109 research outputs found
Glutamate Receptor GluR3 Antibodies and Death of Cortical Cells
AbstractRasmussen's encephalitis (RE), a childhood disease characterized by epileptic seizures associated with progressive destruction of a single cerebral hemisphere, is an autoimmune disease in which one of the autoantigens is a glutamate receptor, GluR3. The improvement of some affected children following plasma exchange that removed circulating GluR3 antibodies (anti-GluR3) suggested that anti-GluR3 gained access to the central nervous system where it exerted deleterious effects. Here, we demonstrate that a subset of rabbits immunized with a GluR3 fusion protein develops a neurological disorder mimicking RE. Anti-GluR3 IgG isolated from serum of both ill and healthy GluR3-immunized animals promoted death of cultured cortical cells by a complement-dependent mechanism. IgG immunoreactivity decorated neurons and their processes in neocortex and hippocampus in ill but not in healthy rabbits. Moreover, both IgG and complement membrane attack complex (MAC) immunoreactivity was evident on neurons and their processes in the cortex of a subset of patients with RE. We suggest that access of IgG to epitopes in the central nervous system triggers complement-mediated neuronal damage and contributes to the pathogenesis of both this animal model and RE
Spitzer View of Young Massive Stars in the LMC HII Complex N44
The HII complex N44 in the Large Magellanic Cloud (LMC) provides an excellent
site to perform a detailed study of star formation in a mild starburst, as it
hosts three regions of star formation at different evolutionary stages and it
is not as complicated and confusing as the 30 Doradus giant HII region. We have
obtained Spitzer Space Telescope observations and complementary ground-based 4m
uBVIJK observations of N44 to identify candidate massive young stellar objects
(YSOs). We further classify the YSOs into Types I, II, and III, according to
their spectral energy distributions (SEDs). In our sample of 60 YSO candidates,
~65% of them are resolved into multiple components or extended sources in
high-resolution ground-based images. We have modeled the SEDs of 36 YSOs that
appear single or dominant within a group. We find good fits for Types I and
I/II YSOs,but Types II and II/III YSOs show deviations between their observed
SEDs and models that do not include PAH emission. We have also found that some
Type III YSOs have central holes in their disk components. YSO counterparts are
found in four ultracompact HII regions and their stellar masses determined from
SED model fits agree well with those estimated from the ionization requirements
of the HII regions. The distribution of YSOs is compared with those of the
underlying stellar population and interstellar gas conditions to illustrate a
correlation between the current formation of O-type stars and previous
formation of massive stars. Evidence of triggered star formation is also
presented.Comment: 63 pages, 15 figures, accepted for publication for ApJ; some figures
in jpeg format to meet the size limit; preprint with high resolution images
can be found at http://www.astro.virginia.edu/~cc5ye/n44yso.pd
Rapid 20th century warming reverses 900-year cooling in the Gulf of Maine
The Gulf of Maine, located in the western North Atlantic, has undergone recent, rapid ocean warming but the lack of long-term, instrumental records hampers the ability to put these significant hydrographic changes into context. Here we present multiple 300-year long geochemical records (oxygen, nitrogen, and previously published radiocarbon isotopes) measured in absolutely-dated Arctica islandica shells from the western Gulf of Maine. These records, in combination with climate model simulations, suggest that the Gulf of Maine underwent a long-term cooling over most of the last 1000 years, driven primarily by volcanic forcing and North Atlantic ocean dynamics. This cooling trend was reversed by warming beginning in the late 1800s, likely due to increased atmospheric greenhouse gas concentrations and changes in western North Atlantic circulation. The climate model simulations suggest that the warming over the last century was more rapid than almost any other 100-year period in the last 1000 years in the region
Spitzer View of Massive Star Formation in the Tidally Stripped Magellanic Bridge
The Magellanic Bridge is the nearest low-metallicity, tidally stripped
environment, offering a unique high-resolution view of physical conditions in
merging and forming galaxies. In this paper we present analysis of candidate
massive young stellar objects (YSOs), i.e., {\it in situ, current} massive star
formation (MSF) in the Bridge using {\it Spitzer} mid-IR and complementary
optical and near-IR photometry. While we definitely find YSOs in the Bridge,
the most massive are , found in the Large
Magellanic Cloud (LMC). The intensity of MSF in the Bridge also appears
decreasing, as the most massive YSOs are less massive than those formed in the
past. To investigate environmental effects on MSF, we have compared properties
of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge
are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical
counterparts, compared to only 56% of LMC sources with the same range of mass,
circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes
are evidently more porous or clumpy in the Bridge's low-metallicity
environment. Second, we have used whole samples of YSOs in the LMC and the
Bridge to estimate the probability of finding YSOs at a given \hi\ column
density, N(HI). We found that the LMC has higher probability than
the Bridge for N(HI) cm, but the trend reverses at
lower N(HI). Investigating whether this lower efficiency relative to HI is due
to less efficient molecular cloud formation, or less efficient cloud collapse,
or both, will require sensitive molecular gas observations.Comment: 41 pages, 20 figures, 6 tables; accepted for publication in ApJ;
several figures are in low resolution due to the size limit here and a high
resolution version can be downloaded via
http://www.astro.virginia.edu/~cc5ye/ms_bridge20140215.pd
Dust Production and Mass Loss in the Galactic Globular Cluster NGC 362
We investigate dust production and stellar mass loss in the Galactic globular
cluster NGC 362. Due to its close proximity to the Small Magellanic Cloud
(SMC), NGC 362 was imaged with the IRAC and MIPS cameras onboard the Spitzer
Space Telescope as part of the Surveying the Agents of Galaxy Evolution
(SAGE-SMC) Spitzer Legacy program. We detect several cluster members near the
tip of the Red Giant Branch that exhibit infrared excesses indicative of
circumstellar dust and find that dust is not present in measurable quantities
in stars below the tip of the Red Giant Branch. We modeled the spectral energy
distribution (SED) of the stars with the strongest IR excess and find a total
cluster dust mass-loss rate of 3.0(+2.0/-1.2) x 10^-9 solar masses per year,
corresponding to a gas mass-loss rate of 8.6(+5.6/-3.4) x 10^-6 solar masses
per year, assuming [Fe/H] = -1.16. This mass loss is in addition to any
dust-less mass loss that is certainly occurring within the cluster. The two
most extreme stars, variables V2 and V16, contribute up to 45% of the total
cluster dust-traced mass loss. The SEDs of the more moderate stars indicate the
presence of silicate dust, as expected for low-mass, low-metallicity stars.
Surprisingly, the SED shapes of the stars with the strongest mass-loss rates
appear to require the presence of amorphous carbon dust, possibly in
combination with silicate dust, despite their oxygen-rich nature. These results
corroborate our previous findings in omega Centauri.Comment: 13 pages, 11 figures. Accepted to Ap
Warm and Dense Molecular Gas in the N159 Region: 12CO J=4-3 and 13CO J=3-2 Observations with NANTEN2 and ASTE
New 12CO J=4-3 and 13CO J=3-2 observations of the N159 region in the Large
Magellanic Cloud have been made. The 12CO J=4-3 distribution is separated into
three clumps. These new measurements toward the three clumps are used in
coupled calculations of molecular rotational excitation and line radiation
transfer, along with other transitions of the 12CO as well as the isotope
transitions of 13CO. The temperatures and densities are determined to be
~70-80K and ~3x10^3 cm-3 in N159W and N159E and ~30K and ~1.6x10^3 cm-3 in
N159S. These results are compared with the star formation activity. The N159E
clump is associated with embedded cluster(s) as observed at 24 micron and the
derived high temperature is explained as due to the heating by these sources.
The N159E clump is likely responsible for a dark lane in a large HII region by
the dust extinction. The N159W clump is associated with embedded clusters
mainly toward the eastern edge of the clump only. These clusters show offsets
of 20"-40" from the 12CO J=4-3 peak and are probably responsible for heating
indicated by the derived high temperature. The N159W clump exhibits no sign of
star formation toward the 12CO J=4-3 peak position and its western region. We
suggest that the N159W peak represents a pre-star-cluster core of ~105M_sol
which deserves further detailed studies. Note that recent star formation took
place between N159W and N159E as indicated by several star clusters and HII
regions, while the natal molecular gas toward the stars have already been
dissipated by the ionization and stellar winds of the OB stars. The N159S clump
shows little sign of star formation as is consistent with the lower temperature
and somewhat lower density. The N159S clump is also a candidate for future star
formation
Spitzer Survey of the Large Magellanic Cloud, Surveying the Agents of a Galaxy's Evolution (SAGE) I: Overview and Initial Results
We are performing a uniform and unbiased, ~7x7 degrees imaging survey of the
Large Magellanic Cloud (LMC), using the IRAC and MIPS instruments on board the
Spitzer Space Telescope in order to survey the agents of a galaxy's evolution
(SAGE), the interstellar medium (ISM) and stars in the LMC. The detection of
diffuse ISM with column densities >1.2x10^21 H cm^-2 permits detailed studies
of dust processes in the ISM. SAGE's point source sensitivity enables a
complete census of newly formed stars with masses >3 solar masses that will
determine the current star formation rate in the LMC. SAGE's detection of
evolved stars with mass loss rates >1x10^-8 solar masses per year will quantify
the rate at which evolved stars inject mass into the ISM of the LMC. The
observing strategy includes two epochs in 2005, separated by three months, that
both mitigate instrumental artifacts and constrain source variability. The SAGE
data are non-proprietary. The data processing includes IRAC and MIPS pipelines
and a database for mining the point source catalogs, which will be released to
the community in support of Spitzer proposal cycles 4 and 5. We present initial
results on the epoch 1 data with a special focus on the N79 and N83 region. The
SAGE epoch 1 point source catalog has ~4 million sources. The point source
counts are highest for the IRAC 3.6 microns band and decrease dramatically
towards longer wavelengths consistent with the fact that stars dominate the
point source catalogs and that the dusty objects, e.g. young stellar objects
and dusty evolved stars that detected at the longer wavelengths, are rare in
comparison. We outline a strategy for identifying foreground MW stars, that may
comprise as much as 18% of the source list, and background galaxies, that may
comprise ~12% of the source list.Comment: Accepted by the Astronomical Journa
Massive stars in the giant molecular cloud G23.3â0.3 and W41
Context. Young massive stars and stellar clusters continuously form in the Galactic disk, generating new Hii regions within their natal giant molecular clouds and subsequently enriching the interstellar medium via their winds and supernovae.Aims. Massive stars are among the brightest infrared stars in such regions; their identification permits the characterisation of the star formation history of the associated cloud as well as constraining the location of stellar aggregates and hence their occurrence as a function of global environment.Methods. We present a stellar spectroscopic survey in the direction of the giant molecular cloud G23.3â0.3. This complex is located at a distance of ~4â5 kpc, and consists of several Hii regions and supernova remnants.Results. We discovered 11 OfK+ stars, one candidate luminous blue variable, several OB stars, and candidate red supergiants. Stars with K-band extinction from ~1.3â1.9 mag appear to be associated with the GMC G23.3â0.3; O and B-types satisfying this criterion have spectrophotometric distances consistent with that of the giant molecular cloud. Combining near-IR spectroscopic and photometric data allowed us to characterize the multiple sites of star formation within it. The O-type stars have masses from ~25â45 Mâ, and ages of 5â8 Myr. Two new red supergiants were detected with interstellar extinction typical of the cloud; along with the two RSGs within the cluster GLIMPSE9, they trace an older burst with an age of 20â30 Myr. Massive stars were also detected in the core of three supernova remnants â W41, G22.7â0.2, and G22.7583â0.4917.Conclusions. A large population of massive stars appears associated with the GMC G23.3â0.3, with the properties inferred for them indicative of an extended history of stars formation
Early results from the SAGE-SMC Spitzer legacy
Early results from the SAGE-SMC (Surveying the Agents of Galaxy Evolution in the tidally-disrupted, low-metallicity Small Magellanic Cloud) Spitzer legacy program are presented. These early results concentrate on the SAGE-SMC MIPS observations of the SMC Tail region. This region is the high H i column density portion of the Magellanic Bridge adjacent to the SMC Wing. We detect infrared dust emission and measure the gas-to-dust ratio in the SMC Tail and find it similar to that of the SMC Body. In addition, we find two embedded cluster regions that are resolved into multiple sources at all MIPS wavelengths. © 2009 International Astronomical Union
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