1,511 research outputs found
Laser-only adaptive optics achieves significant image quality gains compared to seeing-limited observations over the entire sky
Adaptive optics laser guide star systems perform atmospheric correction of
stellar wavefronts in two parts: stellar tip-tilt and high-spatial-order
laser-correction. The requirement of a sufficiently bright guide star in the
field-of-view to correct tip-tilt limits sky coverage. Here we show an
improvement to effective seeing without the need for nearby bright stars,
enabling full sky coverage by performing only laser-assisted wavefront
correction. We used Robo-AO, the first robotic AO system, to comprehensively
demonstrate this laser-only correction. We analyze observations from four years
of efficient robotic operation covering 15,000 targets and 42,000 observations,
each realizing different seeing conditions. Using an autoguider (or a
post-processing software equivalent) and the laser to improve effective seeing
independent of the brightness of a target, Robo-AO observations show a 39+/-19%
improvement to effective FWHM, without any tip-tilt correction. We also
demonstrate that 50% encircled-energy performance without tip-tilt correction
remains comparable to diffraction-limited, standard Robo-AO performance.
Faint-target science programs primarily limited by 50% encircled-energy (e.g.
those employing integral field spectrographs placed behind the AO system) may
see significant benefits to sky coverage from employing laser-only AO.Comment: Accepted for publication in The Astronomical Journal. 7 pages, 6
figure
Recombinant human epoetin beta in the treatment of chemotherapy-related anemia
Anemia is a common complication of systemic anti-cancer treatment. In this context epoetin beta, like other erythropoiesis-stimulating agents (ESAs), has demonstrable efficacy in raising Hb concentration and reducing the requirement for red cell transfusion. Consequently ESA therapy has gained increasing prominence in the management of chemotherapy-related anemia. However, recent trial data have suggested a higher rate of thromboembolic events, enhanced tumor progression and reduced survival in some patients with cancer who receive ESA therapy. In response, regulatory authorities have mandated increasingly restrictive label changes. In light of these new developments we consider the current role of epoetin beta in the management of chemotherapy-related anemia
The Performance of the Robo-AO Laser Guide Star Adaptive Optics System at the Kitt Peak 2.1-m Telescope
Robo-AO is an autonomous laser guide star adaptive optics system recently
commissioned at the Kitt Peak 2.1-m telescope. Now operating every clear night,
Robo-AO at the 2.1-m telescope is the first dedicated adaptive optics
observatory. This paper presents the imaging performance of the adaptive optics
system in its first eighteen months of operations. For a median seeing value of
, the average Strehl ratio is 4\% in the band
and 29\% in the J band. After post-processing, the contrast ratio under
sub-arcsecond seeing for a primary star is five and
seven magnitudes at radial offsets of and
, respectively. The data processing and archiving pipelines
run automatically at the end of each night. The first stage of the processing
pipeline shifts and adds the data using techniques alternately optimized for
stars with high and low SNRs. The second "high contrast" stage of the pipeline
is eponymously well suited to finding faint stellar companions.Comment: 12 pages, 16 figures, to be submitted to PAS
Second generation Robo-AO instruments and systems
The prototype Robo-AO system at the Palomar Observatory 1.5-m telescope is
the world's first fully automated laser adaptive optics instrument. Scientific
operations commenced in June 2012 and more than 12,000 observations have since
been performed at the ~0.12" visible-light diffraction limit. Two new infrared
cameras providing high-speed tip-tilt sensing and a 2' field-of-view will be
integrated in 2014. In addition to a Robo-AO clone for the 2-m IGO and the
natural guide star variant KAPAO at the 1-m Table Mountain telescope, a second
generation of facility-class Robo-AO systems are in development for the 2.2-m
University of Hawai'i and 3-m IRTF telescopes which will provide higher Strehl
ratios, sharper imaging, ~0.07", and correction to {\lambda} = 400 nm.Comment: 11 pages, 4 figures, 3 table
Robo-AO Kepler Survey IV: the effect of nearby stars on 3857 planetary candidate systems
We present the overall statistical results from the Robo-AO Kepler planetary
candidate survey, comprising of 3857 high-angular resolution observations of
planetary candidate systems with Robo-AO, an automated laser adaptive optics
system. These observations reveal previously unknown nearby stars blended with
the planetary candidate host star which alter the derived planetary radii or
may be the source of an astrophysical false positive transit signal. In the
first three papers in the survey, we detected 440 nearby stars around 3313
planetary candidate host stars. In this paper, we present observations of 532
planetary candidate host stars, detecting 94 companions around 88 stars; 84 of
these companions have not previously been observed in high-resolution. We also
report 50 more-widely-separated companions near 715 targets previously observed
by Robo-AO. We derive corrected planetary radius estimates for the 814
planetary candidates in systems with a detected nearby star. If planetary
candidates are equally likely to orbit the primary or secondary star, the
radius estimates for planetary candidates in systems with likely bound nearby
stars increase by a factor of 1.54, on average. We find that 35
previously-believed rocky planet candidates are likely not rocky due to the
presence of nearby stars. From the combined data sets from the complete Robo-AO
KOI survey, we find that 14.5\pm0.5% of planetary candidate hosts have a nearby
star with 4", while 1.2% have two nearby stars and 0.08% have three. We find
that 16% of Earth-sized, 13% of Neptune-sized, 14% of Saturn-sized, and 19% of
Jupiter-sized planet candidates have detected nearby stars.Comment: Accepted to the Astronomical Journa
Robo-AO Kepler Survey V: The effect of physically associated stellar companions on planetary systems
The Kepler light curves used to detect thousands of planetary candidates are
susceptible to dilution due to blending with previously unknown nearby stars.
With the automated laser adaptive optics instrument, Robo-AO, we have observed
620 nearby stars around 3857 planetary candidates host stars. Many of the
nearby stars, however, are not bound to the KOI. In this paper, we quantify the
association probability between each KOI and detected nearby stars through
several methods. Galactic stellar models and the observed stellar density are
used to estimate the number and properties of unbound stars. We estimate the
spectral type and distance to 145 KOIs with nearby stars using multi-band
observations from Robo-AO and Keck-AO. We find most nearby stars within 1" of a
Kepler planetary candidate are likely bound, in agreement with past studies. We
use likely bound stars as well as the precise stellar parameters from the
California Kepler Survey to search for correlations between stellar binarity
and planetary properties. No significant difference between the binarity
fraction of single and multiple planet systems is found, and planet hosting
stars follow similar binarity trends as field stars, many of which likely host
their own non-aligned planets. We find that hot Jupiters are ~4x more likely
than other planets to reside in a binary star system. We correct the radius
estimates of the planet candidates in characterized systems and find that for
likely bound systems, the estimated planetary candidate radii will increase on
average by a factor of 1.77, if either star is equally likely to host the
planet. We find that the planetary radius gap is robust to the impact of
dilution, and find an intriguing 95%-confidence discrepancy between the radius
distribution of small planets in single and binary systems.Comment: 19 pages, 12 figures, submitted to AAS Journal
Local Wellness Policy 5 Years Later: Is It Making a Difference for Students in Low-Income, Rural Colorado Elementary Schools?
IntroductionThe federally mandated Local Wellness Policy (LWP) was intended to promote student health in schools. This study assesses the 5-year effects of the LWP on the health practices of rural elementary schools in Colorado.
MethodsOne year before and 5 years after the LWP mandate, a survey was administered to a random sample of principals, physical education (PE) teachers, and food-service managers in 45 rural, low-income elementary schools in Colorado. Response rates were 71% in 2005 and 89% in 2011.
ResultsMinutes for PE and recess did not increase, nor did offerings of fresh fruits and vegetables. More schools adopted policies prohibiting teachers from taking recess away as punishment (9.7% in 2005 vs 38.5% in 2011, P = .02) or for making up missed instructional time, class work, or tests in other subjects (3.2% in 2005 vs 28.2% in 2011, P = .03). More schools scheduled recess before lunch (22.6% in 2005 vs 46.2% in 2011, P = .04) and developed policies for vending machines (42.9% in 2005 vs 85.7% in 2011, P = .01) and parties (21.4% in 2005 vs 57.9% in 2011, P = .004).
ConclusionChanges in school practices are modest, and arguably the important school practices such as increased PE and recess time and increased offerings of fruits and vegetables in the lunch line have not changed in the 5 years since the mandate went into effect. Further investigation is needed to identify the knowledge, skills, and attitudes as well as financial and physical resources required for school administrators to make changes in school practices
Characterizing the Cool KOIs. VI. H- and K-band Spectra of Kepler M Dwarf Planet-Candidate Hosts
We present H- and K-band spectra for late-type Kepler Objects of Interest
(the "Cool KOIs"): low-mass stars with transiting-planet candidates discovered
by NASA's Kepler Mission that are listed on the NASA Exoplanet Archive. We
acquired spectra of 103 Cool KOIs and used the indices and calibrations of
Rojas-Ayala et al. to determine their spectral types, stellar effective
temperatures and metallicities, significantly augmenting previously published
values. We interpolate our measured effective temperatures and metallicities
onto evolutionary isochrones to determine stellar masses, radii, luminosities
and distances, assuming the stars have settled onto the main-sequence. As a
choice of isochrones, we use a new suite of Dartmouth predictions that reliably
include mid-to-late M dwarf stars. We identify five M4V stars: KOI-961
(confirmed as Kepler 42), KOI-2704, KOI-2842, KOI-4290, and the secondary
component to visual binary KOI-1725, which we call KOI-1725 B. We also identify
a peculiar star, KOI-3497, which has a Na and Ca lines consistent with a dwarf
star but CO lines consistent with a giant. Visible-wavelength adaptive optics
imaging reveals two objects within a 1 arc second diameter; however, the
objects' colors are peculiar. The spectra and properties presented in this
paper serve as a resource for prioritizing follow-up observations and planet
validation efforts for the Cool KOIs, and are all available for download online
using the "data behind the figure" feature.Comment: Accepted for publication in the Astrophysical Journal Supplement
Series (ApJS). Data and table are available in the sourc
Diminishing Effectiveness of Long-Term Maintenance Topical Steroid Therapy in PPI Non-Responsive Eosinophilic Esophagitis
While topical corticosteroids are first-line therapy for eosinophilic esophagitis (EoE), the data regarding long-term effectiveness are lacking. We aimed to determine long-term histologic and endoscopic outcomes of maintenance therapy in EoE steroid responders
Exact Synchronization for Finite-State Sources
We analyze how an observer synchronizes to the internal state of a
finite-state information source, using the epsilon-machine causal
representation. Here, we treat the case of exact synchronization, when it is
possible for the observer to synchronize completely after a finite number of
observations. The more difficult case of strictly asymptotic synchronization is
treated in a sequel. In both cases, we find that an observer, on average, will
synchronize to the source state exponentially fast and that, as a result, the
average accuracy in an observer's predictions of the source output approaches
its optimal level exponentially fast as well. Additionally, we show here how to
analytically calculate the synchronization rate for exact epsilon-machines and
provide an efficient polynomial-time algorithm to test epsilon-machines for
exactness.Comment: 9 pages, 6 figures; now includes analytical calculation of the
synchronization rate; updates and corrections adde
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