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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
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NASA NTRS2016

EVEREST: Pixel Level Decorrelation of K2 Light Curves

We present EPIC Variability Extraction and Removal for Exoplanet Science Targets (EVEREST), an open-source pipeline for removing instrumental noise from K2 light curves. EVEREST employs a variant of pixel level decorrelation to remove systematics introduced by the spacecraft’s pointing error and a Gaussian process to capture astrophysical variability. We apply EVEREST to all K2 targets in campaigns 0–7, yielding light curves with precision comparable to that of the original Kepler mission for stars brighter than K(sub p) ≈ 13, and within a factor of two of the Kepler precision for fainter targets. We perform cross-validation and transit injection and recovery tests to validate the pipeline and compare our light curves to the other de-trended light curves available for download at the MAST High Level Science Products archive. We find that EVEREST achieves the highest average precision of any of these pipelines for unsaturated K2 stars. The improved precision of these light curves will aid in exoplanet detection and characterization, investigations of stellar variability, asteroseismology, and other photometric studies. The EVEREST pipeline can also easily be applied to future surveys, such as the TESS mission, to correct for instrumental systematics and enable the detection of low signal-to-noise transiting exoplanets. The EVEREST light curves and the source code used to generate them are freely available online.

Catalogs↗
NASA NTRS2022

A Detailed Analysis of the Gl 486 Planetary System

Context . The Gl 486 system consists of a very nearby, relatively bright, weakly active M3.5V star at just 8 pc with a warm transiting rocky planet of about 1.3 R ⨁ and 3.0 M ⨁ . It is ideal for both transmission and emission spectroscopy and for testing interior models of telluric planets. Aims . To prepare for future studies, we aim to thoroughly characterise the planetary system with new accurate and precise data collected with state-of-the-art photometers from space and spectrometers and interferometers from the ground. Methods . We collected light curves of seven new transits observed with the CHEOPS space mission and new radial velocities obtained with MAROON-X at the 8.1m Gemini North telescope and CARMENES at the 3.5m Calar Alto telescope, together with previously published spectroscopic and photometric data from the two spectrographs and TESS. We also performed near-infrared interferometric observations with the CHARA Array and new photometric monitoring with a suite of smaller telescopes (AstroLAB, LCOGT, OSN, TJO). This extraordinary and rich data set was the input for our comprehensive analysis. Results . From interferometry, we measure a limb-darkened disc angular size of the star Gl 486 at θ LDD = 0.390 ± 0.018 mas. Together with a corrected Gaia EDR3 parallax, we obtain a stellar radius R * = 0.339 ± 0.015 R ⨀ . We also measure a stellar rotation period at P rot = 49.9 ± 5.5 days, an upper limit to its XUV (5–920 Å) flux informed by new Hubble/STIS data, and, for the first time, a variety of element abundances (Fe, Mg, Si, V, Sr, Zr, Rb) and C/O ratio. Moreover, we imposed restrictive constraints on the presence of additional components, either stellar or sub-stellar, in the system. With the input stellar parameters and the radial-velocity and transit data, we determine the radius and mass of the planet Gl 486 b at R p = 1.343 +0.063 -0.062 R ⨀ and M p = 3.00 +0.13 -0.13 M ⨁ , with relative uncertainties of the planet radius and mass of 4.7% and 4.2%, respectively. From the planet parameters and the stellar element abundances, we infer the most probable models of planet internal structure and composition, which are consistent with a relatively small metallic core with respect to the Earth, a deep silicate mantle, and a thin volatile upper layer. With all these ingredients, we outline prospects for Gl 486 b atmospheric studies, especially with forthcoming James Webb Space Telescope (Webb) observations.

Planetary systems↗
NASA NTRS2022

Asteroid Lightcurves From the Moa-Ii Survey: A Pilot Study

The Microlensing Observations in Astrophysics (MOA-II) survey has performed high cadence, wide field observations of the Galactic Bulge from New Zealand since 2005. The hourly cadence of the survey during eight months of the year, across nearly 50 deg 2 of sky, provides an opportunity to sample asteroid lightcurves in the broad MOA-R filter. We perform photometry of a subset of bright asteroids numbered observed by the survey. We obtain 26 asteroid rotation periods, including for two asteroids where no prior data exist, and present evidence for the possible non-principal axis rotation of (2011) Veteraniya. This archival search could be extended to several thousands of asteroids brighter than 22nd magnitude.

techniques: photometric↗
NASA NTRS2023

Three Saturn-mass planets transiting F-type stars revealed with TESS and HARPS TOI-615b, TOI-622b, and TOI-2641b

While the sample of confirmed exoplanets continues to grow, the population of transiting exoplanets around early-type stars is still limited. These planets allow us to investigate the planet properties and formation pathways over a wide range of stellar masses and study the impact of high irradiation on hot Jupiters orbiting such stars. We report the discovery of TOI-615b, TOI-622b, and TOI-2641b, three Saturn-mass planets transiting main sequence, F-type stars. The planets were identified by the Transiting Exoplanet Survey Satellite (TESS) and confirmed with complementary ground-based and radial velocity observations. TOI-615b is a highly irradiated (∼1277 F⊕) and bloated Saturn-mass planet (1.69+0.05−0.06 RJup and 0.43+0.09−0.08 MJup) in a 4.66 day orbit transiting a 6850 K star. TOI-622b has a radius of 0.82+0.03−0.03 RJup and a mass of 0.30+0.07 −0.08 MJup in a 6.40 day orbit. Despite its high insolation flux (∼600 F⊕), TOI-622b does not show any evidence of radius inflation. TOI-2641b is a 0.39+0.02 −0.04 MJup planet in a 4.88 day orbit with a grazing transit (b = 1.04+0.05 −0.06) that results in a poorly constrained radius of 1.61+0.46−0.64 RJup. Additionally, TOI-615b is considered attractive for atmospheric studies via transmission spectroscopy with ground-based spectrographs and JWST. Future atmospheric and spin-orbit alignment observations are essential since they can provide information on the atmospheric composition, formation, and migration of exoplanets across various stellar types.

planets and satellites↗
NASA NTRS1984

Data compression techniques for astronomy

The photometric and astrometric accuracy of the Minnesota automated dual-plate scanner is summarized. The relation between magnitude and isophotometric image diameter is linear on Schmidt plates over a large useful range. Results of a study of centroid measurement accuracy and image classification ability of parameters derived from both densitometric and isophotometric scanning techniques are presented. The data analyzed for this purpose are synthesized ideal star and galaxy brightness distributions with appropriate random noise added to simulate plate grain and sky background effects. A preliminary study of image classification using real plates and single isophote data finds that a parameter describing the raggedness of the isophote may be useful in distinguising stars from galaxies.

Landau, R.↗
NASA NTRS2022

Galaxy Correlation Function and Local Density from Photometric Redshifts Using the Stochastic Order Redshift Technique (SORT)

The stochastic order redshift technique (SORT) is a simple, efficient, and robust method to improve cosmological redshift measurements. The method relies upon having a small (∼10 per cent) reference sample of high-quality redshifts. Within pencil- beam-like sub-volumes surrounding each galaxy, we use the precise dN/dz distribution of the reference sample to recover new redshifts and assign them one-to-one to galaxies such that the original rank order of redshifts is preserved. Preserving the rank order is motivated by the fact that random variables drawn from Gaussian probability density functions with different means but equal standard deviations satisfy stochastic ordering. This process is repeated for sub-volumes surrounding each galaxy in the survey. This results in every galaxy being assigned multiple ‘recovered’ redshifts from which a new redshift estimate is determined. An earlier paper applied SORT to a mock Sloan Digital Sky Survey at z 0.2 and accurately recovered the two-point correlation function (2PCF) on scales > 4 h−1Mpc. In this paper, we test the performance of SORT in surveys spanning the redshift range 0.75 < z < 2.25. We used two mock surveys extracted from the Small MultiDark–Planck and Bolshoi–Planck N-body simulations with dark matter haloes that were populated by the Santa Cruz semi-analytic model. We find that SORT overall improves redshift estimates, accurately recovers the redshift-space 2PCF ξ (s) on scales > 2.5 h−1Mpc, and provides improved local density estimates in regions of average or higher density, which may allow for improved understanding of how galaxy properties relate to their environments.

James Kakos↗
NASA NTRS1994

Detection of rotational modulation in the coronal extreme-ultraviolet emission from V711 Tauri?

The RS CVn binary V711 Tauri was observed by the Extreme Ultraviolet Explorer satellite (EUVE) twice during the latter half of 1992, for periods lasting several days. Light curves for the waveband 60-180 A derived from the all-sky survey scanning in August and from a pointed calibration observation made in October both exhibit a modulation of about 40%. The modulation in both data sets is very similar, with minimum flux occurring near orbital phase phi = 0.5. Analysis using a two-temperature optically thin plasma emission model reveals that most of the detected extreme ultraviolet (EUV) flux emanates from hot (approximately 10(exp 7) K) coronal plasma. The modulation is probably mostly due to either flare-like activity or to rotational occultation of a long-lived, compact, and especially bright coronal structure on the more active star of the system. The phased data support the latter hypothesis. This coronal structure is then likely to be associated with the presistent spot patterns seen on V711 Tau when using Doppler and photometric surface imaging techniques. Comparison with contemporaneous Stroemgren b-band photometry indicates that the optical minimum light leads the EUV maximum light by 90 deg in phase.

Drake, Jeremy J.↗
NASA NTRSDate not supplied

Camera Exposure Time Determination for Artemis I Lunar Flyby

During Artemis I, a flight test was conducted using the Optical Navigation Camera to image Lunar terrain at low altitude prior to the Return Powered Flyby (RPF) burn. The vehicle descended rapidly toward the surface and transitioned over the Lunar Terminator during the time frame in which the images were to be gathered, creating challenging lighting conditions which required the development of a novel technique for exposure time determination to gather imagery of appropriate quality for post flight analysis. The resulting technique leveraged simple photometric models and simulations, as well as the spacecrafts altitude and pointing direction to determine the necessary change in exposure times over the course of the flyby, resulting in a successful flight test.

Terrain Relative Navigation↗
NASA NTRSDate not supplied

Camera Exposure Time Determination for Artemis I Lunar Flyby

During Artemis I, a flight test was conducted using the Optical Navigation Camera to image Lunar terrain at low altitude prior to the Return Powered Flyby (RPF) burn. The vehicle descended rapidly toward the surface and transitioned over the Lunar Terminator during the time frame in which the images were to be gathered, creating challenging lighting conditions which required the development of a novel technique for exposure time determination to gather imagery of appropriate quality for post flight analysis. The resulting technique leveraged simple photometric models and simulations, as well as the spacecrafts altitude and pointing direction to determine the necessary change in exposure times over the course of the flyby, resulting in a successful flight test.

Terrain Relative Navigation↗
NASA NTRSDate not supplied

Camera Exposure Time Determination for Artemis I Lunar Flyby

During Artemis I, a flight test was conducted using the Optical Navigation Camera to image Lunar terrain at low altitude prior to the Return Powered Flyby (RPF) burn. The vehicle descended rapidly toward the surface and transitioned over the Lunar Terminator during the time frame in which the images were to be gathered, creating challenging lighting conditions which required the development of a novel technique for exposure time determination to gather imagery of appropriate quality for post flight analysis. The resulting technique leveraged simple photometric models and simulations, as well as the spacecrafts altitude and pointing direction to determine the necessary change in exposure times over the course of the flyby, resulting in a successful flight test.

Terrain Relative Navigation↗
NASA NTRS1993

(abstract) Reddening Measurements using CCD uvby (Stromgren) Photometry

Reddening measurements for interstellar clouds have usually relied on one of two techniques: Star counts or spectro-photometric measurements. We present preliminary results for a technique to determine the extinction using CCD uvby (Stromgren) photometry, without the need to perform special classification of the stars. The method relies on the fact that the uvby system allows two independent measurements of the reddening through the m(sub 1)and c(sub 1) indices to select the true intrensic colors for each star. Using observations from the Burrell Schmidt on Kitt Peak, we find that the technique allows reliable reddening measurements to be made down to at least V=15&supm;.

measurements↗
NASA NTRS2007

Photometric Calibration of Consumer Video Cameras

Equipment and techniques have been developed to implement a method of photometric calibration of consumer video cameras for imaging of objects that are sufficiently narrow or sufficiently distant to be optically equivalent to point or line sources. Heretofore, it has been difficult to calibrate consumer video cameras, especially in cases of image saturation, because they exhibit nonlinear responses with dynamic ranges much smaller than those of scientific-grade video cameras. The present method not only takes this difficulty in stride but also makes it possible to extend effective dynamic ranges to several powers of ten beyond saturation levels. The method will likely be primarily useful in astronomical photometry. There are also potential commercial applications in medical and industrial imaging of point or line sources in the presence of saturation.This development was prompted by the need to measure brightnesses of debris in amateur video images of the breakup of the Space Shuttle Columbia. The purpose of these measurements is to use the brightness values to estimate relative masses of debris objects. In most of the images, the brightness of the main body of Columbia was found to exceed the dynamic ranges of the cameras. A similar problem arose a few years ago in the analysis of video images of Leonid meteors. The present method is a refined version of the calibration method developed to solve the Leonid calibration problem. In this method, one performs an endto- end calibration of the entire imaging system, including not only the imaging optics and imaging photodetector array but also analog tape recording and playback equipment (if used) and any frame grabber or other analog-to-digital converter (if used). To automatically incorporate the effects of nonlinearity and any other distortions into the calibration, the calibration images are processed in precisely the same manner as are the images of meteors, space-shuttle debris, or other objects that one seeks to analyze. The light source used to generate the calibration images is an artificial variable star comprising a Newtonian collimator illuminated by a light source modulated by a rotating variable neutral- density filter. This source acts as a point source, the brightness of which varies at a known rate. A video camera to be calibrated is aimed at this source. Fixed neutral-density filters are inserted in or removed from the light path as needed to make the video image of the source appear to fluctuate between dark and saturated bright. The resulting video-image data are analyzed by use of custom software that determines the integrated signal in each video frame and determines the system response curve (measured output signal versus input brightness). These determinations constitute the calibration, which is thereafter used in automatic, frame-by-frame processing of the data from the video images to be analyzed.

Suggs, Robert↗
NASA NTRS1973

Ground-based observations at 34 microns.

Filtering techniques for a new photometric band from 28 to 40 microns are described together with the results of ground-based observations of planets, stars, and galactic nebulae conducted with 28- and 61-in. telescopes in this wavelength interval. The data indicate that high angular resolution and good sensitivity can be obtained at 34 microns from the ground. Some stars have very cold (less than 100 K) circumstellar dust shells or clouds. The Kleinmann-Low nebula in M42 is extremely bright at 34 microns, whereas the Ney-Allen nebula associated with the Trapezium stars is much weaker.

Low, F. J.↗
NASA NTRS1991

The Aries auroral modelling campaign - Characterization and modelling of an evening auroral arc observed from a rocket and a ground-based line of meridian scanners

A summary of the Aries experiments and results is presented with specific attention given to the tomographic analysis developed from ground-based photometric data. The instrumentation includes particle detectors, rocket photometers, plasma probes, and 1-deg meridian scanning photometers, and an all-sky TV system. The geophysical conditions during the observations are described including the auroral features and wavelengths, rocket trajectories, and the effectiveness of particle measurements. The tomographic inversion is explained with examples of rocket-photometer height data and contrasted with ground-based photometric data. The modeling techniques used to derive height profiles are described and indirectly compared to measured auroral intensities and intensity ratios. An enhancement of atomic oxygen is inferred from discrepancies with previous studies which confirm the difference between observed intensity ratios and modeled results.

Jones, A. V.↗
NASA NTRS1977

An experiment to measure variations in nighttime E-region neutral concentration

An experimental procedure is demonstrated which holds promise for the nighttime measurement of ion-neutral collision frequencies or net neutral concentration in the E-region by combining incoherent scatter data with appropriate photometric measurements. Data illustrating the technique are applied to comparing relative variations in atomic oxygen concentrations (from the E-region component of the O I 5577 A emission) near 100 km to those in the net neutral concentration obtained from combined incoherent scatter data and neutral temperature data extracted from Fabry-Perot measurement of the O I 5577 A line profile.

Cogger, L. L.↗
NASA NTRS1971

Digital image processing for the rectification of television camera distortions.

All television systems introduce distortions into the imagery they record which influence the results of quantitative photometric and geometric measurements. Digital computer techniques provide a powerful approach to the calibration and rectification of these systematic effects. Nonlinear as well as linear problems can be attacked with flexibility and precision. Methods which have been developed and applied for the removal of structured system noises and the correction of photometric, geometric, and resolution distortions in vidicon systems are briefly described. Examples are given of results derived primarily from the Mariner Mars 1969 television experiment.

Rindfleisch, T. C.↗
NASA NTRS1985

Focal plane optics in far-infrared and submillimeter astronomy

The construction of airborne observatories, high mountain-top observatories, and space observatories designed especially for infrared and submillimeter astronomy has opened fields of research requiring new optical techniques. A typical far-IR photometric study involves measurement of a continuum spectrum in several passbands between approx 30 microns and 1000 microns and diffraction-limited mapping of the source. At these wavelengths, diffraction effects strongly influence the design of the field optics systems which couple the incoming flux to the radiation sensors (cold bolometers). The Airy diffraction disk for a typical telescope at submillimeter wavelengths approx 100 microns-1000 microns is many millimeters in diameter; the size of the field stop must be comparable. The dilute radiation at the stop is fed through a Winston nonimaging concentrator to a small cavity containing the bolometer. The purpose of this paper is to review the principles and techniques of infrared field optics systems, including spectral filters, concentrators, cavities, and bolometers (as optical elements), with emphasis on photometric systems for wavelengths longer than 60 microns.

Hildebrand, R. H.↗