1,080 research outputs found
A possible technique for cometary studies with high angular and spectral resolution
The echelle spectrographs, designed for and used at the Cassegrain stations of the KPNO and CTIO 4-meter telescopes, are capable of cometary spectroscopy with seeing-limited angular resolution along the slit and with spectral resolving power (lambda/delta lambda) ranging from 10 to the 4th power to 10 to the 5th power. Various gratings, cameras and detectors can be used in combination for specific studies in the 3000A to 10,000A range
Narrow passband imagery of comets
During an emission-line survey of the Milky Way, Comet West was accidently imaged through four different narrow passbands with a wide-field, image-intensified camera. Three passbands recorded very similar head plus tail structure. The fourth passband shows an additional large, diffuse component around the head. It was serendipitous that such was recorded as the filters, being selected for studies of emission nebulae, are not particularly suited for studies of comets. However the imagery, plus subsequent studies, suggests that much can be learned about the structure of comets using narrow passband imagery simultaneously with long slit spectroscopy
Evidence for an interplay between cell cycle progression and the initiation of differentiation between life cycle forms of African trypanosomes
Successful transmission of the African trypanosome between the mammalian host blood-stream and the tsetse fly vector involves dramatic alterations in the parasite's morphology and biochemistry. This differentiation through to the tsetse midgut procyclic form is accompanied by re-entry into a proliferative cell cycle. Using a synchronous differentiation model and a variety of markers diagnostic for progress through both differentiation and the cell cycle, we have investigated the interplay between these two processes. Our results implicate a relationship between the trypanosome cell cycle position and the perception of the differentiation signal and demonstrate that irreversible commitment to the differentiation occurs rapidly after induction. Furthermore, we show that re-entry into the cell cycle in the differentiating population is synchronous, and that once initiated, progress through the differentiation pathway can be uncoupled from progress through the cell cycle
Eta Carinae in the Context of the Most Massive Stars
Eta Car, with its historical outbursts, visible ejecta and massive, variable
winds, continues to challenge both observers and modelers. In just the past
five years over 100 papers have been published on this fascinating object. We
now know it to be a massive binary system with a 5.54-year period. In January
2009, Eta Car underwent one of its periodic low-states, associated with
periastron passage of the two massive stars. This event was monitored by an
intensive multi-wavelength campaign ranging from gamma-rays to radio. A large
amount of data was collected to test a number of evolving models including 3-D
models of the massive interacting winds. August 2009 was an excellent time for
observers and theorists to come together and review the accumulated studies, as
have occurred in four meetings since 1998 devoted to Eta Car. Indeed, Eta Car
behaved both predictably and unpredictably during this most recent periastron,
spurring timely discussions. Coincidently, WR140 also passed through periastron
in early 2009. It, too, is a intensively studied massive interacting binary.
Comparison of its properties, as well as the properties of other massive stars,
with those of Eta Car is very instructive. These well-known examples of evolved
massive binary systems provide many clues as to the fate of the most massive
stars. What are the effects of the interacting winds, of individual stellar
rotation, and of the circumstellar material on what we see as
hypernovae/supernovae? We hope to learn.Comment: 26 pages, 7 figures, IAU General Assembly Joint Discussion on Eta
Carinae in Context of the Most Massive Star
The young Of star HD148937 and its associated interstellar bubble: H 2 region
The star HD148937 and nebulosities surrounding the star are found to be closely inter-related. IUE spectroscopy of HD148937 shows the star to be a young Of star with low mass loss. Properties Of the surrounding interstellar bubble and the H II region support the implied youth of HD148937
Space Telescope Imaging Spectrograph Parallel Observations of the Planetary Nebula M94-20
The planetary nebula M94--20 in the Large Magellanic Cloud was
serendipitously observed with the Space Telescope Imaging Spectrograph on board
the Hubble Space Telescope as part of the Hubble Space Telescope Archival Pure
Parallel Program. We present spatially resolved imaging and spectral data of
the nebula and compare them with ground based data, including detection of
several emission lines from the nebula and the detection of the central star.
We find the total H alpha + [NII] flux = 7.3e-15 erg s^-1 cm^-2 and we estimate
the magnitude of the central star to be m_V = 26.0 +/- 0.2. Many other H alpha
sources have been found in M31, M33 and NGC 205 as well. We discuss the use of
the parallel observations as a versatile tool for planetary nebula surveys and
for other fields of astronomical research.Comment: Latex, 14 pages, 2 JPEG figures, 2 tables. PASP Research Note, June
1999, in pres
IUE observations of Seyfert galaxies
The L alpha/H beta ratio and line profiles for several galaxies are presented. The continuous energy distribution of NGC 4151 and MKN 509 are presented from the X-ray region to the infrared
Superbubbles
Individual massive stars with M sub bol -6 have huge stellar winds that create interstellar bubbles. Stars with masses greater than 8 solar mass are considered supernova progenitors. These massive stars are numerous in OB associations where few supernova remnants are detected. Model calculations describing the evolution of an association show: that large, hot cavities are formed by pushing the ambient gas into neutral shells; that the shell radii change with galactocentric radius; that only thirty percent of the interstellar medium is in the form of supercavities; and that a consequence is that only a small fraction of supernovae form supernova remnants
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