90 research outputs found
Argas (Persicargas) persicus (Oken, 1818) (Ixodida: Argasidae) in Sicily with considerations about its Italian and West-Mediterranean distribution.
Recently, in the province of Trapani (Western Sicily), some overwintering specimens of the argasid tick Argas (Persicargas) persicus (Oken, 1818) were observed and collected. Morphological and genetic analysis were utilized in order to reach a definitive identification. The species was found in two semi-natural sites where, having been found repeatedly, its presence does not appear accidental. Moreover the characteristics of the Sicilian findings seem to exclude a human-induced spread. This record, the first regarding Sicily and South Italy, is discussed together with the previous doubtful citations for Italy. These findings revalue not only all the old citations for Italy but also the hypothesis that the Mediterranean distribution of this argasid is of a natural origin
A warm molecular ring in AG Car: composing the mass-loss puzzle
We present APEX observations of CO J=3-2 and ALMA observations of CO J=2-1,
13CO J=2-1 and continuum toward the galactic luminous blue variable AG Car.
These new observations reveal the presence of a ring-like molecular structure
surrounding the star. Morphology and kinematics of the gas are consistent with
a slowly expanding torus located near the equatorial plane of AG Car. Using
non-LTE line modelling, we derived the physical parameters of the gas, which is
warm (50 K) and moderately dense (10 cm. The total mass of molecular
gas in the ring is 2.70.9 solar masses. We analysed the radio continuum
map, which depicts a point-like source surrounded by a shallow nebula. From the
flux of the point-like source, we derived a current mass-loss date of
solar masses / yr. Finally, to better understand the
complex circumstellar environment of AG Car, we put the newly detected ring in
relation to the main nebula of dust and ionised gas. We discuss possible
formation scenarios for the ring, namely, the accumulation of interstellar
material due to the action of the stellar wind, the remnant of a close binary
interaction or merger, and an equatorially enhanced mass-loss episode. If
molecular gas formed in situ as a result of a mass eruption, it would account
for at least a 30 of the total mass ejected by AG Car. This detection adds
a new piece to the puzzle of the complex mass-loss history of AG Car, providing
new clues about the interplay between LBV stars and their surroundings.Comment: 16 pages, 13 figures. Accepted for publication in MNRA
The distance to CRL 618 through its radio expansion parallax
CRL 618 is a post-AGB star that has started to ionize its ejecta. Its central
HII region has been observed over the last 40 years and has steadily increased
in flux density at radio wavelengths. In this paper, we present data that we
obtained with the Very Large Array in its highest frequency band (43 GHz) in
2011 and compare these with archival data in the same frequency band from 1998.
By applying the so-called expansion-parallax method, we are able to estimate an
expansion rate of 4.00.4 mas yr along the major axis of the nebula
and derive a distance of 1.10.2 kpc. Within errors, this distance
estimation is in good agreement with the value of ~900 pc derived from the
expansion of the optical lobes.Comment: 6 pages, 6 figures, accepted for publication on MNRA
Study of the Galactic radio sources in the SCORPIO survey resolved by ATCA at 2.1 GHz
We present a catalogue of a large sample of extended radio sources in the
SCORPIO field, observed and resolved by the Australia Telescope Compact Array.
SCORPIO, a pathfinder project for addressing the early operations of the
Australia SKA Pathfinder, is a survey of ~5 square degrees between 1.4 and 3.1
GHz, centered at l=343.5{\deg}, b=0.75{\deg} and with an angular resolution of
about 10 arcsec. It is aimed at understanding the scientific and technical
challenges to be faced by future Galactic surveys. With a mean sensitivity
around 100 Jy/beam and the possibility to recover angular scales at least
up to 4 arcmin, we extracted 99 extended sources, 35 of them detected for the
first time. Among the 64 known sources 55 had at least a tentative
classification in literature. Studying the radio morphology and comparing the
radio emission with infrared we propose as candidates 6 new H II regions, 2 new
planetary nebulae, 2 new luminous blue variable or Wolf--Rayet stars and 3 new
supernova remnants. This study provides an overview of the potentiality of
future radio surveys in terms of Galactic source extraction and
characterization and a discussion on the difficulty to reduce and analyze
interferometric data on the Galactic plane
Imaging of SNR IC443 and W44 with the Sardinia Radio Telescope at 1.5 GHz and 7 GHz
Observations of supernova remnants (SNRs) are a powerful tool for
investigating the later stages of stellar evolution, the properties of the
ambient interstellar medium, and the physics of particle acceleration and
shocks. For a fraction of SNRs, multi-wavelength coverage from radio to ultra
high-energies has been provided, constraining their contributions to the
production of Galactic cosmic rays. Although radio emission is the most common
identifier of SNRs and a prime probe for refining models, high-resolution
images at frequencies above 5 GHz are surprisingly lacking, even for bright and
well-known SNRs such as IC443 and W44. In the frameworks of the Astronomical
Validation and Early Science Program with the 64-m single-dish Sardinia Radio
Telescope, we provided, for the first time, single-dish deep imaging at 7 GHz
of the IC443 and W44 complexes coupled with spatially-resolved spectra in the
1.5-7 GHz frequency range. Our images were obtained through on-the-fly mapping
techniques, providing antenna beam oversampling and resulting in accurate
continuum flux density measurements. The integrated flux densities associated
with IC443 are S_1.5GHz = 134 +/- 4 Jy and S_7GHz = 67 +/- 3 Jy. For W44, we
measured total flux densities of S_1.5GHz = 214 +/- 6 Jy and S_7GHz = 94 +/- 4
Jy. Spectral index maps provide evidence of a wide physical parameter scatter
among different SNR regions: a flat spectrum is observed from the brightest SNR
regions at the shock, while steeper spectral indices (up to 0.7) are observed
in fainter cooling regions, disentangling in this way different populations and
spectra of radio/gamma-ray-emitting electrons in these SNRs.Comment: 13 pages, 9 figures, accepted for publication to MNRAS on 18 May 201
CAESAR source finder: recent developments and testing
A new era in radioastronomy will begin with the upcoming large-scale surveys
planned at the Australian Square Kilometre Array Pathfinder (ASKAP). ASKAP
started its Early Science program in October 2017 and several target fields
were observed during the array commissioning phase. The SCORPIO field was the
first observed in the Galactic Plane in Band 1 (792-1032 MHz) using 15
commissioned antennas. The achieved sensitivity and large field of view already
allow to discover new sources and survey thousands of existing ones with
improved precision with respect to previous surveys. Data analysis is currently
ongoing to deliver the first source catalogue. Given the increased scale of the
data, source extraction and characterization, even in this Early Science phase,
have to be carried out in a mostly automated way. This process presents
significant challenges due to the presence of extended objects and diffuse
emission close to the Galactic Plane. In this context we have extended and
optimized a novel source finding tool, named CAESAR , to allow extraction of
both compact and extended sources from radio maps. A number of developments
have been done driven by the analysis of the SCORPIO map and in view of the
future ASKAP Galactic Plane survey. The main goals are the improvement of
algorithm performances and scalability as well as of software maintainability
and usability within the radio community. In this paper we present the current
status of CAESAR and report a first systematic characterization of its
performance for both compact and extended sources using simulated maps. Future
prospects are discussed in light of the obtained results.Comment: 15 pages, 10 figure
Classification of compact radio sources in the Galactic plane with supervised machine learning
Generation of science-ready data from processed data products is one of the
major challenges in next-generation radio continuum surveys with the Square
Kilometre Array (SKA) and its precursors, due to the expected data volume and
the need to achieve a high degree of automated processing. Source extraction,
characterization, and classification are the major stages involved in this
process. In this work we focus on the classification of compact radio sources
in the Galactic plane using both radio and infrared images as inputs. To this
aim, we produced a curated dataset of ~20,000 images of compact sources of
different astronomical classes, obtained from past radio and infrared surveys,
and novel radio data from pilot surveys carried out with the Australian SKA
Pathfinder (ASKAP). Radio spectral index information was also obtained for a
subset of the data. We then trained two different classifiers on the produced
dataset. The first model uses gradient-boosted decision trees and is trained on
a set of pre-computed features derived from the data, which include
radio-infrared colour indices and the radio spectral index. The second model is
trained directly on multi-channel images, employing convolutional neural
networks. Using a completely supervised procedure, we obtained a high
classification accuracy (F1-score>90%) for separating Galactic objects from the
extragalactic background. Individual class discrimination performances, ranging
from 60% to 75%, increased by 10% when adding far-infrared and spectral index
information, with extragalactic objects, PNe and HII regions identified with
higher accuracies. The implemented tools and trained models were publicly
released, and made available to the radioastronomical community for future
application on new radio data.Comment: 27 pages, 15 figures, 9 table
New high-frequency radio observations of the Cygnus Loop supernova remnant with the Italian radio telescopes
Supernova remnants (SNRs) represent a powerful laboratory to study the
Cosmic-Ray acceleration processes at the shocks, and their relation to the
properties of the circumstellar medium. With the aim of studying the
high-frequency radio emission and investigating the energy distribution of
accelerated electrons and the magnetic field conditions, we performed
single-dish observations of the large and complex Cygnus Loop SNR from 7.0 to
24.8 GHz with the Medicina and the Sardinia Radio Telescope, focusing on the
northern filament (NGC 6992) and the southern shell. Both regions show a
spectrum well fitted by a power-law function (), with
spectral index for NGC 6992 and for
the southern shell and without any indication of a spectral break. The spectra
are significantly flatter than the whole Cygnus Loop spectrum
(), suggesting a departure from the plain shock
acceleration mechanisms, which for NGC 6992 could be related to the ongoing
transition towards a radiative shock. We model the integrated spectrum of the
whole SNR considering the evolution of the maximum energy and magnetic field
amplification. Through the radio spectral parameters, we infer a magnetic field
at the shock of 10 G. This value is compatible with a pure adiabatic
compression of the interstellar magnetic field, suggesting that the
amplification process is currently inefficient.Comment: 19 pages, 13 figure
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