453 research outputs found
Sher 25: pulsating but apparently alone
The blue supergiant Sher25 is surrounded by an asymmetric, hourglass-shaped
circumstellar nebula, which shows similarities to the triple-ring structure
seen around SN1987A. From optical spectroscopy over six consecutive nights, we
detect periodic radial velocity variations in the stellar spectrum of Sher25
with a peak-to-peak amplitude of ~12 km/s on a timescale of about 6 days,
confirming the tentative detec-tion of similar variations by Hendry et al. From
consideration of the amplitude and timescale of the signal, coupled with
observed line profile variations, we propose that the physical origin of these
variations is related to pulsations in the stellar atmosphere, rejecting the
previous hypothesis of a massive, short-period binary companion. The radial
velocities of two other blue supergiants with similar bipolar nebulae, SBW1 and
HD 168625, were also monitored over the course of six nights, but these did not
display any significant radial velocity variations.Comment: 9 pages, 7 figures. Accepted for publication in MNRA
Streptozocin Diabetes Elevates all Isoforms of TGF-β in the Rat Kidney
Transforming growth factor beta (TGF-β) is a major
promoter of diabetic nephropathy. While TGF-β1 is
the most abundaft renal isoform, types 2 and 3 are
present as well and have identical in vitro effects.
Whole kidney extracts were studied 2 weeks after
induction of streptozocin diabetes and in control
rats. Mean glomerular area was 25% greater in the
diabetic animals. TGF-β1 showed a 2-fold increase
in message with a 3-fold increase in protein. TGF-β2
mRNA increased approximately 6% while its
protein doubled. TGF-β-message increased by 25%,
producing a 35% increase in its protein. TGF-β-
inducible gene H3 mRNA was increased 35% in the
diabetic animals, consistent with increased activity
of this growth factor. All isoforms of TGF-β are
increased in the diabetic rat kidney. Future studies
need to address the specific role that each isoform
plays in diabetic nephropathy as well as the impact
of therapies on each isoform
Highly Collimated Jets and Wide-Angle Outflows in HH46/47: New Evidence from Spitzer IR Images
We present new details of the structure and morphology of the jets and
outflows in HH46/47 as seen in Spitzer infrared images from IRAC and MIPS,
reprocessed using the ``HiRes'' deconvolution technique. HiRes improves the
visualization of spatial morphology by enhancing resolution (to sub-arcsec
levels in IRAC bands) and removing the contaminating side lobes from bright
sources. In addition to sharper views of previously reported bow shocks, we
have detected: (i) the sharply-delineated cavity walls of the wide-angle
biconical outflow, seen in scattered light on both sides of the protostar, (ii)
several very narrow jet features at distances 400 AU to 0.1 pc from the star,
and, (iii) compact emissions at MIPS 24 micron coincident with the jet heads,
tracing the hottest atomic/ionic gas in the bow shocks.Comment: 11 pages, 4 Figures, Accepted for publication in ApJ(Letters
Phase-Field Model of Mode III Dynamic Fracture
We introduce a phenomenological continuum model for mode III dynamic fracture
that is based on the phase-field methodology used extensively to model
interfacial pattern formation. We couple a scalar field, which distinguishes
between ``broken'' and ``unbroken'' states of the system, to the displacement
field in a way that consistently includes both macroscopic elasticity and a
simple rotationally invariant short scale description of breaking. We report
two-dimensional simulations that yield steady-state crack motion in a strip
geometry above the Griffith threshold.Comment: submitted to PR
Electron Abundance in Protostellar Cores
The determination of the fractional electron abundance, Xe, in protostellar
cores relies on observations of molecules, such as DCO+, H13CO+ and CO, and on
chemical models to interpret their abundance. Studies of protostellar cores
have revealed significant variations of Xe from core to core within a range
10^-8<Xe<10^-6. The physical origin of these large variations in Xe is not well
understood, unless unlikely variations in the cosmic ray ionization rate or ad
hoc values of metal depletion are assumed. In this work we explore other
potential causes of these variations in Xe, including core age, extinction and
density. We compute numerically the intensity of the radiation field within a
density distribution generated by supersonic turbulence. Taking into account
the lines of sight in all directions, the effective visual extinction in dense
regions is found to be always much lower than the extinction derived from the
column density along a fixed line of sight. Dense cores with volume and column
densities comparable to observed protostellar cores have relatively low
mass-averaged visual extinction, 2mag <= A_V <= 5mag, such that
photo-ionization can sometimes be as important as cosmic ray ionization.
Chemical models, including gas-grain chemistry and time dependent gas depletion
and desorption, are computed for values of visual extinction in the range 2mag
<= A_V <= 6mag, and for a hydrogen gas density of 10^4cm^-3$, typical of
protostellar cores. The models presented here can reproduce some of the
observed variations of ion abundance from core to core as the combined effect
of visual extinction and age variations. The range of electron abundances
predicted by the models is relatively insenstive to density over 10^4 to 10^6
cm^{-3}.Comment: 25 pages, 9 figures. Astrophysical Journal, in pres
Probing ISM Structure in Trumpler 14 & Carina I Using The Stratospheric Terahertz Observatory 2
We present observations of the Trumpler 14/Carina I region carried out using
the Stratospheric Terahertz Observatory 2 (STO2). The Trumpler 14/Carina I
region is in the west part of the Carina Nebula Complex, which is one of the
most extreme star-forming regions in the Milky Way. We observed Trumpler
14/Carina I in the 158 m transition of [C\,{\sc ii}] with a spatial
resolution of 48 and a velocity resolution of 0.17 km s. The
observations cover a 0.25 by 0.28 area with central position
{\it l} = 297.34, {\it b} = -0.60. The kinematics show that
bright [C\,{\sc ii}] structures are spatially and spectrally correlated with
the surfaces of CO clouds, tracing the photodissociation region and ionization
front of each molecular cloud. Along 7 lines of sight that traverse Tr 14 into
the dark ridge to the southwest, we find that the [C\,{\sc ii}] luminosity from
the HII region is 3.7 times that from the PDR. In same los we find in the PDRs
an average ratio of 1:4.1:5.6 for the mass in atomic gas:dark-CO gas: molecular
gas traced by CO. Comparing multiple gas tracers including HI 21cm, [C\,{\sc
ii}], CO, and radio recombination lines, we find that the HII regions of the
Carina Nebula Complex are well-described as HII regions with one-side freely
expanding towards us, consistent with the champagne model of ionized gas
evolution. The dispersal of the GMC in this region is dominated by EUV
photoevaporation; the dispersal timescale is 20-30 Myr.Comment: ApJ accepte
Structure Function Scaling in the Taurus and Perseus Molecular Cloud Complexes
We compute the structure function scaling of the integrated intensity images
of two J=1-0 13CO maps of Taurus and Perseus. The scaling exponents of the
structure functions follow the velocity scaling of supersonic turbulence,
suggesting that turbulence plays an important role in the fragmentation of cold
interstellar clouds. The data also allows to verify the validity of the two
basic assumptions of the hierarchical symmetry model, originally proposed for
the derivation of the velocity structure function scaling. This shows that the
same hierarchical symmetry holds for the projected density field of cold
interstellar clouds.Comment: submitted to Ap
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