1,031 research outputs found
Discovery of the first tau Sco analogues: HD 66665 and HD 63425
The B0.2 V magnetic star tau Sco stands out from the larger population of
massive OB stars due to its high X-ray activity, peculiar wind diagnostics and
highly complex magnetic field. This paper presents the discovery of the first
two tau Sco analogues - HD 66665 and HD 63425, identified by the striking
similarity of their UV spectra to that of tau Sco. ESPaDOnS spectropolarimetric
observations were secured by the Magnetism in Massive Stars CFHT Large Program,
in order to characterize the stellar and magnetic properties of these stars.
CMFGEN modelling of optical ESPaDOnS spectra and archived IUE UV spectra showed
that these stars have stellar parameters similar to those of tau Sco. A
magnetic field of similar surface strength is found on both stars, reinforcing
the connection between the presence of a magnetic field and wind peculiarities.
However, additional phase-resolved observations will be required in order to
assess the potential complexity of the magnetic fields, and verify if the wind
anomalies are linked to this property.Comment: 6 pages, 2 tables, 3 figures. Accepted for publication in MNRAS. The
definitive version will be available at www.blackwel-synergy.co
Improving LIGO calibration accuracy by tracking and compensating for slow temporal variations
Calibration of the second-generation LIGO interferometric gravitational-wave
detectors employs a method that uses injected periodic modulations to track and
compensate for slow temporal variations in the differential length response of
the instruments. These detectors utilize feedback control loops to maintain
resonance conditions by suppressing differential arm length variations. We
describe how the sensing and actuation functions of these servo loops are
parameterized and how the slow variations in these parameters are quantified
using the injected modulations. We report the results of applying this method
to the LIGO detectors and show that it significantly reduces systematic errors
in their calibrated outputs.Comment: 13 pages, 8 figures. This is an author-created, un-copyedited version
of an article published in Classical and Quantum Gravity. IOP Publishing Ltd
is not responsible for any errors or omissions in this version of the
manuscript or any version derived from i
Submillimeter-wave antennas on thin membranes
Submillimeter-wave antennas with bismuth microbolometer detectors have been fabricated on 1-μm thick silicon-oxynitride membranes. This approach results in better patterns than previous lens-coupled integrated circuit antennas, and eliminates the dielectric loss associated with the substrate lens. Measurements on a wideband log-periodic antenna at 700 GHz, 380 GHz and 167 GHz, and on a 700 GHz log-periodic imaging array, show no sidelobee and a 3-dB beamwidth between 40° and 50°. Also, the effective area can be increased by 5 dB by the use of a back-shorting mirror. Possible application areas are superconducting tunnel junction receivers for radio astronomy and imaging arrays for plasma diagnostics
Calibration Uncertainty for Advanced LIGO's First and Second Observing Runs
Calibration of the Advanced LIGO detectors is the quantification of the
detectors' response to gravitational waves. Gravitational waves incident on the
detectors cause phase shifts in the interferometer laser light which are read
out as intensity fluctuations at the detector output. Understanding this
detector response to gravitational waves is crucial to producing accurate and
precise gravitational wave strain data. Estimates of binary black hole and
neutron star parameters and tests of general relativity require well-calibrated
data, as miscalibrations will lead to biased results. We describe the method of
producing calibration uncertainty estimates for both LIGO detectors in the
first and second observing runs.Comment: 15 pages, 21 figures, LIGO DCC P160013
Reconstructing the calibrated strain signal in the Advanced LIGO detectors
Advanced LIGO's raw detector output needs to be calibrated to compute
dimensionless strain h(t). Calibrated strain data is produced in the time
domain using both a low-latency, online procedure and a high-latency, offline
procedure. The low-latency h(t) data stream is produced in two stages, the
first of which is performed on the same computers that operate the detector's
feedback control system. This stage, referred to as the front-end calibration,
uses infinite impulse response (IIR) filtering and performs all operations at a
16384 Hz digital sampling rate. Due to several limitations, this procedure
currently introduces certain systematic errors in the calibrated strain data,
motivating the second stage of the low-latency procedure, known as the
low-latency gstlal calibration pipeline. The gstlal calibration pipeline uses
finite impulse response (FIR) filtering to apply corrections to the output of
the front-end calibration. It applies time-dependent correction factors to the
sensing and actuation components of the calibrated strain to reduce systematic
errors. The gstlal calibration pipeline is also used in high latency to
recalibrate the data, which is necessary due mainly to online dropouts in the
calibrated data and identified improvements to the calibration models or
filters.Comment: 20 pages including appendices and bibliography. 11 Figures. 3 Table
Optical spectroscopy and Doppler tomography of Cygnus X-2
We present phase resolved optical spectroscopy and Doppler tomography of
V1341 Cygni, the optical counterpart to the neutron star low mass X-ray binary
Cygnus X-2. We derive a radial velocity curve for the secondary star, finding a
projected radial velocity semi-amplitude of K2 = 79 +/- 3 km/s, leading to a
mass function of 0.51 +/- 0.06 Msun, ~30% lower than the previous estimate. We
tentatively attribute the lower value of K2 (compared to that obtained by other
authors) to variations in the X-ray irradiation of the secondary star at
different epochs of observations. The limited phase coverage and/or longer
timebase of previous observations may also contribute to the difference in K2.
Our value for the mass function implies a primary mass of 1.5 +/- 0.3 Msun,
somewhat lower than previous dynamical estimates, but consistent with the value
found by analysis of type-I X-ray bursts from this system. Our Doppler
tomography of the broad He II 4686 line reveals that most of the emission from
this line is produced on the irradiated face of the donor star, with little
emission from the accretion disc. In contrast, the Doppler tomogram of the N
III 4640.64 Bowen blend line shows bright emission from near the gas
stream/accretion disc impact region, with fainter emission from the gas stream
and secondary star. This is the first LMXB for which the Bowen blend is
dominated by emission from the gas stream/accretion disc impact region, without
comparable emission from the secondary star. This has implications for the
interpretation of Bowen blend Doppler tomograms of other LMXBs for which the
ephemeris may not be accurately known.Comment: 11 pages, 10 figures, 4 tables; Accepted for publication in MNRA
The Advanced LIGO Photon Calibrators
The two interferometers of the Laser Interferometry Gravitaional-wave
Observatory (LIGO) recently detected gravitational waves from the mergers of
binary black hole systems. Accurate calibration of the output of these
detectors was crucial for the observation of these events, and the extraction
of parameters of the sources. The principal tools used to calibrate the
responses of the second-generation (Advanced) LIGO detectors to gravitational
waves are systems based on radiation pressure and referred to as Photon
Calibrators. These systems, which were completely redesigned for Advanced LIGO,
include several significant upgrades that enable them to meet the calibration
requirements of second-generation gravitational wave detectors in the new era
of gravitational-wave astronomy. We report on the design, implementation, and
operation of these Advanced LIGO Photon Calibrators that are currently
providing fiducial displacements on the order of
m/ with accuracy and precision of better than 1 %.Comment: 14 pages, 19 figure
Quantitative spectroscopy of Galactic BA-type supergiants. I. Atmospheric parameters
BA-type supergiants show a high potential as versatile indicators for modern
astronomy. The focus here is on the determination of accurate and precise
atmospheric parameters for a sample of 35 Galactic BA-type supergiants. Some
first applications include a recalibration of functional relationships between
spectral-type, intrinsic colours, bolometric corrections and effective
temperature, and an exploration of the reddening-free Johnson Q and Str\"omgren
[c_1] and beta-indices as photometric indicators for effective temperatures and
gravities of BA-type supergiants. An extensive grid of theoretical spectra is
computed based on a hybrid non-LTE approach. The atmospheric parameters are
derived spectroscopically by line-profile fits to high-resolution and high-S/N
spectra obtained at various observatories. Ionization equilibria of multiple
metals and the Stark-broadened H and the neutral He lines constitute our
primary indicators for the parameter determination, supplemented by
(spectro-)photometry. Data on Teff, logg, helium abundances, microturbulence,
macroturbulence and rotational velocities are presented. The interstellar
reddening and the ratio of total-to-selective extinction towards the stars are
determined. Our empirical spectral-type-Teff scale is steeper than reference
relations, the stars are significantly bluer, and bolometric corrections differ
significantly from established literature values. Photometric
Teff-determinations based on the reddening-free Q-index are found to be of
limited use for studies of BA-type supergiants because of large errors of
typically +-5%+-3% (1sigma statistical, 1sigma systematic), compared to a
spectroscopically achieved precision of 1-2%. The reddening-free [c_1]-index
and beta on the other hand are found to provide useful starting values for
further analyses, with uncertainties of +-1%+-2.5% in Teff, and +-0.04+-0.13dex
in log g. [abriged]Comment: 18 pages, 18 figures; A&
Community-based interventions for adolescents following traumatic brain injury: a systematic review
Background: Chronic impairment following childhood traumatic brain injury has the potential to increase risk of negative outcomes. This highlights potential value of community-based rehabilitation programs. Objectives: To identify research studies examining existing intervention programmes available in community-based rehabilitation to adolescents following TBI to assist with the transition back into the community. Methods: A systematic review of community-based interventions was conducted across different national contexts. All included studies involved a clinical population with TBI, aged 11 to 25 years inclusive. Risk of bias was rated for each included study. Results: Seventeen studies were identified for inclusion in the review, of these eleven distinct interventions were found. The quality of evidence was largely weak and highly variable. Conclusion: The results suggest some improvement in adolescent outcomes following community-based interventions, however higher quality evidence is needed to support specific interventions
Just add milk: a productivity analysis of the revolutionary changes in nineteenth century Danish dairying
The late nineteenth century Danish agricultural revolution saw the
modernization and growth of the dairy industry. Denmark rapidly
caught up with the leading economies, and Danish dairying led the
world in terms of productivity. Uniquely in a world perspective, high
quality micro-level data exist documenting this episode. These allow
the use of the tool of modern agricultural economists, stochastic
frontier analysis, to estimate production functions for milk and thus
find the determinants of these productivity and efficiency advances.
We identify the contribution of modernization through specific new
technologies and practices.Paul Sharp would like to acknowledge generous support from the Carlsberg Foundation, while Markus Lampe
appreciates funding by Spain’s Ministerio de Ciencia e Innovación (project ECO2011-25713). Some of this paper
was written while Markus Lampe was visiting the Department of Economics, University of Copenhagen funded by a
grant from UC3M
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