11,240 research outputs found
No surviving evolved companions to the progenitor of supernova SN 1006
Type Ia supernovae are thought to occur as a white dwarf made of carbon and
oxygen accretes sufficient mass to trigger a thermonuclear explosion. The
accretion could occur slowly from an unevolved (main-sequence) or evolved
(subgiant or giant) star, that being dubbed the single-degenerate
channel, or rapidly as it breaks up a smaller orbiting white dwarf (the double-
degenerate channel). Obviously, a companion will survive the explosion
only in the single-degenerate channel. Both channels might contribute to
the production of type Ia supernovae but their relative proportions
still remain a fundamental puzzle in astronomy. Previous searches for remnant
companions have revealed one possible case for SN 1572, though that has
been criticized. More recently, observations have restricted surviving
companions to be small, main-sequence stars, ruling out giant
companions, though still allowing the single-degenerate channel. Here we report
the result of a search for surviving companions to the progenitor of SN
1006. None of the stars within 4' of the apparent site of the explosion
is associated with the supernova remnant, so we can firmly exclude all giant
and subgiant companions to the progenitor. Combined with the previous results,
less than 20 per cent of type Iae occur through the single degenerate channel.Comment: Published as a letter in Nature (2012 September 27
No surviving companion in Kepler's supernova
We have surveyed Kepler's supernova remnant in search of the companion star
of the explosion. We have gone as deep as 2.6 solar luminosities in the stars
within 20% of the radius of the remnant. We use FLAMES at the VLT-UT2 telescope
to obtain high resolution spectra of the stellar candidates selected from HST
images. The resulting set of stellar parameters suggests that these stars come
from a rather ordinary mixture of field stars (mostly giants). A few of the
stars seem to have low [Fe/H] (< -1) and they are consistent with being
metal-poor giants. The radial velocities and rotational velocities vrot sin i
are very well determined. There are no fast rotating stars as vrot sin i < 20
km/s. The radial velocities from the spectra and the proper motions determined
from HST images are compatible with those expected from the Besan\c{c}on model
of the Galaxy. The strong limits placed on luminosity suggest that this
supernova could have arisen either from the core-degenerate scenario or from
the double-degenerate scenario.Comment: ApJ accepted, 7 figures and 7 table
Natural History, Phenology, and Stream Use of Hyla plicata from the Arroyo los Axolotes, State of Mexico, Mexico
Optical and near infrared observations of SN 1998bu
Infrared and optical spectra of SN 1998bu at an age of one year after
explosion are presented. The data show evidence for the radioactive decay of
56Co to 56Fe, long assumed to be the powering source for the supernova light
curve past maximum light. The spectra provide direct evidence for at least 0.4
solar masses of iron being present in the ejecta of the supernova. The fits to
the data also show that the widths of the emission lines increase with time.
Photometric measurements in the H-band show that the supernova is not fading
during the observation period. This is consistent with theoretical
expectations.Comment: accepted A&A, 7 pages, 9 figure
Sediment stress, water turbidity and sewage impacts on threatened Elkhorn Coral (Acropora palmata) Stands at Vega Baja, Puerto Rico.
Walls talk: Microbial biogeography of homes spanning urbanization.
Westernization has propelled changes in urbanization and architecture, altering our exposure to the outdoor environment from that experienced during most of human evolution. These changes might affect the developmental exposure of infants to bacteria, immune development, and human microbiome diversity. Contemporary urban humans spend most of their time indoors, and little is known about the microbes associated with different designs of the built environment and their interaction with the human immune system. This study addresses the associations between architectural design and the microbial biogeography of households across a gradient of urbanization in South America. Urbanization was associated with households' increased isolation from outdoor environments, with additional indoor space isolation by walls. Microbes from house walls and floors segregate by location, and urban indoor walls contain human bacterial markers of space use. Urbanized spaces uniquely increase the content of human-associated microbes-which could increase transmission of potential pathogens-and decrease exposure to the environmental microbes with which humans have coevolved
Failed limb salvage by microsurgery, resolved by super-microsurgery
Advances in perforating artery flaps have improved reconstruction in various body parts, particularly the lower extremities, offering benefits in patient quality of life and reduced public health service costs. The use of flaps and microsurgery extends beyond trauma to address conditions like osteomyelitis, tumor resection, osteoarthritis, and post-radiation necrosis. Notably, the superficial circumflex iliac artery perforator flap (SCIP) is highlighted for its thin profile and utility in limb coverage, minimizing donor site morbidity. Microsurgical techniques contribute to limb salvage, reducing amputation risks in severe fractures and post-osteosynthesis complications. A 29-year-old male with cerebral palsy suffered bimalleolar fracture from a high-energy motor vehicle accident. Initial ALT flap reconstruction failed, leading to flap removal and osteosynthesis exposure. After 48 hours, removal of the flap was necessary due to venous thrombosis. Salvage with SCIP flap involved anastomosis to perforators of both posterior tibial artery and vein. This case details a patient with a bimalleolar fracture post-motorcycle accident, initially treated with conventional microsurgery using an ALT flap. Complications arose from venous thrombosis, necessitating flap removal. Salvage was achieved through a SCIP flap with supermicrosurgery techniques, employing 0.5 mm anastomosis for improved functionality and reduced complications in flap recovery and donor site comorbidities. Successful outcomes in microsurgery and supermicrosurgery necessitate comprehensive training. Specialized limb salvage centers must possess specific equipment and instruments for these techniques. The literature reviewed doesn't indicate contraindications related to the patient's mental state for the execution of microsurgery and supermicrosurgery
Prediction of early response to radiation therapy using FDG-PET standard uptake value in advanced head and neck cancer
Enhancement of Electrical Conduction and Phonon Scattering in Ga2O3(ZnO)9-In2O3(ZnO)9 Compounds by Modification of Interfaces at the Nanoscale
The Ga2O3(ZnO)9 and In2O3(ZnO)9 homologous phases have attracted attention as thermoelectric (TE) oxides due to their layered structures. Ga2O3(ZnO)9 exhibits low thermal conductivity, while In2O3(ZnO)9 possesses higher electrical conductivity. The TE properties of the solid solution of Ga2O3(ZnO)9-In2O3(ZnO)9 were explored and correlated with changes in the crystal structure. High-quality (1−x)Ga2O3(ZnO)9-(ZnO)9 (x = 0.0 to 1.0) ceramics were prepared by the solid-state route using B2O3 and Nd2O3 as additives. The crystal structures were analysed by x-ray diffraction, high-resolution transmission electron microscopy and atomic resolution scanning transmission electron microscopy–high-angle annular dark field imaging–energy dispersive x-ray spectroscopy (STEM–HAADF–EDS) techniques. A layered superstructure with compositional modulations was observed in all samples in the (1−x)Ga2O3(ZnO)9-xIn2O3(ZnO)9 system. All the ceramics exhibited nanoscale structural features identified as Ga- and In-rich inversion boundaries (IBs). Substitution of 20 mol.% In (x = 0.2) in the Ga2O3(ZnO)9 compounds generated basal and pyramidal indium IBs typically found in the In2O3(ZnO)m system. The (Ga0.8In0.2)2O3(ZnO)9 compound does not exhibit the structural features of the Cmcm Ga2O3(ZnO)9 compound, which is formed by a stacking of Ga-rich IBs along the pyramidal plane of the wurtzite ZnO, but features that resemble the crystal structure exhibited by the R3¯¯¯m In2O3(ZnO)m with basal and pyramidal indium IBs. The structural changes led to improved TE performance. For example, (Ga0.8In0.2)2O3(ZnO)9 showed a low thermal conductivity of 2 W/m K and a high power factor of 150 μW/m K2 giving a figure of merit (ZT) of 0.07 at 900 K. This is the highest ZT for Ga2O3(ZnO)9-based homologous compounds and is comparable with the highest ZT reported for In2O3(ZnO)9 homologous compounds
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