212 research outputs found
The TRENDS High-Contrast Imaging Survey. V. Discovery of an Old and Cold Benchmark T-dwarf Orbiting the Nearby G-star HD 19467
The nearby Sun-like star HD 19467 shows a subtle radial velocity (RV)
acceleration of -1.37+/-0.09 m/s/yr over an 16.9 year time baseline (an RV
trend), hinting at the existence of a distant orbiting companion. We have
obtained high-contrast adaptive optics images of the star using NIRC2 at Keck
Observatory and report the direct detection of the body that causes the
acceleration. The companion, HD 19467 B, is dK=12.57+/-0.09 mag fainter than
its parent star (contrast ratio of 9.4e-6), has blue colors J-K_s=-0.36+/-0.14
(J-H=-0.29+/-0.15), and is separated by 1.653+/-0.004" (51.1+/-1.0 AU).
Follow-up astrometric measurements obtained over an 1.1 year time baseline
demonstrate physical association through common parallactic and proper motion.
We calculate a firm lower-limit of m>51.9^{+3.6}_{-4.3}Mjup for the companion
mass from orbital dynamics using a combination of Doppler observations and
imaging. We estimate a model-dependent mass of m=56.7^{+4.6}_{-7.2}Mjup from a
gyrochronological age of 4.3^{+1.0}_{-1.2} Gyr. Isochronal analysis suggests a
much older age of Gyr, which corresponds to a mass of
m=67.4^{+0.9}_{-1.5}Mjup. HD 19467 B's measured colors and absolute magnitude
are consistent with a late T-dwarf [~T5-T7]. We may infer a low metallicity of
[Fe/H]=-0.15+/-0.04 for the companion from its G3V parent star. HD 19467 B is
the first directly imaged benchmark T-dwarf found orbiting a Sun-like star with
a measured RV acceleration.Comment: Updated to reflect ApJ versio
Adolescents’ and adults’ perceptions of ‘natural’, ‘organic’ and ‘additive-free’ cigarettes, and the required disclaimers
We sought to investigate adolescents’ and adults’ perceptions of an American Spirit advertisement with “natural,” “organic,” and “additive-free” descriptors and related disclaimers
How hearing about harmful chemicals affects smokers' interest in dual use of cigarettes and e-cigarettes
Substantial harm could result from concurrent cigarette and e-cigarette use (i.e., dual use) were it to undermine smoking cessation. Perceptions of chemical exposure and resulting harms may influence dual use. We conducted a probability-based phone survey of 1164 U.S. adult cigarette smokers in 2014–2015 and analyzed results in 2016. In a between-subjects experiment, smokers heard a hypothetical scenario in which cigarettes and e-cigarettes had the same amount of harmful chemicals or cigarettes had more chemicals than e-cigarettes (10× more, 100× more, or chemicals were present only in cigarettes). Smokers indicated how the scenario would change their interest in dual use and perceived health harms. Few smokers (7%) who heard that the products have the same amount of chemicals were interested in initiating or increasing dual use. However, more smokers were interested when told that cigarettes have 10× more chemicals than e-cigarettes (31%), 100× more chemicals than e-cigarettes (32%), or chemicals were present only in cigarettes (43%) (all p < .001). Individuals told that cigarettes have more chemicals were more likely than those in the “same amount” scenario to perceive that cigarettes would be more harmful than e-cigarettes (79% vs. 41%, OR = 5.41, 95% CI = 4.08–7.17). These harm perceptions partially explained the relationship between chemical scenario and dual use interest. Smokers associated higher chemical amounts in cigarettes versus e-cigarettes with greater health harms from cigarettes and thus expressed increased interest in dual use. The findings suggest that disclosing amounts of chemicals in cigarette smoke and e-cigarette aerosol could unintentionally encourage dual use
NASA SpaceCube Edge TPU SmallSat Card for Autonomous Operations and Onboard Science-Data Analysis
Using state-of-the-art artificial intelligence (AI)frameworks onboard spacecraft is challenging because common spacecraft processors cannot provide comparable performance to data centers with server-grade CPUs and GPUs available for terrestrial applications and advanced deep-learning networks. This limitation makes small, low-power AI microchip architectures, such as the Google Coral Edge Tensor Processing Unit (TPU), attractive for space missions where the application-specific design enables both high-performance and power-efficient computing for AI applications. To address these challenging considerations for space deployment, this research introduces the design and capabilities of a CubeSat-sized Edge TPU-based co-processor card, known as the SpaceCube Low-power Edge Artificial Intelligence Resilient Node (SC-LEARN). This design conforms to NASA’s CubeSat Card Specification (CS2) for integration into next-generation SmallSat and CubeSat systems. This paper describes the overarching architecture and design of the SC-LEARN, as well as, the supporting test card designed for rapid prototyping and evaluation. The SC-LEARN was developed with three operational modes: (1) a high-performance parallel-processing mode,(2)a fault-tolerant mode for onboard resilience, and (3) a power-saving mode with cold spares. Importantly, this research also elaborates on both training and quantization of TensorFlow models for the SC-LEARN for use onboard with representative, open-source datasets. Lastly, we describe future research plans, including radiation-beam testing and flight demonstration
Communicating about cigarette smoke constituents: an experimental comparison of two messaging strategies
Federal law now requires FDA to disseminate information on chemicals in cigarette smoke, but it is unclear how best to do so. In a 2 × 2 between-subjects experiment, participants received a message about chemicals in cigarette smoke (e.g., “Cigarette smoke has benzene.”) along with an additional randomly assigned messaging strategy: a “found-in” (e.g., “This is found in gasoline.”), a health effect (e.g., “This causes heart disease.”), both, or neither. Participants were U.S. probability phone samples of 5000 adults and 1123 adolescents, and an online convenience sample of 4130 adults. Adding a health effect elicited greater discouragement from wanting to smoke cigarettes (all p < .05) as did adding a found-in (all p < .05). However, including both messaging strategies added little or nothing above including just one. These findings can help the FDA and other agencies develop effective and parsimonious messages about cigarette smoke constituents
Adolescents' Responses to Pictorial Warnings on Their Parents' Cigarette Packs
Pictorial cigarette pack warnings are a promising policy solution to increase smoking cessation among adults. However, little is known regarding adolescents' responses to pictorial warnings, particularly in real-world settings
The Dynamical Mass and Three-Dimensional Orbit of HR7672B: A Benchmark Brown Dwarf with High Eccentricity
The companion to the G0V star HR7672 directly imaged by Liu et al. (2002) has
moved measurably along its orbit since the discovery epoch, making it possible
to determine its dynamical properties. Originally targeted with adaptive optics
because it showed a long-term radial velocity acceleration (trend), we have
monitored this star with precise Doppler measurements and have now established
a 24 year time baseline. The radial velocity variations show significant
curvature (change in the acceleration) including an inflection point. We have
also obtained a recent image of HR7672B with NIRC2 at Keck. The astrometry also
shows curvature. In this paper, we use jointly-fitted Doppler and astrometric
models to calculate the three-dimensional orbit and dynamical mass of the
companion. The mass of the host star is determined using a direct radius
measurement from CHARA interferometry in combination with high resolution
spectroscopic modeling. We find that HR7672B has a highly eccentric,
, near edge-on, deg, orbit with
semimajor axis, AU. The mass of the companion is
at the 68.2% confidence level. HR7672B thus resides
near the substellar boundary, just below the hydrogen-fusing limit. These
measurements of the companion mass are independent of its brightness and
spectrum and establish HR7672B as a rare and precious "benchmark" brown dwarf
with a well-determined mass, age, and metallicity essential for testing
theoretical evolutionary models and synthetic spectral models. It is presently
the only directly imaged L,T,Y-dwarf known to produce an RV trend around a
solar-type star.Comment: accepted to Ap
Benchmarking Substellar Evolutionary Models Using New Age Estimates for HD 4747 B and HD 19467 B
Constraining substellar evolutionary models (SSEMs) is particularly difficult
due to a degeneracy between the mass, age, and luminosity of a brown dwarf. In
cases where a brown dwarf is found as a directly imaged companion to a star, as
in HD 4747 and HD 19467, the mass, age, and luminosity of the brown dwarf are
determined independently, making them ideal objects to use to benchmark SSEMs.
Using the Center for High Angular Resolution Astronomy Array, we measured the
angular diameters and calculated the radii of the host stars HD 4747 A and HD
19467 A. After fitting their parameters to the Dartmouth Stellar Evolution
Database, MESA Isochrones and Stellar Tracks, and Yonsei-Yale isochronal
models, we adopt age estimates of Gyr for HD 4747 A and
Gyr for HD 19467 A. Assuming the brown dwarf companions
HD 4747 B and HD 19467 B have the same ages as their host stars, we show that
many of the SSEMs under-predict bolometric luminosities by 0.75 dex for
HD 4747 B and dex for HD 19467 B. The discrepancies in luminosity
correspond to over-predictions of the masses by 12\% for HD 4747 B and
30\% for HD 19467 B. We also show that SSEMs that take into account the
effect of clouds reduce the under-prediction of luminosity to dex
and the over-prediction of mass to for HD 4747 B, an L/T transition
object that is cool enough to begin forming clouds. One possible explanation
for the remaining discrepancies is missing physics in the models, such as the
inclusion of metallicity effects.Comment: 12 pages, 6 figures, 5 tables, accepted to Ap
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