1,434 research outputs found
Far infrared and submillimeter brightness temperatures of the giant planets
The brightness temperatures of Jupiter, Saturn, Uranus, and Neptune in the range 35 to 1000 micron. The effective temperatures derived from the measurements, supplemented by shorter wavelength Voyager data for Jupiter and Saturn, are 126.8 + or - 4.5 K, 93.4 + or - 3.3 K, 58.3 + or - 2.0 K, and 60.3 + or - 2.0 K, respectively. The implications of the measurements for bolometric output and for atmospheric structure and composition are discussed. The temperature spectrum of Jupiter shows a strong peak at approx. 350 microns followed by a deep valley at approx. 450 to 500 microns. Spectra derived from model atmospheres qualitatively reproduced these features but do not fit the data closely
Molecular excitation in the Eagle nebula's fingers
Context: The M16 nebula is a relatively nearby Hii region, powered by O stars
from the open cluster NGC 6611, which borders to a Giant Molecular Cloud.
Radiation from these hot stars has sculpted columns of dense obscuring material
on a few arcmin scales. The interface between these pillars and the hot ionised
medium provides a textbook example of a Photodissociation Region (PDR).
Aims: To constrain the physical conditions of the atomic and molecular
material with submillimeter spectroscopic observations.
Methods: We used the APEX submillimeter telescope to map a ~3'x3' region in
the CO J=3-2, 4-3 and 7-6 rotational lines, and a subregion in atomic carbon
lines. We also observed C18O(3-2) and CO(7-6) with longer integrations on five
peaks found in the CO(3-2) map. The large scale structure of the pillars is
derived from the molecular lines' emission distribution. We estimate the
magnitude of the velocity gradient at the tips of the pillars and use LVG
modelling to constrain their densities and temperatures. Excitation
temperatures and carbon column densities are derived from the atomic carbon
lines.
Results: The atomic carbon lines are optically thin and excitation
temperatures are of order 60 K to 100 K, well consistent with observations of
other Hii region-molecular cloud interfaces. We derive somewhat lower
temperatures from the CO line ratios, of order 40 K. The Ci/CO ratio is around
0.1 at the fingers tips.Comment: 4 pages, APEX A&A special issue, accepte
Discovery of a 500 pc shell in the nucleus of Centaurus A
Spitzer Space Telescope mid-infrared images of the radio galaxy Centaurus A
reveal a shell-like, bipolar, structure 500 pc to the north and south of the
nucleus. This shell is seen in 5.8, 8.0 and 24 micron broad-band images. Such a
remarkable shell has not been previously detected in a radio galaxy and is the
first extragalactic nuclear shell detected at mid-infrared wavelengths. We
estimate that the shell is a few million years old and has a mass of order
million solar masses. A conservative estimate for the mechanical energy in the
wind driven bubble is 10^53 erg. The shell could have created by a small few
thousand solar mass nuclear burst of star formation. Alternatively, the
bolometric luminosity of the active nucleus is sufficiently large that it could
power the shell. Constraints on the shell's velocity are lacking. However, if
the shell is moving at 1000 km/s then the required mechanical energy would be
100 times larger.Comment: submitted to ApJ Letter
The Spitzer Space Telescope Mission
The Spitzer Space Telescope, NASA's Great Observatory for infrared astronomy,
was launched 2003 August 25 and is returning excellent scientific data from its
Earth-trailing solar orbit. Spitzer combines the intrinsic sensitivity
achievable with a cryogenic telescope in space with the great imaging and
spectroscopic power of modern detector arrays to provide the user community
with huge gains in capability for exploration of the cosmos in the infrared.
The observatory systems are largely performing as expected and the projected
cryogenic lifetime is in excess of 5 years. This paper summarizes the on-orbit
scientific, technical and operational performance of Spitzer. Subsequent papers
in this special issue describe the Spitzer instruments in detail and highlight
many of the exciting scientific results obtained during the first six months of
the Spitzer mission.Comment: Accepted for publication in the Astrophyscial Journal Supplement
Spitzer Special Issue, 22 pages, 3 figures. Higher resolution versions of the
figures are available at http://ssc.spitzer.caltech.edu/pubs/journal2004.htm
Nonsynchronous, episodic incision: Evidence of threshold exceedance and complex response as controls of terrace formation
Terrace sequences can represent regional or continental scale factors such as climatic fluctuations, neotectonic activity, and base-level change. However, they can also reflect random incision events brought about by local scale, geomorphic threshold exceedance, and subsequent complex response. This study explores the formative processes of three discontinuous, but adjacent, late Pleistocene to late Holocene stepterrace sequences in southeastern Australia. Correlation of river terrace fills was undertaken by comparing terrace remnants based on topography, morphology, sedimentology, stratigraphy, and chronology. A geomorphic model of floodplain abandonment and terrace formation for this valley setting is presented. Most of southeastern Australia has shown no evidence of tectonic uplift during the late Quaternary. Bedrock bars on the Hunter River isolate the study reach from downstream base-level changes. The nonsynchronous, episodic behavior of incision events in this catchment strongly indicates that climate is not a dominant control on terrace formation. With the exclusion of climatic fluctuations, tectonic uplift and base-level change as causes of incision, catastrophic floods, and the exceedance of geomorphic thresholds emerge as the dominant controls of terrace formation. Crow
Strong absorption by interstellar hydrogen fluoride: Herschel/HIFI observations of the sight-line to G10.6-0.4 (W31C)
We report the detection of strong absorption by interstellar hydrogen
fluoride along the sight-line to the submillimeter continuum source G10.6-0.4
(W31C). We have used Herschel's HIFI instrument, in dual beam switch mode, to
observe the 1232.4763 GHz J=1-0 HF transition in the upper sideband of the Band
5a receiver. The resultant spectrum shows weak HF emission from G10.6-0.4 at
LSR velocities in the range -10 to -3 km/s, accompanied by strong absorption by
foreground material at LSR velocities in the range 15 to 50 km/s. The spectrum
is similar to that of the 1113.3430 GHz 1(11)-0(00) transition of para-water,
although at some frequencies the HF (hydrogen fluoride) optical depth clearly
exceeds that of para-H2O. The optically-thick HF absorption that we have
observed places a conservative lower limit of 1.6E+14 cm-2 on the HF column
density along the sight-line to G10.6-0.4. Our lower limit on the HF abundance,
6E-9 relative to hydrogen nuclei, implies that hydrogen fluoride accounts for
between ~ 30 and 100% of the fluorine nuclei in the gas phase along this
sight-line. This observation corroborates theoretical predictions that -
because the unique thermochemistry of fluorine permits the exothermic reaction
of F atoms with molecular hydrogen - HF will be the dominant reservoir of
interstellar fluorine under a wide range of conditions.Comment: Accepted for publication in Astronomy and Astrophysics (Herschel
special issue). This revised version corrects a typographic error in the HTML
abstract, in which the lower limit on the HF abundance (should be 6E-9) was
previously misstated. The abstract in the PDF version is correct and the
latter has not been modifie
Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study - A Randomized Clinical Trial
Background: Pimobendan is effective in treatment of dogs with congestive heart failure (CHF) secondary to myxomatous mitral valve disease (MMVD). Its effect on dogs before the onset of CHF is unknown. Hypothesis/Objectives: Administration of pimobendan (0.4-0.6 mg/kg/d in divided doses) to dogs with increased heart size secondary to preclinical MMVD, not receiving other cardiovascular medications, will delay the onset of signs of CHF, cardiac-related death, or euthanasia. Animals: 360 client-owned dogs with MMVD with left atrial-to-aortic ratio >= 1.6, normalized left ventricular internal diameter in diastole >= 1.7, and vertebral heart sum >10.5. Methods: Prospective, randomized, placebo-controlled, blinded, multicenter clinical trial. Primary outcome variable was time to a composite of the onset of CHF, cardiac-related death, or euthanasia. Results: Median time to primary endpoint was 1228 days (95% CI: 856-NA) in the pimobendan group and 766 days (95% CI: 667-875) in the placebo group (P = .0038). Hazard ratio for the pimobendan group was 0.64 (95% CI: 0.47-0.87) compared with the placebo group. The benefit persisted after adjustment for other variables. Adverse events were not different between treatment groups. Dogs in the pimobendan group lived longer (median survival time was 1059 days (95% CI: 952-NA) in the pimobendan group and 902 days (95% CI: 747-1061) in the placebo group) (P = .012). Conclusions and Clinical Importance: Administration of pimobendan to dogs with MMVD and echocardiographic and radiographic evidence of cardiomegaly results in prolongation of preclinical period and is safe and well tolerated. Prolongation of preclinical period by approximately 15 months represents substantial clinical benefit
European regulatory agenices should employ full time statisticians
No abstract available
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