440 research outputs found
Hypertrophic pyloric stenosis: tips and tricks for ultrasound diagnosis
We describe a systematic approach to the ultrasound (US) examination of the antropyloric region in children. US is the modality of choice for the diagnosis of hypertrophic pyloric stenosis (HPS). The imaging features of the normal pylorus and the diagnostic findings in HPS are reviewed and illustrated in this pictorial essay. Common difficulties in performing the examination and tips to help overcome them will also be discussed
Swift detection of the super-swift switch-on of the super-soft phase in nova V745 Sco (2014)
V745 Sco is a recurrent nova, with the most recent eruption occurring in
February 2014. V745 Sco was first observed by Swift a mere 3.7 hr after the
announcement of the optical discovery, with the super-soft X-ray emission being
detected around four days later and lasting for only ~two days, making it both
the fastest follow-up of a nova by Swift and the earliest switch-on of
super-soft emission yet detected. Such an early switch-on time suggests a
combination of a very high velocity outflow and low ejected mass and, together
with the high effective temperature reached by the super-soft emission, a high
mass white dwarf (>1.3 M_sun). The X-ray spectral evolution was followed from
an early epoch where shocked emission was evident, through the entirety of the
super-soft phase, showing evolving column density, emission lines, absorption
edges and thermal continuum temperature. UV grism data were also obtained
throughout the super-soft interval, with the spectra showing mainly emission
lines from lower ionization transitions and the Balmer continuum in emission.
V745 Sco is compared with both V2491 Cyg (another nova with a very short
super-soft phase) and M31N 2008-12a (the most rapidly recurring nova yet
discovered). The longer recurrence time compared to M31N 2008-12a could be due
to a lower mass accretion rate, although inclination of the system may also
play a part. Nova V745 Sco (2014) revealed the fastest evolving super-soft
source phase yet discovered, providing a detailed and informative dataset for
study.Comment: 14 pages, 11 figures (4 in colour), accepted for publication in MNRA
Simulations of the X-ray imaging capabilities of the Silicon Drift Detectors (SDD) for the LOFT Wide Field Monitor
The Large Observatory For X-ray Timing (LOFT), selected by ESA as one of the
four Cosmic Vision M3 candidate missions to undergo an assessment phase, will
revolutionize the study of compact objects in our galaxy and of the brightest
supermassive black holes in active galactic nuclei. The Large Area Detector
(LAD), carrying an unprecedented effective area of 10 m^2, is complemented by a
coded-mask Wide Field Monitor, in charge of monitoring a large fraction of the
sky potentially accessible to the LAD, to provide the history and context for
the sources observed by LAD and to trigger its observations on their most
interesting and extreme states. In this paper we present detailed simulations
of the imaging capabilities of the Silicon Drift Detectors developed for the
LOFT Wide Field Monitor detection plane. The simulations explore a large
parameter space for both the detector design and the environmental conditions,
allowing us to optimize the detector characteristics and demonstrating the
X-ray imaging performance of the large-area SDDs in the 2-50 keV energy band.Comment: Proceedings of SPIE, Vol. 8443, Paper No. 8443-210, 201
Collimation and asymmetry of the hot blast wave from the recurrent nova V745 Scorpii
The recurrent symbiotic nova V745 Sco exploded on 2014 February 6 and was
observed on February 22 and 23 by the Chandra X-ray Observatory Transmission
Grating Spectrometers. By that time the supersoft source phase had already
ended and Chandra spectra are consistent with emission from a hot, shock-heated
circumstellar medium with temperatures exceeding 10^7K. X-ray line profiles are
more sharply peaked than expected for a spherically-symmetric blast wave, with
a full width at zero intensity of approximately 2400 km/s, a full width at half
maximum of 1200 +/- 30 km/s and an average net blueshift of 165 +/- 10 km/s.
The red wings of lines are increasingly absorbed toward longer wavelengths by
material within the remnant. We conclude that the blast wave was sculpted by an
aspherical circumstellar medium in which an equatorial density enhancement
plays a role, as in earlier symbiotic nova explosions. Expansion of the
dominant X-ray emitting material is aligned close to the plane of the sky and
most consistent with an orbit seen close to face-on. Comparison of an
analytical blast wave model with the X-ray spectra, Swift observations and
near-infrared line widths indicates the explosion energy was approximately
10^43 erg, and confirms an ejected mass of approximately 10^-7 Msun. The total
mass lost is an order of magnitude lower than the accreted mass required to
have initiated the explosion, indicating the white dwarf is gaining mass and is
a supernova Type 1a progenitor candidate.Comment: To appear in the Astrophysical Journa
The 21Na(p,gamma)22Mg Reaction and Oxygen-Neon Novae
The 21Na(p,gamma)22Mg reaction is expected to play an important role in the
nucleosynthesis of 22Na in Oxygen-Neon novae. The decay of 22Na leads to the
emission of a characteristic 1.275 MeV gamma-ray line. This report provides the
first direct measurement of the rate of this reaction using a radioactive 21Na
beam, and discusses its astrophysical implications. The energy of the important
state was measured to be E= 205.7 0.5 keV with a resonance
strength meV.Comment: Accepted for publication in Physical Review Letter
The Extraordinary X-ray Light Curve of the Classical Nova V1494 Aquilae (1999 #2) in Outburst: The Discovery of Pulsations and a "Burst"
V1494 Aql (Nova Aql 1999 No. 2) was discovered on 2 December 1999. We
obtained Chandra ACIS-I spectra on 15 April and 7 June 2000 which appear to
show only emission lines. Our third observation, on 6 August, showed that its
spectrum had evolved to that characteristic of a Super Soft X-ray Source. We
then obtained Chandra LETG+HRC-S spectra on 28 September (8 ksec) and 1 October
(17 ksec). We analyzed the X-ray light curve of our grating observations and
found both a short time scale ``burst'' and oscillations. Neither of these
phenomena have previously been seen in the light curve of a nova in outburst.
The ``burst'' was a factor of 10 rise in X-ray counts near the middle of the
second observation, and which lasted about 1000 sec; it exhibited at least two
peaks, in addition to other structure. Our time series analysis of the combined
25 ksec observation shows a peak at 2500 s which is present in independent
analyses of both the zeroth order image and the dispersed spectrum and is not
present in similar analyses of grating data for HZ 43 and Sirius B. Further
analyses of the V1494 Aql data find other periods present which implies that we
are observing non-radial g+ modes from the pulsating, rekindled white dwarf.Comment: ApJ accepte
7Be in the outburst of the ONe nova V6595 Sgr
We report on the search for the 7Be ii isotope in the outbursts of the classical nova V6595 Sgr by means of high-resolution Ultraviolet and Visual Echelle Spectrograph (UVES) observations taken at the European Southern Observatory's Very Large Telescope in 2021 April, about two weeks after its discovery and under difficult circumstances due to the pandemic. Narrow absorption components with velocities at -2620 and-2820 km s-1, superposed on broader and shallow absorption, are observed in the outburst spectra for the 7Be ii λλ313.0583, 313.1228 nm doublet resonance lines, as well as in several other elements such as Ca ii, Fe i, Mg i, Na i, H i and Li i. Using the Ca ii K line as a reference element, we infer N(7Be)/N(H) ≈ 7.4 × 10-6, or ≈ 9.8 × 10-6 when the 7Be decay is taken into account. The 7Be abundance is about half of the value most frequently measured in novae. The possible presence of overionization in the layers where 7Be ii is detected is also discussed. Observations taken at the Telescopio Nazionale Galileo in La Palma 91 days after discovery showed prominent emission lines of oxygen and neon, which allow us to classify the nova as ONe type. Therefore, although 7Be is expected to be higher in CO novae, it is found at comparable levels in both nova types
Detection of 7Be II in the Small Magellanic Cloud
We analyse high-resolution spectra of two classical novae that exploded in the Small Magellanic Cloud (SMC). 7 Be II resonance transitions are detected in both ASASSN-19qv and ASASSN-20ni novae. This is the first detection outside the Galaxy and confirms that thermo-nuclear runaway reactions, leading to the 7 Be formation, are ef fecti ve also in the low-metallicity regime, characteristic of the SMC. Derived yields are of N( 7 Be = 7 Li)/N(H) = (5.3 ±0.2) ×10 −6 which are a factor 4 lower than the typical values of the Galaxy. Inspection of two historical novae in the Large Magellanic Cloud observed with IUE in 1991 and 1992 showed also the possible presence of 7 Be and similar yields. For an ejecta of M H , ej = 10 −5 M ⊙, the amount of 7 Li produced is of M 7 Li = (3 . 7 ±0 . 6) ×10 −10 M ⊙per nova event. Detailed chemical evolutionary model for the SMC shows that no vae could hav e made an amount of lithium in the SMC corresponding to a fractional abundance of A(Li) ≈2.6. Therefore, it is argued that a comparison with the abundance of Li in the SMC, as measured by its interstellar medium, could ef fecti vely constrain the amount of the initial abundance of primordial Li, which is currently contro v ersial
7Be detection in the 2021 outburst of RS Oph
The recurrent nova RS Oph underwent a new outburst on August 8, 2021,
reaching a visible brightness of V = 4.8 mag. Observations of the 2021 outburst
made with the high resolution UVES spectrograph at the Kueyen-UT2 telescope of
ESO-VLT in Paranal enabled detection of the possible presence of 7Be freshly
made in the thermonuclear runaway reactions. The 7Be yields can be estimated in
N(Be)/N(H) = 5.7 x 10^(-6), which are close to the lowest yields measured in
classical novae so far. 7Be is short-lived and decays only into 7Li. By means
of a spectrum taken during the nebular phase we estimated an ejected mass of
about 1.1 x 10^(-5) Msun, providing an amount of about 4.4x 10^(-10) Msun of
7Li created in the 2021 event. Recurrent novae of the kind of RS Oph may
synthesize slightly lower amount of 7Li per event as classical novae, but occur
10^3 times more frequently. The recurrent novae fraction is in the range of
10-30% and they could have contributed to the making of 7Li we observe today.
The detection of 7Be in RS Oph provides further support to the recent
suggestion that novae are the most effective source of 7Li in the Galaxy.Comment: Accepted 2022 September 17. Received 2022 September 16; in original
form 2022 April 20. 12 pages, 13 figure
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