Burlington, MA, United States
Burlington, MA, United States
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Croll B.,Massachusetts Institute of Technology | Croll B.,NASA | Rappaport S.,Massachusetts Institute of Technology | Devore J.,Visidyne, Inc. | And 11 more authors.
Astrophysical Journal | Year: 2014

We present multiwavelength photometry, high angular resolution imaging, and radial velocities of the unique and confounding disintegrating low-mass planet candidate KIC 12557548b. Our high angular resolution imaging, which includes space-based Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) observations in the optical (∼0.53 μm and ∼0.77 μm), and ground-based Keck/NIRC2 observations in K′ band (∼2.12 μm), allow us to rule out background and foreground candidates at angular separations greater than 0.″2 that are bright enough to be responsible for the transits we associate with KIC 12557548. Our radial velocity limit from Keck/HIRES allows us to rule out bound, low-mass stellar companions (∼0.2 M) to KIC 12557548 on orbits less than 10 yr, as well as placing an upper limit on the mass of the candidate planet of 1.2 Jupiter masses; therefore, the combination of our radial velocities, high angular resolution imaging, and photometry are able to rule out most false positive interpretations of the transits. Our precise multiwavelength photometry includes two simultaneous detections of the transit of KIC 12557548b using Canada-France-Hawaii Telescope/Wide-field InfraRed Camera (CFHT/WIRCam) at 2.15 μm and the Kepler space telescope at 0.6 μm, as well as simultaneous null-detections of the transit by Kepler and HST/WFC3 at 1.4 μm. Our simultaneous HST/WFC3 and Kepler null-detections provide no evidence for radically different transit depths at these wavelengths. Our simultaneous CFHT/WIRCam detections in the near-infrared and with Kepler in the optical reveal very similar transit depths (the average ratio of the transit depths at ∼2.15 μm compared with ∼0.6 μm is: 1.02 ± 0.20). This suggests that if the transits we observe are due to scattering from single-size particles streaming from the planet in a comet-like tail, then the particles must be ∼0.5 μm in radius or larger, which would favor that KIC 12557548b is a sub-Mercury rather than super-Mercury mass planet. © 2014. The American Astronomical Society. All rights reserved.

Wilbert S.,German Aerospace Center | Reinhardt B.,German Aerospace Center | DeVore J.,Visidyne, Inc. | Roger M.,Institute of Solar Research | And 3 more authors.
Journal of Solar Energy Engineering, Transactions of the ASME | Year: 2013

Due to forward scattering of direct sunlight in the atmosphere, the circumsolar region closely surrounding the solar disk looks very bright. The radiation coming from this region, the circumsolar radiation, is in large part included in common direct normal irradiance (DNI) measurements, but only partially intercepted by the receivers of focusing collectors. This effect has to be considered in the performance analysis of concentrating collectors in order to avoid overestimation of the intercepted irradiance. At times, the overestimation reaches more than 10% for highly concentrating systems even for sky conditions with relevant DNI above 200 W/m2. The amount of circumsolar radiation varies strongly with time, location and sky conditions. However, no representative sunshape measurements exist for locations that are now of particular interest for concentrating solar power (CSP) or concentrating photovoltaics (CPV). A new sunshape measurement system is developed and analyzed in this study. The system consists of the sun and aureole measurement instrument (SAM), an AERONET sun photometer and postprocessing software. A measurement network is being created with the presented system. The uncertainty of this system is significantly lower than what was obtained with previous devices. In addition, the spectral optical properties of circumsolar radiation are determined. As a result, the necessary information for CSP and CPV systems, and a basis for the development of modeling methods for circumsolar radiation, can now be achieved. Copyright © 2013 by ASME.

Rappaport S.,Massachusetts Institute of Technology | Barclay T.,NASA | Devore J.,Visidyne, Inc. | Rowe J.,Search for Extraterrestrial Intelligence Institute | And 3 more authors.
Astrophysical Journal | Year: 2014

Kepler planet candidate KOI-2700b (KIC 8639908b), with an orbital period of 21.84 hr, exhibits a distinctly asymmetric transit profile, likely indicative of the emission of dusty effluents, and reminiscent of KIC 1255b. The host star has T eff = 4435 K, M ≃ 0.63 M, and R ≃ 0.57 R, comparable to the parameters ascribed to KIC 12557548. The transit egress can be followed for ∼25% of the orbital period and, if interpreted as extinction from a dusty comet-like tail, indicates a long lifetime for the dust grains of more than a day. We present a semiphysical model for the dust tail attenuation and fit for the physical parameters contained in that expression. The transit is not sufficiently deep to allow for a study of the transit-to-transit variations, as is the case for KIC 1255b; however, it is clear that the transit depth is slowly monotonically decreasing by a factor of ∼2 over the duration of the Kepler mission. We infer a mass-loss rate in dust from the planet of ∼2 lunar masses per Gyr. The existence of a second star hosting a planet with a dusty comet-like tail would help to show that such objects may be more common and less exotic than originally thought. According to current models, only quite small planets with Mp ≲ 0.03 M ⊕ are likely to release a detectable quantity of dust. Thus, any "normal-looking" transit that is inferred to arise from a rocky planet of radius greater than ∼1/2R⊕ should not exhibit any hint of a dusty tail. Conversely, if one detects an asymmetric transit due to a dusty tail, then it will be very difficult to detect the hard body of the planet within the transit because, by necessity, the planet must be quite small (i.e., ≲0.3R ⊕). © 2014. The American Astronomical Society. All rights reserved..

Devore J.G.,Visidyne, Inc. | Kristl J.A.,Visidyne, Inc. | Rappaport S.A.,Massachusetts Institute of Technology
Journal of Geophysical Research: Atmospheres | Year: 2013

The aureoles around stars caused by thin cirrus limit nighttime measurement opportunities for ground-based astronomy, but can provide information on high-altitude ice crystals for climate research. In this paper we attempt to demonstrate quantitatively how this works. Aureole profiles can be followed out to ∼0.2°from stars and ∼0.5°from Jupiter. Interpretation of diffracted starlight is similar to that for sunlight, but emphasizes larger particles. Stellar diffraction profiles are very distinctive, typically being approximately flat out to a critical angle followed by gradually steepening power-law falloff with slope less steep than -3. Using the relationship between the phase function for diffraction and the average Fourier transform of the projected area of complex ice crystals, we show that defining particle size in terms of average projected area normal to the propagation direction of the starlight leads to a simple, analytic approximation representing large-particle diffraction that is nearly independent of crystal habit. A similar analytic approximation for the diffraction aureole allows it to be separated from the point spread function and the sky background. Multiple scattering is deconvolved using the Hankel transform leading to the diffraction phase function. Application of constrained numerical inversion to the phase function then yields a solution for the particle size distribution in the range between ∼50 μm and ∼400 μm. Stellar aureole measurements can provide one of the very few, as well as least expensive, methods for retrieving cirrus microphysical properties from ground-based observations. © 2013. American Geophysical Union. All Rights Reserved.

DeVore J.,Visidyne, Inc. | Rappaport S.,Massachusetts Institute of Technology | Sanchis-Ojeda R.,University of California at Berkeley | Hoffman K.,Search for Extraterrestrial Intelligence Institute | Rowe J.,University Of Montrealqc
Monthly Notices of the Royal Astronomical Society | Year: 2016

We present a way of searching for non-transiting exoplanets with dusty tails. In the transiting case, the extinction by dust during the transit removes more light from the beam than is scattered into it. Thus, the forward scattering component of the light is best seen either just prior to ingress, or just after egress, but with reduced amplitude over the larger peak that is obscured by the transit. This picture suggests that it should be equally productive to search for positive-going peaks in the flux from non-transiting exoplanets with dusty tails. We discuss what amplitudes are expected for different orbital inclination angles. The signature of such objects should be distinct from normal transits, starspots, and most - but not all - types of stellar pulsations. © 2016 The Authors.

This paper describes an improvement in the diffraction approximation used to retrieve the size distribution of atmospheric particles from solar aureole radiance measurements. Normalization using total optical thickness based on measurement of the solar disk radiance is replaced with one based on the aureole profile radiance itself. Retrievals involving model calculations for power-law distributions of water droplets show significant improvement using the new algorithm. Tests involving two empirical particle size distributions, one for cirrus and another for aerosols, also show improvement using the new normalization algorithm. Comparisons of the diffraction approximation algorithms with a numerical inversion algorithm found that the accuracy of the latter was higher for two different bimodal aerosol distributions. The role envisioned for the diffraction approximation is in estimating the size distribution of large particles in clouds and especially cirrus. © 2011 American Meteorological Society.

DeVore J.G.,Visidyne, Inc.
Journal of Atmospheric and Oceanic Technology | Year: 2011

This paper describes a simple relationship between the slope of particulate optical depth as a function of wavelength and the size distribution of spherical particles. It is based on approximating extinction using a truncated geometric optics relationship and is applicable when optical depth decreases with wavelength. The new relationship suggests that extinction versus wavelength measurements are most sensitive to particles that are comparable in size to the wavelength. When optical depth is expressed as a power-law function of wavelength, the resulting particle size distribution is also a power-law function of size, with the two exponents reproducing the well-known relationship between theÅngström and Junge exponents. Examples of applying the new relationship are shown using both numerical calculations based on Mie theory and measurements from the Aerosol Robotic Network (AERONET) sun photometer at NASA Goddard Space Flight Center (GSFC). Since the truncated geometric approximation makes no assumptions per se concerning the form of the particle size distribution, it may find application in supplementing solar aureole profile measurements in retrieving the size distributions of particles in thin clouds-for example, cirrus-or when they are present. © 2011 American Meteorological Society.

De Vore J.,Visidyne, Inc. | Villanucci D.,Visidyne, Inc. | LePage A.,Visidyne, Inc.
Applied Optics | Year: 2012

Two methods of determining instrumental scattering for correcting aureolegraph measurements of particulate solar scattering are presented. One involves subtracting measurements made with and without an external occluding ball and the other is a modification of the Langley Plot method and involves extrapolating aureolegraph measurements collected through a large range of solar zenith angles. Examples of internal scattering correction determinations using the latter method show similar power-law dependencies on scattering, but vary by roughly a factor of 8 and suggest that changing aerosol conditions during the determinations render this method problematic. Examples of corrections of scattering profiles using the former method are presented for a range of atmospheric particulate layers from aerosols to cumulus and cirrus clouds. © 2012 Optical Society of America.

DeVore J.G.,Visidyne, Inc. | Stair Jr. A.T.,Visidyne, Inc. | LePage A.J.,Visidyne, Inc. | Villanucci D.,Visidyne, Inc.
Journal of Geophysical Research: Atmospheres | Year: 2012

Scattering calculations for optically thin cirrus clouds based on retrievals of optical thickness and effective particle size from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua are compared with solar disk radiance and aureole measurements from Visidyne's Sun and Aureole Measurement (SAM) instrument. In the four examples presented, the calculated solar disk radiance differs from the measurement by a factor ranging from 2 to 8. The shape of the aureole radiance profile also differs and indicates that either the effective particle size retrieved by the MODIS daytime cirrus algorithm is too small or there is another problem with the phase functions underlying the MODIS algorithm. Copyright 2012 by the American Geophysical Union.

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 149.90K | Year: 2011

Atmospheric particles act to cool the Earth by reflecting incoming solar radiation if they are small (e.g., aerosols), and they can either warm or cool the earth through thermal absorption and emission if they are large (e.g., cirrus) depending upon their altitude. Climate change monitoring and modeling have improved significantly from advances attributable to the AERONET global network of ground-based sun photometers measuring the properties of aerosols. The climate impact of cirrus cloud particles is much less certain because they occur high in the atmosphere and are more difficult to monitor. Recent work pioneered by Visidyne has employed measurements of the solar aureole profiles caused by cirrus particles to retrieve their size distributions during the daytime. We propose a novel technique to extend this work to nighttime and to the larger, more thermally significant, particles. The basic idea is to determine the profile of aureole scattering patterns around stars at small angles (_1500 to 1_), and to invert this profile to determine the ice particle size distribution over the range D & apos; 50 mm to 10 mm, where D is the effective size of the ice particle. Such measurements are of intrinsic interest to cloud scientists and to climatologists, alike. Our approach utilizes only a good camera lens and a medium-quality astronomical CCD camera. We have carried out some preliminary observations to demonstrate how well, and under what conditions it will yield the desired results. Our approach has the advantages over in-situ measurements in that (i) it can be carried out on virtually any night when thin cirrus clouds are visible, (ii) it is relatively inexpensive to implement, and (iii) the measurements do not disturb the cloud environment or the particles themselves. Finally, we show how such stellar aureole measurements can be run autonomously to enhance existing, ground-based climate monitoring networks with instruments designed to measure stellar aureoles, thereby filling a gap in the information on cirrus clouds necessary for assessing and monitoring their climate impact. Our ultimate goal is long-term monitoring of cirrus ice-crystal size distributions as a function of altitude, season, and geographic latitude

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