4,767 research outputs found
<i>Herschel</i> observations of B1-bS and B1-bN: two first hydrostatic core candidates in the Perseus star-forming cloud
We report far-infrared Herschel observations obtained between 70 μm and 500 μm of two star-forming dusty condensations, [HKM99] B1-bS and [HKM99] B1-bN, in the B1 region of the Perseus star-forming cloud. In the western part of the Perseus cloud, B1-bS is the only source detected in all six PACS and SPIRE photometric bands, but it is not visible in the Spitzer map at 24 μm. B1-bN is clearly detected between 100 μm and 250 μm. We have fitted the spectral energy distributions of these sources to derive their physical properties, and find that a simple greybody model fails to reproduce the observed spectral energy distributions. At least a two-component model is required, consisting of a central source surrounded by a dusty envelope. The properties derived from the fit, however, suggest that the central source is not a Class 0 object. We then conclude that while B1-bS and B1-bN appear to be more evolved than a pre-stellar core, the best-fit models suggest that their central objects are younger than a Class 0 source. Hence, they may be good candidates to be examples of the first hydrostatic core phase. The projected distance between B1-bS and B1-bN is a few Jeans lengths. If their physical separation is close to this value, this pair would allow studying the mutual interactions between two forming stars at a very early stage of their evolution
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
Strangeness Report
The paper provides a short report on strangeness production in
ultrarelativistic nucleus-nucleus collision, with the main stress on strange
particle abundances.Comment: Proceedings of Quark Matter 200
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.
Characterizing the structure of diffuse emission in Hi-GAL maps
We present a study of the structure of the Galactic interstellar medium
through the Delta-variance technique, related to the power spectrum and the
fractal properties of infrared/sub-mm maps. Through this method, it is possible
to provide quantitative parameters which are useful to characterize different
morphological and physical conditions, and to better constrain the theoretical
models. In this respect, the Herschel Infrared Galactic Plane Survey carried
out at five photometric bands from 70 to 500 \mu m constitutes an unique
database for applying statistical tools to a variety of regions across the
Milky Way. In this paper, we derive a robust estimate of the power-law portion
of the power spectrum of four contiguous 2{\deg}x2{\deg} Hi-GAL tiles located
in the third Galactic quadrant (217{\deg} < l < 225{\deg}, -2{\deg} < b <
0{\deg}). The low level of confusion along the line of sight testified by CO
observations makes this region an ideal case. We find very different values of
the power spectrum slope from tile to tile but also from wavelength to
wavelength (2 < \beta < 3), with similarities between fields attributable to
components located at the same distance. Thanks to the comparison with models
of turbulence, an explanation of the determined slopes in terms of the fractal
geometry is also provided, and possible relations with the underlying physics
are investigated. In particular, an anti-correlation between ISM fractal
dimension and star formation efficiency is found for the two main distance
components observed in these fields. A possible link between the fractal
properties of the diffuse emission and the resulting clump mass function is
discussed.Comment: Accepted by Ap
A new Perspective on the Scalar meson Puzzle, from Spontaneous Chiral Symmetry Breaking Beyond BCS
We introduce coupled channels of Bethe-Salpeter mesons both in the boundstate
equation for mesons and in the mass gap equation for chiral symmetry.
Consistency is insured by the Ward Identities for axial currents, which
preserve the Goldstone boson nature of the pion and prevents a systematic shift
of the hadron spectrum. We study the decay of a scalar meson coupled to a pair
of pseudoscalars. We also show that coupled channels reduce the breaking of
chiral symmetry, with the same Feynman diagrams that appear in the coupling of
a scalar meson to a pair of pseudoscalar mesons. Exact calculations are
performed in a particular confining quark model, where we find that the
groundstate meson is the f_0(980) with a partial decay
width of 40MeV. We also find a 30% reduction of the chiral condensate due to
coupled channels.Comment: 17 pages, Revtex, 8 eps figures, and several eps diagrams in
equation
Serum and cerebrospinal fluid biomarkers in neuromyelitis optica spectrum disorder and myelin oligodendrocyte glycoprotein associated disease
The term neuromyelitis optica spectrum disorder (NMOSD) describes a group of clinical-MRI syndromes characterized by longitudinally extensive transverse myelitis, optic neuritis, brainstem dysfunction and/or, less commonly, encephalopathy. About 80% of patients harbor antibodies directed against the water channel aquaporin-4 (AQP4-IgG), expressed on astrocytes, which was found to be both a biomarker and a pathogenic cause of NMOSD. More recently, antibodies against myelin oligodendrocyte glycoprotein (MOG-IgG), have been found to be a biomarker of a different entity, termed MOG antibody-associated disease (MOGAD), which has overlapping, but different pathogenesis, clinical features, treatment response, and prognosis when compared to AQP4-IgG-positive NMOSD. Despite important refinements in the accuracy of AQP4-IgG and MOG-IgG testing assays, a small proportion of patients with NMOSD still remain negative for both antibodies and are called "seronegative" NMOSD. Whilst major advances have been made in the diagnosis and treatment of these conditions, biomarkers that could help predict the risk of relapses, disease activity, and prognosis are still lacking. In this context, a number of serum and/or cerebrospinal fluid biomarkers are emerging as potentially useful in clinical practice for diagnostic and treatment purposes. These include antibody titers, cytokine profiles, complement factors, and markers of neuronal (e.g., neurofilament light chain) or astroglial (e.g., glial fibrillary acidic protein) damage. The aim of this review is to summarize current evidence regarding the role of emerging diagnostic and prognostic biomarkers in patients with NMOSD and MOGAD
The Herschel view of the on-going star formation in the Vela-C molecular cloud
As part of the Herschel guaranteed time key program 'HOBYS', we present the
photometric survey of the star forming region Vela-C, one of the nearest sites
of low-to-high-mass star formation in the Galactic plane. Vela-C has been
observed with PACS and SPIRE in parallel mode between 70 um and 500 um over an
area of about 3 square degrees. A photometric catalogue has been extracted from
the detections in each band, using a threshold of 5 sigma over the local
background. Out of this catalogue we have selected a robust sub-sample of 268
sources, of which 75% are cloud clumps and 25% are cores. Their Spectral Energy
Distributions (SEDs) have been fitted with a modified black body function. We
classify 48 sources as protostellar and 218 as starless. For two further
sources, we do not provide a secure classification, but suggest they are Class
0 protostars.
From SED fitting we have derived key physical parameters. Protostellar
sources are in general warmer and more compact than starless sources. Both
these evidences can be ascribed to the presence of an internal source(s) of
moderate heating, which also causes a temperature gradient and hence a more
peaked intensity distribution. Moreover, the reduced dimensions of protostellar
sources may indicate that they will not fragment further. A virial analysis of
the starless sources gives an upper limit of 90% for the sources
gravitationally bound and therefore prestellar. We fit a power law N(logM) prop
M^-1.1 to the linear portion of the mass distribution of prestellar sources.
This is in between that typical of CO clumps and those of cores in nearby
star-forming regions. We interpret this as a result of the inhomogeneity of our
sample, which is composed of comparable fractions of clumps and cores.Comment: 9 pages, 7 figures, accepted by A&
Uncovering current pyroregions in Italy using wildfire metrics
Background: Pyrogeography is a major field of investigation in wildfire science because of its capacity to describe the spatial and temporal variations of fire disturbance. We propose a systematic pyrogeographic analytical approach to cluster regions on the basis of their pyrosimilarities. We employed the Affinity Propagation algorithm to cluster pyroregions using Italian landscape as a test bed and its current wildfire metrics in terms of density, seasonality and stand replacing fire ratio. A discussion follows on how pyrogeography varies according to differences in the human, biophysical, socioeconomic, and climatic spheres. Results: The algorithm identified seven different pyroregion clusters. Two main gradients were identified that partly explain the variability of wildfire metrics observed in the current pyroregions. First, a gradient characterized by increasing temperatures and exposure to droughts, which coincides with a decreasing latitude, and second, a human pressure gradient displaying increasing population density in areas at lower elevation. These drivers exerted a major influence on wildfire density, burnt area over available fuels and stand replacing, which were associated to warm-dry climate and high human pressure. The study statistically highlighted the importance of a North–South gradient, which represents one of the most important drivers of wildfire regimes resulting from the variations in climatic conditions but showing collinearity with socioeconomic aspects as well. Conclusion: Our fully replicable analytical approach can be applied at multiple scales and used for the entire European continent to uncover new and larger pyroregions. This could create a basis for the European Commission to promote innovative and collaborative funding programs between regions that demonstrate pyrosimilarities
Identifying Young Stellar Objects in the Outer Galaxy: l = 224 deg Region in Canis Major
We study a very young star-forming region in the outer Galaxy that is the
most concentrated source of outflows in the Spitzer Space Telescope GLIMPSE360
survey. This region, dubbed CMa-l224, is located in the Canis Major OB1
association. CMa-l224 is relatively faint in the mid-infrared, but it shines
brightly at the far-infrared wavelengths as revealed by the Herschel Space
Observatory data from the Hi-GAL survey. Using the 3.6 and 4.5 m data from
the Spitzer/GLIMPSE360 survey, combined with the JHK 2MASS and the 70-500
m Herschel/Hi-GAL data, we develop a young stellar object (YSO) selection
criteria based on color-color cuts and fitting of the YSO candidates' spectral
energy distributions with YSO 2D radiative transfer models. We identify 293 YSO
candidates and estimate physical parameters for 210 sources well-fit with YSO
models. We select an additional 47 sources with GLIMPSE360-only photometry as
`possible YSO candidates'. The vast majority of these sources are associated
with high H column density regions and are good targets for follow-up
studies. The distribution of YSO candidates at different evolutionary stages
with respect to Herschel filaments supports the idea that stars are formed in
the filaments and become more dispersed with time. Both the supernova-induced
and spontaneous star formation scenarios are plausible in the environmental
context of CMa-l224. However, our results indicate that a spontaneous
gravitational collapse of filaments is a more likely scenario. The methods
developed for CMa-l224 can be used for larger regions in the Galactic plane
where the same set of photometry is available.Comment: Accepted for publication in the Astrophysical Journal Supplement
Series; 54 pages including appendice
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