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Bryden, Geoffrey

Publications and source records attributed to Bryden, Geoffrey.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A Detailed Characterization of HR 8799's Debris Disk with ALMA in Band 7

The exoplanetary system of HR 8799 is one of the rare systems in which multiple planets have been directly imaged. Its architecture is strikingly similar to that of the solar system, with the four imaged giant planets surrounding a warm dust belt analogous to the Asteroid Belt, and themselves being surrounded by a cold dust belt analog to the Kuiper Belt. Previous observations of this cold belt with ALMA in Band 6 (1.3 mm) revealed its inner edge, but analyses of the data differ on its precise location. It was therefore unclear whether or not the outermost planet HR 8799 b was dynamically sculpting it. We present here new ALMA observations of this debris disk in Band 7 (340 GHz, 880 μm). These are the most detailed observations of this disk obtained so far, with a resolution of 1″ (40 au) and sensitivity of 9.8 μJy beam{sup −1}, which allowed us to recover the disk structure with high confidence. In order to constrain the disk morphology, we fit its emission using radiative transfer models combined with a Markov Chain Monte Carlo procedure. We find that this disk cannot be adequately represented by a single power law with sharp edges. It exhibits a smoothly rising inner edge and smoothly falling outer edge, with a peak in between, as expected from a disk that contains a high-eccentricity component, hence confirming previous findings. Whether this excited population and inner edge shape stem from the presence of an additional planet remains, however, an open question.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2018

Automatic detection of microlensing events in the galactic bulge using machine learning techniques

The Wide Field Infrared Survey Telescope (WFIRST) is a NASA flagship mission scheduled to launch in mid-2020, with more than one year of its lifetime dedicated to microlensing survey. The survey is to discover thousands of exoplanets near or beyond the snowline via their microlensing light curve signatures, enabling a Kepler-like statistical analysis of planets at ~1-10 AU from their host stars and potentially revolutionizing our understanding of planet formation. The goal of our work is to create an automated system that has the ability to efficiently process and classify large-scale astronomical datasets that missions such as WFIRST will produce. In this paper, we discuss our framework that utilizes features election and parameter optimization for classification models to automatically differentiate the different types of stellar variability and detect microlensing events.

Shvartzvald, Yossi↗
NASA NTRS2016

Making High Accuracy Null Depth Measurements for the LBTI ExoZodi Survey

The characterization of exozodiacal light emission is both important for the understanding of planetary systems evolution and for the preparation of future space missions aiming to characterize low mass planets in the habitable zone of nearby main sequence stars. The Large Binocular Telescope Interferometer (LBTI) exozodi survey aims at providing a ten-fold improvement over current state of the art, measuring dust emission levels down to a typical accuracy of approximately 12 zodis per star, for a representative ensemble of approximately 30+ high priority targets. Such measurements promise to yield a final accuracy of about 2 zodis on the median exozodi level of the targets sample. Reaching a 1 sigma measurement uncertainty of 12 zodis per star corresponds to measuring interferometric cancellation (null) levels, i.e visibilities at the few 100 ppm uncertainty level. We discuss here the challenges posed by making such high accuracy mid-infrared visibility measurements from the ground and present the methodology we developed for achieving current best levels of 500 ppm or so. We also discuss current limitations and plans for enhanced exozodi observations over the next few years at LBTI.

exozodiacal light emission↗
NASA NTRS2016

Making High Accuracy Null Depth Measurements for the LBTI Exozodi Survey

The characterization of exozodiacal light emission is both important for the understanding of planetary systems evolution and for the preparation of future space missions aiming to characterize low mass planets in the habitable zone of nearby main sequence stars. The Large Binocular Telescope Interferometer (LBTI) exozodi survey aims at providing a ten-fold improvement over current state of the art, measuring dust emission levels down to a typical accuracy of 12 zodis per star, for a representative ensemble of 30+ high priority targets. Such measurements promise to yield a final accuracy of about 2 zodis on the median exozodi level of the targets sample. Reaching a 1 sigma measurement uncertainty of 12 zodis per star corresponds to measuring interferometric cancellation (null) levels, i.e visibilities at the few 100 ppm uncertainty level. We discuss here the challenges posed by making such high accuracy mid-infrared visibility measurements from the ground and present the methodology we developed for achieving current best levels of 500 ppm or so. We also discuss current limitations and plans for enhanced exozodi observations over the next few years at LBTI.

exozodiacal light emission↗
NASA NTRS2016

Making high accuracy null depth measurements for the LBTI Exozodi survey

The characterization of exozodiacal light emission is both important for the understanding of planetary systems evolution and for the preparation of future space missions aiming to characterize low mass planets in the habitable zone of nearby main sequence stars. The Large Binocular Telescope Interferometer (LBTI) exozodi survey aims at providing a ten-fold improvement over current state of the art, measuring dust emission levels down to a typical accuracy of ~12 zodis per star, for a representative ensemble of ~30+ high priority targets. Such measurements promise to yield a final accuracy of about 2 zodis on the median exozodi level of the targets sample. Reaching a 1σ measurement uncertainty of 12 zodis per star corresponds to measuring interferometric cancellation (“null”) levels, i.e visibilities at the few 100 ppm uncertainty level. We discuss here the challenges posed by making such high accuracy mid-infrared visibility measurements from the ground and present the methodology we developed for achieving current best levels of 500 ppm or so. We also discuss current limitations and plans for enhanced exozodi observations over the next few years at LBTI.

Mennesson, Bertrand↗
NASA NTRS2014

Exo-C: a Probe-Scale Space Mission to Directly Image and Spectroscopically Characterize Exoplanetary Systems Using an Internal Coronagraph

"Exo-C" is NASA's first community study of a modest aperture space telescope designed for high contrast observations of exoplanetary systems. The mission will be capable of taking optical spectra of nearby exoplanets in reflected light, discover previously undetected planets, and imaging structure in a large sample of circumstellar disks. It will obtain unique science results on planets down to super-Earth sizes and serve as a technology pathfinder toward an eventual flagship-class mission to find and characterize habitable exoplanets. We present the mission/payload design and highlight steps to reduce mission cost/risk relative to previous mission concepts. At the study conclusion in 2015, NASA will evaluate it for potential development at the end of this decade. Keywords: Exoplanets, high contrast imaging, optical astronomy, space mission concepts

high contrast imaging↗
NASA NTRS2013

The Debris Disk Explorer: A Balloon-Borne Coronagraph for Observing Debris Disks

The Debris Disk Explorer (DDX) is a proposed balloon-borne investigation of debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. DDX will measure the size, shape, brightness, and color of tens of disks. These measurements will enable us to place the Solar System in context. By imaging debris disks around nearby stars, DDX will reveal the presence of perturbing planets via their influence on disk structure, and explore the physics and history of debris disks by characterizing the size and composition of disk dust. The DDX instrument is a 0.75-m diameter off-axis telescope and a coronagraph carried by a stratospheric balloon. DDX will take high-resolution, multi-wavelength images of the debris disks around tens of nearby stars. Two flights are planned; an overnight test flight within the United States followed by a month-long science flight launched from New Zealand. The long flight will fully explore the set of known debris disks accessible only to DDX. It will achieve a raw contrast of 10(exp -7), with a processed contrast of 10(exp -8). A technology benefit of DDX is that operation in the near-space environment will raise the Technology Readiness Level of internal coronagraphs, deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope for high-contrast exoplanet imaging.

High Altitude Balloon↗
NASA NTRS2012

WISE Detections of Dust in the Habitable Zones of Planet-Bearing Stars

We use data from the Wide-field Infrared Survey Explorer (WISE) all-sky release to explore the incidence of warm dust in the habitable zones around exoplanet-host stars. Dust emission at 12 and/or 22 microns (T(sub dust) approx.300 and/or approx.150 K) traces events in the terrestrial planet zones; its existence implies replenishment by evaporation of comets or collisions of asteroids, possibly stirred by larger planets. Of the 591 planetary systems (728 extrasolar planets) in the Exoplanet Encyclopedia as of 2012 January 31, 350 are robustly detected by WISE at > or = 5(sigma) level. We perform detailed photosphere subtraction using tools developed for Spitzer data and visually inspect all the WISE images to confirm bona fide point sources. We find nine planet-bearing stars show dust excess emission at 12 and/or 22 microns at > or = 3(sigma) level around young, main-sequence, or evolved giant stars. Overall, our results yield an excess incidence of approx.2.6% for stars of all evolutionary stages, but approx.1% for planetary debris disks around main-sequence stars. Besides recovering previously known warm systems, we identify one new excess candidate around the young star UScoCTIO 108.

Morales, Farisa Y.↗
NASA NTRS2012

Coronagraphic Imaging of Debris Disks from a High Altitude Balloon Platform

Debris disks around nearby stars are tracers of the planet formation process, and they are a key element of our understanding of the formation and evolution of extrasolar planetary systems. With multi-color images of a significant number of disks, we can probe important questions: can we learn about planetary system evolution; what materials are the disks made of; and can they reveal the presence of planets? Most disks are known to exist only through their infrared flux excesses as measured by the Spitzer Space Telescope, and through images measaured by Herschel. The brightest, most extended disks have been imaged with HST, and a few, such as Fomalhaut, can be observed using ground-based telescopes. But the number of good images is still very small, and there are none of disks with densities as low as the disk associated with the asteroid belt and Edgeworth-Kuiper belt in our own Solar System. Direct imaging of disks is major observational challenge, demanding high angular resolution and extremely high dynamic range close to the parent star. The ultimate experiment requires a space-based platform, but demonstrating much of the needed technology, mitigating the technical risks of a space-based coronagraph, and performing valuable measurements of circumstellar debris disks, can be done from a high-altitude balloon platform. In this paper we present a balloon-borne telescope concept based on the Zodiac II design that could undertake compelling studies of a sample of debris disks.

Unwin, Stephen↗
NASA NTRS2012

Coronagraphic Imaging of Debris Disks from a High Altitude Balloon Platform

Debris disks around nearby stars are tracers of the planet formation process, and they are a key element of our understanding of the formation and evolution of extrasolar planetary systems. With multi-color images of a significant number of disks, we can probe important questions: can we learn about planetary system evolution; what materials are the disks made of; and can they reveal the presence of planets? Most disks are known to exist only through their infrared flux excesses as measured by the Spitzer Space Telescope, and through images measured by Herschel. The brightest, most extended disks have been imaged with HST, and a few, such as Fomalhaut, can be observed using ground-based telescopes. But the number of good images is still very small, and there are none of disks with densities as low as the disk associated with the asteroid belt and Edgeworth-Kuiper belt in our own Solar System. Direct imaging of disks is a major observational challenge, demanding high angular resolution and extremely high dynamic range close to the parent star. The ultimate experiment requires a space-based platform, but demonstrating much of the needed technology, mitigating the technical risks of a space-based coronagrap, and performing valuable measurements of circumstellar debris disks, can be done from a high-altitude balloon platform. In this paper we present a balloon-borne telescope experiment based on the Zodiac II design that would undertake compelling studies of a sample of debris disks.

debris disk↗
NASA NTRS2012

Coronagraphic Imaging of Debris Disks from a High-Altitude Balloon Platform

Debris disks are rings of micron-size dust orbiting in the outer regions of planetary systems. Asteroid and comet collisions are the probable sources of the dust. Radiation pressure and Poynting-Robertson drag. Planets shepherd and sculpt the dust into a ring. The dust ring is bright enough to be imaged, brighter than the planets themselves. So debris disk images are our connection to as-yet unseen planets, comets, and asteroids.

high-contrast imaging↗
NASA NTRS2012

Hubble Space Telescope Observations of the HD 202628 Debris Disk

A ring-shaped debris disk around the G2V star HD 202628 (d = 24.4 pc) was imaged in scattered light at visible wavelengths using the coronagraphic mode of the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The ring is inclined by approx.64deg from face-on, based on the apparent major/minor axis ratio, with the major axis aligned along PA = 130deg. It has inner and outer radii (> 50% maximum surface brightness) of 139 AU and 193 AU in the northwest ansae and 161 AU and 223 AU in the southeast ((Delta)r/r approx. = 0.4). The maximum visible radial extent is approx. 254 AU. With a mean surface brightnesses of V approx. = 24 mag arcsec.(sup -2), this is the faintest debris disk observed to date in reflected light. The center of the ring appears offset from the star by approx.28 AU (deprojected). An ellipse fit to the inner edge has an eccentricity of 0.18 and a = 158 AU. This offset, along with the relatively sharp inner edge of the ring, suggests the influence of a planetary-mass companion. There is a strong similarity with the debris ring around Fomalhaut, though HD 202628 is a more mature star with an estimated age of about 2 Gyr. We also provide surface brightness limits for nine other stars in our study with strong Spitzer excesses around which no debris disks were detected in scattered light (HD 377, HD 7590, HD 38858, HD 45184, HD 73350, HD 135599, HD 145229, HD 187897, and HD 201219).

Krist, John E.↗
NASA NTRS2012

The Exozodiacal Dust Problem for Direct Observations of ExoEarths

Debris dust in the habitable zones of stars otherwise known as exozodiacal dust comes from extrasolar asteroids and comets and is thus an expected part of a planetary system. Background flux from the Solar Systems zodiacal dust and the exozodiacal dust in the target system is likely to be the largest source of astrophysical noise in direct observations of terrestrial planets in the habitable zones of nearby stars. Furthermore, dust structures like clumps, thought to be produced by dynamical interactions with exoplanets, are a possible source of confusion. In this paper, we qualitatively assess the primary impact of exozodical dust on high-contrast direct imaging at optical wavelengths, such as would be performed with a coronagraph. Then we present the sensitivity of previous, current, and near-term facilities to thermal emission from debris dust at all distances from nearby solar-type stars, as well as our current knowledge of dust levels from recent surveys. Finally, we address the other method of detecting debris dust, through high-contrast imaging in scattered light. This method is currently far less sensitive than thermal emission observations, but provides high spatial resolution for studying dust structures. This paper represents the first report of NASA's Exoplanet Exploration Program Analysis Group (ExoPAG).

Roberge, Aki↗
NASA NTRS2011

Common Warm Dust Temperatures Around Main Sequence Stars

We compare the properties of warm dust emission from a sample of main-sequence A-type stars (B8-A7) to those of dust around solar-type stars (F5-KO) with similar Spitzer Space Telescope Infrared Spectrograph/MIPS data and similar ages. Both samples include stars with sources with infrared spectral energy distributions that show evidence of multiple components. Over the range of stellar types considered, we obtain nearly the same characteristic dust temperatures (∼ 190 K and ∼60 K for the inner and outer dust components, respectively)-slightly above the ice evaporation temperature for the inner belts. The warm inner dust temperature is readily explained if populations of small grains are being released by sublimation of ice from icy planetesimals. Evaporation of low-eccentricity icy bodies at ∼ 150 K can deposit particles into an inner/warm belt, where the small grains are heated to dust Temperatures of -190 K. Alternatively, enhanced collisional processing of an asteroid belt-like system of parent planetesimals just interior to the snow line may account for the observed uniformity in dust temperature. The similarity in temperature of the warmer dust across our B8-KO stellar sample strongly suggests that dust-producing planetesimals are not found at similar radial locations around all stars, but that dust production is favored at a characteristic temperature horizon.

Morales, Farisa↗
NASA NTRS2011

SKARPS: The Search for Kuiper Belts around Radial-Velocity Planet Stars

The Search for Kuiper belts Around Radial-velocity Planet Stars - SKARPS -is a Herschel survey of solar-type stars known to have orbiting planets. When complete, the 100-star SKARPS sample will be large enough for a meaningful statistical comparison against stars not known to have planets. (This control sample has already been observed by Herschel's DUst around NEarby Stars - DUNES - key program). Initial results include previously known disks that are resolved for the first time and newly discovered disks that are fainter and colder than those typically detected by Spitzer. So far, with only half of the sample in hand, there is no measured correlation between inner RV planets and cold outer debris. While this is consistent with the results from Spitzer, it is in contrast with the relationship suggested by the prominent debris disks in imaged-planet systems.

Bryden, Geoffrey↗