5,631 research outputs found
The antenna DSA 3 and its potential use for Radio Astronomy
The European Space Agency (ESA) will inaugurate its third Deep Space Antenna
(DSA 3) by the end of 2012. DSA 3 will be located in Argentina near the city of
Malarg"ue in the Mendoza province. While the instrument will be primarily
dedicated to communications with interplanetary missions, the characteristics
of its antenna and receivers will also enable standalone leading scientific
contributions, with a high scientific-technological return. We outline here
scientific proposals for a radio astronomical use of DSA 3.Comment: 4 pages, submitted as Proceedings for the BAA
The radio surroundings of the microquasar GRO J1655-40
We report the results of a study of the radio surroundings of the superluminal microquasar GRO J1655-40. We have searched for extended continuum structures that might be indicative of the presence of a supernova remnant (SNR) associated with the formation of the compact object in the binary system. We also carried out HI-line observations of the region looking for a local minimum created by an explosive event. Our results indicate that there is, in fact, a bubble in the large-scale HI distribution around GRO J1655-40. We suggest that this structure might be created by the original supernova explosion occurred a few hundred thousand years ago and whose signatures can be traced by the overabundance of alpha-elements recently found by Israelian et al. (1999) in the companion star
INTEGRAL-ISGRI observations of the CygOB2 region: earching for hard X-ray point sources in a region containing several non-thermal emitting massive stars
Aims: We analyze INTEGRAL-ISGRI data in order to probe the hard X-ray
emission (above 20 keV) from point sources in the Cyg OB2 region and to
investigate the putative non-thermal high-energy emission from early-type stars
(Wolf-Rayet and O-type stars). Among the targets located in the field of view,
we focus on the still unidentified EGRET source 3EG 2033+4118 that may be
related to massive stars known to produce non-thermal emission in the radio
domain, and on the wide colliding-wind binary WR 140. Methods: Using a large
set of data obtained with the IBIS-ISGRI imager onboard INTEGRAL, we run the
OSA software package in order to find point sources in the fully coded field of
view of the instrument. Results: Our data do not allow the detection of a
lower-energy counterpart of 3EG J2033+4118 nor of any other new point sources
in the field of view, and we derive upper limits on the high-energy flux for a
few targets: 3EG J2033+4118, TeV J2032+4130, WR140, WR146 and WR147. The
results are discussed in the context of the multiwavelength investigation of
these objects. Conclusions: The upper limits derived are valuable constraints
for models aimed at understanding the acceleration of particles in non-thermal
emitting massive stars, and of the still unidentified very-high gamma-ray
source TeV J2032+4130.Comment: 6 page, 2 figures including one figure in GIF format, accepted for
publication by A&
On the multiplicity of the O-star Cyg OB2 #8A and its contribution to the gamma-ray source 3EG J2033+4118
We present the results of an intensive spectroscopic campaign in the optical
waveband revealing that Cyg OB2 #8A is an O6 + O5.5 binary system with a period
of about 21.9 d. Cyg OB2 #8A is a bright X-ray source, as well as a non-thermal
radio emitter. We discuss the binarity of this star in the framework of a
campaign devoted to the study of non-thermal emitters, from the radio waveband
to gamma-rays. In this context, we attribute the non-thermal radio emission
from this star to a population of relativistic electrons, accelerated by the
shock of the wind-wind collision. These relativistic electrons could also be
responsible for a putative gamma-ray emission through inverse Compton
scattering of photospheric UV photons, thus contributing to the yet
unidentified EGRET source 3EG J2033+4118.Comment: 8 pages, 4 figures, conference on "The Multiwavelength Approach to
Gamma-Ray Sources", to appear in Ap&S
The HI shell G132.6-0.7-25.3: A Supernova Remnant or an Old Wind-Blown Bubble?
Data from the Canadian Galactic Plane Survey reveal an abundance of HI shells
and arcs in the disk of our galaxy. While their shape is suggestive of stellar
winds or supernovae influence, very few of these structures have been examined
in detail thus far. A fine example is an HI shell in the outer Galaxy with no
continuum counterpart discovered in the survey's pilot project. Its size and
kinematics suggest that it was created by the winds of a single late-type O
star which has since evolved off the main sequence or by a supernova explosion.
A B1 Ia star at the centre of the shell, in projection, is a possible candidate
for energy source if the shell is assumed to be wind-blown. The shell's shape
implies a surprisingly small scale height of less than about 30 pc for the
surrounding gas if the elongation is due to evolution in a density gradient.Comment: 25 pages, 6 figures. Accepted for publication in the Astronomical
Journa
A variability analysis of low-latitude unidentified gamma-ray sources
We present a study of 40 low-latitude unidentified 3EG gamma-ray sources
which were found to be not positionally coincident with any known class of
potential gamma-ray emitters in the Galaxy (Romero, Benaglia & Torres, 1999).
We have performed a variability analysis which reveals that many of these 40
sources are variable. These sources have, in addition, a steep mean value of
the gamma-ray spectral index, , which, combined with
the high level of variability seems to rule out a pulsar origin. The positional
coincidences with uncatalogued candidates to supernova remnants were also
studied. Only 7 sources in the sample are spatially coincident with these
candidates, a result that is shown to be consistent with the expected level of
pure chance association. A complementary search for weak radio counterparts was
also conducted and the results are presented as an extensive table containing
all significant point-like radio sources within the 40 EGRET fields. We argue
that in order to produce the high variability, steep gamma-ray spectra, and
absence of strong radio counterparts observed in some of the gamma-ray sources
of our sample a new class of objects should be postulated, and we analyze a
viable candidate.Comment: Paper updated to match the accepted version to appear in Astronomy
and Astrophysics, 2001. Tables 5,6,7 and 8 are in ascii format and need to be
printed separately. they can also be obtained from
http://www.iar.unlp.edu.ar/garra Table 5 is 62 pages long. Download the
source to obtain the table
Multiwavelength studies of WR 21a and its surroundings
We present results of high-resolution radio continuum observations towards
the binary star WR 21a (Wack 2134) obtained with the Australia Telescope
Compact Array (ATCA) at 4.8 and 8.64 GHz. We detected the system at 4.8 GHz (6
cm) with a flux density of 0.25+-0.06 mJy and set an upper limit of 0.3 mJy at
8.64 GHz (3 cm). The derived spectral index of alpha < 0.3
[S(nu)=k.nu**(alpha)] suggests the presence of non-thermal emission, probably
originating in a colliding-wind region. A second, unrelated radio source was
detected ~10" north of WR 21a at (RA, Dec)(J2000)=(10h 25m 56.49, -57deg 48'
34.4", with flux densities of 0.36 and 0.55 mJy at 4.8 and 8.64 GHz,
respectively, resulting in alpha = 0.72. HI observations in the area are
dominated by absorption against the prominent HII region RCW 49. Analysis of a
complete set of archived X-ray observations of WR 21a confirms its strong
variability but throws into doubt previous suggestions by Reig (1999) of a
period of years for the system. Finally, we comment on the association with the
nearby EGRET source 3EG J1027-5817.Comment: 9 pages, 5 figures, accepted (Astronomy & Astrophysics
A Catalytic Reactor for the Organocatalyzed Enantioselective Continuous Flow Alkylation of Aldehydes
The use of immobilized metal-free catalysts offers the unique possibility to develop sustainable processes in flow mode. The challenging intermolecular organocatalyzed enantioselective alkylation of aldehydes was performed for the first time under continuous flow conditions. By using a packed-bed reactor filled with readily available supported enantiopure imidazolidinone, different aldehydes were treated with three distinct cationic electrophiles. In the organocatalyzed α-alkylation of aldehydes with 1,3-benzodithiolylium tetrafluoroborate, excellent enantioselectivities, in some cases even better than those obtained in the flask process (up to 95 % ee at 25 °C), and high productivity (more than 3800 h−1) were obtained, which thus shows that a catalytic reactor may continuously produce enantiomerically enriched compounds. Treatment of the alkylated products with Raney-nickel furnished enantiomerically enriched α-methyl derivatives, key intermediates for active pharmaceutical ingredients and natural products
Mother to child transmission of Hepatitis C Virus in a province of Northern Italy
NTRODUCTION: Study reports of mother to child transmission of hepatitis C virus (HCV) have shown transmission rates ranging from 3 to 37%, according to maternal viremia and HIV-1 coinfection. The present study evaluated the prevalence of the HCV infection in the general population and the incidence of vertical transmission, from women who delivered in the Obstetric Clinic of the Hospital of Parma from January 1st 1996 to 31st 2001 December. METHODS: Mothers and children were tested for the presence of HCV-RNA within one week after delivery. Children were considered to be infected when they were found positive at least twice for viral RNA or antibodies were still detectable at the end of the follow-up period (18 months) in blood. RESULTS: Out of 13,025 women, 110 (0.8%) were found positive for anti-HCV antibodies; 72 of them (65.4%) were HCV-RNA positive. All 110 children were positive for anti-HCV antibodies in the first blood sample (time 0); 8 of them were HCV-RNA positive. Three children were still viremic at the end of the follow-up whereas 5 showed a clearance. No significant differences were found between viremic and nonviremic children with respect to gestational week, maternal alanine aminotransferase (ALT) levels and newborns weight at birth. CONCLUSION: This investigation shows that vertical transmission may occur in a general obstetric population despite a low prevalence of HCV-positive subjects
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