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Lisse C.M.,JHU APL | Sitko M.L.,University of Cincinnati | Sitko M.L.,Space Science Institute | Marengo M.,Iowa State University
Astrophysical Journal Letters | Year: 2015

We have utilized the NASA/IRTF 3 m SpeX instrument's high-resolution spectral mode to observe and characterize the near-infrared flux emanating from the unusual Kepler light curve system KIC 8462852. By comparing the resulting 0.8-4.2 μm spectrum to a mesh of model photospheric spectra, the 6 emission line analyses of the Rayner et al. catalog, and the 25 system collections of debris disks we have observed to date using SpeX under the Near InfraRed Debris disk Survey, we have been able to additionally characterize the system. Within the errors of our measurements, this star looks like a normal solar abundance main-sequence F1V to F3V dwarf star without any obvious traces of significant circumstellar dust or gas. Using Connelley & Greene's emission measures, we also see no evidence of significant ongoing accretion onto the star nor any stellar outflow away from it. Our results are inconsistent with large amounts of static close-in obscuring material or the unusual behavior of a YSO system, but are consistent with the favored episodic giant comet models of a Gyr old stellar system favored by Boyajian et al. We speculate that KIC 8462852, like the ∼1.4 Gyr old F2V system η Corvi, is undergoing a late heavy bombardment, but is only in its very early stages. © 2015. The American Astronomical Society. All rights reserved. Source

The Radiation Belt Storm Probe (RBSP) spacecraft used the Direct Field Acoustic Testing (DFAT) method to meet the program's acoustic test requirement. Leading up to the flight test, a representative test article (Mockup) was tested by the direct field acoustic method and in a reverberant chamber. The Mockup was designed to be a pathfinder for RBSP spacecraft by mimicking the overall shape and construction of the flight satellites. Microphone placement relative to the Mockup and accelerometer locations remained consistent between the tests allowing for detailed comparisons. Mockup accelerometer responses to a reverberant field are compared to accelerometer responses generated from a direct acoustic field using MIMO control. In addition, microphones 9" from the panel surfaces are compared between reverberant and DFAT tests. Flight RBSP accelerometer responses are presented for selected areas. Source

Lui A.T.Y.,JHU APL | Cogger L.L.,University of Calgary | Howarth A.,University of Calgary | Yau A.W.,University of Calgary
Geophysical Research Letters | Year: 2015

We report the first satellite imaging of auroral pulsations by the Fast Auroral Imager (FAI) on board the Enhanced Polar Outflow Probe (e-POP) satellite. The near-infrared camera of FAI is capable of providing up to two auroral images per second, ideal for investigation of pulsating auroras. The auroral pulsations were observed within the auroral bulge formed during a substorm interval on 19 February 2014. This first satellite view of these pulsations from FAI reveals that (1) several pulsating auroral channels (PACs) occur within the auroral bulge, (2) periods of the intensity pulsations span over one decade within the auroral bulge, and (3) there is no apparent trend of longer pulsation periods associated with higher latitudes for these PACs. Although PACs resemble in some respect stable pulsating auroras reported previously, they have several important differences in characteristics. ©2015. American Geophysical Union. All Rights Reserved. Source

Johnson B.C.,Purdue University | Lisse C.M.,JHU APL | Chen C.H.,STS Inc | Melosh H.J.,Purdue University | And 7 more authors.
Astrophysical Journal | Year: 2012

Spectral modeling of the large infrared excess in the Spitzer IRS spectra of HD 172555 suggests that there is more than 1019 kg of submicron dust in the system. Using physical arguments and constraints from observations, we rule out the possibility of the infrared excess being created by a magma ocean planet or a circumplanetary disk or torus. We show that the infrared excess is consistent with a circumstellar debris disk or torus, located at 6 AU, that was created by a planetary scale hypervelocity impact. We find that radiation pressure should remove submicron dust from the debris disk in less than one year. However, the system's mid-infrared photometric flux, dominated by submicron grains, has been stable within 4% over the last 27 years, from the Infrared Astronomical Satellite (1983) to WISE (2010). Our new spectral modeling work and calculations of the radiation pressure on fine dust in HD 172555 provide a self-consistent explanation for this apparent contradiction. We also explore the unconfirmed claim that 1047 molecules of SiO vapor are needed to explain an emission feature at 8 μm in the Spitzer IRS spectrum of HD 172555. We find that unless there are 1048 atoms or 0.05 M ⊕ of atomic Si and O vapor in the system, SiO vapor should be destroyed by photo-dissociation in less than 0.2 years. We argue that a second plausible explanation for the 8 μm feature can be emission from solid SiO, which naturally occurs in submicron silicate "smokes" created by quickly condensing vaporized silicate. © 2012. The American Astronomical Society. All rights reserved.. Source

Lui A.T.Y.,JHU APL | Zong Q.-G.,Beijing Institute of Technology | Zong Q.-G.,University of Massachusetts Lowell | Wang C.,Chinese Academy of Sciences | Dunlop M.W.,Rutherford Appleton Laboratory
Journal of Geophysical Research: Space Physics | Year: 2012

We examine the strength of the electron source associated with dipolarization at the outer boundary of the radiation belts using multisatellite observations from THEMIS. This topic is relevant to the determination on the relative roles of inward radial diffusion versus internal local acceleration for the origin of the relativistic electrons in the outer radiation belt. We focus on the electron phase space density (PSD) as a function of the first adiabatic invariant () for equatorially mirroring population over a broad energy range. It is found that the source strength associated with dipolarization for non-storm periods at the outer boundary of the radiation belts can be well above the observed fluxes of relativistic electrons inside the outer radiation belt. The PSD change due to the magnetic field strength variation dominates over PSD change from the energy flux increase with dipolarization, resulting in a strong anticorrelation between magnetic field strength and PSD values at a given . If observations from closely spaced satellites during the same event can be used to indicate radial transport of electrons with dipolarization, then the observed PSD at these satellites indicates frequent occurrence of non-adiabatic process during their radial transport. © 2012. American Geophysical Union. All Rights Reserved. Source

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