2,838 research outputs found
Numerically Modeling the First Peak of the Type IIb SN 2016gkg
Many Type IIb supernovae (SNe) show a prominent additional early peak in
their light curves, which is generally thought to be due to the shock cooling
of extended hydrogen-rich material surrounding the helium core of the exploding
star. The recent SN 2016gkg was a nearby Type IIb SN discovered shortly after
explosion, which makes it an excellent candidate for studying this first peak.
We numerically explode a large grid of extended envelope models and compare
these to SN 2016gkg to investigate what constraints can be derived from its
light curve. This includes exploring density profiles for both a convective
envelope and an optically thick steady-state wind, the latter of which has not
typically been considered for Type IIb SNe models. We find that roughly
of extended material with a radius of
reproduces the photometric light curve data,
consistent with pre-explosion imaging. These values are independent of the
assumed density profile of this material, although a convective profile
provides a somewhat better fit. We infer from our modeling that the explosion
must have occurred within of the first observed data
point, demonstrating that this event was caught very close to the moment of
explosion. Nevertheless, our best-fitting one-dimensional models overpredict
the earliest velocity measurements, which suggests that the hydrogen-rich
material is not distributed in a spherically symmetric manner. We compare this
to the asymmetries seen in the SN IIb remnant Cas A, and we discuss the
implications of this for Type IIb SN progenitors and explosion models.Comment: 8 pages, 8 figures, updated version accepted for publication in The
Astrophysical Journa
The Metallicity of the HD 98800 System
Pre-main sequence (PMS) binaries and multiples enable critical tests of
stellar models if masses, metallicities, and luminosities of the component
stars are known. We have analyzed high-resolution, high signal-to-noise echelle
spectra of the quadruple-star system HD 98800 and using spectrum synthesis,
computed fits to the composite spectrum for a full range of plausible stellar
parameters for the components. We consistently find that sub-solar metallicity
yields fits with lower values, with an overall best-fit of . This metallicity appears to be consistent with PMS evolutionary
tracks for the measured masses and luminosities of the components of HD 98800
but additional constraints on the system and modelling are needed.Comment: 6 pages, 3 figures, 5 tables. Online-only material: color figure.
Accepted in Ap
The involvement of autonomic nervous system and inflammatory mechanisms in chronic fatigue: Perspectives for future studies [letter to the editor]
Cardiac embolization of an implanted fiducial marker for hepatic stereotactic body radiotherapy: a case report
<p>Abstract</p> <p>Introduction</p> <p>In liver stereotactic body radiotherapy, reduction of normal tissue irradiation requires daily image guidance. This is typically accomplished by imaging a surrogate to the tumor. The surrogate is often an implanted metal fiducial marker. There are few reports addressing the specific risks of hepatic fiducial marker implantation. These risks are assumed to be similar to percutaneous liver biopsies which are associated with a 1-4% complication rate - almost always pain or bleeding. To the best of our knowledge, we present the first case of such a fiducial marker migrating to the heart.</p> <p>Case presentation</p> <p>An 81-year-old Caucasian man (5 years post-gastrectomy for a gastric adenocarcinoma) was referred post-second line palliative chemotherapy for radiotherapy of an isolated liver metastasis. It was decided to proceed with treatment and platinum fiducials were chosen for radiation targeting. Under local anesthesia, three Nester embolization coils (Cook Medical Inc., Bloomington, IN, USA) were implanted under computed tomography guidance. Before the placement of each coil, the location of the tip of the delivery needle was confirmed by computed tomography imaging. During the procedure, the third coil unexpectedly migrated through the hepatic vein to the inferior vena cava and lodged at the junction of the vena cava and the right atrium. The patient remained asymptomatic. He was immediately referred to angiography for extraction of the coil. Using fluoroscopic guidance, an EN Snare Retrieval System (Hatch Medical L.L.C., Snellville, GA, USA) was introduced through a jugular catheter; it successfully grasped the coil and the coil was removed. The patient was kept overnight for observation and no immediate or delayed complications were encountered due to the migration or retrieval of the coil. He subsequently went on to be treated using the remaining fiducials.</p> <p>Conclusion</p> <p>Implanted fiducial markers are increasingly used for stereotactic radiotherapy. There is sparse literature on the risks of such procedures. Although uncommon, the risk of migration does exist and therefore physicians (surgeons, oncologists and radiologists) and patients should be aware of this possibility.</p
Medindo a sustentabilidade na aquicultura
Atualmente há uma forte preocupação por parte da sociedade em se respeitar os preceitos da sustentabilidade nos sistemas, incluindo a produção de alimentos. No entanto, diversas são as definições para o termo sustentável, em decorrência de sua concepção sobre o grau de importância dado à economia e meio ambiente. Consequentemente, vários são os métodos elaborados e usados para avaliar a sustentabilidade. Alguns deles foram desenvolvidos exclusivamente para a aquicultura, enquanto outros são aplicações de métodos gerais em sistemas aqüÃcolas. Apresentaremos aqui uma breve descrição dessas metodologias e suas aplicações nos sistemas de aqüicultura.Fil: Kimpara, Janaina M.. Universidade Federal Do Espirito Santo; Brasil. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Zajdband, Ariel David. Universidad de Buenos Aires. Facultad de Agronomia. Departamento de Producción Animal; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Valenti, Wagner C.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasi
An empirical limit on the kilonova rate from the DLT40 one day cadence Supernova Survey
Binary neutron star mergers are important to understand stellar evolution,
the chemical enrichment of the universe via the r-process, the physics of short
gamma-ray bursts, gravitational waves and pulsars. The rates at which these
coalescences happen is uncertain, but it can be constrained in different ways.
One of those is to search for the optical transients produced at the moment of
the merging, called a kilonova, in ongoing SN searches. However, until now,
only theoretical models for kilonovae light curve were available to estimate
their rates. The recent kilonova discovery AT~2017gfo/DLT17ck gives us the
opportunity to constrain the rate of kilonovae using the light curve of a real
event. We constrain the rate of binary neutron star mergers using the DLT40
Supernova search, and the native AT~2017gfo/DLT17ck light curve obtained with
the same telescope and software system. Excluding AT~2017gfo/DLT17ck due to
visibility issues, which was only discovered thanks to the aLIGO/aVirgo
trigger, no other similar transients detected during 13 months of daily cadence
observations of 2200 nearby (40 Mpc) galaxies. We find that the rate
of BNS mergers is lower than 0.47 - 0.55 kilonovae per 100 years per
(depending on the adopted extinction distribution). In volume,
this translates to <0.99\times
10^{-4}\,_{-0.15}^{+0.19},\rm{Mpc^{-3}}\,\rm{yr^{-1}}(SNe Ia-like extinction
distribution), consistent with previous BNS coalescence rates. Based on our
rate limit, and the sensitivity of aLIGO/aVirgo during O2, it is very unlikely
that kilonova events are lurking in old pointed galaxy SN search datasets.Comment: 3 figures, 2 table
Environment reporters and U.S. journalists: A comparative analysis
This study provides baseline data regarding environment reporters in the twenty-first century, and then compares this baseline information about a specialized journalism beat to existing studies of U.S. journalists in general. This comparison between 652 environmental journalists working at daily newspapers and television stations and more than 1,000 U.S. journalists in general found that these reporters share many individual and work-related characteristics, perhaps due in part to their similar backgrounds and to the basic professional training received by most journalists. The authors propose a uniform theory of journalism education, arguing that journalists are journalists first because they are linked by their studies, training, and experience, and that differences among reporters may be related to variations in their education. The researchers also found that newspapers employ more specialized reporters than do television stations, and that the bigger the newspaper, the more specialists, suggesting that bigger is better for specialized reporting
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