1,173 research outputs found
A Submillimeter Study of the Star-Forming Region NGC7129
New molecular (13CO J=3-2) and dust continuum (450 and 850 micron) SCUBA maps
of the NGC7129 star forming region are presented, complemented by C18O J=3-2
spectra at several positions within the mapped region. The maps include the
Herbig Ae/Be star LkHalpha 234, the far-infrared source NGC 7129 FIRS2 and
several other pre-stellar sources embedded within the molecular ridge.
The SCUBA maps help us understand the nature of the pre-main sequence stars
in this actively star forming region. A deeply embedded submillimeter source,
SMM2, not clearly seen in any earlier data set, is shown to be a pre-stellar
core or possibly a protostar. The highest continuum peak emission is identified
with the deeply embedded source IRS6, a few arcseconds away from LkHalpha 234,
and also responsible for both the optical jet and the molecular outflow. The
gas and dust masses are found to be consistent, suggesting little or no CO
depletion onto grains. The dust emissivity index is lower towards the dense
compact sources, beta ~1 - 1.6, and higher, beta ~ 2.0, in the surrounding
cloud, implying small size grains in the PDR ridge, whose mantles have been
evaporated by the intense UV radiation.Comment: Accepted by Ap
A molecular line study of NGC 1333/IRAS 4
Molecular line surveys and fully sampled spectral line maps at 1.3 and 0.87 mm are used to examine the
physical and chemical characteristics of the extreme Class I sources IRAS 4A and 4B in the L1450/NGC 1333
molecular cloud complex. A very well collimated, jetlike molecular outflow emanates from IRAS 4A, with a
dynamical age of a few thousand years. Symmetric, clumpy structure along the outflow lobes suggests that
there is considerable variability in the mass-loss rate or wind velocity even at this young age. Molecular emission
lines toward IRAS 4A and 4B are observed to be weak in the velocity range corresponding to quiescent
material surrounding the young stellar objects (YSOs). Depletion factors of 10-20 are observed for αll molecules,
including CO, even for very conservative mass estimates from the measured millimeter and submillimeter
dust continuum. However, abundances scaled with respect to CO are similar to other dark
molecular cloud cores. Such depletions could be mimicked by high dust optical depths or increased grain
emissivities at the observing frequencies of 230 and 345 GHz, but the millimeter and submillimeter spectral
energy distributions suggest that this is unlikely over the single-dish size scales of 5000-10,000 AU.
Dense, outflowing gas is found to be kinematically, but not spatially, distinct from the quiescent material on
these size scales. If CO is used as a chemical standard for the high-velocity gas, we find substantial enhancements
in the abundances of several molecules in outflowing material, most notably CS, SiO, and CH_30H. The
SiO emission is kinematically well displaced from the bulk cloud velocity and likely arises from directly
shocked material. As is the case for CO, however, the outflow features from more volatile species are centered
near the cloud velocity and are often characterized by quite low rotational temperatures. We suggest that
grain-grain collisions induced by velocity shear zones surrounding the outflow axes transiently desorb the
grain mantles, resulting in large abundance enhancements of selected species. Similar results have recently
been obtained in several other low-mass YSOs, where the outflowing gas is often both kinematically and spatially
distinct, and are illustrative of the ability of accretion and outflow processes to simultaneously modify
the composition of the gas and dust surrounding young stars
CH radio emission from heiles cloud 2 as a tracer of molecular cloud evolution
A mapping observation of the -type doubling transition (3.3
GHz) of CH has been conducted toward Heiles Cloud 2 (HCL2) in the Taurus
molecular cloud complex to reveal its molecular cloud-scale distribution. The
observations were carried out with the Effelsberg 100 m telescope. The CH
emission is found to be extended over the whole region of HCL2. It is brighter
in the southeastern part, which encloses the TMC-1 cyanopolyyne peak than in
the northwestern part. Its distribution extends continuously from the peak of
the neutral carbon emission (CI peak) to the TMC-1 ridge, as if it were
connecting the distributions of the [C I] and CO emissions. Since CH is
an intermediate in gas-phase chemical reactions from C to CO, its emission
should trace the transition region. The above distribution of the CH emission
is consistent with this chemical behavior. Since the CH abundance is subject to
the chemical evolutionary effect, the CH column density in HCL2 no longer
follows a linear correlation wit the H column density reported for diffuse
and translucent clouds. More importantly, the CH line profile is found to be
composed of the narrow and broad components. Although the broad component is
dominant around the CI peak, the narrow component appears in the TMC-1 ridge
and dense core regions such as L1527 and TMC-1A. This trend seems to reflect a
narrowing of the line width during the formation of dense cores. These results
suggest that the 3.3 GHz CH line is a useful tool for tracing the chemical and
physical evolution of molecular clouds.Comment: 8 page
High Spatial Resolution Observations of Two Young Protostars in the R Corona Australis Region
We present multi-wavelength, high spatial resolution imaging of the IRS 7
region in the R Corona Australis molecular cloud. Our observations include 1.1
mm continuum and HCO^+ J = images from the SMA, ^{12}CO J =
outflow maps from the DesertStar heterodyne array receiver on the HHT, 450
m and 850 m continuum images from SCUBA, and archival Spitzer IRAC
and MIPS 24 \micron images. The accurate astrometry of the IRAC images allow us
to identify IRS 7 with the cm source VLA 10W (IRS 7A) and the X-ray source X_W.
The SMA 1.1 mm image reveals two compact continuum sources which are also
distinguishable at 450 m. SMA 1 coincides with X-ray source CXOU
J190156.4-365728 and VLA cm source 10E (IRS 7B) and is seen in the IRAC and
MIPS images. SMA 2 has no infrared counterpart but coincides with cm source VLA
9. Spectral energy distributions constructed from SMA, SCUBA and Spitzer data
yield bolometric temperatures of 83 K for SMA 1 and 70 K for SMA 2. These
temperatures along with the submillimeter to total luminosity ratios indicate
that SMA 2 is a Class 0 protostar, while SMA 1 is a Class 0/Class I
transitional object (L= \Lsun). The ^{12}CO J = outflow map
shows one major and possibly several smaller outflows centered on the IRS 7
region, with masses and energetics consistent with previous work. We identify
the Class 0 source SMA 2/VLA 9 as the main driver of this outflow. The complex
and clumpy spatial and velocity distribution of the HCO^+ J =
emission is not consistent with either bulk rotation, or any known molecular
outflow activity.Comment: 31 pages, 8 figures, Accepted to Ap
Towards the automated reduction and calibration of SCUBA data from the James Clerk Maxwell Telescope
The Submillimetre Common User Bolometer Array (SCUBA) instrument has been
operating on the James Clerk Maxwell Telescope (JCMT) since 1997. The data
archive is now sufficiently large that it can be used to investigate
instrumental properties and the variability of astronomical sources. This paper
describes the automated calibration and reduction scheme used to process the
archive data with particular emphasis on `jiggle-map' observations of compact
sources. We demonstrate the validity of our automated approach at both 850- and
450-microns and apply it to several of the JCMT secondary flux calibrators. We
determine light curves for the variable sources IRC+10216 and OH231.8. This
automation is made possible by using the ORAC-DR data reduction pipeline, a
flexible and extensible data reduction pipeline that is used on UKIRT and the
JCMT.Comment: 9 pages, 8 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
A Massive Protostar Forming by Ordered Collapse of a Dense, Massive Core
We present 30 and 40 micron imaging of the massive protostar G35.20-0.74 with
SOFIA-FORCAST. The high surface density of the natal core around the protostar
leads to high extinction, even at these relatively long wavelengths, causing
the observed flux to be dominated by that emerging from the near-facing outflow
cavity. However, emission from the far-facing cavity is still clearly detected.
We combine these results with fluxes from the near-infrared to mm to construct
a spectral energy distribution (SED). For isotropic emission the bolometric
luminosity would be 3.3x10^4 Lsun. We perform radiative transfer modeling of a
protostar forming by ordered, symmetric collapse from a massive core bounded by
a clump with high mass surface density, Sigma_cl. To fit the SED requires
protostellar masses ~20-34 Msun depending on the outflow cavity opening angle
(35 - 50 degrees), and Sigma_cl ~ 0.4-1 g cm-2. After accounting for the
foreground extinction and the flashlight effect, the true bolometric luminosity
is ~ (0.7-2.2)x10^5 Lsun. One of these models also has excellent agreement with
the observed intensity profiles along the outflow axis at 10, 18, 31 and 37
microns. Overall our results support a model of massive star formation
involving the relatively ordered, symmetric collapse of a massive, dense core
and the launching bipolar outflows that clear low density cavities. Thus a
unified model may apply for the formation of both low and high mass stars.Comment: 6 pages, 4 figures, 1 table, accepted to Ap
Wide-Field Infrared Imaging Polarimetry of the NGC 6334 Region: A Nest of Infrared Reflection Nebulae
We report the detection of eighteen infrared reflection nebulae (IRNe) in the
, , & linear polarimetric observations of the NGC 6334 massive
star-formation complex, of which 16 IRNe are new discoveries. Our images cover
180 square arcminutes, one of the widest near-infrared polarization data
in star-formation regions so far. These IRNe are most likely associated with
embedded young OB stars at different evolutionary phases, showing a variety of
sizes, morphologies, and polarization properties, which can be divided into
four categories. We argue the different nebula characteristics to be a possible
evolutionary sequence of circumstellar structures around young massive stars.Comment: 4 pages, 1 figur
Massive Clumps in the NGC 6334 Star Forming Region
We report observations of dust continuum emission at 1.2 mm toward the star
forming region NGC 6334 made with the SEST SIMBA bolometer array. The
observations cover an area of square degrees with approximately
uniform noise. We detected 181 clumps spanning almost three orders of magnitude
in mass (3\Msun \Msun) and with sizes in the range 0.1--1.0 pc.
We find that the clump mass function is well fit with a power law
of the mass with exponent -0.6 (or equivalently ). The
derived exponent is similar to those obtained from molecular line emission
surveys and is significantly different from that of the stellar initial mass
function. We investigated changes in the mass spectrum by changing the
assumptions on the temperature distribution of the clumps and on the
contribution of free-free emission to the 1.2 mm emission, and found little
changes on the exponent. The Cumulative Mass Distribution Function is also
analyzed giving consistent results in a mass range excluding the high-mass end
where a power-law fit is no longer valid. The masses and sizes of the clumps
observed in NGC 6334 indicate that they are not direct progenitors of stars and
that the process of fragmentation determines the distribution of masses later
on or occurs at smaller spatial scales. The spatial distribution of the clumps
in NGC 6334 reveals clustering which is strikingly similar to that exhibited by
young stars in other star forming regions. A power law fit to the surface
density of companions gives .Comment: 16 pages, 11 figures, 4 tables. To appear in the Astrophysical
Journa
Gene therapy for articular cartilage repair
Articular cartilage serves as the gliding surface of joints. It is susceptible to damage from trauma and from degenerative diseases. Restoration of damaged articular cartilage may be achievable through the use of cell-regulatory molecules that augment the reparative activities of the cells, inhibit the cells\u27; degradative activities, or both. A variety of such molecules have been identified. These include insulin-like growth factor I, fibroblast growth factor 2, bone morphogenetic proteins 2, 4, and 7, and interleukin-1 receptor antagonist. It is now possible to transfer the genes encoding such molecules into articular cartilage and synovial lining cells. Although preliminary, data from in-vitro and in-vivo studies suggest that gene therapy can deliver such potentially therapeutic agents to protect existing cartilage and to build new cartilage.
Keywords: gene therapy, vectors, articular cartilage, arthritis, animal model
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