2,536 research outputs found
IRAS 23385+6053: a candidate protostellar massive object
We present the results of a multi-line and continuum study towards the source
IRAS 23385+6053,performed with the IRAM-30m telescope, the Plateau de Bure
Interferometer, the Very Large Array Interferometer and the James Clerk Maxwell
Telescope. The new results confirm our earlier findings, namely that IRAS
23385+6053 is a good candidate high-mass protostellar object, precursor of an
ultracompact H region. The source is roughly composed of two regions: a
molecular core pc in size, with a temperature of K
and an H volume density of the order of 10 cm, and an
extended halo of diameter 0.4 pc, with an average kinetic temperature of
K and H volume density of the order of 10 cm. The
core temperature is much smaller than what is typically found in molecular
cores of the same diameter surrounding massive ZAMS stars. We deduce that the
core luminosity is between 150 and , and we believe
that the upper limit is near the ``true'' source luminosity. Moreover, by
comparing the H volume density obtained at different radii from the IRAS
source, we find that the halo has a density profile of the type . This suggests that the source is gravitationally
unstable. Finally, we demonstrate that the temperature at the core surface is
consistent with a core luminosity of and conclude that we
might be observing a protostar still accreting material from its parental
cloud, whose mass at present is .Comment: 18 pages, 20 figure
Detection and characterization of a 500 ÎŒm dust emissivity excess in the Galactic plane using Herschel/Hi-GAL observations
Context. Past and recent observations have revealed unexpected variations in the far-infrared â millimeter (FIR-mm) dust emissivity in the interstellar medium. In the Herschel spectral range, those are often referred to as a 500 ÎŒm emission excess. Several dust emission models have been developed to interpret astrophysical data in the FIR-mm domain. However, these are commonly unable to fully reconcile theoretical predictions with observations. In contrast, the recently revised two level system (TLS) model, based on the disordered internal structure of amorphous dust grains, seems to provide a promising way of interpreting existing data.
Aims. The newly available Herschel infrared GALactic (Hi-GAL) data, which covers most of the inner Milky Way, offers a unique opportunity to investigate possible variations in the dust emission properties both with wavelength and environment. The goal of our analysis is to constrain the internal structure of the largest dust grains on Galactic scales, in the framework of the TLS model.
Methods. By combining the IRIS (Improved Reprocessing of the IRAS Survey) 100 ÎŒm with the Hi-GAL 160, 250, 350, and 500 ÎŒm data, we model the dust emission spectra in each pixel of the Hi-GAL maps, using both the TLS model and, for comparison, a single modified black-body fit. The effect of temperature mixing along the line of sight is investigated to test the robustness of our results.
Results. We find a slight decrease in the dust temperature with distance from the Galactic center, confirming previous results. We also report the detection of a significant 500 ÎŒm emissivity excess in the peripheral regions of the plane (35° < |l| < 70°) of about 13â15% of the emissivity, which can reach up to 20% in some HII regions. We present the spatial distributions of the best-fit values for the two main parameters of the TLS model, i.e. the charge correlation length, lc, used to characterize the disordered charge distribution (DCD) part of the model, and the amplitude A of the TLS processes with respect to the DCD effect. These distributions illustrate the variations in the dust properties with environment, in particular the plausible existence of an overall gradient with distance to the Galactic center. A comparison with previous findings in the solar neighborhood shows that the local value of the excess is less than expected from the Galactic gradient observed here
Double lenses
The analysis of the shear induced by a single cluster on the images of a
large number of background galaxies is all centered around the curl-free
character of a well-known vector field that can be derived from the data. Such
basic property breaks down when the source galaxies happen to be observed
through two clusters at different redshifts, partially aligned along the line
of sight. In this paper we address the study of double lenses and obtain five
main results. (i) First we generalize the procedure to extract the available
information, contained in the observed shear field, from the case of a single
lens to that of a double lens. (ii) Then we evaluate the possibility of
detecting the signature of double lensing given the known properties of the
distribution of clusters of galaxies. (iii) As a different astrophysical
application, we demonstrate how the method can be used to detect the presence
of a dark cluster that might happen to be partially aligned with a bright
cluster studied in terms of statistical lensing. (iv) In addition, we show that
the redshift distribution of the source galaxies, which in principle might also
contribute to break the curl-free character of the shear field, actually
produces systematic effects typically two orders of magnitude smaller than the
double lensing effects we are focusing on. (v) Remarkably, a discussion of
relevant contributions to the noise of the shear measurement has brought up an
intrinsic limitation of weak lensing analyses, since one specific contribution,
associated with the presence of a non-vanishing two-galaxy correlation
function, turns out not to decrease with the density of source galaxies (and
thus with the depth of the observations).Comment: 40 pages, 15 figures. Accepted for publication in ApJ main journa
Acceleration of hemiacetal cleavage through hydrogen bonding : a new synthetic catalyst with balanced conformational flexibility and preorganization
Hemiacetal cleavage catalyst 1 was designed, synthesized, and shown to be effective in promoting glycolaldehyde dimer dissociation and tetramethylglucose mutarotation
Two massive star-forming regions at early evolutionary stages
We report sensitive ATCA radio-continuum observations toward IRAS 15596-5301
and 16272-4837, two luminous objects (> 2x10^4 Lsun) thought to represent
massive star-forming regions in early stages of evolution (due to previously
undetected radio emission at the 1-sigma level of 2 mJy per beam). Also
reported are 1.2-millimeter continuum and a series of molecular-line
observations made with the SEST telescope. For IRAS 15596-5301, the
observations reveal the presence of three distinct compact radio-continuum
sources associated with a dense molecular core. We suggest that this core
contains a cluster of B stars which are exciting compact HII regions that are
in pressure equilibrium with the dense molecular surroundings. No radio
continuum emission was detected from IRAS 16272-4837 (3-sigma limit of 0.2
mJy). However, a dense molecular core has been detected. The high luminosity
and lack of radio emission from this massive core suggests that it hosts an
embedded young massive protostar that is still undergoing an intense accretion
phase. This scenario is supported by the observed characteristics of the line
profiles and the presence of a bipolar outflow detected from observations of
the SiO emission. We suggest that IRAS 16272-4837 is a bona fide massive star-
forming region in a very early evolutionary stage, being the precursor of an
ultra compact HII region.Comment: 25 pages, 9 figures, accepted for publication in The Astrophysical
Journa
Star Formation in the Milky Way. The Infrared View
I present a brief review of some of the most recent and active topics of star
formation process in the Milky Way using mid and far infrared observations, and
motivated by the research being carried out by our science group using data
gathered by the Spitzer and Herschel space telescopes. These topics include
bringing together the scaling relationships found in extragalactic systems with
that of the local nearby molecular clouds, the synthetic modeling of the Milky
Way and estimates of its star formation rate.Comment: 12 pages, 9 figures. To apper in "Cosmic-ray induced phenomenology in
star-forming environments: Proceedings of the 2nd Session of the Sant Cugat
Forum of Astrophysics" (April 16-19, 2012), Olaf Reimer and Diego F. Torres
(eds.
Direct Estimate of Cirrus Noise in Herschel Hi-GAL Images
In Herschel images of the Galactic plane and many star forming regions, a
major factor limiting our ability to extract faint compact sources is cirrus
confusion noise, operationally defined as the "statistical error to be expected
in photometric measurements due to confusion in a background of fluctuating
surface brightness". The histogram of the flux densities of extracted sources
shows a distinctive faint-end cutoff below which the catalog suffers from
incompleteness and the flux densities become unreliable. This empirical cutoff
should be closely related to the estimated cirrus noise and we show that this
is the case. We compute the cirrus noise directly, both on Herschel images from
which the bright sources have been removed and on simulated images of cirrus
with statistically similar fluctuations. We connect these direct estimates with
those from power spectrum analysis, which has been used extensively to predict
the cirrus noise and provides insight into how it depends on various
statistical properties and photometric operational parameters. We report
multi-wavelength power spectra of diffuse Galactic dust emission from Hi-GAL
observations at 70 to 500 microns within Galactic plane fields at l= 30 degrees
and l= 59 degrees. We find that the exponent of the power spectrum is about -3.
At 250 microns, the amplitude of the power spectrum increases roughly as the
square of the median brightness of the map and so the expected cirrus noise
scales linearly with the median brightness. Generally, the confusion noise will
be a worse problem at longer wavelengths, because of the combination of lower
angular resolution and the rising power spectrum of cirrus toward lower spatial
frequencies, but the photometric signal to noise will also depend on the
relative spectral energy distribution of the source compared to the cirrus.Comment: 4 pages (in journal), 3 figures, Astronomy and Astrophysics, accepted
for publication 13 May 201
Mapping the column density and dust temperature structure of IRDCs with Herschel
Infrared dark clouds (IRDCs) are cold and dense reservoirs of gas potentially
available to form stars. Many of these clouds are likely to be pristine
structures representing the initial conditions for star formation. The study
presented here aims to construct and analyze accurate column density and dust
temperature maps of IRDCs by using the first Herschel data from the Hi-GAL
galactic plane survey. These fundamental quantities, are essential for
understanding processes such as fragmentation in the early stages of the
formation of stars in molecular clouds. We have developed a simple
pixel-by-pixel SED fitting method, which accounts for the background emission.
By fitting a grey-body function at each position, we recover the spatial
variations in both the dust column density and temperature within the IRDCs.
This method is applied to a sample of 22 IRDCs exhibiting a range of angular
sizes and peak column densities. Our analysis shows that the dust temperature
decreases significantly within IRDCs, from background temperatures of 20-30 K
to minimum temperatures of 8-15 K within the clouds, showing that dense
molecular clouds are not isothermal. Temperature gradients have most likely an
important impact on the fragmentation of IRDCs. Local temperature minima are
strongly correlated with column density peaks, which in a few cases reach NH2 =
1 x 10^{23} cm^{-2}, identifying these clouds as candidate massive prestellar
cores. Applying this technique to the full Hi-GAL data set will provide
important constraints on the fragmentation and thermal properties of IRDCs, and
help identify hundreds of massive prestellar core candidates.Comment: Accepted for publication in A&A Herschel special issu
HST NICMOS Images of the HH 7/11 Outflow in NGC1333
We present near infrared images in H2 at 2.12um of the HH 7/11 outflow and
its driving source SVS 13 taken with HST NICMOS 2 camera, as well as archival
Ha and [SII] optical images obtained with the WFPC2 camera. The NICMOS high
angular resolution observations confirm the nature of a small scale jet arising
from SVS 13, and resolve a structure in the HH 7 working surface that could
correspond to Mach disk H2 emission. The H2 jet has a length of 430 AU (at a
distance of 350 pc), an aspect ratio of 2.2 and morphologically resembles the
well known DG Tau optical micro-jet. The kinematical age of the jet (approx. 10
yr) coincides with the time since the last outburst from SVS 13. If we
interpret the observed H2 flux density with molecular shock models of 20-30
km/s, then the jet has a density as high as 1.e+5 cc. The presence of this
small jet warns that contamination by H2 emission from an outflow in studies
searching for H2 in circumstellar disks is possible. At the working surface,
the smooth H2 morphology of the HH 7 bowshock indicates that the magnetic field
is strong, playing a major role in stabilizing this structure. The H2 flux
density of the Mach disk, when compared with that of the bowshock, suggests
that its emission is produced by molecular shocks of less than 20 km/s. The
WFPC2 optical images display several of the global features already inferred
from groundbased observations, like the filamentary structure in HH 8 and HH
10, which suggests a strong interaction of the outflow with its cavity. The H2
jet is not detected in {SII] or Ha, however, there is a small clump at approx.
5'' NE of SVS 13 that could be depicting the presence either of a different
outburst event or the north edge of the outflow cavity.Comment: 13 pages, 5 figures (JPEGs
Hepatic arterial infusion of chemotherapy for advanced hepatobiliary cancers: State of the art
Liver functional failure is one of the leading causes of cancer-related death. Primary liver tumors grow up mainly in the liver, and thus happens for liver metastases deriving from other organs having a lower burden of disease at the primary site. Systemic chemotherapy usually offers a modest benefit in terms of disease control rate, progression-free survival, and overall survival at the cost of a significant percentage of adverse events. Liver malignancies are mostly perfused by the hepatic artery while the normal liver parenchyma by the portal vein network. On these bases, the therapeutic strategy consisting of hepatic arterial infusion (HAI) of chemotherapy takes place. In literature, HAI chemotherapy was applied for the treatment of advanced hepatobiliary cancers with encouraging results. Different chemotherapeutic agents were used such as Oxaliplatin, Cisplatin, Gemcitabine, Floxuridine, 5-Fluorouracil, Epirubicin, individually or in combination. However, the efficacy of this treatment strategy remains controversial. Therefore, this review aims to summarize the current knowledge on this approach from different points of view, such as techniques, drugs pharmacology and pharmacokinetics, and clinical outcomes for advanced hepatobiliary cancers
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