308 research outputs found
Extremely red compact radio sources - The empty field objects
10 μm radiation .has been detected from 1413 + 135, one of the very red objects discovered by Rieke, Lebofsky, and Kinman at near-infrared wavelengths. The spectrum of this object flattens at wavelengths longer than 2.2 μm. Upper limits are also given for the 10 μm emission from 2255 + 14, 0026 + 34, and 0406+ 121. Photometry between 1.25 and 2.2 μm confirms the variability of 1413+135 2255+41, and 0406+121. Five percent resolution spectra of 1413+135 and 0406+ 121 between 1.5 and 2.4 μm. show no emission or absorption lines. The spectral data rule out the possibility that 1413+135 is a quasar with normal line strengths and a redshift 1.3 > z > 4. The lack of features of the 1.5-2.4 μm spectra, the rapid variability, and the overall shape of the radio, infrared, and X-ray energy distributtions are consistent with a BL Lac nature for these objects
Deuterated Ammonia in Galactic Protostellar Cores
We report on a survey of \nh2d towards protostellar cores in low-mass star
formation and quiescent regions in the Galaxy. Twenty-three out of thirty-two
observed sources have significant (\gsim 5\sigma) \nh2d emission.
Ion-molecule chemistry, which preferentially enhances deuterium in molecules
above its cosmological value of \scnot{1.6}{-5} sufficiently explains these
abundances. NH2D/NH3 ratios towards Class 0 sources yields information about
the ``fossil remnants'' from the era prior to the onset of core collapse and
star formation. We compare our observations with predictions of gas-phase
chemical networks.Comment: 16 Pages, 7 Figures, Accepted to Ap.J., to appear in the June 20,
2001 editio
On the Sunyaev-Zel'dovich effect from dark matter annihilation or decay in galaxy clusters
We revisit the prospects for detecting the Sunyaev Zel'dovich (SZ) effect
induced by dark matter (DM) annihilation or decay. We show that with standard
(or even extreme) assumptions for DM properties, the optical depth associated
with relativistic electrons injected from DM annihilation or decay is much
smaller than that associated with thermal electrons, when averaged over the
angular resolution of current and future experiments. For example, we find:
(depending on the assumptions) for \mchi
= 1 GeV and a density profile for a template cluster
located at 50 Mpc and observed within an angular resolution of , compared
to . This, together with a full spectral
analysis, enables us to demonstrate that, for a template cluster with generic
properties, the SZ effect due to DM annihilation or decay is far below the
sensitivity of the Planck satellite. This is at variance with previous claims
regarding heavier annihilating DM particles. Should DM be made of lighter
particles, the current constraints from 511 keV observations on the
annihilation cross section or decay rate still prevent a detectable SZ effect.
Finally, we show that spatial diffusion sets a core of a few kpc in the
electron distribution, even for very cuspy DM profiles, such that improving the
angular resolution of the instrument, e.g. with ALMA, does not necessarily
improve the detection potential. We provide useful analytical formulae
parameterized in terms of the DM mass, decay rate or annihilation cross section
and DM halo features, that allow quick estimates of the SZ effect induced by
any given candidate and any DM halo profile.Comment: 27 p, 6 figs, additional section on spatial diffusion effects.
Accepted for publication in JCA
Observations of gas flows inside a protoplanetary gap
Gaseous giant planet formation is thought to occur in the first few million
years following stellar birth. Models predict that giant planet formation
carves a deep gap in the dust component (shallower in the gas). Infrared
observations of the disk around the young star HD142527, at ~140pc, found an
inner disk ~10AU in radius, surrounded by a particularly large gap, with a
disrupted outer disk beyond 140AU, indicative of a perturbing planetary-mass
body at ~90 AU. From radio observations, the bulk mass is molecular and lies in
the outer disk, whose continuum emission has a horseshoe morphology. The
vigorous stellar accretion rate would deplete the inner disk in less than a
year, so in order to sustain the observed accretion, matter must flow from the
outer-disk into the cavity and cross the gap. In dynamical models, the putative
protoplanets channel outer-disk material into gap-crossing bridges that feed
stellar accretion through the inner disk. Here we report observations with the
Atacama Large Millimetre Array (ALMA) that reveal diffuse CO gas inside the
gap, with denser HCO+ gas along gap-crossing filaments, and that confirm the
horseshoe morphology of the outer disk. The estimated flow rate of the gas is
in the range 7E-9 to 2E-7 Msun/yr, which is sufficient to maintain accretion
onto the star at the present rate
CO J=1-0 observations of molecular gas interacting with galactic supernova remnants G5.4-1.2, G5.55+0.32 and G5.71-0.08
The field just West of the galactic supernova remnant W28
(l=6.4\degr, b=-0.2\degr) harbors 3 of 5 newly-discovered 1720 OH maser spots
and two recently-discovered candidate supernova candidates (one of which is a
-ray source), as well as several compact and classical HII regions.
Here, we analyze a datacube of CO J=1-0 emission having 1\arcmin and 1 \kms
resolution, made with on-the-fly mapping over the region 5\degr \le l \le
6\degr, -1\degr \le b \le 0.5\degr}. {Extended and often very bright CO
emission was detected at the velocities of the 1720 MHz OH masers and around
the supernova remnant G5.55+0.32 which lacks a maser. A new bipolar outflow
which is marginally resolved at 1\arcmin resolution and strong in CO (12K) was
detected at the periphery of G5.55+0.32, coincident with an MSX source; there
is also a bright rim of CO just beyond the periphery of the radio remnant. The
OH maser near G5.71-0.08 lies on a shell of strongly-emitting molecular gas (up
to 20K) . At the -21 \kms velocity of G5.4-1.2, CO covers much of the field but
is weak (3 K) and undisturbed near the remnant. The extended molecular gas
around the compact H II region and outflow in G5.89-0.39 (W28A2) is shown for
the first time.}Comment: 6 Pages, 3 figures submitted to A&A 4 May 200
Diagnostic accuracy of the T-MACS decision aid with a contemporary point-of-care troponin assay.
OBJECTIVES: The rapid turnaround time of point-of-care (POC) cardiac troponin (cTn) assays is highly attractive for crowded emergency departments (EDs). We evaluated the diagnostic accuracy of the Troponin-only Manchester Acute Coronary Syndromes (T-MACS) decision aid with a POC cTn assay. METHODS: In a prospective diagnostic accuracy study at eight EDs, we included patients with suspected acute coronary syndromes (ACS). Blood drawn on arrival and 3 hours later was analysed for POC cTnI (i-Stat, Abbott Point of Care). The primary outcome was a diagnosis of ACS, which included both an adjudicated diagnosis of acute myocardial infarction (AMI) based on serial laboratory cTn testing and major adverse cardiac events (death, AMI or coronary revascularisation) within 30 days. RESULTS: Of 716 patients included, 105 (14.7%) had ACS. Using serial POC cTnI concentrations over 3 hours could have 'ruled out' ACS in 198 (31.2%) patients with a sensitivity of 99.0% (95% CI 94.4% to 100.0%) and negative predictive value 99.5% (95% CI 96.5% to 99.9%). No AMIs were missed. T-MACS 'ruled in' ACS for 65 (10.4%) patients with a positive predictive value of 91.2% (95% CI 82.1% to 95.9%) and specificity 98.9% (97.6% to 99.6%). CONCLUSION: With a POC cTnI assay, T-MACS could 'rule out' ACS for approximately one-third of patients within 3 hours while 'ruling in' ACS for another 10%. The rapid turnaround time and portability of the POC assay make this an attractive pathway for use in crowded EDs or urgent care centres. Future work should also evaluate use in the prehospital environment
VLA Observations of H2O Masers in the Class 0 Protostar S106 FIR: Evidence for a 10 AU-Scale Accelerating Jet-like Flow
We conducted VLA observations at 0".06 resolution of the 22 GHz water masers
toward the Class 0 source S106 FIR (d=600 pc; 15" west of S106-IRS4) on two
epochs separated by ~3 months. Two compact clusters of the maser spots were
found in the center of the submillimeter core of S106 FIR. The separation of
the clusters was ~80 mas (48 AU) along P. A. = 70 degrees and the size of each
cluster was ~20 mas x 10 mas. The western cluster, which had three maser
components, was 7.0 km/s redshifted with respect to the ambient cloud velocity.
Each component was composed of a few spatially localized maser spots and was
aligned on a line connecting the clusters. We found relative proper motions of
the components with ~30 mas/yr (18 AU/yr) along the line. In addition, a series
of single-dish observations show that the maser components drifted with a
radial acceleration of ~1 km/s/yr.
These facts indicate that the masers could be excited by a 10 AU-scale
jet-like accelerating flow ejected from an assumed protostar located between
the two clusters. The outflow size traced by the masers was 50 AU x 5 AU after
correction for an inclination angle of 10 degrees which was derived from the
relative proper motions and radial velocities of the maser components. The
three-dimensional outflow velocity ranged from 40 to 70 km/s assuming symmetric
motions for the blue and red components. Since no distinct CO molecular
outflows have been detected so far, we suggest that S106 FIR is an extremely
young protostar observed just after the onset of outflowing activity.Comment: 24 pages, 6 figures, No. 5 color. Accepted, Astrophysical Journa
Probing MHD Shocks with high-J CO observations: W28F
Context. Observing supernova remnants (SNRs) and modelling the shocks they
are associated with is the best way to quantify the energy SNRs re-distribute
back into the Interstellar Medium (ISM). Aims. We present comparisons of shock
models with CO observations in the F knot of the W28 supernova remnant. These
comparisons constitute a valuable tool to constrain both the shock
characteristics and pre-shock conditions. Methods. New CO observations from the
shocked regions with the APEX and SOFIA telescopes are presented and combined.
The integrated intensities are compared to the outputs of a grid of models,
which were combined from an MHD shock code that calculates the dynamical and
chemical structure of these regions, and a radiative transfer module based on
the 'large velocity gradient' (LVG) approximation. Results. We base our
modelling method on the higher J CO transitions, which unambiguously trace the
passage of a shock wave. We provide fits for the blue- and red-lobe components
of the observed shocks. We find that only stationary, C-type shock models can
reproduce the observed levels of CO emission. Our best models are found for a
pre-shock density of 104 cm-3, with the magnetic field strength varying between
45 and 100 {\mu}G, and a higher shock velocity for the so-called blue shock
(\sim25 km s-1) than for the red one (\sim20 km s-1). Our models also
satisfactorily account for the pure rotational H2 emission that is observed
with Spitzer.Comment: 8 pages, 6 figures, 1 table, accepted for A&A SOFIA/GREAT Special
Issu
The magnetic field of IRAS 16293-2422 as traced by shock-induced H2O masers
Shock-induced H2O masers are important magnetic field tracers at very high
density gas. Water masers are found in both high- and low-mass star-forming
regions, acting as a powerful tool to compare magnetic field morphologies in
both mass regimes. In this paper, we show one of the first magnetic field
determinations in the low-mass protostellar core IRAS 16293-2422 at volume
densities as high as 10^(8-10) cm^-3. Our goal is to discern if the collapsing
regime of this source is controlled by magnetic fields or other factors like
turbulence. We used the Very Large Array (VLA) to carry out
spectro-polarimetric observations in the 22 GHz Zeeman emission of H2O masers.
From the Stokes V line profile, we can estimate the magnetic field strength in
the dense regions around the protostar. A blend of at least three maser
features can be inferred from our relatively high spatial resolution data set
(~ 0.1"), which is reproduced in a clear non-Gaussian line profile. The
emission is very stable in polarization fraction and position angle across the
channels. The maser spots are aligned with some components of the complex
outflow configuration of IRAS 16293-2422, and they are excited in zones of
compressed gas produced by shocks. The post-shock particle density is in the
range of 1-3 x 10^9 cm^-3, consistent with typical water masers pumping
densities. Zeeman emission is produced by a very strong line-of-sight magnetic
field (B ~ 113 mG). The magnetic field pressure derived from our data is
comparable to the ram pressure of the outflow dynamics. This indicates that the
magnetic field is energetically important in the dynamical evolution of IRAS
16293-2422.Comment: 7 pages, 6 figures, accepted for publication in A&
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