567 research outputs found
Hot Interstellar Gas and Stellar Energy Feedback in the Antennae Galaxies
We have analyzed Chandra archival observations of the Antennae galaxies to
study the distribution and physical properties of its hot interstellar gas.
Eleven distinct diffuse X-ray emission regions are selected according to their
underlying interstellar structures and star formation activity. The X-ray
spectra of these regions are used to determine their thermal energy contents
and cooling timescales. Young star clusters in these regions are also
identified and their photometric measurements are compared to evolutionary
stellar population synthesis models to assess their masses and ages. The
cluster properties are then used to determine the stellar wind and supernova
energies injected into the ISM. Comparisons between the thermal energy in the
hot ISM and the expected stellar energy input show that young star clusters are
sufficient to power the X-ray-emitting gas in some, but not all, active star
formation regions. Super-star clusters, with masses >= 1x10^5 M_sol, heat the
ISM, but the yield of hot interstellar gas is not directly proportional to the
cluster mass. Finally, there exist diffuse X-ray emission regions which do not
show active star formation or massive young star clusters. These regions may be
powered by field stars or low-mass clusters formed within the last ~100 Myr.Comment: 36 pages, 6 figures, 8 tables, 2 appendices, to appear in the
Astrophysical Journal, April 20 issu
An Interstellar Conduction Front Within a Wolf-Rayet Ring Nebula Observed with the GHRS
With the High Resolution Spectrograph aboard the Hubble Space Telescope we
obtained high signal-to-noise (S/N > 200 - 600 per 17 km/s resolution element)
spectra of narrow absorption lines toward the Wolf-Rayet star HD 50896. The
ring nebula S308 that surrounds this star is thought to be caused by a
pressure-driven bubble bounded by circumstellar gas (most likely from a red
supergiant or luminous blue variable progenitor) pushed aside by a strong
stellar wind. Our observation has shown for the first time that blueshifted
(approximately 70 km/s relative to the star) absorption components of C IV and
N V arise in a conduction front between the hot interior of the bubble and the
cold shell of swept-up material. These lines set limits on models of the
conduction front. Nitrogen in the shell appears to be overabundant by a factor
~10. The P Cygni profiles of N V and C IV are variable, possibly due to a
suspected binary companion to HD 50896.Comment: 32 pages, Latex, to appear in the Astrophysical Journal, April, 199
HST/WFPC2 and VLT/ISAAC observations of PROPLYDS in the giant HII region NGC 3603
We report the discovery of three proplyd-like structures in the giant HII
region NGC 3603. The emission nebulae are clearly resolved in narrow-band and
broad-band HST/WFPC2 observations in the optical and broad-band VLT/ISAAC
observations in the near-infrared. All three nebulae are tadpole shaped, with
the bright ionization front at the head facing the central cluster and a
fainter ionization front around the tail pointing away from the cluster.
Typical sizes are 6,000 A.U. x 20,000 A.U. The nebulae share the overall
morphology of the proplyds (``PROto PLanetarY DiskS'') in Orion, but are 20 to
30 times larger in size. Additional faint filaments located between the nebulae
and the central ionizing cluster can be interpreted as bow shocks resulting
from the interaction of the fast winds from the high-mass stars in the cluster
with the evaporation flow from the proplyds. The striking similarity of the
tadpole shaped emission nebulae in NGC 3603 to the proplyds in Orion suggests
that the physical structure of both types of objects might be the same. We
present 2D radiation hydrodynamical simulations of an externally illuminated
star-disk-envelope system, which was still in its main accretion phase when
first exposed to ionizing radiation from the central cluster. The simulations
reproduce the overall morphology of the proplyds in NGC 3603 very well, but
also indicate that mass-loss rates of up to 10^-5 Mo/yr are required in order
to explain the size of the proplyds. (abbreviated)Comment: 10 pages, 4 Postscript figures, uses emulateapj.sty and psfig.tex.
Astronomical Journal, in press (January 2000 issue
ROSAT observations of X-ray emission from planetary nebulae
We have searched the entire ROSAT archive for useful observations to study
X-ray emission from Galactic planetary nebulae (PNs). The search yields a
sample of 63 PNs, which we call the ROSAT PN sample. About 20-25% of this
sample show X-ray emission; these include 13 definite detections and three
possible detections (at a 2-sigma level). All X-ray sources in these PNs are
concentrated near the central stars. Only A 30, BD+30 3639, and NGC 6543 are
marginally resolved by the ROSAT instruments. Three types of X-ray spectra are
seen in PNs. Type 1 consists of only soft X-ray emission (<0.5 keV), peaks at
0.1-0.2 keV, and can be fitted by blackbody models at temperatures 1-2 10^5 K.
Type 2 consists of harder X-ray emission, peaks at >0.5 keV, and can be fitted
by thin plasma emission models at temperatures of a few 10^6 K. Type 3 is a
composite of a bright Type 1 component and a fainter Type 2 component.
Unresolved soft sources with Type 1 spectra or the soft component of Type 3
spectra are most likely photospheric emission from the hot central stars.
Absorption cross sections are large for these soft-energy photons; therefore,
only large, tenuous, evolved PNs with hot central stars and small absorption
column densities have been detected. The origin of hard X-ray emission from PNs
is uncertain. PNs with Type 2 spectra are small, dense, young nebulae with
relatively cool (<<10^5 K) central stars, while PNs with Type 3 X-ray spectra
are large, tenuous, evolved nebulae with hot central stars. The hard X-ray
luminosities are also different between these two types of PNs, indicating
perhaps different origins of their hard X-ray emission. Future Chandra and XMM
observations with high spatial and spectral resolution will help to understand
the origin of hard X-ray emission from PNs.Comment: To be published in The Astrophysical Journal Supplement Series. 21
pages, 7 figures, 5 table
The Distance Scale of Planetary Nebulae
By collecting distances from the literature, a set of 73 planetary nebulae
with mean distances of high accuracy is derived. This sample is used for
recalibration of the mass-radius relationship, used by many statistical
distance methods. An attempt to correct for a statistical peculiarity, where
errors in the distances influences the mass--radius relationship by increasing
its slope, has been made for the first time. Distances to PNe in the Galactic
Bulge, derived by this new method as well as other statistical methods from the
last decade, are then used for the evaluation of these methods as distance
indicators. In order of achieving a Bulge sample that is free from outliers we
derive new criteria for Bulge membership. These criteria are much more
stringent than those used hitherto, in the sense that they also discriminate
against background objects. By splitting our Bulge sample in two, one with
optically thick (small) PNe and one with optically thin (large) PNe, we find
that our calibration is of higher accuracy than most other calibrations.
Differences between the two subsamples, we believe, are due to the
incompleteness of the Bulge sample, as well as the dominance of optical
diameters in the ``thin'' sample and radio diameters in the ``thick'' sample.
Our final conclusion is that statistical methods give distances that are at
least as accurate as the ones obtained from many individual methods. Also, the
`long' distance scale of Galactic PNe is confirmed.Comment: 15 pages, 9 figures, accepted for publication in A&
Ten Million Degree Gas in M 17 and the Rosette Nebula: X-ray Flows in Galactic H II Regions
We present the first high-spatial-resolution X-ray images of two high-mass
star forming regions, the Omega Nebula (M 17) and the Rosette Nebula (NGC
2237--2246), obtained with the Chandra X-ray Observatory Advanced CCD Imaging
Spectrometer (ACIS) instrument. The massive clusters powering these H II
regions are resolved at the arcsecond level into >900 (M 17) and >300 (Rosette)
stellar sources similar to those seen in closer young stellar clusters.
However, we also detect soft diffuse X-ray emission on parsec scales that is
spatially and spectrally distinct from the point source population. The diffuse
emission has luminosity L_x ~ 3.4e33 ergs/s in M~17 with plasma energy
components at kT ~0.13 and ~0.6 keV (1.5 and 7 MK), while in Rosette it has L_x
\~6e32 ergs/s with plasma energy components at kT ~0.06 and ~0.8 keV (0.7 and 9
MK). This extended emission most likely arises from the fast O-star winds
thermalized either by wind-wind collisions or by a termination shock against
the surrounding media. We establish that only a small portion of the wind
energy and mass appears in the observed diffuse X-ray plasma; in these blister
H II regions, we suspect that most of it flows without cooling into the
low-density interstellar medium. These data provide compelling observational
evidence that strong wind shocks are present in H II regions.Comment: 35 pages, including 11 figures; to appear in ApJ, August 20, 2003. A
version with high-resolution figures is available at
ftp://ftp.astro.psu.edu/pub/townsley/diffuse.ps.g
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Mycolactone-dependent depletion of endothelial cell thrombomodulin is strongly associated with fibrin deposition in Buruli ulcer lesions
A well-known histopathological feature of diseased skin in Buruli ulcer (BU) is coagulative necrosis caused by the Mycobacterium ulcerans macrolide exotoxin mycolactone. Since the underlying mechanism is not known, we have investigated the effect of mycolactone on endothelial cells, focussing on the expression of surface anticoagulant molecules involved in the protein C anticoagulant pathway. Congenital deficiencies in this natural anticoagulant pathway are known to induce thrombotic complications such as purpura fulimans and spontaneous necrosis. Mycolactone profoundly decreased thrombomodulin (TM) expression on the surface of human dermal microvascular endothelial cells (HDMVEC) at doses as low as 2ng/ml and as early as 8hrs after exposure. TM activates protein C by altering thrombin's substrate specificity, and exposure of HDMVEC to mycolactone for 24 hours resulted in an almost complete loss of the cells' ability to produce activated protein C. Loss of TM was shown to be due to a previously described mechanism involving mycolactone-dependent blockade of Sec61 translocation that results in proteasome-dependent degradation of newly synthesised ER-transiting proteins. Indeed, depletion from cells determined by live-cell imaging of cells stably expressing a recombinant TM-GFP fusion protein occurred at the known turnover rate. In order to determine the relevance of these findings to BU disease, immunohistochemistry of punch biopsies from 40 BU lesions (31 ulcers, nine plaques) was performed. TM abundance was profoundly reduced in the subcutis of 78% of biopsies. Furthermore, it was confirmed that fibrin deposition is a common feature of BU lesions, particularly in the necrotic areas. These findings indicate that there is decreased ability to control thrombin generation in BU skin. Mycolactone's effects on normal endothelial cell function, including its ability to activate the protein C anticoagulant pathway are strongly associated with this. Fibrin-driven tisischemia could contribute to the development of the tissue necrosis seen in BU lesions
Roles of Molecular Layer Interneurons in Sensory Information Processing in Mouse Cerebellar Cortex Crus II In Vivo
Cerebellar cortical molecular layer interneurons (MLIs) play essential roles in sensory information processing by the cerebellar cortex. However, recent experimental and modeling results are questioning traditional roles for molecular layer inhibition in the cerebellum. receptors uncovered larger EPSCs in PCs whose time to peak, half-width and 10–90% rising time were also significantly slower than in MLIs. Biocytin labeling indicated that the MLIs (but not PCs) are dye-coupled.These findings indicate that tactile face stimulation evokes rapid excitation in MLIs and inhibition occurring at later latencies in PCs in mouse cerebellar cortex Crus II. These results support previous suggestions that the lack of parallel fiber driven PC activity is due to the effect of MLI inhibition
Synaptic Responses Evoked by Tactile Stimuli in Purkinje Cells in Mouse Cerebellar Cortex Crus II In Vivo
Sensory stimuli evoke responses in cerebellar Purkinje cells (PCs) via the mossy fiber-granule cell pathway. However, the properties of synaptic responses evoked by tactile stimulation in cerebellar PCs are unknown. The present study investigated the synaptic responses of PCs in response to an air-puff stimulation on the ipsilateral whisker pad in urethane-anesthetized mice.Thirty-three PCs were recorded from 48 urethane-anesthetized adult (6-8-week-old) HA/ICR mice by somatic or dendritic patch-clamp recording and pharmacological methods. Tactile stimulation to the ipsilateral whisker pad was delivered by an air-puff through a 12-gauge stainless steel tube connected with a pressurized injection system. Under current-clamp conditions (I = 0), the air-puff stimulation evoked strong inhibitory postsynaptic potentials (IPSPs) in the somata of PCs. Application of SR95531, a specific GABA(A) receptor antagonist, blocked IPSPs and revealed stimulation-evoked simple spike firing. Under voltage-clamp conditions, tactile stimulation evoked a sequence of transient inward currents followed by strong outward currents in the somata and dendrites in PCs. Application of SR95531 blocked outward currents and revealed excitatory postsynaptic currents (EPSCs) in somata and a temporal summation of parallel fiber EPSCs in PC dendrites. We also demonstrated that PCs respond to both the onset and offset of the air-puff stimulation.These findings indicated that tactile stimulation induced asynchronous parallel fiber excitatory inputs onto the dendrites of PCs, and failed to evoke strong EPSCs and spike firing in PCs, but induced the rapid activation of strong GABA(A) receptor-mediated inhibitory postsynaptic currents in the somata and dendrites of PCs in the cerebellar cortex Crus II in urethane-anesthetized mice
Phosphorylation of LCRMP-1 by GSK3β Promotes Filopoda Formation, Migration and Invasion Abilities in Lung Cancer Cells
LCRMP-1, a novel isoform of CRMP-1, can promote cancer cell migration, invasion and associate with poor clinical outcome in patients with non-small-cell lung cancer (NSCLC). However, the underlying regulatory mechanisms of LCRMP-1 in cancer cell invasiveness still remain obscure. Here, we report that GSK3β can phosphorylate LCRMP-1 at Thr-628 in consensus sequences and this phosphorylation is crucial for function of LCRMP-1 to promote filopodia formation, migration and invasion in cancer cells. Impediment of Thr-628 phosphorylation attenuates the stimulatory effects of LCRMP-1 on filopodia forming, migration and invasion abilities in cancer cells; simultaneously, kinase-dead GSK3β diminishes regulation of LCRMP-1 on cancer cell invasion. Furthermore, we also found that patients with low-level Ser-9-phosphorylated GSK3β expression and high-level LCRMP-1 expression have worse overall survival than those with high-level inactive GSK3β expressions and low-level LCRMP-1 expressions (P<0.0001). Collectively, these results demonstrate that GSK3β-dependent phosphorylation of LCRMP-1 provides an important mechanism for regulation of LCRMP-1 on cancer cell invasiveness and clinical outcome
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