to Comet Hale-Bopp while Comet Q4 NEAT is more similar to Comet
Hyakutake. It is unclear, however, due to such a small sample size, whether
there is a clear distinction between a Hale-Bopp and Hyakutake class of comet
or whether comets have a continuous range of molecular production rate ratios.Comment: Accepted for Publication in the Astrophysical Journa
Comet dust as a mixture of aggregates and solid particles: model consistent with ground-based and space-mission results
The most successful model of comet dust presents comet particles as
aggregates of submicron grains. It qualitatively explains the spectral and
angular change in the comet brightness and polarization and is consistent with
the thermal infrared data and composition of the comet dust obtained {\it in
situ} for comet 1P/Halley. However, it experiences some difficulties in
providing a quantitative fit to the observational data. Here we present a model
that considers comet dust as a mixture of aggregates and compact particles. The
model is based on the Giotto and Stardust mission findings that both aggregates
(made mainly of organics, silicates, and carbon) and solid silicate particles
are present in the comet dust. We simulate aggregates as {\bf Ballistic
Cluster-Cluster Aggregates (BCCA)} and compact particles as polydisperse
spheroids with some distribution of the aspect ratio. The particles follow a
power-law size distribution with the power -3 that is close to the one obtained
for comet dust {\it in situ}, at studies of the Stardust returned samples, and
the results of ground-based observations of comets. The model provides a good
fit to the angular polarization curve. It also reproduces the positive spectral
gradient of polarization, red color of the dust, and {\bf low albedo. It also
has the ratio of compact to fluffy particles close to the one found {\it in
situ} for comet 1P/Halley} and the mass ratio of silicate to carbonaceous
materials equal to unity that is in accordance with the elemental abundances of
Halley's dust found by Giotto mission.Comment: "Earth and Planetary Science" (Japan), in pres
Lighting the Spark: COMET Program Mobilizes the Ranks for Construction Organizing
This article describes the COMET (Construction Organizing Membership Education Training) program. Faced with declining membership and market share and an erosion of bargaining strength and political influence, building trades unions have undertaken a number of Initiatives to reverse their fortunes. COMET, an educational program that generates membership support and participation in organizing, has emerged as one of the most noteworthy of these new initiatives. Before COMET, organizing efforts were stymied by the reluctance of many union members and leaders to recruit into membership the large nonunion workforce. COMET appears to have transformed the political culture within those local unions that have utilized it by placing organizing on the top of their agendas. Although organizing activity and effectiveness are growing, it may be too soon to tell if construction unions can use COMET to successfully re-unionize the industry
Seeing Halley's Comet: A guide for observers in the Northern Hemisphere
A guide for the observation of Halley's comet is presented. The path of the comet is described for the fly by dates and charts are provided for location of the comet in the morning or evening skies. Suggestions for visual observation and photography of Halley's comet are included
Effects of the Planar Galactic Tides and Stellar Mass on Comet Cloud Dynamics
We report the first results of a research program to explore the sensitivity
of the orbits of Oort cloud comets to changes in the strength of the Galactic
tides in the plane of the disk and also to changes in the mass of the host
star. We performed 2D simulations that confirm that the effects of the tides on
comet orbits are sensitive to a star's distance from the Galactic center. A
comet cloud closer to the Galactic center than the Sun will have comet
perihelia reduced to the region of the inner planets more effectively by the
planar tides alone. Similar results are found for a star of smaller mass. We
also show how this phenomenon of comet injection persists for a set of
alternative Galactic potential models. These preliminary results suggest a
fruitful line of research, one that aims to generalize the study of comet cloud
dynamics to systems different from the Solar System. In particular, it will
allow us to study the roles played by comet clouds in defining the boundaries
of the Galactic Habitable Zone.Comment: Published by The Open Astronomy Journal; some slight differences from
published versio
Follow-up observations of Comet 17P/Holmes after its extreme outburst in brightness end of October 2007
We present follow-up observations of comet 17/P Holmes after its extreme
outburst in brightness, which occurred end of October 2007. We obtained 58
V-band images of the comet between October 2007 and February 2008, using the
Cassegrain-Teleskop-Kamera (CTK) at the University Observatory Jena. We present
precise astrometry of the comet, which yields its most recent Keplerian orbital
elements. Furthermore, we show that the comet's coma expands quite linearly
with a velocity of about 1650km/s between October and December 2007. The
photometric monitoring of comet 17/P Holmes shows that its photometric activity
level decreased by about 5.9mag within 105 days after its outburst.Comment: AN accepted, 6 pages, 4 figures, 5 tabl
The unusual volatile composition of the Halley-type comet 8P/Tuttle: Addressing the existence of an Inner Oort Cloud
We measured organic volatiles (CH4, CH3OH, C2H6, H2CO), CO, and water in
comet 8P/Tuttle, a comet from the Oort cloud reservoir now in a short-period
Halley-type orbit. We compare its composition with two other comets in
Halley-type orbits, and with comets of the "organics-normal" and
"organics-depleted" classes. Chemical gradients are expected in the
comet-forming region of the proto-planetary disk, and an individual comet
should reflect its specific heritage. If Halley-type comets came from the inner
Oort cloud as proposed, we see no common characteristics that could distinguish
such comets from those that were stored in the outer Oort cloud.Comment: 14 pages, including 1 figure and 2 Table
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