1,721 research outputs found
Interacting coronae of two T Tauri stars: first observational evidence for solar-like helmet streamers
Context {The young binary system V773 Tau A exhibits a persistent radio
flaring activity that gradually increases from a level of a few mJy at
apoastron to more than 100 mJy at periastron. Interbinary collisions between
very large (> 15 R) magnetic structures anchored on the two rotating stars of
the system have been proposed to be the origin of these periodic radio flares.
Magnetic structures extended over tens of stellar radii, that can also account
for the observed fast decay of the radio flares, seem to correspond to the
typical solar semi-open quite extended magnetic configurations called helmet
streamers.} Aims {We aim to find direct observational evidence for the
postulated, solar-like, coronal topologies.} Methods {We performed
seven-consecutive-day VLBI observations at 8.4 GHz using an array consisting of
the VLBA and the 100-m Effelsberg telescope.} Results {Two distintive
structures appear in the radio images here presented. They happen to be
associated with the primary and secondary stars of the V773 Tau A system. In
one image (Fig.2-B) the two features are extended up to 18 R each and are
nearly parallel revealing the presence of two interacting helmet streamers. One
image (Fig.2-E) taken a few hours after a flare monitored by the 100-m
Effelsberg telescope shows one elongated fading structure substantially rotated
with respect to those seen in the B run. The same decay scenario is seen in
Fig.2-G for the helmet streamer associated with the other star.} Conclusions
{This is the very first direct evidence revealing that even if the flare origin
is magnetic reconnection due to interbinary collision, both stars independently
emit in the radio range with structures of their own. These structures are
helmet streamers, observed for the first time in stars other than the Sun.}Comment: 7 pages, 3 figures, A&A in pres
Triggered massive-star formation on the borders of Galactic HII regions. II. Evidence for the collect and collapse process around RCW 79
We present SEST-SIMBA 1.2-mm continuum maps and ESO-NTT SOFI JHK images of
the Galactic HII region RCW 79. The millimetre continuum data reveal the
presence of massive fragments located in a dust emission ring surrounding the
ionized gas. The two most massive fragments are diametrically opposite each
other in the ring. The near-IR data, centred on the compact HII region located
at the south-eastern border of RCW 79, show the presence of an IR-bright
cluster containing massive stars along with young stellar objects with near-IR
excesses. A bright near- and mid-IR source is detected towards maser emissions,
1.2 pc north-east of the compact HII region centre. Additional information,
extracted from the Spitzer GLIMPSE survey, are used to discuss the nature of
the bright IR sources observed towards RCW 79. Twelve luminous Class I sources
are identified towards the most massive millimetre fragments. All these facts
strongly indicate that the massive-star formation observed at the border of the
HII region RCW 79 has been triggered by its expansion, most probably by the
collect and collapse process.Comment: 14 pages, 15 figures. Accepted for publication in A&A. The images
have been highly compressed for astro-ph. A version of this paper with
higher-resolution figures is available at
http://www.oamp.fr/matiere/rcw79.pd
Triggered massive-star formation on the borders of Galactic HII regions. III. Star formation at the periphery of Sh2-219
Context. Massive-star formation triggered by the expansion of HII regions.
Aims. To understand if sequential star formation is taking place at the
periphery of the HII region Sh2-219. Methods. We present 12CO(2-1) line
observations of this region, obtained at the IRAM 30-m telescope (Pico Veleta,
Spain). Results. In the optical, Sh2-219 is spherically symmetric around its
exciting star; furthermore it is surrounded along three quarters of its
periphery by a ring of atomic hydrogen. This spherical symmetry breaks down at
infrared and millimetre wavelengths. A molecular cloud of about 2000\msol lies
at the southwestern border of Sh2-219, in the HI gap. Two molecular
condensations, elongated along the ionization front, probably result from the
interaction between the expanding HII region and the molecular cloud. In this
region of interaction there lies a cluster containing many highly reddened
stars, as well as a massive star exciting an ultracompact HII region. More
surprisingly, the brightest parts of the molecular cloud form a `chimney',
perpendicular to the ionization front. This chimney is closed at its south-west
extremity by H-alpha walls, thus forming a cavity. The whole structure is 7.5
pc long. A luminous H-alpha emission-line star, lying at one end of the chimney
near the ionization front, may be responsible for this structure. Confrontation
of the observations with models of HII region evolution shows that Sh2-219 is
probably 10^5 yr old. The age and origin of the near-IR cluster observed on the
border of Sh2-219 remain unknown.Comment: 11 pages, 10 figures. To be published in A&
Disc brake squeal characterization through simplified test rigs
Cataloged from PDF version of article.This paper presents a review of recent investigations on brake squeal noise carried out on simplified experimental rigs. The common theme of these works is that of approaching the study of squeal noise on experimental set-ups that are much simpler than commercial disc brakes, providing the possibility of repeatable measurements of squeal occurrence. As a consequence, it is possible to build consistent and robust models of the experimental apparatus to simulate the squeal events and to understand the physics behind squeal instabilities. (C) 2009 Published by Elsevier Ltd
Evidence of an asymmetrical Keplerian disk in the Br{\gamma} and He I emission lines around the Be star HD 110432
Context. HD 110432 was classified as a "\gamma Cas X-ray analog" since it has
similar peculiar X-ray and optical characteristics, i.e. a hard-thermal X-ray
variable emission and an optical spectrum affected by an extensive disk. Lopes
de Oliveira et al. (2007) suggest that it might be a Be star harboring an
accreting white dwarf or that the X-rays may come from an interaction between
the surface of the star and its disk. Aims. To investigate the disk around this
Be star we used the VLTI/AMBER instrument, which combines high spectral
(R=12000) and high spatial (\theta min =4 mas) resolutions. Methods. We
constrain the geometry and kinematics of its circumstellar disk from the
highest spatial resolution ever achieved on this star. Results. We obtain a
disk extension in the Br{\gamma} line of 10.2 D\ast and 7.8 D\ast in the He I
line at 2.05 \mu m assuming a Gaussian disk model. The disk is clearly
following a Keplerian rotation. We obtained an inclination angle of 55\degree,
and the star is a nearly critical rotator with Vrot /Vc =1.000.2. This
inclination is greater than the value found for \gamma Cas (about 42\degree,
Stee et al. 2012), and is consistent with the inference from optical Fe II
emission profiles by Smith & Balona (2006) that the inclination should be more
than the \gamma Cas value. In the near-IR continuum, the disk of HD 110432 is 3
times larger than \gamma Cas's disk. We have no direct evidence of a companion
around HD 110432, but it seems that we have a clear signature for disk
inhomogeneities as detected for {\zeta} Tau. This asymmetrical disk detection
may be interpreted within the one-armed oscillation viscous disk framework.
Another finding is that the disk size in the near-IR is similar to other Be
stars with different spectral types and thus may be independent of the stellar
parameters, as found for classical Be stars.Comment: 9 page
Molecular clouds under the influence of massive stars in the Galactic HII region G353.2+0.9
The Galactic HII region G353.2+0.9 is excited by the massive open cluster
Pismis-24. By analyzing (sub-)mm molecular-line and -continuum we study the
detailed morphology of the gas and dust, as well as their physical parameters
and their variation across the PDR. We observed various molecules and
transitions to derive the physical properties of the molecular gas through line
ratios, and both LTE and non-LTE analyses. The physical properties of the gas
were derived with a Bayesian approach for the non-LTE analysis. Based on the
continuum data at 870 micron, we derived the dust mass and the column density
of H2, and thus the molecular abundances. The total mass of the gas in the
region is ca. 2000 Mo, while that of the dust is ca. 21 Mo. A velocity gradient
in the region suggests that the expansion of the ionized gas is pushing the
molecular gas away from the observer. We unambiguously identify the ionization
front, at the location of which we detect an increase in gas density and
temperature. We find at least 14 clumps at different positions and LSR
velocities. We derive kinetic temperatures in the ranges 11-45 K (CS) and 20-45
K (CN). The H2 number density is typically around 1e5 cm^-3 from CS and few 1e5
cm^-3 from CN, with maxima above 1e6 cm^-3. The abundances of the molecules
observed vary across the region, and appear to be higher in regions further
away from the ionization front.Comment: 14 pages, 11 figures. Accepted for publication in Astronomy and
Astrophysic
Total cost of ownership of electric vehicles using energy from a renewable-based microgrid
This work aims at analyzing the integration between
electric mobility and renewable energy sources studying the case
of the grid-connected microgrid under construction at the
University of Trieste, Italy. A general model able to estimate the
charging price and the resulting total cost of ownership per
kilometer considering the match between the demand and the
production of a photovoltaic generator is presented. The result is
that the electric vehicle is mainly charged with the produced renewable energy (72%) and that the 60% of it flows through the
storage unit. The study also presents a sensitivity analysis to show how the battery size and cost, together with the travelled distance, influence the charging price and the total cost of ownership per kilometer. Considering the current Italian prices and subsidies, results show that the use of an electric car is today feasibl
Full genome sequence-based comparative study of wild-type and vaccine strains of infectious laryngotracheitis virus from Italy
Infectious laryngotracheitis (ILT) is an acute and highly contagious respiratory disease of chickens caused by an alphaherpesvirus, infectious laryngotracheitis virus (ILTV). Recently, full genome sequences of wild-type and vaccine strains have been determined worldwide, but none was from Europe. The aim of this study was to determine and analyse the complete genome sequences of five ILTV strains. Sequences were also compared to reveal the similarity of strains across time and to discriminate between wild-type and vaccine strains. Genomes of three ILTV field isolates from outbreaks occurred in Italy in 1980,2007 and 2011, and two commercial chicken embryo origin (CEO) vaccines were sequenced using the 454 Life Sciences technology. The comparison with the Serva genome showed that 35 open reading frames (ORFs) differed across the five genomes. Overall, 54 single nucleotide polymorphisms (SNPs) and 27 amino acid differences in 19 ORFs and two insertions in the UL52 and ORFC genes were identified. Similarity among the field strains and between the field and the vaccine strains ranged from 99.96% to 99.99%. Phylogenetic analysis revealed a close relationship among them, as well. This study generated data on genomic variation among Italian ILTV strains revealing that, even though the genetic variability of the genome is well conserved across time and between wild-type and vaccine strains, some mutations may help in differentiating among them and maybe involved in ILTV virulence/attenuation. The results of this study can contribute to the understanding of the molecular bases of ILTV pathogenicity and provide genetic markers to differentiate between wild-type and vaccine strains
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