1,518 research outputs found
The magnetic fields of hot subdwarf stars
Detection of magnetic fields has been reported in several sdO and sdB stars.
Recent literature has cast doubts on the reliability of most of these
detections. We revisit data previously published in the literature, and we
present new observations to clarify the question of how common magnetic fields
are in subdwarf stars. We consider a sample of about 40 hot subdwarf stars.
About 30 of them have been observed with the FORS1 and FORS2 instruments of the
ESO VLT. Here we present new FORS1 field measurements for 17 stars, 14 of which
have never been observed for magnetic fields before. We also critically review
the measurements already published in the literature, and in particular we try
to explain why previous papers based on the same FORS1 data have reported
contradictory results. All new and re-reduced measurements obtained with FORS1
are shown to be consistent with non-detection of magnetic fields. We explain
previous spurious field detections from data obtained with FORS1 as due to a
non-optimal method of wavelength calibration. Field detections in other surveys
are found to be uncertain or doubtful, and certainly in need of confirmation.
There is presently no strong evidence for the occurrence of a magnetic field in
any sdB or sdO star, with typical longitudinal field uncertainties of the order
of 2-400 G. It appears that globally simple fields of more than about 1 or 2 kG
in strength occur in at most a few percent of hot subdwarfs, and may be
completely absent at this strength. Further high-precision surveys, both with
high-resolution spectropolarimeters and with instruments similar to FORS1 on
large telescopes, would be very valuable
First Attempt at Spectroscopic Detection of Gravity Modes in a Long-Period Pulsating Subdwarf B Star -- PG 1627+017
In the first spectroscopic campaign for a PG 1716 variable (or long-period
pulsating subdwarf B star), we succeeded in detecting velocity variations due
to g-mode pulsations at a level of 1.0-1.5 km/s.The observations were obtained
during 40 nights on 2-m class telescopes in Arizona, South Africa,and
Australia. The target,PG1627+017, is one of the brightest and largest amplitude
stars in its class.It is also the visible component of a post-common envelope
binary.Our final radial velocity data set includes 84 hours of time-series
spectroscopy over a time baseline of 53 days. Our derived radial velocity
amplitude spectrum, after subtracting the orbital motion, shows three potential
pulsational modes 3-4 sigma above the mean noise level, at 7201.0s,7014.6s and
7037.3s.Only one of the features is statistically likely to be real,but all
three are tantalizingly close to, or a one day alias of, the three strongest
periodicities found in the concurrent photometric campaign. We further
attempted to detect pulsational variations in the Balmer line amplitudes. The
single detected periodicity of 7209 s, although weak, is consistent with
theoretical expectations as a function of wavelength.Furthermore, it allows us
to rule out a degree index of l= 3 or l= 5 for that mode. Given the extreme
weakness of g-mode pulsations in these stars,we conclude that anything beyond
simply detecting their presence will require larger telescopes,higher
efficiency spectral monitoring over longer time baselines,improved longitude
coverage, and increased radial velocity precision.Comment: 39 pages, 9 figures, 4 tables, ApJ accepted. See postscript for full
abtrac
Discrimination of Disposable Vapes from Batteries Using the Magnetic Polarizability Tensor
Disposable vapes pose an environmental and fire hazard to waste streams when disposed of incorrectly. The lithium battery inside disposable vapes can produce an exothermic reaction when the lithium inside the battery is inadvertently exposed to air and moisture. New sensing technologies may be needed to screen waste streams for these vape hazards and this paper considers the potential of inductive techniques based on the magnetic polarisability tensor (MPT) representation. The MPT can be described by three complex components based on a target regardless of orientation. In this paper, the rank 2 MPT is measured and calculated for 10 vapes and 37 batteries for 28 logarithmically spaced frequencies from 119 Hz to 95.4 KHz. The 168 features of each object are reduced down to 2 features using principal component analysis (PCA) and linear discriminant analysis. The reduction of the features allows for the visualisation and grouping of the objects. Three clear groups of objects can be seen when the maximum feature scales the measurement and a two-component PCA transform is applied. The first group is the vapes, which are grouped away from the other batteries. The second is the batteries, which are grouped by size. Finally, zinc batteries are grouped away from the rest due to their case material.<br/
Elementary Forms of the Metaphorical Life : Tropes at Work in Durkheimâs Theory of the Religious
Peer reviewedPostprin
Recognition of cancer warning signs and anticipated time to help-seeking in a population sample of adults in the UK
Background: Not recognising a symptom as suspicious is a common reason given by cancer patients for delayed help-seeking; but inevitably this is retrospective. We therefore investigated associations between recognition of warning signs for breast, colorectal and lung cancer and anticipated time to help-seeking for symptoms of each cancer.
Methods: Computer-assisted telephone interviews were conducted with a population-representative sample (N=6965) of UK adults age greater than or equal to50 years, using the Awareness and Beliefs about Cancer scale. Anticipated time to help-seeking for persistent cough, rectal bleeding and breast changes was categorised as >2 vs less than or equal to2 weeks. Recognition of persistent cough, unexplained bleeding and unexplained lump as cancer warning signs was assessed (yes/no). Associations between recognition and help-seeking were examined for each symptom controlling for demographics and perceived ease of health-care access.
Results: For each symptom, the odds of waiting for >2 weeks were significantly increased in those who did not recognise the related warning sign: breast changes: OR=2.45, 95% CI 1.47â4.08; rectal bleeding: OR=1.77, 1.36â2.30; persistent cough: OR=1.30, 1.17â1.46, independent of demographics and health-care access.
Conclusion: Recognition of warning signs was associated with anticipating faster help-seeking for potential symptoms of cancer. Strategies to improve recognition are likely to facilitate earlier diagnosis
Analysis and Evaluation of the Dynamic Performance of SMA Actuators for Prosthetic Hand Design
Substellar companions and the formation of hot subdwarf stars
"Copyright 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics."We give a brief review over the observational evidence for close substellar companions to hot subdwarf stars. The formation of these core helium-burning objects requires huge mass loss of their red giant progenitors. It has been suggested that besides stellar companions substellar objects in close orbits may be able to trigger this mass loss. Such objects can be easily detected around hot subdwarf stars by medium or high resolution spectroscopy with an RV accuracy at the km s(-1)-level. Eclipsing systems of Vir type stick out of transit surveys because of their characteristic light curves. The best evidence that substellar objects in close orbits around sdBs exist and that they are able to trigger the required mass loss is provided by the eclipsing system SDSS J0820+0008, which was found in the course of the MUCHFUSS project. Furthermore, several candidate systems have been discovered.Final Accepted Versio
Follow-up observations of pulsating subdwarf B stars: Multisite campaigns on PG 1618+563B and PG 0048+091
We present follow-up observations of pulsating subdwarf B (sdB) stars as part
of our efforts to resolve the pulsation spectra for use in asteroseismological
analyses. This paper reports on multisite campaigns of the pulsating sdB stars
PG 1618+563B and PG 0048+091. Data were obtained from observatories placed
around the globe for coverage from all longitudes. For PG 1618+563B, our
five-site campaign uncovered a dichotomy of pulsation states: Early during the
campaign the amplitudes and phases (and perhaps frequencies) were quite
variable while data obtained late in the campaign were able to fully resolve
five stable pulsation frequencies. For PG 0048+091, our five-site campaign
uncovered a plethora of frequencies with short pulsation lifetimes. We find
them to have observed properties consistent with stochastically excited
oscillations, an unexpected result for subdwarf B stars. We discuss our
findings and their impact on subdwarf B asteroseismology.Comment: 50 pages including 17 figures and 10 tables. Accepted for publication
in the Astrophysical Journa
Analytical maximum likelihood estimation of stellar magnetic fields
The polarised spectrum of stellar radiation encodes valuable information on
the conditions of stellar atmospheres and the magnetic fields that permeate
them. In this paper, we give explicit expressions to estimate the magnetic
field vector and its associated error from the observed Stokes parameters. We
study the solar case where specific intensities are observed and then the
stellar case, where we receive the polarised flux. In this second case, we
concentrate on the explicit expression for the case of a slow rotator with a
dipolar magnetic field geometry. Moreover, we also give explicit formulae to
retrieve the magnetic field vector from the LSD profiles without assuming mean
values for the LSD artificial spectral line. The formulae have been obtained
assuming that the spectral lines can be described in the weak field regime and
using a maximum likelihood approach. The errors are recovered by means of the
hermitian matrix. The bias of the estimators are analysed in depth.Comment: accepted for publication in MNRA
Particulate matter concentrations in residences: an intervention study evaluating standâalone filters and air conditioners
This study, a randomized controlled trial, evaluated the effectiveness of freeâstanding air filters and window air conditioners (ACs) in 126 lowâincome households of children with asthma. Households were randomized into a control group, a group receiving a freeâstanding HEPA filter placed in the childâs sleeping area, and a group receiving the filter and a windowâmounted AC. Indoor air quality (IAQ) was monitored for weekâlong periods over three to four seasons. High concentrations of particulate matter (PM) and carbon dioxide were frequently seen. When IAQ was monitored, filters reduced PM levels in the childâs bedroom by an average of 50%. Filter use varied greatly among households and declined over time, for example, during weeks when pollutants were monitored, filter use was initially high, averaging 84â±â27%, but dropped to 63â±â33% in subsequent seasons. In months when households were not visited, use averaged only 34â±â30%. Filter effectiveness did not vary in homes with central or room ACs. The study shows that measurements over multiple seasons are needed to characterize air quality and filter performance. The effectiveness of interventions using freeâstanding air filters depends on occupant behavior, and strategies to ensure filter use should be an integral part of interventions. Practical Implications Environmental tobacco smoke (ETS) increased particulate matter (PM) levels by about 14âÎŒg/m 3 and was often detected using ETSâspecific tracers despite restrictions on smoking in the house as reported on questionnaires administered to caregivers. PM concentrations depended on season, filter usage, relative humidity, air exchange ratios, number of children, outdoor PM levels, sweeping/dusting, and presence of a central air conditioner (AC). Freeâstanding air filters can be an effective intervention that provides substantial reductions in PM concentrations if the filters are used. However, filter use was variable across the study population and declined over the study duration, and thus strategies are needed to encourage and maintain use of filters. The variability in filter use suggests that exposure misclassification is a potential problem in intervention studies using filters. The installation of a room AC in the bedroom, intended to limit air exchange ratios, along with an air filter, did not lower PM levels more than the filter alone.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91183/1/j.1600-0668.2011.00761.x.pd
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