162 research outputs found
PSR J1024β0719: A Millisecond Pulsar in an Unusual Long-period Orbit
PSR J1024β0719 is a millisecond pulsar that was long thought to be isolated. However, puzzling results concerning its velocity, distance, and low rotational period derivative have led to a reexamination of its properties. We present updated radio timing observations along with new and archival optical data which show that PSR J1024β0719 is most likely in a long-period (2β20 kyr) binary system with a low-mass (β0.4 Mβ), low-metallicity (z β -0.9 dex) main-sequence star. Such a system can explain most of the anomalous properties of this pulsar. We suggest that this system formed through a dynamical exchange in a globular cluster that ejected it into a halo orbit, which is consistent with the low observed metallicity for the stellar companion. Further astrometric and radio timing observations such as measurement of the third period derivative could strongly constrain the range of orbital parameters
PSR J1024β0719: A Millisecond Pulsar in an Unusual Long-period Orbit
PSR J1024β0719 is a millisecond pulsar that was long thought to be isolated. However, puzzling results concerning its velocity, distance, and low rotational period derivative have led to a reexamination of its properties. We present updated radio timing observations along with new and archival optical data which show that PSR J1024β0719 is most likely in a long-period (2β20 kyr) binary system with a low-mass (β0.4 Mβ), low-metallicity (z β -0.9 dex) main-sequence star. Such a system can explain most of the anomalous properties of this pulsar. We suggest that this system formed through a dynamical exchange in a globular cluster that ejected it into a halo orbit, which is consistent with the low observed metallicity for the stellar companion. Further astrometric and radio timing observations such as measurement of the third period derivative could strongly constrain the range of orbital parameters
The Zwicky Transient Facility: Surveys and Scheduler
We present a novel algorithm for scheduling the observations of time-domain
imaging surveys. Our Integer Linear Programming approach optimizes an observing
plan for an entire night by assigning targets to temporal blocks, enabling
strict control of the number of exposures obtained per field and minimizing
filter changes. A subsequent optimization step minimizes slew times between
each observation. Our optimization metric self-consistently weights
contributions from time-varying airmass, seeing, and sky brightness to maximize
the transient discovery rate. We describe the implementation of this algorithm
on the surveys of the Zwicky Transient Facility and present its on-sky
performance.Comment: Published in PASP Focus Issue on the Zwicky Transient Facility
(https://dx.doi.org/10.1088/1538-3873/ab0c2a). 13 Pages, 11 Figure
Small Near-Earth Asteroids in the Palomar Transient Factory Survey: a Real-Time Streak-detection System
Near-Earth asteroids (NEAs) in the 1β100 meter size range are estimated to be ~1,000 times more numerous than the ~15,000 currently cataloged NEAs, most of which are in the 0.5β10 kilometer size range. Impacts from 10β100 meter size NEAs are not statistically life-threatening, but may cause significant regional damage, while 1β10 meter size NEAs with low velocities relative to Earth are compelling targets for space missions. We describe the implementation and initial results of a real-time NEA-discovery system specialized for the detection of small, high angular rate (visually streaked) NEAs in Palomar Transient Factory (PTF) images. PTF is a 1.2-m aperture, 7.3 deg^2 field of view (FOV) optical survey designed primarily for the discovery of extragalactic transients (e.g., supernovae) in 60-second exposures reaching ~20.5 visual magnitude. Our real-time NEA discovery pipeline uses a machine-learned classifier to filter a large number of false-positive streak detections, permitting a human scanner to efficiently and remotely identify real asteroid streaks during the night. Upon recognition of a streaked NEA detection (typically within an hour of the discovery exposure), the scanner triggers follow-up with the same telescope and posts the observations to the Minor Planet Center for worldwide confirmation. We describe our 11 initial confirmed discoveries, all small NEAs that passed 0.3β15 lunar distances from Earth. Lastly, we derive useful scaling laws for comparing streaked-NEA-detection capabilities of different surveys as a function of their hardware and survey-pattern characteristics. This work most directly informs estimates of the streak-detection capabilities of the Zwicky Transient Facility (ZTF, planned to succeed PTF in 2017), which will apply PTF's current resolution and sensitivity over a 47-deg^2 FOV
Seasonal Movements, Aggregations and Diving Behavior of Atlantic Bluefin Tuna (Thunnus thynnus) Revealed with Archival Tags
Electronic tags were used to examine the seasonal movements, aggregations and diving behaviors of Atlantic bluefin tuna (Thunnus thynnus) to better understand their migration ecology and oceanic habitat utilization. Implantable archival tags (nβ=β561) were deployed in bluefin tuna from 1996 to 2005 and 106 tags were recovered. Movement paths of the fish were reconstructed using light level and sea-surface-temperature-based geolocation estimates. To quantify habitat utilization we employed a weighted kernel estimation technique that removed the biases of deployment location and track length. Throughout the North Atlantic, high residence times (167Β±33 days) were identified in four spatially confined regions on a seasonal scale. Within each region, bluefin tuna experienced distinct temperature regimes and displayed different diving behaviors. The mean diving depths within the high-use areas were significantly shallower and the dive frequency and the variance in internal temperature significantly higher than during transit movements between the high-use areas. Residence time in the more northern latitude high-use areas was significantly correlated with levels of primary productivity. The regions of aggregation are associated with areas of abundant prey and potentially represent critical foraging habitats that have seasonally abundant prey. Throughout the North Atlantic mean diving depth was significantly correlated with the depth of the thermocline, and dive behavior changed in relation to the stratification of the water column. In this study, with numerous multi-year tracks, there appear to be repeatable patterns of clear aggregation areas that potentially are changing with environmental conditions. The high concentrations of bluefin tuna in predictable locations indicate that Atlantic bluefin tuna are vulnerable to concentrated fishing efforts in the regions of foraging aggregations
Grazing incidence optics designs for future gamma-ray missions
Sensitive nuclear line spectroscopy for observations of prompt emission from supernovae, as well as mapping of remnants has been a primary goal of gamma-ray astrophysics since its inception. A number of key lines lie in the energy band from 10 - 600 keV. In this region of the spectrum, observations have to-date been limited by high background and poor angular resolution. In this paper, we present several designs capable of extending the sensitivity of grazing incidence optics into this energy range. In particular, we discuss a 15 m focal length design for NASA's High-Sensitivity Spectroscopic Imaging Mission concept, as well as a 50 m focal length design which can extend ESA's XEUS mission into this band. We demonstrate that an unprecedented line sensitivity of 10^(-7) cm^(-2) s^(-1) can be achieved for the most important lines in this energy band
Thermochromic Metal Halide Perovskite Windows with Ideal Transition Temperatures
Urban centers across the globe are responsible for a significant fraction of
energy consumption and CO2 emission. As urban centers continue to grow, the
popularity of glass as cladding material in urban buildings is an alarming
trend. Dynamic windows reduce heating and cooling loads in buildings by passive
heating in cold seasons and mitigating solar heat gain in hot seasons. In this
work, we develop a mesoscopic building energy model that demonstrates reduced
building energy consumption when thermochromic windows are employed. Savings
are realized across eight disparate climate zones of the United States. We use
the model to determine the ideal critical transition temperature of 20 to 27.5
{\deg}C for thermochromic windows based on metal halide perovskite materials.
Ideal transition temperatures are realized experimentally in composite metal
halide perovskite film composed of perovskite crystals and an adjacent
reservoir phase. The transition temperature is controlled by co-intercalating
methanol, instead of water, with methylammonium iodide and tailoring the
hydrogen-bonding chemistry of the reservoir phase. Thermochromic windows based
on metal halide perovskites represent a clear opportunity to mitigate the
effects of energy-hungry buildings
Processing Images from the Zwicky Transient Facility
The Zwicky Transient Facility is a new robotic-observing program, in which a
newly engineered 600-MP digital camera with a pioneeringly large field of view,
47~square degrees, will be installed into the 48-inch Samuel Oschin Telescope
at the Palomar Observatory. The camera will generate ~petabyte of raw
image data over three years of operations. In parallel related work, new
hardware and software systems are being developed to process these data in real
time and build a long-term archive for the processed products. The first public
release of archived products is planned for early 2019, which will include
processed images and astronomical-source catalogs of the northern sky in the
and bands. Source catalogs based on two different methods will be
generated for the archive: aperture photometry and point-spread-function
fitting.Comment: 6 pages, 4 figures, submitted to RTSRE Proceedings (www.rtsre.org
Small Near-Earth Asteroids in the Palomar Transient Factory Survey: a Real-Time Streak-detection System
Near-Earth asteroids (NEAs) in the 1β100 meter size range are estimated to be ~1,000 times more numerous than the ~15,000 currently cataloged NEAs, most of which are in the 0.5β10 kilometer size range. Impacts from 10β100 meter size NEAs are not statistically life-threatening, but may cause significant regional damage, while 1β10 meter size NEAs with low velocities relative to Earth are compelling targets for space missions. We describe the implementation and initial results of a real-time NEA-discovery system specialized for the detection of small, high angular rate (visually streaked) NEAs in Palomar Transient Factory (PTF) images. PTF is a 1.2-m aperture, 7.3 deg^2 field of view (FOV) optical survey designed primarily for the discovery of extragalactic transients (e.g., supernovae) in 60-second exposures reaching ~20.5 visual magnitude. Our real-time NEA discovery pipeline uses a machine-learned classifier to filter a large number of false-positive streak detections, permitting a human scanner to efficiently and remotely identify real asteroid streaks during the night. Upon recognition of a streaked NEA detection (typically within an hour of the discovery exposure), the scanner triggers follow-up with the same telescope and posts the observations to the Minor Planet Center for worldwide confirmation. We describe our 11 initial confirmed discoveries, all small NEAs that passed 0.3β15 lunar distances from Earth. Lastly, we derive useful scaling laws for comparing streaked-NEA-detection capabilities of different surveys as a function of their hardware and survey-pattern characteristics. This work most directly informs estimates of the streak-detection capabilities of the Zwicky Transient Facility (ZTF, planned to succeed PTF in 2017), which will apply PTF's current resolution and sensitivity over a 47-deg^2 FOV
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