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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Navy precision optical interferometer measurements of 10 stellar oscillators

Using the Navy Precision Optical Interferometer, we measured the angular diameters of 10 stars that have previously measured solar-like oscillations. Our sample covered a range of evolutionary stages but focused on evolved subgiant and giant stars. We combined our angular diameters with Hipparcos parallaxes to determine the stars' physical radii, and used photometry from the literature to calculate their bolometric fluxes, luminosities, and effective temperatures. We then used our results to test the scaling relations used by asteroseismology groups to calculate radii and found good agreement between the radii measured here and the radii predicted by stellar oscillation studies. The precision of the relations is not as well constrained for giant stars as it is for less evolved stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

EXO-ZODI MODELING FOR THE LARGE BINOCULAR TELESCOPE INTERFEROMETER

Habitable zone dust levels are a key unknown that must be understood to ensure the success of future space missions to image Earth analogs around nearby stars. Current detection limits are several orders of magnitude above the level of the solar system's zodiacal cloud, so characterization of the brightness distribution of exo-zodi down to much fainter levels is needed. To this end, the Large Binocular Telescope Interferometer (LBTI) will detect thermal emission from habitable zone exo-zodi a few times brighter than solar system levels. Here we present a modeling framework for interpreting LBTI observations, which yields dust levels from detections and upper limits that are then converted into predictions and upper limits for the scattered light surface brightness. We apply this model to the HOSTS survey sample of nearby stars; assuming a null depth uncertainty of 10{sup –4} the LBTI will be sensitive to dust a few times above the solar system level around Sun-like stars, and to even lower dust levels for more massive stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Gravitational waves at interferometer scales and primordial black holes in axion inflation

We study the prospects of detection at terrestrial and space interferometers, as well as at pulsar timing array experiments, of a stochastic gravitational wave background which can be produced in models of axion inflation. This potential signal, and the development of these experiments, open a new window on inflation on scales much smaller than those currently probed with Cosmic Microwave Background and Large Scale Structure measurements. The sourced signal generated in axion inflation is an ideal candidate for such searches, since it naturally grows at small scales, and it has specific properties (chirality and non-gaussianity) that can distinguish it from an astrophysical background. We study under which conditions such a signal can be produced at an observable level, without the simultaneous overproduction of scalar perturbations in excess of what is allowed by the primordial black hole limits. We also explore the possibility that scalar perturbations generated in a modified version of this model may provide a distribution of primordial black holes compatible with the current bounds, that can act as a seeds of the present black holes in the universe.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Detection prospects for the Cosmic Neutrino Background using laser interferometers

The cosmic neutrino background is a key prediction of Big Bang cosmology which has not been observed yet. The movement of the earth through this neutrino bath creates a force on a pendulum, as if it were exposed to a cosmic wind. We revise here estimates for the resulting pendulum acceleration and compare it to the theoretical sensitivity of an experimental setup where the pendulum position is measured using current laser interferometer technology as employed in gravitational wave detectors. We discuss how a significant improvement of this setup can be envisaged in a micro gravity environment. The proposed setup could also function as a dark matter detector in the sub-MeV range, which currently eludes direct detection constraints.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

NAVY PRECISION OPTICAL INTERFEROMETER OBSERVATIONS OF THE EXOPLANET HOST {kappa} CORONAE BOREALIS AND THEIR IMPLICATIONS FOR THE STAR'S AND PLANET'S MASSES AND AGES

We used the Navy Precision Optical Interferometer to measure the limb-darkened angular diameter of the exoplanet host star {kappa} CrB and obtained a value of 1.543 {+-} 0.009 mas. We calculated its physical radius (5.06 {+-} 0.04 R{sub Sun }) and used photometric measurements from the literature with our diameter to determine {kappa} CrB's effective temperature (4788 {+-} 17 K) and luminosity (12.13 {+-} 0.09 L{sub Sun }). We then placed the star on an Hertzsprung-Russell diagram to ascertain the star's age (3.42{sup +0.32}{sub -0.25} Gyr) and mass (1.47 {+-} 0.04 M{sub Sun }) using a metallicity of [Fe/H] = +0.15. With this mass, we calculated the system's mass function with the orbital elements from a variety of sources, which produced a range of planetary masses: m{sub p}sin i = 1.61-1.88 M{sub Jup}. We also updated the extent of the habitable zone for the system using our new temperature.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

PLANETARY TRANSITS WITH THE ATACAMA LARGE MILLIMETER/SUBMILLIMETER ARRAY RADIO INTERFEROMETER

Planetary transits are commonly observed at visible wavelengths. Here we investigate the shape of a planetary transit observed at radio wavelengths. Solar maps at 17 GHz are used as a proxy for the stellar eclipse by several sizes of planets from super-Earths to hot Jupiters. The relative depth at mid-transit is the same as observed at visible wavelengths, but the limb brightening of the stellar disk at 17 GHz is clearly seen in the shape of the transit light curve. Moreover, when the planet occults an active region the depth of the transit decreases even further, depending on the brightness of the active region relative to the surrounding disk. For intense active region, with 50 times the brightness temperature of the surrounding disk, the decrease can supercede the unperturbed transit depth depending on the size of the eclipsing planet. For a super-Earth (R{sub p} = 0.02 R{sub s} ) crossing, the decrease in intensity is 0.04%, increasing to 0.86% in the case when a strong active region is present. On the other hand, for a hot Jupiter with R{sub p} = 0.17R{sub s} , the unperturbed transit depth is 3% increasing to 4.7% when covering this strong active region. This kind of behavior can be verified with observation of planetary transits with the Atacama Large Millimeter/submillimeter Array radio interferometer.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The Tianlai dish pathfinder array: design, operation, and performance of a prototype transit radio interferometer

ABSTRACT The Tianlai Dish Pathfinder Array is a radio interferometer designed to test techniques for 21 cm intensity mapping in the post-reionization universe as a means for measuring large-scale cosmic structure. It performs drift scans of the sky at constant declination. We describe the design, calibration, noise level, and stability of this instrument based on the analysis of about 5% of 6200 h of on-sky observations through 2019 October. Beam pattern determinations using drones and the transit of bright sources are in good agreement, and compatible with electromagnetic simulations. Combining all the baselines, we make maps around bright sources and show that the array behaves as expected. A few hundred hours of observations at different declinations have been used to study the array geometry and pointing imperfections, as well as the instrument noise behaviour. We show that the system temperature is below 80 K for most feed antennas and that noise fluctuations decrease as expected with integration time, at least up to a few hundred seconds. Analysis of long integrations, from 10 nights of observations of the North Celestial Pole (NCP), yielded visibilities with amplitudes of 20–30 mK, consistent with the expected signal from the NCP radio sky with ${\lt}10\,$ mK precision for 1 MHz × 1 min binning. Hi-pass filtering the spectra to remove smooth spectrum signal yields a residual consistent with zero signal at the $0.5\,$ mK level.

(cosmology:) large-scale structure of the Universe↗
DOE OSTI2019

Atmospheric Emitted Radiance Interferometer Optimal Estimation (AERIoe) Value-Added Product Report

The Atmospheric Emitted Radiance Interferometer (AERI) Optimal Estimation (AERIoe) algorithm (Turner and Löhnert 2014, Turner and Blumberg 2019) retrieves boundary-layer profiles of temperature and water vapor mixing ratio, together with cloud properties for a single-layer cloud (i.e., LWP, effective radius), from AERI-observed infrared radiance spectra and other measurements. The current AERIoe Value-Added Product (VAP) uses version 2.8 of David Turner's code, which uses additional inputs to constrain the retrieval including surface meteorology, microwave radiometer brightness temperatures at any number of frequencies (the U.S. Department of Energy Atmospheric Radiation Measurement [ARM] user facility typically used observations at 23.8 and 30.0 GHz), and Rapid Refresh numerical weather prediction model output. The method is a physical iterative retrieval that uses the optimal estimation framework (Rodgers 2000), so a full error covariance of the solution and the information content (in the form of degrees of freedom for signal) is provided for each retrieval.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

A High-Temperature Multipoint Hydrogen Sensor Using an Intrinsic Fabry–Perot Interferometer in Optical Fiber

This paper presents a multiplexable fiber optic chemical sensor with the capability of monitoring hydrogen gas concentration at high temperatures up to 750 °C. The Pd-nanoparticle infused TiO 2 films coated on intrinsic Fabry–Perot interferometer (IFPI) array were used as sensory films. Strains induced upon exposure to hydrogen with varied concentrations can be monitored by IFPI sensors. The fiber sensor shows a repetitive and reversible response when exposed to a low level (1–6%) of hydrogen gas. Uniform sensory behavior across all the sensing cavities is demonstrated and reported in this paper.

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

A Coaxial Cable Fabry-Perot Interferometer for Sensing Applications

This paper reports a novel coaxial cable Fabry-Perot interferometer for sensing applications. The sensor is fabricated by drilling two holes half-way into a coaxial cable. The device physics was described. The temperature and strain responses of the sensor were tested. The measurement error was calculated and analyzed.

temperature and strain measurement↗
DOE OSTI2016

NULLING DATA REDUCTION AND ON-SKY PERFORMANCE OF THE LARGE BINOCULAR TELESCOPE INTERFEROMETER

The Large Binocular Telescope Interferometer (LBTI) is a versatile instrument designed for high angular resolution and high-contrast infrared imaging (1.5–13 μ m). In this paper, we focus on the mid-infrared (8–13 μ m) nulling mode and present its theory of operation, data reduction, and on-sky performance as of the end of the commissioning phase in 2015 March. With an interferometric baseline of 14.4 m, the LBTI nuller is specifically tuned to resolve the habitable zone of nearby main-sequence stars, where warm exozodiacal dust emission peaks. Measuring the exozodi luminosity function of nearby main-sequence stars is a key milestone to prepare for future exo-Earth direct imaging instruments. Thanks to recent progress in wavefront control and phase stabilization, as well as in data reduction techniques, the LBTI demonstrated in 2015 February a calibrated null accuracy of 0.05% over a 3 hr long observing sequence on the bright nearby A3V star β Leo. This is equivalent to an exozodiacal disk density of 15–30 zodi for a Sun-like star located at 10 pc, depending on the adopted disk model. This result sets a new record for high-contrast mid-infrared interferometric imaging and opens a new window on the study of planetary systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

CONFRONTING STANDARD MODELS OF PROTO-PLANETARY DISKS WITH NEW MID-INFRARED SIZES FROM THE KECK INTERFEROMETER

We present near- and mid-infrared (MIR) interferometric observations made with the Keck Interferometer Nuller and near-contemporaneous spectro-photometry from the infrared telescope facilities (IRTFs) of 11 well-known young stellar objects, several of which were observed for the first time in these spectral and spatial resolution regimes. With au-level spatial resolution, we first establish characteristic sizes of the infrared emission using a simple geometrical model consisting of a hot inner rim and MIR disk emission. We find a high degree of correlation between the stellar luminosity and the MIR disk sizes after using near-infrared data to remove the contribution from the inner rim. We then use a semi-analytical physical model to also find that the very widely used “star + inner dust rim + flared disk” class of models strongly fails to reproduce the spectral energy distribution (SED) and spatially resolved MIR data simultaneously; specifically a more compact source of MIR emission is required than results from the standard flared disk model. We explore the viability of a modification to the model whereby a second dust rim containing smaller dust grains is added, and find that the 2-rim model leads to significantly improved fits in most cases. This complexity is largely missed when carrying out SED modeling alone, although detailed silicate feature fitting by McClure et al. recently came to a similar conclusion. As has been suggested recently by Menu et al., the difficulty in predicting MIR sizes from the SED alone might hint at “transition disk”-like gaps in the inner au; however, the relatively high correlation found in our MIR disk size versus stellar luminosity relation favors layered disk morphologies and points to missing disk model ingredients instead.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

An accurate and efficient algorithm for detection of radio bursts with an unknown dispersion measure, for single-dish telescopes and interferometers

Astronomical radio signals are subjected to phase dispersion while traveling through the interstellar medium. To optimally detect a short-duration signal within a frequency band, we have to precisely compensate for the unknown pulse dispersion, which is a computationally demanding task. We present the “fast dispersion measure transform” algorithm for optimal detection of such signals. Our algorithm has a low theoretical complexity of 2N{sub f}N{sub t}+N{sub t}N{sub Δ}log{sub 2}(N{sub f}), where N{sub f}, N{sub t}, and N{sub Δ} are the numbers of frequency bins, time bins, and dispersion measure bins, respectively. Unlike previously suggested fast algorithms, our algorithm conserves the sensitivity of brute-force dedispersion. Our tests indicate that this algorithm, running on a standard desktop computer and implemented in a high-level programming language, is already faster than the state-of-the-art dedispersion codes running on graphical processing units (GPUs). We also present a variant of the algorithm that can be efficiently implemented on GPUs. The latter algorithm’s computation and data-transport requirements are similar to those of a two-dimensional fast Fourier transform, indicating that incoherent dedispersion can now be considered a nonissue while planning future surveys. We further present a fast algorithm for sensitive detection of pulses shorter than the dispersive smearing limits of incoherent dedispersion. In typical cases, this algorithm is orders of magnitude faster than enumerating dispersion measures and coherently dedispersing by convolution. We analyze the computational complexity of pulsed signal searches by radio interferometers. We conclude that, using our suggested algorithms, maximally sensitive blind searches for dispersed pulses are feasible using existing facilities. We provide an implementation of these algorithms in Python and MATLAB.

79 ASTRONOMY AND ASTROPHYSICS↗