489 research outputs found
Shock processing of interstellar dust and polycyclic aromatic hydrocarbons in the supernova remnant N132D
We observed the oxygen-rich Large Magellanic Cloud (LMC) supernova remnant
N132D (SNR 0525-69.6), using all instruments onboard the Spitzer Space
Telescope, IRS, IRAC, and MIPS (Infrared Spectrograph, Infrared Array Camera,
Multiband Imaging Photometer for Spitzer). The 5-40 micron IRS spectra toward
the southeastern shell of the remnant show a steeply rising continuum with
[NeIII] and [OIV] as well as PAH emission. We also present the spectrum of a
fast moving ejecta knot, previously detected at optical wavelengths, which is
dominated by strong [NeIII] and [OIV] emission lines. We interpret the
continuum as thermal emission from swept-up, shock-heated dust grains in the
expanding shell of N132D, which is clearly visible in the MIPS 24 micron image.
A 15-20 micron emission hump appears superposed on the dust continuum, and we
attribute this to PAH C-C-C bending modes. We also detect the well-known 11.3
micron PAH C-H bending feature, and find the integrated strength of the 15-20
micron hump about a factor of seven stronger than the 11.3 micron band in the
shell of the remnant. IRAC 3-9 micron images do not show clear evidence of
large-scale, shell-like emission from the remnant, partly due to confusion with
the ambient ISM material. However, we identified several knots of shocked
interstellar gas based on their distinct infrared colors. We discuss the bright
infrared continuum and the polycyclic aromatic hydrocarbon features with
respect to dust processing in young supernova remnants.Comment: Accepted by Ap
Discovery of superthermal hydroxyl (OH) in the HH211 outflow
We present a 5-37 micron infrared spectrum obtained with the Spitzer Space
Telescope toward the southeastern lobe of the young protostellar outflow HH211.
The spectrum shows an extraordinary sequence of OH emission lines arising in
highly excited rotational levels up to an energy E/k~28200K above the ground
level. This is, to our knowledge, by far the highest rotational excitation of
OH observed outside Earth. The spectrum also contains several pure rotational
transitions of H2O (v=0), H2 (v=0) S(0) to S(7), HD (v=0) R(3) to R(6), and
atomic fine-structure lines of [Fe II], [Si II], [Ne II], [S I], and [Cl I].
The origin of the highly excited OH emission is most likely the
photodissociation of H2O by the UV radiation generated in the terminal outflow
shock of HH211.Comment: ApJ Letters, in pres
Freshly Formed Dust in the Cassiopeia A Supernova Remnant as Revealed by the Spitzer Space Telescope
We performed Spitzer Infrared Spectrograph mapping observations covering
nearly the entire extent of the Cassiopeia A supernova remnant (SNR), producing
mid-infrared (5.5-35 micron) spectra every 5-10". Gas lines of Ar, Ne, O, Si, S
and Fe, and dust continua were strong for most positions. We identify three
distinct ejecta dust populations based on their continuum shapes. The dominant
dust continuum shape exhibits a strong peak at 21 micron. A line-free map of 21
micron-peak dust made from the 19-23 micron range closely resembles the [Ar
II], [O IV], and [Ne II] ejecta-line maps implying that dust is freshly formed
in the ejecta. Spectral fitting implies the presence of SiO2, Mg
protosilicates, and FeO grains in these regions. The second dust type exhibits
a rising continuum up to 21 micron and then flattens thereafter. This ``weak 21
micron'' dust is likely composed of Al2O3 and C grains. The third dust
continuum shape is featureless with a gently rising spectrum and is likely
composed of MgSiO3 and either Al2O3 or Fe grains. Using the least massive
composition for each of the three dust classes yields a total mass of 0.02
Msun. Using the most-massive composition yields a total mass of 0.054 Msun. The
primary uncertainty in the total dust mass stems from the selection of the dust
composition necessary for fitting the featureless dust as well as 70 micron
flux. The freshly formed dust mass derived from Cas A is sufficient from SNe to
explain the lower limit on the dust masses in high redshift galaxies.Comment: 8 figures: Accepted for the publication in Ap
Chronic nonbacterial osteomyelitis in childhood: prospective follow-up during the first year of anti-inflammatory treatment
Introduction: Chronic nonbacterial osteomyelitis (CNO) is an inflammatory disorder of unknown etiology. In children and adolescents CNO predominantly affects the metaphyses of the long bones, but lesions can occur at any site of the skeleton. Prospectively followed cohorts using a standardized protocol in diagnosis and treatment have rarely been reported. Methods: Thirty-seven children diagnosed with CNO were treated with naproxen continuously for the first 6 months. If assessment at that time revealed progressive disease or no further improvement, sulfasalazine and short-term corticosteroids were added. The aims of our short-term follow-up study were to describe treatment response in detail and to identify potential risk factors for an unfavorable outcome. Results: Naproxen treatment was highly effective in general, inducing a symptom-free status in 43% of our patients after 6 months. However, four nonsteroidal anti-inflammatory drug (NSAID) partial-responders were additionally treated with sulfasalazine and short-term corticosteroids. The total number of clinical detectable lesions was significantly reduced. Mean disease activity estimated by the patient/physician and the physical aspect of health-related quality of life including functional ability (global assessment/childhood health assessment questionnaire and childhood health assessment questionnaire) and pain improved significantly. Forty-one percent of our patients showed radiological relapses, but 67% of them were clinically silent. Conclusions: Most children show a favorable clinical course in the first year of anti-inflammatory treatment with NSAIDs. Relapses and new radiological lesions can occur at any time and at any site in the skeleton but may not be clinically symptomatic. Whole-body magnetic resonance imaging proved to be very sensitive for initial and follow-up diagnostics
Enhanced ionization in small rare gas clusters
A detailed theoretical investigation of rare gas atom clusters under intense
short laser pulses reveals that the mechanism of energy absorption is akin to
{\it enhanced ionization} first discovered for diatomic molecules. The
phenomenon is robust under changes of the atomic element (neon, argon, krypton,
xenon), the number of atoms in the cluster (16 to 30 atoms have been studied)
and the fluency of the laser pulse. In contrast to molecules it does not
dissappear for circular polarization. We develop an analytical model relating
the pulse length for maximum ionization to characteristic parameters of the
cluster
Dust Formation Observed in Young Supernova Remnants with Spitzer
We present dust features and masses observed in young supernova remnants
(SNRs) with Spitzer IRS mapping and staring observations of four youngest
supernova remnants: SNR 1E102.2-7219 (E0102) in the SMC, Cas A and G11.2-0.3 in
our Galaxy, and N132D in the LMC. The spectral mapping data revealed a number
of dust features which include 21 micron-peak dust and featureless dust in Cas
A and 18-micron peak dust in E0102 and N132D. The 18 micron-peak feature is
fitted by a mix of MgSiO and solid Si dust grains, while the 21-micron peak
dust is by a mix of silicates and FeO; we also explore dust fitting using
Continuous Distribution of Ellipsoid grain models. We report detection of CO
fundamental band from Cas A in near-infrared. We review dust features observed
and identified in other SNRs. The dust emission is spatially correlated with
the ejecta emission, showing dust is formed in SN ejecta. The spectra of E0102
show rich gas lines from ejecta including strong ejecta lines of Ne and O,
including two [Ne III] lines and two [Ne V] lines which allow us to diagnostic
density and temperature of the ejecta and measure the ejecta masses. E0102 and
N132D show weak or lacking Ar, Si, and Fe ejecta, whereas the young Galactic
SNR Cas A show strong Ar, Si, and S and weak Fe. We discuss compositions and
masses of dust and association with those of ejecta and finally, dust
contribution from SNe to early Universe.Comment: conference proceeding for "Cosmic Dust - Near and Far" (Heidelberg,
Germany), 11pages and 7 figure
Waves on the surface of the Orion molecular cloud
Massive stars influence their parental molecular cloud, and it has long been
suspected that the development of hydrodynamical instabilities can compress or
fragment the cloud. Identifying such instabilities has proved difficult. It has
been suggested that elongated structures (such as the `pillars of creation')
and other shapes arise because of instabilities, but alternative explanations
are available. One key signature of an instability is a wave-like structure in
the gas, which has hitherto not been seen. Here we report the presence of
`waves' at the surface of the Orion molecular cloud near where massive stars
are forming. The waves seem to be a Kelvin-Helmholtz instability that arises
during the expansion of the nebula as gas heated and ionized by massive stars
is blown over pre-existing molecular gas.Comment: Preprint of publication in Natur
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