1,186 research outputs found
The quest for the ideal photodetector for the next generation deep-underwater neutrino telescopes
We review photodetectors used in present running neutrino telescopes. After a
brief historical discourse, the photodetector requirements for the next
generation deep underwater neutrino telescopes are discussed. It is shown that
large area vacuum hybrid phototubes are the closest to the ideal photodetector
for such kind of applications when compared with other vacuum phototubes.Comment: 5 pages, 5 figure
The long-period binary central stars of the planetary nebulae NGC 1514 and LoTr 5
The importance of long-period binaries on the formation and evolution of
planetary nebulae is still rather poorly understood, in part due to the lack of
central star systems known to comprise such long-period binaries.
Here, we report on the latest results from the on-going Mercator-HERMES
survey for variability in the central stars of planetary nebulae.
We present a study of the central stars of NGC 1514, BD+30623, the
spectrum of which shows features associated with a hot nebular progenitor as
well as a possible A-type companion. Cross-correlation of high-resolution
HERMES spectra against synthetic spectra shows the system to be a highly
eccentric (), double-lined binary with a period of 3300 days.
Previous studies indicated that the cool component might be a Horizontal Branch
star of mass 0.55 M but the observed radial velocity amplitudes
rule out such a low mass. Assuming the nebular symmetry axis and binary orbital
plane are perpendicular, the data are more consistent with a post-main-sequence
star ascending towards the Giant Branch.
We also present the continued monitoring of the central star of LoTr 5, HD
112313, which has now completed one full cycle, allowing the orbital period
(P2700 days) and eccentricity () to be derived.
To date, the orbital periods of BD+30623 and HD 112313 are the
longest to have been measured spectroscopically in the central stars of
planetary nebulae. Furthermore, these systems, along with BD+332642,
comprise the only spectroscopic wide-binary central stars currently known.Comment: 4 pages, 4 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysics Letter
A new look inside Planetary Nebula LoTr 5: A long-period binary with hints of a possible third component
LoTr 5 is a planetary nebula with an unusual long-period binary central star.
As far as we know, the pair consists of a rapidly rotating G-type star and a
hot star, which is responsible for the ionization of the nebula. The rotation
period of the G-type star is 5.95 days and the orbital period of the binary is
now known to be 2700 days, one of the longest in central star of
planetary nebulae. The spectrum of the G central star shows a complex H
double-peaked profile which varies with very short time scales, also reported
in other central stars of planetary nebulae and whose origin is still unknown.
We present new radial velocity observations of the central star which allow us
to confirm the orbital period for the long-period binary and discuss the
possibility of a third component in the system at 129 days to the G star.
This is complemented with the analysis of archival light curves from SuperWASP,
ASAS and OMC. From the spectral fitting of the G-type star, we obtain a
effective temperature of = 5410250 K and surface gravity of
= 2.70.5, consistent with both giant and subgiant stars. We also
present a detailed analysis of the H double-peaked profile and conclude
that it does not present correlation with the rotation period and that the
presence of an accretion disk via Roche lobe overflow is unlikely.Comment: 12 pages, 12 figures, accepted for publication in MNRA
Multiple Tidal Disruptions as an Indicator of Binary Super-Massive Black Hole Systems
We find that the majority of systems hosting multiple tidal disruptions are
likely to contain hard binary SMBH systems, and also show that the rates of
these repeated events are high enough to be detected by LSST over its lifetime.
Therefore, these multiple tidal disruption events provide a novel method to
identify super-massive black hole (SMBH) binary systems with parsec to
sub-parsec separations. The rates of tidal disruptions are investigated using
simulations of non-interacting stars initially orbiting a primary SMBH and the
potential of the model stellar cusp. The stars are then evolved forward in time
and perturbed by a secondary SMBH inspiraling from the edge of the cusp to its
stalling radius. We find with conservative magnitude estimates that the next
generation transient survey LSST should detect multiple tidal disruptions in
approximately 3 galaxies over 5 years of observation, though less conservative
estimates could increase this rate by an order of magnitude.Comment: 5 pages, 3 figure
Physico-chemical spectroscopic mapping of the planetary nebula NGC 40 and the 2D_NEB, a new 2D algorithm to study ionised nebulae
In this paper we present an analysis of the physical and chemical conditions
of the planetary nebula NGC 40 through spatially-resolved spectroscopic maps.
We also introduce a new algorithm --2D_NEB-- based on the well-established IRAF
nebular package, which was developed to enable the use of the spectroscopic
maps to easily estimate the astrophysical quantities of ionised nebulae. The
2D_NEB was benchmarked, and we clearly show that it works properly, since it
compares nicely with the IRAF nebular software.
Using this software, we derive the maps of several physical parameters of NGC
40. From these maps, we conclude that Te[NII] shows only a slight temperature
variation from region to region, with its values constrained between ~8,000 K
and ~9,500 K. Electron densities, on the other hand, have a much more prominent
spatial variation, as Ne[SII] values vary from ~1,000 cm^(-3) to ~3,000
cm^(-3). Maps of the chemical abundances also show significant variations. From
the big picture of our work, we strongly suggest that analysis with spatial
resolution be mandatory for more complete study of the physical and chemical
properties of planetary nebulae.Comment: 15 pages, 10 figures, 8 tables; Accepted for publication in MNRA
The optical module of the Baikal deep underwater neutrino telescope
A deep underwater Cherenkov telescope has been operating since 1993 in stages
of growing size at 1.1 km depth in Lake Baikal. The key component of the
telescope is the Optical Module (OM) which houses the highly sensitive
phototube QUASAR-370. We describe design and parameters of the QUASAR-370, the
layout of the optical module, the front-end electronics and the calibration
procedures, and present selected results from the five-year operation
underwater. Also, future developments with respect to a telescope consisting
from several thousand OMs are discussed.Comment: 30 pages, 24 figure
Discordant bioinformatic predictions of antimicrobial resistance from whole-genome sequencing data of bacterial isolates: an inter-laboratory study.
Antimicrobial resistance (AMR) poses a threat to public health. Clinical microbiology laboratories typically rely on culturing bacteria for antimicrobial-susceptibility testing (AST). As the implementation costs and technical barriers fall, whole-genome sequencing (WGS) has emerged as a 'one-stop' test for epidemiological and predictive AST results. Few published comparisons exist for the myriad analytical pipelines used for predicting AMR. To address this, we performed an inter-laboratory study providing sets of participating researchers with identical short-read WGS data from clinical isolates, allowing us to assess the reproducibility of the bioinformatic prediction of AMR between participants, and identify problem cases and factors that lead to discordant results. We produced ten WGS datasets of varying quality from cultured carbapenem-resistant organisms obtained from clinical samples sequenced on either an Illumina NextSeq or HiSeq instrument. Nine participating teams ('participants') were provided these sequence data without any other contextual information. Each participant used their choice of pipeline to determine the species, the presence of resistance-associated genes, and to predict susceptibility or resistance to amikacin, gentamicin, ciprofloxacin and cefotaxime. We found participants predicted different numbers of AMR-associated genes and different gene variants from the same clinical samples. The quality of the sequence data, choice of bioinformatic pipeline and interpretation of the results all contributed to discordance between participants. Although much of the inaccurate gene variant annotation did not affect genotypic resistance predictions, we observed low specificity when compared to phenotypic AST results, but this improved in samples with higher read depths. Had the results been used to predict AST and guide treatment, a different antibiotic would have been recommended for each isolate by at least one participant. These challenges, at the final analytical stage of using WGS to predict AMR, suggest the need for refinements when using this technology in clinical settings. Comprehensive public resistance sequence databases, full recommendations on sequence data quality and standardization in the comparisons between genotype and resistance phenotypes will all play a fundamental role in the successful implementation of AST prediction using WGS in clinical microbiology laboratories
SBS 1150+599A: an extremely oxygen-poor planetary nebula in the Galactic halo?
We report results of a spectrophotometric study of SBS 1150+599A and discuss
the nature of this object based upon our data. Our study shows that SBS
1150+599A is most probably a planetary nebula located in the Galactic halo and
not a cataclysmic variable as originally proposed by the authors of the Second
Byurakan Survey from low resolution spectroscopy. We have further elaborated on
the properties of SBS 1150+599A (now becoming PN G135.9+55.9) with tools used
for planetary nebula analysis. Our photoionization models show that, in order
to match the observational constraints, the oxygen abundance in the nebula is
probably extremely low, around 1/500 solar, which is one order of magnitude
lower than the most oxygen-poor planetary nebulae known so far. This finding
has strong implications on our understanding of the formation of planetary
nebulae and of the evolution of the Galactic halo.Comment: 13 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
Remarkable preservation of microbial mats in Neoproterozoic siliciclastic settings : Implications for Ediacaran taphonomic models
The authors thank Duncan McIlroy and Alex Liu for their discussions, help, comments and field support, the National Trust for access to Longmyndian localities, and the staff of the British Geological Survey Palaeontology unit and the Oxford University Museum of Natural History for their assistance with access to materials. The comments and suggestions of two anonymous reviewers and Nora Noffke significantly improved the manuscript.Peer reviewedPostprin
- …