1,452 research outputs found
Hypervelocity Stars. I. The Spectroscopic Survey
We discuss our targeted search for hypervelocity stars (HVSs), stars
traveling with velocities so extreme that dynamical ejection from a massive
black hole is their only suggested origin. Our survey, now half complete, has
successfully identified a total of four probable HVSs plus a number of other
unusual objects. Here we report the most recently discovered two HVSs: SDSS
J110557.45+093439.5 and possibly SDSS J113312.12+010824, traveling with
Galactic rest-frame velocities at least +508+-12 and +418+-10 km/s,
respectively. The other late B-type objects in our survey are consistent with a
population of post main-sequence stars or blue stragglers in the Galactic halo,
with mean metallicity [Fe/H]=-1.3 and velocity dispersion 108+-5 km/s.
Interestingly, the velocity distribution shows a tail of objects with large
positive velocities that may be a mix of low-velocity HVSs and high-velocity
runaway stars. Our survey also includes a number of DA white dwarfs with
unusually red colors, possibly extremely low mass objects. Two of our objects
are B supergiants in the Leo A dwarf, providing the first spectroscopic
evidence for star formation in this dwarf galaxy within the last ~30 Myr.Comment: 10 pages, uses emulateapj, accepted by Ap
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
Observing Strategies for the Detection of Jupiter Analogs
To understand the frequency, and thus the formation and evolution, of planetary systems like our own solar system, it is critical to detect Jupiter-like planets in Jupiter-like orbits. For long-term radial-velocity monitoring, it is useful to estimate the observational effort required to reliably detect such objects, particularly in light of severe competition for limited telescope time. We perform detailed simulations of observational campaigns, maximizing the realism of the sampling of a set of simulated observations. We then compute the detection limits for each campaign to quantify the effect of increasing the number of observational epochs and varying their time coverage. We show that once there is sufficient time baseline to detect a given orbital period, it becomes less effective to add further time coverage-rather, the detectability of a planet scales roughly as the square root of the number of observations, independently of the number of orbital cycles included in the data string. We also show that no noise floor is reached, with a continuing improvement in detectability at the maximum number of observations N = 500 tested here.Peer reviewe
Elementary Forms of the Metaphorical Life : Tropes at Work in Durkheimâs Theory of the Religious
Peer reviewedPostprin
First Kepler results on compact pulsators II: KIC 010139564, a new pulsating subdwarf B (V361 Hya) star with an additional low-frequency mode
We present the discovery of nonradial pulsations in a hot subdwarf B star
based on 30.5 days of nearly continuous time-series photometry using the
\emph{Kepler} spacecraft. KIC 010139564 is found to be a short-period pulsator
of the V361 Hya (EC 14026) class with more than 10 independent pulsation modes
whose periods range from 130 to 190 seconds. It also shows one periodicity at a
period of 3165 seconds. If this periodicity is a high order g-mode, then this
star may be the hottest member of the hybrid DW Lyn stars. In addition to the
resolved pulsation frequencies, additional periodic variations in the light
curve suggest that a significant number of additional pulsation frequencies may
be present. The long duration of the run, the extremely high duty cycle, and
the well-behaved noise properties allow us to explore the stability of the
periodic variations, and to place strong constraints on how many of them are
independent stellar oscillation modes. We find that most of the identified
periodicities are indeed stable in phase and amplitude, suggesting a rotation
period of 2-3 weeks for this star, but further observations are needed to
confirm this suspicion.Comment: 10 pages, accepted for publication in MNRA
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
The Microbiome in Pediatric Cystic Fibrosis Patients: The Role of Shared Environment Suggests a Window of Intervention
Cystic fibrosis (CF) is caused by mutations in the CFTR gene that predispose the airway to infection. Chronic infection by pathogens such as Pseudomonas aeruginosa leads to inflammation that gradually degrades lung function, resulting in morbidity and early mortality. In a previous study of CF monozygotic twins, we demonstrate that genetic modifiers significantly affect the establishment of persistent P. aeruginosa colonization in CF. Recognizing that bacteria other than P. aeruginosa contribute to the CF microbiome and associated pathology, we used deep sequencing of sputum from pediatric monozygotic twins and nontwin siblings with CF to characterize pediatric bacterial communities and the role that genetics plays in their evolution.
We found that the microbial communities in sputum from pediatric patients living together were much more alike than those from pediatric individuals living apart, regardless of whether samples were taken from monozygous twins or from nontwin CF siblings living together, which we used as a proxy for dizygous twins. In contrast, adult communities were comparatively monolithic and much less diverse than the microbiome of pediatric patients
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
Multicolour correlative imaging using phosphor probes
Correlative light and electron microscopy exploits the advantages of optical methods, such as multicolour probes and their use in hydrated live biological samples, to locate functional units, which are then correlated with structural details that can be revealed by the superior resolution of electron microscopes. One difficulty is locating the area imaged by the electron beam in the much larger optical field of view. Multifunctional probes that can be imaged in both modalities and thus register the two images are required. Phosphor materials give cathodoluminescence (CL) optical emissions under electron excitation. Lanthanum phosphate containing thulium or terbium or europium emits narrow bands in the blue, green and red regions of the CL spectrum; they may be synthesised with very uniform-sized crystals in the 10- to 50-nm range. Such crystals can be imaged by CL in the electron microscope, at resolutions limited by the particle size, and with colour discrimination to identify different probes. These materials also give emissions in the optical microscope, by
multiphoton excitation. They have been deposited on the surface of glioblastoma cells and imaged by CL. Gadolinium oxysulphide doped with terbium emits green photons by either ultraviolet or electron excitation. Sixty-nanometre crystals of this phosphor have been imaged in the atmospheric scanning electron microscope (JEOL ClairScope). This probe and microscope combination allow correlative imaging in hydrated samples. Phosphor probes should prove to be very useful in correlative light and electron microscopy, as fiducial
markers to assist in image registration, and in high/super resolution imaging studies
Leadership in the British civil service: an interpretation
This article is essentially a polemic. The argument is that when politicians and officials now talk of âleadershipâ in the British civil service they do not use that word in the way in which it was previously used. In the past leading civil servants, acting in partnership with ministers and within constitutional constraints, exercised leadership in the sense of setting example, inspiring confidence and encouraging loyalty. The loosening of traditional constitutional patterns, the marginalization of senior officials in the policy process and the emergence of business methods as the preferred model for public Âadministration have led to a political and administrative environment in which leadership in the British civil service is now about encouraging patterns of behaviour which fit in with these changes. Leadership skills are now about âdeliveryâ; they are not about motivation. It is time for politicians, officials and scholars to be open about this
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