341 research outputs found
MATRIMONIAL DOMICIL AND MARITAL RIGHTS IN MOVABLES
The American decisions in Conflicts of Laws relating to the rights acquired by one spouse in the property of the other by virtue of the fact of marriage stand as a monument to Joseph Story . Almost without exception the cases discussed hereafter have been decided on the basis of his thorough analysis of the law of the Pandects and the eighteenth century civilians. Even where his principles have not been approved, the courts have departed from them only after real and serious consideration. This fact, kept in mind, greatly simplifies the study of the cases themselves
Periodic Optical Variability of Radio Detected Ultracool Dwarfs
A fraction of very low mass stars and brown dwarfs are known to be radio
active, in some cases producing periodic pulses. Extensive studies of two such
objects have also revealed optical periodic variability and the nature of this
variability remains unclear. Here we report on multi-epoch optical photometric
monitoring of six radio detected dwarfs, spanning the M8 - L3.5 spectral
range, conducted to investigate the ubiquity of periodic optical variability in
radio detected ultracool dwarfs. This survey is the most sensitive ground-based
study carried out to date in search of periodic optical variability from
late-type dwarfs, where we obtained 250 hours of monitoring, delivering
photometric precision as low as 0.15%. Five of the six targets exhibit
clear periodicity, in all cases likely associated with the rotation period of
the dwarf, with a marginal detection found for the sixth. Our data points to a
likely association between radio and optical periodic variability in
late-M/early-L dwarfs, although the underlying physical cause of this
correlation remains unclear. In one case, we have multiple epochs of monitoring
of the archetype of pulsing radio dwarfs, the M9 TVLM 513-46546, spanning a
period of 5 years, which is sufficiently stable in phase to allow us to
establish a period of 1.95958 0.00005 hours. This phase stability may be
associated with a large-scale stable magnetic field, further strengthening the
correlation between radio activity and periodic optical variability. Finally,
we find a tentative spin-orbit alignment of one component of the very low mass
binary LP 349-25.Comment: Accepted to The Astrophysical Journal; 22 pages; 12 figure
Impact of Electron Precipitation on Brown Dwarf Atmospheres and the Missing Auroral H Emission
Recent observations have demonstrated that very-low mass stars and brown
dwarfs are capable of sustaining strong magnetic fields despite their cool and
neutral atmospheres. These kG field strengths are inferred based on strong
highly circularly polarized GHz radio emission, a consequence of the electron
cyclotron maser instability. Crucially, these observations imply the existence
of energetic non-thermal electron populations, associated with strong current
systems, as are found in the auroral regions of the magnetized planets of the
Solar System. Intense auroral electron precipitation will lead to electron
collisions with the H gas that should ultimately generate the ion
H. With this motivation, we targeted a sample of ultracool dwarfs,
known to exhibit signatures associated with aurorae, in search of the K-band
emission features of H using the Keck telescopes on Mauna Kea. From
our sample of 9 objects, we found no clear indication of H emission
features in our low-medium resolution spectra (R3600). We also modeled
the impact of an auroral electron beam on a brown dwarf atmosphere, determining
the depth at which energetic beams deposit their energy and drive particle
impact ionization. We find that the H non-detections can be explained
by electron beams of typical energies 2-10~keV, which penetrate deeply
enough that any H produced is chemically destroyed before radiating
energy through its infrared transitions. Strong electron beams could further
explain the lack of UV detections, and suggest that most or nearly all of the
precipitating auroral energy must ultimately emerge as thermal emissions deep
in brown dwarf atmospheres.Comment: accepted to Ap
Smartphone scene generator for efficient characterization of visible imaging detectors
Full characterization of imaging detectors involves subjecting them to
spatially and temporally varying illumination patterns over a large dynamic
range. Here we present a scene generator that fulfills many of these functions.
Based on a modern smartphone, it has a number of good features, including the
ability to generate nearly arbitrary optical scenes, high spatial resolution
(13 um), high dynamic range (~10^4), near-Poisson limited illumination
stability over time periods from 100 ms to many days, and no background noise.
The system does not require any moving parts and may be constructed at modest
cost. We present the optical, mechanical, and software design, test data
validating the performance, and application examples.Comment: 14 pages. This version includes code, available here:
https://github.com/Leo-Nea
Electron multiplication CCD detector technology advancement for the WFIRST-AFTA coronagraph
The WFIRST-AFTA (Wide Field InfraRed Survey Telescope-Astrophysics Focused Telescope Asset) is a NASA space observatory. It will host two major astronomical instruments: a wide-field imager (WFI) to search for dark energy and carry out wide field near infrared (NIR) surveys, and a coronagraph instrument (CGI) to image and spectrally characterize extrasolar planets. In this paper, we discuss the work that has been carried out at JPL in advancing Electron Multiplying CCD (EMCCD) technology to higher flight maturity, with the goal of reaching a NASA technology readiness level of 6 (TRL-6) by early-to-mid 2016. The EMCCD has been baselined for both the coronagraph's imager and integral field spectrograph (IFS) based on its sub-electron noise performance at extremely low flux levels - the regime where the AFTA CGI will operate. We present results from a study that fully characterizes the beginning of life performance of the EMCCD. We also discuss, and present initial results from, a recent radiation test campaign that was designed and carried out to mimic the conditions of the WFIRST-AFTA space environment in an L2 orbit, where we sought to assess the sensor's end of life performance, particularly degradation of its charge transfer efficiency, in addition to other parameters such as dark current, electron multiplication gain, clock induced charge and read noise
Detection of a Faint Fast-moving Near-Earth Asteroid Using the Synthetic Tracking Technique
We report a detection of a faint near-Earth asteroid (NEA) using our synthetic tracking technique and the CHIMERA instrument on the Palomar 200 inch telescope. With an apparent magnitude of 23 (H = 29, assuming detection at 20 lunar distances), the asteroid was moving at 6º.32 day^(–1) and was detected at a signal-to-noise ratio (S/N) of 15 using 30 s of data taken at a 16.7 Hz frame rate. The detection was confirmed by a second observation 77 minutes later at the same S/N. Because of its high proper motion, the NEA moved 7 arcsec over the 30 s of observation. Synthetic tracking avoided image degradation due to trailing loss that affects conventional techniques relying on 30 s exposures; the trailing loss would have degraded the surface brightness of the NEA image on the CCD down to an approximate magnitude of 25 making the object undetectable. This detection was a result of our 12 hr blind search conducted on the Palomar 200 inch telescope over two nights, scanning twice over six (5º.3 × 0º.046) fields. Detecting only one asteroid is consistent with Harris's estimates for the distribution of the asteroid population, which was used to predict a detection of 1.2 NEAs in the H-magnitude range 28-31 for the two nights. The experimental design, data analysis methods, and algorithms are presented. We also demonstrate milliarcsecond-level astrometry using observations of two known bright asteroids on the same system with synthetic tracking. We conclude by discussing strategies for scheduling observations to detect and characterize small and fast-moving NEAs using the new technique
WFIRST coronagraph detector trap modeling results and improvements
The WFIRST coronagraph is being designed to detect and characterize mature exoplanets through the starlight reflected from their surfaces and atmospheres. The light incident on the detector from these distant exoplanets is estimated to be on the order of a few photons per pixel per hour. To measure such small signals, the project has baselined the CCD201 detector made by e2v, a low-noise and high-efficiency electron-multiplying charge-coupled device (EMCCD), and has instituted a rigorous test and modeling program to characterize the device prior to flight. An important consideration is detector performance degradation over the proposed mission lifetime due to radiation exposure in space. To quantify this estimated loss in performance, the project has built a detector trap model that takes into account detailed trap interactions at the sub-pixel level, including stochastic trap capture and release, and the deferment of charge into subsequent pixels during parallel and serial clocking of the pseudo-two-phase CCD201 device. This paper describes recent detector trap model improvements and modeling results
Cryogenic irradiation of an EMCCD for the WFIRST coronagraph: preliminary performance analysis
The Wide Field Infra-Red Survey Telescope (WFIRST) is a NASA observatory scheduled to launch in the next decade that will settle essential questions in exoplanet science. The Wide Field Instrument (WFI) offers Hubble quality imaging over a 0.28 square degree field of view and will gather NIR statistical data on exoplanets through gravitational microlensing. An on-board coronagraph will for the first time perform direct imaging and spectroscopic analysis of exoplanets with properties analogous to those within our own solar system, including cold Jupiters, mini Neptunes and potentially super Earths.
The Coronagraph Instrument (CGI) will be required to operate with low signal flux for long integration times, demanding all noise sources are kept to a minimum. The Electron Multiplication (EM)-CCD has been baselined for both the imaging and spectrograph cameras due its ability to operate with sub-electron effective read noise values with appropriate multiplication gain setting. The presence of other noise sources, however, such as thermal dark signal and Clock Induced Charge (CIC), need to be characterized and mitigated. In addition, operation within a space environment will subject the device to radiation damage that will degrade the Charge Transfer Effciency (CTE) of the device throughout the mission lifetime. Irradiation at the nominal instrument operating temperature has the potential to provide the best estimate of performance degradation that will be experienced in-flight, since the final population of silicon defects has been shown to be dependent upon the temperature at which the sensor is irradiated.
Here we present initial findings from pre- and post- cryogenic irradiation testing of the e2v CCD201-20 BI EMCCD sensor, baselined for the WFIRST coronagraph instrument. The motivation for irradiation at cryogenic temperatures is discussed with reference to previous investigations of a similar nature. The results are presented in context with those from a previous room temperature irradiation investigation that was performed on a CCD201-20 operated under the same conditions. A key conclusion is that the measured performance degradation for a given proton fluence is seen to measurably differ for the cryogenic case compared to the room temperature equivalent for the conditions of this study
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