6,274 research outputs found
Polarization of the changing-look quasar J1011+5442
If the disappearance of the broad emission lines observed in changing-look
quasars were caused by the obscuration of the quasar core through moving dust
clouds in the torus, high linear polarization typical of type 2 quasars would
be expected. We measured the polarization of the changing-look quasar
J1011+5442 in which the broad emission lines have disappeared between 2003 and
2015. We found a polarization degree compatible with null polarization. This
measurement suggests that the observed change of look is not due to a change of
obscuration hiding the continuum source and the broad line region, and that the
quasar is seen close to the system axis. Our results thus support the idea that
the vanishing of the broad emission lines in J1011+5442 is due to an intrinsic
dimming of the ionizing continuum source that is most likely caused by a rapid
decrease in the rate of accretion onto the supermassive black hole.Comment: Accepted for publication in Astronomy and Astrophysics Letter
Propuesta de aplicaciĂłn y adaptaciĂłn del test de Hislop y Montgomery para cuantificar la fuerza abdominal en una poblaciĂłn escolar
How much dark matter is there inside early-type galaxies?
We study the luminous mass as a function of the dynamical mass inside the
effective radius (r_e) of early-type galaxies (ETGs) to search for differences
between these masses. We assume Newtonian dynamics and that any difference
between these masses is due to the presence of dark matter. We use several
samples of ETGs -ranging from 19 000 to 98 000 objects- from the ninth data
release of the Sloan Digital Sky Survey. We perform Monte Carlo (MC)
simulations of galaxy samples and compare them with real samples. The main
results are: i) MC simulations show that the distribution of the dynamical vs.
luminous mass depends on the mass range where the ETGs are distributed
(geometric effect). This dependence is caused by selection effects and
intrinsic properties of the ETGs. ii) The amount of dark matter inside r_e is
approximately 7% +- 22%. iii) This amount of dark matter is lower than the
minimum estimate (10%) found in the literature and four times lower than the
average (30%) of literature estimates. However, if we consider the associated
error, our estimate is of the order of the literature average.Comment: 24 pages, 12 figures. MNRAS accepte
Integrability in Theories with Local U(1) Gauge Symmetry
Using a recently developed method, based on a generalization of the zero
curvature representation of Zakharov and Shabat, we study the integrability
structure in the Abelian Higgs model. It is shown that the model contains
integrable sectors, where integrability is understood as the existence of
infinitely many conserved currents. In particular, a gauge invariant
description of the weak and strong integrable sectors is provided. The
pertinent integrability conditions are given by a U(1) generalization of the
standard strong and weak constraints for models with two dimensional target
space. The Bogomolny sector is discussed, as well, and we find that each
Bogomolny configuration supports infinitely many conserved currents. Finally,
other models with U(1) gauge symmetry are investigated.Comment: corrected typos, version accepted in J. Phys.
Expansion for the solutions of the Bogomolny equations on the torus
We show that the solutions of the Bogomolny equations for the Abelian Higgs
model on a two-dimensional torus, can be expanded in powers of a quantity
epsilon measuring the departure of the area from the critical area. This allows
a precise determination of the shape of the solutions for all magnetic fluxes
and arbitrary position of the Higgs field zeroes. The expansion is carried out
to 51 orders for a couple of representative cases, including the unit flux
case. We analyse the behaviour of the expansion in the limit of large areas, in
which case the solutions approach those on the plane. Our results suggest
convergence all the way up to infinite area.Comment: 26 pages, 8 figures, slightly revised version as published in JHE
Model selection for spectro-polarimetric inversions
Inferring magnetic and thermodynamic information from spectropolarimetric
observations relies on the assumption of a parameterized model atmosphere whose
parameters are tuned by comparison with observations. Often, the choice of the
underlying atmospheric model is based on subjective reasons. In other cases,
complex models are chosen based on objective reasons (for instance, the
necessity to explain asymmetries in the Stokes profiles) but it is not clear
what degree of complexity is needed. The lack of an objective way of comparing
models has, sometimes, led to opposing views of the solar magnetism because the
inferred physical scenarios are essentially different. We present the first
quantitative model comparison based on the computation of the Bayesian evidence
ratios for spectropolarimetric observations. Our results show that there is not
a single model appropriate for all profiles simultaneously. Data with moderate
signal-to-noise ratios favor models without gradients along the line-of-sight.
If the observations shows clear circular and linear polarization signals above
the noise level, models with gradients along the line are preferred. As a
general rule, observations with large signal-to-noise ratios favor more complex
models. We demonstrate that the evidence ratios correlate well with simple
proxies. Therefore, we propose to calculate these proxies when carrying out
standard least-squares inversions to allow for model comparison in the future.Comment: 16 pages, 2 figures, 8 tables, accepted for publication in Ap
High spatial resolution optical imaging of the multiple T Tauri system LkH{\alpha} 262/LkH{\alpha} 263
We report high spatial resolution i' band imaging of the multiple T Tauri
system LkH 262/LkH 263 obtained during the first commissioning
period of the Adaptive Optics Lucky Imager (AOLI) at the 4.2 m William Herschel
Telescope, using its Lucky Imaging mode. AOLI images have provided photometry
for each of the two components LkH 263 A and B (0.41 arcsec separation)
and marginal evidence for an unresolved binary or a disc in LkH 262.
The AOLI data combined with previously available and newly obtained optical and
infrared imaging show that the three components of LkH 263 are
co-moving, that there is orbital motion in the AB pair, and, remarkably, that
LkH 262-263 is a common proper motion system with less than 1 mas/yr
relative motion. We argue that this is a likely five-component gravitationally
bounded system. According to BT-settl models the mass of each of the five
components is close to 0.4 M and the age is in the range 1-2 Myr. The
presence of discs in some of the components offers an interesting opportunity
to investigate the formation and evolution of discs in the early stages of
multiple very low-mass systems. In particular, we provide tentative evidence
that the disc in 263C could be coplanar with the orbit of 263AB.Comment: 11 pages, 7 figures, Accepted 2016 May
Management of risk factors associated with chronic oral lesions in sheep
Oral disorders constitute a significant cause of weight loss in sheep. In a study of disorders of the oral cavity of 36, 033 sheep from 60 meat sheep flocks in Spain, we looked for management risk factors associated with chronic oral lesions. Mandibular and maxillary disorders were assessed as an external manifestation of oral lesions by palpation, searching for tissue swellings, fistulae, or open wounds. The prevalence of flocks containing sheep with jaw disorders was 98.3%, with an average individual prevalence of 5.5%. The majority of lesions were located in in the mid-region of the mandible, and the most relevant risk factor was increasing age. Use of acidic diets based on silage and inclusion of hard foods, such as maize straw or hay, was associated with the occurrence of jaw inflammation. It was concluded that hard diets containing plant material with edges and sharp areas, plus acidic foods including silage, are more likely to cause lesions of the gingiva, enabling entry of pathogens to the oral mucosa that eventually establish locally in bony tissues, usually as mandibular osteomyelitis. It was also observed that mineral supplementation appears to prevent the occurrence of these lesions
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