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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.

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.

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..

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.

Lisse C.M.,JHU APL | Lisse C.M.,Johns Hopkins University | Wyatt M.C.,University of Cambridge | Chen C.H.,STS Inc | And 7 more authors.
Astrophysical Journal | Year: 2012

We have analyzed Spitzer and NASA/IRTF 2-35μm spectra of the warm, 350K circumstellar dust around the nearby MS star η Corvi (F2V, 1.4 ± 0.3 Gyr). The spectra show clear evidence for warm, water- and carbon-rich dust at ∼ 3AU from the central star, in the system's terrestrial habitability zone. Spectral features due to ultra-primitive cometary material were found, in addition to features due to impact produced silica and high-temperature carbonaceous phases. At least 9 × 1018 kg of 0.1-100μm warm dust is present in a collisional equilibrium distribution with dn/da ∼ a -3.5, the equivalent of a 130km radius Kuiper Belt object (KBO) of 1.0 g cm3 density and similar to recent estimates of the mass delivered to the Earth at 0.6-0.8 Gyr during the late-heavy bombardment. We conclude that the parent body was a Kuiper Belt body or bodies which captured a large amount of early primitive material in the first megayears of the system's lifetime and preserved it in deep freeze at ∼150AU. At ∼1.4 Gyr they were prompted by dynamical stirring of their parent Kuiper Belt into spiraling into the inner system, eventually colliding at 5-10kms-1 with a rocky planetary body of mass ≤M Earth at ∼3AU, delivering large amounts of water (>0.1% of M Earth 's Oceans) and carbon-rich material. The Spitzer spectrum also closely matches spectra reported for the Ureilite meteorites of the Sudan Almahata Sitta fall in 2008, suggesting that one of the Ureilite parent bodies was a KBO. © 2012. The American Astronomical Society. All rights reserved.

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