689 research outputs found
Near-infrared follow-up to the May 2008 activation of SGR 1627-41
On 28 May 2008, the Swift satellite detected the first reactivation of SGR
1627-41 since its discovery in 1998.
Following this event we began an observing campaign in near infrared
wavelengths to search for a possible counterpart inside the error circle of
this SGR, which is expected to show flaring activity simultaneous to the high
energy flares or at least some variability as compared to the quiescent state.
For the follow-up we used the 0.6m REM robotic telescope at La Silla
Observatory, which allowed a fast response within 24 hours and, through
director discretionary time, the 8.2m Very Large Telescope at Paranal
Observatory. There, we observed with NACO to produce high angular resolution
imaging with the aid of adaptive optics.
These observations represent the fastest near infrared observations after an
activation of this SGR and the deepest and highest spatial resolution
observations of the Chandra error circle.
5 sources are detected in the immediate vicinity of the most precise X-ray
localisation of this source. For 4 of them we do not detect variability,
although the X-ray counterpart experimented a significant decay during our
observation period. The 5th source is only detected in one epoch, where we have
the best image quality, so no variability constrains can be imposed and remains
as the only plausible counterpart. We can impose a limit of Ks > 21.6
magnitudes to any other counterpart candidate one week after the onset of the
activity. Our adaptive optics imaging, with a resolution of 0.2" provides a
reference frame for subsequent studies of future periods of activity.Comment: Accepted for publication in A&
The Discovery of Infrared Rings in the Planetary Nebula NGC 1514 During the WISE All-Sky Survey
We report the discovery of a pair of infrared, axisymmetric rings in the
planetary nebula NGC 1514 during the course of the WISE all-sky mid-infrared
survey. Similar structures are seen at visible wavelengths in objects such as
the "Engraved Hourglass Nebula" (MyCn 18) and the "Southern Crab Nebula" (Hen
2-104). However, in NGC 1514 we see only a single pair of rings and they are
easily observed only in the mid-infrared. These rings are roughly 0.2 pc in
diameter, are separated by 0.05 pc, and are dominated by dust emission with a
characteristic temperature of 160 K. We compare the morphology and color of the
rings to the other nebular structures seen at visible, far-infrared, and radio
wavelengths, and close with a discussion of a physical model and formation
scenario for NGC 1514.Comment: 16 pages, 10 figures, final version published in 2010 December
Astronomical Journa
Study of the luminous blue variable star candidate G26.47+0.02 and its environment
The luminous blue variable (LBV) stars are peculiar very massive stars. The
study of these stellar objects and their surroundings is important for
understanding the evolution of massive stars and its effects on the
interstellar medium. We study the LBV star candidate G26.47+0.02. Using several
large-scale surveys in different frequencies we performed a multiwavelength
study of G26.47+0.02 and its surroundings. We found a molecular shell (seen in
the 13CO J=1-0 line) that partially surrounds the mid-infrared nebula of
G26.47+0.02, which suggests an interaction between the strong stellar winds and
the molecular gas. From the HI absorption and the molecular gas study we
conclude that G26.47+0.02 is located at a distance of ~4.8 kpc. The radio
continuum analysis shows a both thermal and non-thermal emission toward this
LBV candidate, pointing to wind-wind collision shocks from a binary system.
This hypothesis is supported by a search of near-IR sources and the Chandra
X-ray analysis. Additional multiwavelength and long-term observations are
needed to detect some possible variable behavior, and if that is found, to
confirm the binary nature of the system.Comment: accepted in A&A 01/05/201
Near-infrared spectro-interferometry of three OH/IR Stars with the VLTI/AMBER instrument
We investigate the molecular and dusty environment of OH/IR stars in order to
characterize the mass-loss process during the tip-AGB superwind phase.
Employing the AMBER instrument at the VLT Interferometer we obtained
near-infrared H- and K-band spectro-interferometric observations of the three
OH/IR stars IRAS 13479-5436, IRAS 14086-6907 and IRAS 17020-5254 with a
spectral resolution of about 35. We use a two-component geometrical model,
consisting of a uniform disk and a Gaussian disk, to obtain characteristic
angular sizes of the central stellar sources and their dust envelopes, as well
as the flux ratios between these components. Angular uniform disk diameters of
the three central components of the objects above have values between 3.2 mas
and 5.4 mas. For their dust envelopes, we find FWHM values between 17.1 mas and
25.2 mas. According to distance estimates from the literature, the central
stellar components have radii between 900 R_sun and 1400 R_sun, while their
dust envelopes reach FWHM values between 9000 R_sun and 13000 R_sun. The
visibility functions of all three sources exhibit wavelength variations that
resemble those of earlier VLTI/AMBER observations of semi-regular and Mira
variable AGB stars. These are interpreted as characteristic of atmospheric
molecular layers lying above the photosphere. We also find that the dust
envelopes have a clearly larger optical depth than those known for Mira stars.
We interpret this as an expected result of the "superwind" phase, the final 10
000 to 30 000 years of AGB-evolution, when the mass-loss rate increases by a
factor of 10-100. By their different optical depths, the three dust shells
studied here may represent different stages of the "superwind" and different
initial masses.Comment: 5 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
Magnetic susceptibility of EuTe/PbTe Heisenberg superlattices: experimental and theoretical studies
We report results on the temperature dependence of the susceptibilities of a
set of MBE-grown short-period EuTe/PbTe antiferromagnetic superlattices having
different EuTe layer thicknesses. In-plane and orthogonal susceptibilities have
been measured and display a strong anisotropy at low temperature, confirming
the occurrence of a magnetic phase transition in the thicker samples, as seen
also in neutron diffraction studies. We suggest that dipolar interactions
stabilize antiferromagnetic long-range order in an otherwise isotropic system
and we present numerical and analytical results for the low-temperature
orthogonal susceptibility.Comment: 30 pages, 8 ps figures, RevTe
White Dwarf - Red Dwarf Systems Resolved with the Hubble Space Telescope: I. First Results
First results are presented for a Hubble Space Telescope Advanced Camera for
Surveys snapshot study of white dwarfs with likely red dwarf companions. Of 48
targets observed and analyzed so far, 27 are totally or partially resolved into
two or more components, while an additional 15 systems are almost certainly
unresolved binaries. These results provide the first direct empirical evidence
for a bimodal distribution of orbital separations among binary systems
containing at least one white dwarf.Comment: 46 pages, 3 figures, 5 tables, accepted to ApJ. Full-resolution
images available upon request. A few table entries correcte
Complete O(v^2) corrections to the static interquark potential from SU(3) gauge theory
For the first time, we determine the complete spin- and momentum-dependent
order v^2 corrections to the static interquark potential from simulations of
QCD in the valence quark approximation at inverse lattice spacings of 2-3 GeV.
A new flavor dependent correction to the central potential is found. We report
a 1/r^2 contribution to the long range spin-orbit potential V_1'. The other
spin-dependent potentials turn out to be short ranged and can be well
understood by means of perturbation theory. The momentum-dependent potentials
qualitatively agree with minimal area law expectations. In view of spectrum
calculations, we discuss the matching of the effective nonrelativistic theory
to QCD as well as renormalization of lattice results. In a first survey of the
resulting bottomonia and charmonia spectra we reproduce the experimental levels
within average errors of 12.5 MeV and 22 MeV, respectively.Comment: 54 pages REVTeX with 24 encapsuled ps figure
Ab Initio Calculation of Relativistic Corrections to the Static Interquark potential I: SU(2) Gauge Theory
We test the capability of state-of-the-art lattice techniques for a precise
determination of relativistic corrections to the static interquark potential,
by use of SU(2) gauge theory. Emphasis is put on the short range structure of
the spin dependent potentials, with lattice resolution a ranging from a approx
0.04 fm (at beta=2.74) down to a approx 0.02 fm (at beta=2.96) on volumes of
32^4 and 48^4 lattice sites. We find a new short range Coulomb-like
contribution to the spin-orbit potential V_1'.Comment: 37 pages REVTeX with 20 encapsuled ps figure
Randomised Controlled Trials Assessing the Clinical Value of Urodynamic Studies: A Systematic Review and Meta-analysis
Context: The role of urodynamic studies (UDSs) in the diagnosis of lower urinary tract symptoms (LUTS) is crucial. Although expert statements and guidelines underline their value for clinical decision-making in various clinical settings, the academic debate as to their impact on patient outcomes continues. Objective: To summarise the evidence from all randomised controlled trials assessing the clinical usefulness of UDS in the management of LUTS. Evidence acquisition: For this systematic review, searches were performed without language restrictions in three electronic databases until November 18, 2020. The inclusion criteria were randomised controlled study design and allocation to receive UDS or not prior to any clinical management. Quality assessment was performed by two reviewers independently, using the Cochrane Collaboration's tool for assessing the risk of bias. A random-effect meta-analysis was performed on the uniformly reported outcome parameters. Evidence synthesis: Eight trials were included, and all but two focused on women with pure or predominant stress urinary incontinence (SUI). A meta-analysis of six studies including 942 female patients was possible for treatment success, as defined by the authors (relative risk 1.00, 95% confidence interval: 0.93–1.07), indicating no difference in efficacy when managing women with UDS. Conclusions: Although UDSs are not replaceable in diagnostics, since there is no other equivalent method to find out exactly what the lower urinary tract problem is, there are little data supporting its impact on outcomes. Randomised controlled trials have focussed on a small group of women with uncomplicated SUI and showed no added value, but these findings cannot be extrapolated to the overall patient population with LUTS, warranting further well-designed trials. Patient summary: Despite urodynamics being the gold standard to assess lower urinary tract symptoms (LUTS), as it is the only method that can specify lower urinary tract dysfunction, more studies assessing the clinical usefulness of urodynamic studies (UDSs) in the management of LUTS are needed. UDS investigation is not increasing the probability of success in the treatment of stress urinary incontinence
Thermostatistics of deformed bosons and fermions
Based on the q-deformed oscillator algebra, we study the behavior of the mean
occupation number and its analogies with intermediate statistics and we obtain
an expression in terms of an infinite continued fraction, thus clarifying
successive approximations. In this framework, we study the thermostatistics of
q-deformed bosons and fermions and show that thermodynamics can be built on the
formalism of q-calculus. The entire structure of thermodynamics is preserved if
ordinary derivatives are replaced by the use of an appropriate Jackson
derivative and q-integral. Moreover, we derive the most important thermodynamic
functions and we study the q-boson and q-fermion ideal gas in the thermodynamic
limit.Comment: 14 pages, 2 figure
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