847 research outputs found
An 8.8 minute orbital period eclipsing detached double white dwarf binary
We report the discovery of ZTF J2243+5242, an eclipsing double white dwarf
binary with an orbital period of just minutes, the second known eclipsing
binary with an orbital period less than ten minutes. The system likely consists
of two low-mass white dwarfs, and will merge in approximately 400,000 years to
form either an isolated hot subdwarf or an R Coronae Borealis star. Like its
counterpart, ZTF J1539+5027, ZTF J2243+5242 will be among the
strongest gravitational wave sources detectable by the space-based
gravitational-wave detector The Laser Space Interferometer Antenna (LISA)
because its gravitational-wave frequency falls near the peak of LISA's
sensitivity. Based on its estimated distance of ,
LISA should detect the source within its first few months of operation, and
should achieve a signal-to-noise ratio of after four years. We find
component masses of and
, radii of
and , and effective temperatures of
and . We
determined all of these properties, and the distance to this system, using only
photometric measurements, demonstrating a feasible way to estimate parameters
for the large population of optically faint ()
gravitational-wave sources which the Vera Rubin Observatory (VRO) and LISA
should identify.Comment: 12 pages, 7 figures, 3 tables, submitte
Global Kidney Exchange Should Expand Wisely.
We read with great interest and appreciation the careful consideration and analysis by Ambagtsheer et al. of the most critical ethical objections to Global Kidney Exchange (GKE). Ambagtsheer et al. conclude that implementation of GKE is a means to increase access to transplantation ethically and effectively
A Catalog of Spectroscopically Identified White Dwarf Stars in the First Data Release of the Sloan Digital Sky Survey
We present the full spectroscopic white dwarf and hot subdwarf sample from
the SDSS first data release, DR1. We find 2551 white dwarf stars of various
types, 240 hot subdwarf stars, and an additional 144 objects we have identified
as uncertain white dwarf stars. Of the white dwarf stars, 1888 are non-magnetic
DA types and 171, non-magnetic DBs. The remaining (492) objects consist of all
different types of white dwarf stars: DO, DQ, DC, DH, DZ, hybrid stars like
DAB, etc., and those with non-degenerate companions. We fit the DA and DB
spectra with a grid of models to determine the Teff and log(g) for each object.
For all objects, we provide coordinates, proper motions, SDSS photometric
magnitudes, and enough information to retrieve the spectrum/image from the SDSS
public database. This catalog nearly doubles the known sample of
spectroscopically-identified white dwarf stars. In the DR1 imaged area of the
sky, we increase the known sample of white dwarf stars by a factor of 8.5. We
also comment on several particularly interesting objects in this sample.Comment: To be published ApJ, 20May04. 52 pages, 13 figures, 12 tables. Full
tables are available at the (now-corrected) SDSS DR1 Value-added catalog at
http://www.sdss.org/dr1/products/value_added/index.htm
An Eclipsing 47 minute Double White Dwarf Binary at 400 pc
We present the discovery of the eclipsing double white dwarf (WD) binary WDJ
022558.21-692025.38 that has an orbital period of 47.19 min. Following
identification with the Transiting Exoplanet Survey Satellite, we obtained
time-series ground based spectroscopy and high-speed multi-band ULTRACAM
photometry which indicate a primary DA WD of mass 0.40 +- 0.04 Msol and a 0.28
+- 0.02 Msol mass secondary WD, which is likely of type DA as well. The system
becomes the third-closest eclipsing double WD binary discovered with a distance
of approximately 400 pc and will be a detectable source for upcoming
gravitational wave detectors in the mHz frequency range. Its orbital decay will
be measurable photometrically within 10 yrs to a precision of better than 1%.
The fate of the binary is to merge in approximately 41 Myr, likely forming a
single, more massive WD.Comment: Accepted for publication in MNRAS, 8 pages + 2 appendix pages, 6
figure
Association of Accelerometry-Measured Physical Activity and Cardiovascular Events in Mobility-Limited Older Adults: The LIFE (Lifestyle Interventions and Independence for Elders) Study.
BACKGROUND:Data are sparse regarding the value of physical activity (PA) surveillance among older adults-particularly among those with mobility limitations. The objective of this study was to examine longitudinal associations between objectively measured daily PA and the incidence of cardiovascular events among older adults in the LIFE (Lifestyle Interventions and Independence for Elders) study. METHODS AND RESULTS:Cardiovascular events were adjudicated based on medical records review, and cardiovascular risk factors were controlled for in the analysis. Home-based activity data were collected by hip-worn accelerometers at baseline and at 6, 12, and 24 months postrandomization to either a physical activity or health education intervention. LIFE study participants (n=1590; age 78.9±5.2 [SD] years; 67.2% women) at baseline had an 11% lower incidence of experiencing a subsequent cardiovascular event per 500 steps taken per day based on activity data (hazard ratio, 0.89; 95% confidence interval, 0.84-0.96; P=0.001). At baseline, every 30 minutes spent performing activities â„500 counts per minute (hazard ratio, 0.75; confidence interval, 0.65-0.89 [P=0.001]) were also associated with a lower incidence of cardiovascular events. Throughout follow-up (6, 12, and 24 months), both the number of steps per day (per 500 steps; hazard ratio, 0.90, confidence interval, 0.85-0.96 [P=0.001]) and duration of activity â„500 counts per minute (per 30 minutes; hazard ratio, 0.76; confidence interval, 0.63-0.90 [P=0.002]) were significantly associated with lower cardiovascular event rates. CONCLUSIONS:Objective measurements of physical activity via accelerometry were associated with cardiovascular events among older adults with limited mobility (summary score >10 on the Short Physical Performance Battery) both using baseline and longitudinal data. CLINICAL TRIAL REGISTRATION:URL: http://www.clinicaltrials.gov. Unique identifier: NCT01072500
Estimating Distribution of Hidden Objects with Drones: From Tennis Balls to Manatees
Unmanned aerial vehicles (UAV), or drones, have been used widely in military applications, but more recently civilian applications have emerged (e.g., wildlife population monitoring, traffic monitoring, law enforcement, oil and gas pipeline threat detection). UAV can have several advantages over manned aircraft for wildlife surveys, including reduced ecological footprint, increased safety, and the ability to collect high-resolution geo-referenced imagery that can document the presence of species without the use of a human observer. We illustrate how geo-referenced data collected with UAV technology in combination with recently developed statistical models can improve our ability to estimate the distribution of organisms. To demonstrate the efficacy of this methodology, we conducted an experiment in which tennis balls were used as surrogates of organisms to be surveyed. We used a UAV to collect images of an experimental field with a known number of tennis balls, each of which had a certain probability of being hidden. We then applied spatially explicit occupancy models to estimate the number of balls and created precise distribution maps. We conducted three consecutive surveys over the experimental field and estimated the total number of balls to be 328 (95%CI: 312, 348). The true number was 329 balls, but simple counts based on the UAV pictures would have led to a total maximum count of 284. The distribution of the balls in the field followed a simulated environmental gradient. We also were able to accurately estimate the relationship between the gradient and the distribution of balls. Our experiment demonstrates how this technology can be used to create precise distribution maps in which discrete regions of the study area are assigned a probability of presence of an object. Finally, we discuss the applicability and relevance of this experimental study to the case study of Florida manatee distribution at power plants
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