694 research outputs found
Exploring the circumstellar environment of the young eruptive star V2492 Cyg
Context. V2492 Cyg is a young eruptive star that went into outburst in 2010.
The near-infrared color changes observed since the outburst peak suggest that
the source belongs to a newly defined sub-class of young eruptive stars, where
time-dependent accretion and variable line-of-sight extinction play a combined
role in the flux changes.
Aims. In order to learn about the origin of the light variations and to
explore the circumstellar and interstellar environment of V2492 Cyg, we
monitored the source at ten different wavelengths, between 0.55 \mu m and 2.2
\mu m from the ground and between 3.6 \mu m and 160 \mu m from space.
Methods. We analyze the light curves and study the color-color diagrams via
comparison with the standard reddening path. We examine the structure of the
molecular cloud hosting V2492 Cyg by computing temperature and optical depth
maps from the far-infrared data.
Results. We find that the shapes of the light curves at different wavelengths
are strictly self-similar and that the observed variability is related to a
single physical process, most likely variable extinction. We suggest that the
central source is episodically occulted by a dense dust cloud in the inner
disk, and, based on the invariability of the far-infrared fluxes, we propose
that it is a long-lived rather than a transient structure. In some respects,
V2492 Cyg can be regarded as a young, embedded analog of UX Orionis-type stars.
Conclusions. The example of V2492 Cyg demonstrates that the light variations
of young eruptive stars are not exclusively related to changing accretion. The
variability provided information on an azimuthally asymmetric structural
element in the inner disk. Such an asymmetric density distribution in the
terrestrial zone may also have consequences for the initial conditions of
planet formation.Comment: 9 pages, 7 figures, 2 online tables, accepted for publication in A&
The SED of Low-Luminosity AGNs at high-spatial resolution
The inner structure of AGNs is expected to change below a certain luminosity
limit. The big blue bump, footprint of the accretion disk, is absent for the
majority of low-luminosity AGNs (LLAGNs). Moreover, recent simulations suggest
that the torus, a keystone in the Unified Model, vanishes for nuclei with L_bol
< 10^42 erg/s. However, the study of LLAGN is a complex task due to the
contribution of the host galaxy, which light swamps these faint nuclei. This is
specially critical in the IR range, at the maximum of the torus emission, due
to the contribution of the old stellar population and/or dust in the nuclear
region. Adaptive optics imaging in the NIR (VLT/NaCo) together with diffraction
limited imaging in the mid-IR (VLT/VISIR) permit us to isolate the nuclear
emission for some of the nearest LLAGNs in the Southern Hemisphere. These data
were extended to the optical/UV range (HST), radio (VLA, VLBI) and X-rays
(Chandra, XMM-Newton, Integral), in order to build a genuine spectral energy
distribution (SED) for each AGN with a consistent spatial resolution (< 0.5")
across the whole spectral range. From the individual SEDs, we construct an
average SED for LLAGNs sampled in all the wavebands mentioned before. Compared
with previous multiwavelength studies of LLAGNs, this work covers the mid-IR
and NIR ranges with high-spatial resolution data. The LLAGNs in the sample
present a large diversity in terms of SED shapes. Some of them are very well
described by a self-absorbed synchrotron (e.g. NGC 1052), while some other
present a thermal-like bump at ~1 micron (NGC 4594). All of them are
significantly different when compared with bright Seyferts and quasars,
suggesting that the inner structure of AGNs (i.e. the torus and the accretion
disk) suffers intrinsic changes at low luminosities.Comment: 8 pages, 5 figures. To appear in the proceedings of "Astrophysics at
High Angular Resolution" (AHAR 2011
Resonant neutrino spin-flavor precession and supernova shock revival
A new mechanism of supernova shock revival is proposed, which involves
resonant spin--flavor precession of neutrinos with a transition magnetic moment
in the magnetic field of the supernova. The mechanism can be operative in
supernovae for transition magnetic moments as small as provided
the neutrino mass squared difference is in the range . It is shown that this mechanism can increase the
neutrino--induced shock reheating energy by about 60\%.Comment: 16 pages, latex, 2 figures. added few reference
Inner disc rearrangement revealed by dramatic brightness variations in the young star PV Cep
Young Sun-like stars at the beginning of the pre-main sequence (PMS)
evolution are surrounded by accretion discs and remnant protostellar envelopes.
Photometric and spectroscopic variations of these stars are driven by
interactions of the star with the disc. Time scales and wavelength dependence
of the variability carry information on the physical mechanisms behind these
interactions. We conducted multi-epoch, multi-wavelength study of PV Cep, a
strongly variable, accreting PMS star. By combining our own observations from
2004-2010 with archival and literature data, we show that PV Cep started a
spectacular fading in 2005, reaching an I_C-band amplitude of 4 mag. Analysis
of variation of the optical and infrared fluxes, colour indices, and emission
line fluxes suggests that the photometric decline in 2005-2009 resulted from an
interplay between variable accretion and circumstellar extinction: since the
central luminosity of the system is dominated by accretion, a modest drop in
the accretion rate could induce the drastic restructuring of the inner disc.
Dust condensation in the inner disc region might have resulted in the
enhancement of the circumstellar extinction.Comment: 11 pages, 4 figures, accepted for publication by MNRAS. 3 online
tables adde
Use of quercetin in animal feed : effects on the P-gp expression and pharmacokinetics of orally administrated enrofloxacin in chicken
Modulation of P-glycoprotein (P-gp, encoded by Mdr1) by xenobiotics plays central role in pharmacokinetics of various drugs. Quercetin has a potential to modulate P-gp in rodents, however, its effects on P-gp modulation in chicken are still unclear. Herein, study reports role of quercetin in modulation of P-gp expression and subsequent effects on the pharmacokinetics of enrofloxacin in broilers. Results show that P-gp expression was increased in a dose-dependent manner following exposure to quercetin in Caco-2 cells and tissues of chicken. Absorption rate constant and apparent permeability coefficient of rhodamine 123 were decreased, reflecting efflux function of P-gp in chicken intestine increased by quercetin. Quercetin altered pharmacokinetic of enrofloxacin by decreasing area under curve, peak concentration, and time to reach peak concentration and by increasing clearance rate. Molecular docking shows quercetin can form favorable interactions with binding pocket of chicken xenobiotic receptor (CXR). Results provide convincing evidence that quercetin induced P-gp expression in tissues by possible interaction with CXR, and consequently reducing bioavailability of orally administered enrofloxacin through restricting its intestinal absorption and liver/kidney clearance in broilers. The results can be further extended to guide reasonable use of quercetin to avoid drug-feed interaction occurred with co-administered enrofloxacin or other similar antimicrobials.Peer reviewedFinal Published versio
Extra dimensions and atomic transition frequencies
New unification theories predict Large Extra Dimensions (LEDs). If that is
the case, gravity would be stronger at short ranges than what Newtonian gravity
predicts. LEDs could also have effects at atomic level. In this paper we
propose a new method to constrain the size of gravity-only LEDs by analyzing
how these LEDs modify the energy of the atomic transitions 1s-2s and 2s-2p
(Lamb shift), for the particular case of the hydrogen and muonium atoms. We
estimate these effects by using Bethe's non-relativistic treatment of Lamb
shift. For the particular case of three LEDs, which may be a candidate to
explain the interaction mechanism of dark matter particles, we have found that
current knowledge in atomic spectroscopy could constrain their sizes to be less
than 10 * 10^(-6) m. Although our contributions do not reach the sensitivity
given by SN1987a, they are still slightly better than recent constraints given
by Inverse Square Law tests of Eot-Wash group at Washington University, which
gave R3 < 36.6 * 10^(-6) m.Comment: 8 pages, 1 figur
Global Analysis of the post-SNO Solar Neutrino Data for Standard and Non-Standard Oscillation Mechanisms
What can we learn from solar neutrino observations? Is there any solution to
the solar neutrino anomaly which is favored by the present experimental
panorama? After SNO results, is it possible to affirm that neutrinos have mass?
In order to answer such questions we analyze the current available data from
the solar neutrino experiments, including the recent SNO result, in view of
many acceptable solutions to the solar neutrino problem based on different
conversion mechanisms, for the first time, using the same statistical
procedure. This allows us to do a direct comparison of the goodness of the fit
among different solutions, from which we can discuss and conclude on the
current status of each proposed dynamical mechanism. These solutions are based
on different assumptions: (a) neutrino mass and mixing, (b) non-vanishing
neutrino magnetic moment, (c) the existence of non-standard flavor-changing and
non-universal neutrino interactions and (d) the tiny violation of the
equivalence principle. We investigate the quality of the fit provided by each
one of these solutions not only to the total rate measured by all the solar
neutrino experiments but also to the recoil electron energy spectrum measured
at different zenith angles by the Super-Kamiokande collaboration. We conclude
that several non-standard neutrino flavor conversion mechanisms provide a very
good fit to the experimental data which is comparable with (or even slightly
better than) the most famous solution to the solar neutrino anomaly based on
the neutrino oscillation induced by mass.Comment: Minor changes in the solar magnetic field profile used, and some
refferences added. Final version to appear in PR
Constraints from Solar and Reactor Neutrinos on Unparticle Long-Range Forces
We have investigated the impact of long-range forces induced by unparticle
operators of scalar, vector and tensor nature coupled to fermions in the
interpretation of solar neutrinos and KamLAND data. If the unparticle couplings
to the neutrinos are mildly non-universal, such long-range forces will not
factorize out in the neutrino flavour evolution. As a consequence large
deviations from the observed standard matter-induced oscillation pattern for
solar neutrinos would be generated. In this case, severe limits can be set on
the infrared fix point scale, Lambda_u, and the new physics scale, M, as a
function of the ultraviolet (d_UV) and anomalous (d) dimension of the
unparticle operator. For a scalar unparticle, for instance, assuming the
non-universality of the lepton couplings to unparticles to be of the order of a
few per mil we find that, for d_UV=3 and d=1.1, M is constrained to be M >
O(10^9) TeV (M > O(10^10) TeV) if Lambda_u= 1 TeV (10 TeV). For given values of
Lambda_u and d, the corresponding bounds on M for vector [tensor] unparticles
are approximately 100 [3/Sqrt(Lambda_u/TeV)] times those for the scalar case.
Conversely, these results can be translated into severe constraints on
universality violation of the fermion couplings to unparticle operators with
scales which can be accessible at future colliders.Comment: 13 pages, 3 figures. Minor changes due to precision in numerical
factors and correction in figure labels. References added. Conclusions remain
unchange
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