3,372 research outputs found
SiO collimated outflows driven by high-mass YSOs in G24.78+0.08
We imaged the molecular outflows towards the cluster of high-mass young
stellar objects G24.78+0.08 at high-angular resolution using SiO emission,
which is considered the classical tracer of protostellar jets. We performed SiO
observations with the VLA interferometer in the J = 1-0 v=0 transition and with
the SMA array in the 5-4 transition. A complementary IRAM 30-m single-dish
survey in the (2-1), (3-2), (5-4), and (6-5) SiO lines was also carried out.
Two collimated SiO high-velocity outflows driven by the A2 and C millimeter
continuum massive cores have been imaged. On the other hand, we detected no SiO
outflow driven by the young stellar objects in more evolved evolutionary phases
that are associated with ultracompact (B) or hypercompact (A1) HII regions. The
LVG analysis reveals high-density gas (10^3-10^4 cm-3), with well constrained
SiO column densities (0.5-1 10^15 cm-2). The driving source of the A2 outflow
is associated with typical hot core tracers such as methyl formate, vinyl
cyanide, cyanoacetilene, and acetone. The driving source of the main SiO
outflow in G24 has an estimated luminosity of a few 10^4 Lsun (typical of a
late O-type star) and is embedded in the 1.3 mm continuum core A2, which in
turn is located at the centre of a hot core that rotates on a plane
perpendicular to the outflow main axis. The present SiO images support a
scenario similar to the low-mass case for massive star formation, where jets
that are clearly traced by SiO emission, create outflows of swept-up ambient
gas usually traced by CO.Comment: Astronomy & Astrophysics, in pres
Italian Science Case for ALMA Band 2+3
The Premiale Project "Science and Technology in Italy for the upgraded ALMA
Observatory - iALMA" has the goal of strengthening the scientific,
technological and industrial Italian contribution to the Atacama Large
Millimeter/submillimeter Array (ALMA), the largest ground based international
infrastructure for the study of the Universe in the microwave. One of the main
objectives of the Science Working Group (SWG) inside iALMA, the Work Package 1,
is to develop the Italian contribution to the Science Case for the ALMA Band 2
or Band 2+3 receiver. ALMA Band 2 receiver spans from ~67 GHz (bounded by an
opaque line complex of ozone lines) up to 90 GHz which overlaps with the lower
frequency end of ALMA Band 3. Receiver technology has advanced since the
original definition of the ALMA frequency bands. It is now feasible to produce
a single receiver which could cover the whole frequency range from 67 GHz to
116 GHz, encompassing Band 2 and Band 3 in a single receiver cartridge, a so
called Band 2+3 system. In addition, upgrades of the ALMA system are now
foreseen that should double the bandwidth to 16 GHz. The science drivers
discussed below therefore also discuss the advantages of these two enhancements
over the originally foreseen Band 2 system.Comment: 43 pages, 21 figure
Near infrared and optical morphology of the dusty galaxy NGC972
Near infrared (NIR) and optical surface photometric analyses of the dusty
galaxy NGC972 are presented. The photometric profiles in the BVRJHK bands can
be fitted with a combination of gaussian and exponential profiles,
corresponding to a starburst nucleus and a stellar disk respectively. The
exponential scale length in the B-band is 2.8 times larger than in the K-band,
which implies a central B-band optical depth as high as 11. A bulge is absent
even in the NIR bands and hence the galaxy must be of a morphological type
later than the usually adopted Sb type. Relatively low rotational velocity and
high gas content also favor a later type, probably Sd, for the galaxy. Only one
arm can be traced in the distribution of old stars; the second arm, however,
can be traced in the distribution of dust and HII regions. Data suggest a short
NIR bar, which ends inside the nuclear ring. The slowly rising nature of the
rotation curve rules out a resonance origin of the the nuclear ring. The ring
is most likely not in the plane of the galaxy, given its circular appearance in
spite of the moderately high inclination of the galaxy. The off-planar nature
of the star forming ring, the unusually high fraction (30%) of the total mass
in molecular form, the presence of a nuclear starburst and the asymmetry of
spiral arms, are probably the result of a merger with a gas-rich companion
galaxy.Comment: Uses aas2pp4.sty and epsfig.sty, 12 pages To appear in Astronomical
Journal, October 199
Protostellar Outflows at the EarliesT Stages (POETS). II. A possible radio synchrotron jet associated with the EGO G035.02+0.35
Centimeter continuum observations of protostellar jets have revealed the
presence of knots of shocked gas where the flux density decreases with
frequency. This spectrum is characteristic of nonthermal synchrotron radiation
and implies the presence of both magnetic fields and relativistic electrons in
protostellar jets. Here, we report on one of the few detections of nonthermal
jet driven by a young massive star in the star-forming region G035.020.35.
We made use of the NSF's Karl G. Jansky Very Large Array (VLA) to observe this
region at C, Ku, and K bands with the A- and B-array configurations, and
obtained sensitive radio continuum maps down to a rms of 10 Jy
beam. These observations allow for a detailed spectral index analysis of
the radio continuum emission in the region, which we interpret as a
protostellar jet with a number of knots aligned with extended 4.5 m
emission. Two knots clearly emit nonthermal radiation and are found at similar
distances, of approximately 10,000 au, each side of the central young star,
from which they expand at velocities of hundreds km s. We estimate both
the mechanical force and the magnetic field associated with the radio jet, and
infer a lower limit of M yr km s and
values in the range mG, respectively.Comment: 10 pages, 4 figures, 5 tables, accepted by Astronomy & Astrophysic
Neurological signs and MRI findings in 12 dogs with multiple myeloma
Vertebral lesions and associated neurological signs occur in dogs with multiple myeloma, however, veterinary literature describing MRI findings is currently lacking. The objective of this multicenter, retrospective, case series study was to describe neurological signs and MRI findings in a group of dogs that presented for spinal pain or other neurological deficits and had multiple myeloma. Electronic records of four veterinary referral hospitals were reviewed. Dogs were included if they had a pathologically confirmed diagnosis of multiple myeloma, had presented for spinal pain or other neurological signs, and had undergone MRI of the vertebral column. The MRI studies were evaluated and the anatomical location of lesion(s), signal intensity, presence of extraâdural material, degree of spinal cord compression, extent of vertebral lesions, and contrast enhancement were recorded. Twelve dogs met inclusion criteria. Most dogs (n = 8) had a chronic progressive history, with varying degrees of proprioceptive ataxia and paresis (n = 11), and spinal pain was a feature in all dogs. The MRI findings were variable but more consistent features included the presence of multiple expansile vertebral lesions without extension beyond the outer cortical limits of affected vertebrae, and associated extradural material causing spinal cord compression. The majority of lesions were hyperâ to isointense on T2 (n = 12) and T1âweighted (n = 8) sequences, with variable but homogeneous contrastâenhancement (n = 12). These described MRI characteristics of multiple myeloma may be used to aid early identification and guide subsequent confirmatory diagnostic steps, to ultimately improve therapeutic approach and longâterm outcome
Bandwidth and dynamic range of a widely tunable Josephson parametric amplifier
The ability to manipulate quantum information encoded in microwave fields has
led to a renewed interest in Josephson parametric amplifiers (JPAs). For these
applications the ability of JPAs to amplify signals with the least amount of
added noise is critical. Unfortunately JPAs are typically narrow band
amplifiers with small dynamic range. It is therefore important to understand
the bandwidth and dynamic range of any particular JPA in order to determine if
it is appropriate for these applications. We recently introduced a new kind of
JPA. Although it is still narrow band, the amplified band can be tuned over a
full octave. We have shown that it has good noise performance and can squeeze
the vacuum noise by 10 dB. Here we characterize other important parameters of
this amplifier, specifically the signal-bandwidth, dynamic range and saturation
power.Comment: Accepted for publication in IEEE Transactions on Applied
Superconductivity; Special Issue from the Applied Superconductivity
Conferenc
Candidate Rotating Toroids around High-Mass (Proto)Stars
Using the OVRO, Nobeyama, and IRAM mm-arrays, we searched for
``disk''-outflow systems in three high-mass (proto)star forming regions:
G16.59-0.05, G23.01-0.41, and G28.87+0.07. These were selected from a sample of
NH3 cores associated with OH and H2O maser emission and with no or very faint
continuum emission. Our imaging of molecular line (including rotational
transitions of CH3CN and 3mm dust continuum emission revealed that these are
compact, massive, and hot molecular cores (HMCs), that is likely sites of
high-mass star formation prior to the appearance of UCHII regions. All three
sources turn out to be associated with molecular outflows from CO and/or HCO+
J=1--0 line imaging. In addition, velocity gradients of 10 -- 100 km/s per pc
in the innermost densest regions of the G23.01 and G28.87 HMCs are identified
along directions roughly perpendicular to the axes of the corresponding
outflows. All the results suggest that these cores might be rotating about the
outflow axis, although the contribution of rotation to gravitational
equilibrium of the HMCs appears to be negligible. Our analysis indicates that
the 3 HMCs are close to virial equilibrium due to turbulent pressure support.
Comparison with other similar objects where rotating toroids have been
identified so far shows that in our case rotation appears to be much less
prominent; this can be explained by the combined effect of unfavorable
projection, large distance, and limited angular resolution with the current
interferometers.Comment: Accepted by ApJ main journal, the paper with the original quality
figures are available from
http://subarutelescope.org/staff/rsf/publication.htm
Strongly quadrature-dependent noise in superconducting micro-resonators measured at the vacuum-noise limit
We measure frequency- and dissipation-quadrature noise in superconducting
lithographed microwave resonators with sensitivity near the vacuum noise level
using a Josephson parametric amplifier. At an excitation power of 100~nW, these
resonators show significant frequency noise caused by two-level systems. No
excess dissipation-quadrature noise (above the vacuum noise) is observed to our
measurement sensitivity. These measurements demonstrate that the excess
dissipation-quadrature noise is negligible compared to vacuum fluctuations, at
typical readout powers used in micro-resonator applications. Our results have
important implications for resonant readout of various devices such as
detectors, qubits and nano-mechanical oscillators.Comment: 13 pages, 4 figure
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