SEARCH · Engineering Papers

Results for “RADIAL VELOCITY”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14

All sources NASA NTRS DOE OSTI

NASA NTRS2015

Simultaneous Radar and Satellite Data Storm-Scale Assimilation Using an Ensemble Kalman Filter Approach for 24 May 2011

Assimilating high-resolution radar reflectivity and radial velocity into convection-permitting numerical weather prediction models has proven to be an important tool for improving forecast skill of convection. The use of satellite data for the application is much less well understood, only recently receiving significant attention. Since both radar and satellite data provide independent information, combing these two sources of data in a robust manner potentially represents the future of high-resolution data assimilation. This research combines Geostationary Operational Environmental Satellite 13 (GOES-13) cloud water path (CWP) retrievals with Weather Surveillance Radar-1988 Doppler (WSR-88D) reflectivity and radial velocity to examine the impacts of assimilating each for a severe weather event occurring in Oklahoma on 24 May 2011. Data are assimilated into a 3-km model using an ensemble adjustment Kalman filter approach with 36 members over a 2-h assimilation window between 1800 and 2000 UTC. Forecasts are then generated for 90 min at 5-min intervals starting at 1930 and 2000 UTC. Results show that both satellite and radar data are able to initiate convection, but that assimilating both spins up a storm much faster. Assimilating CWP also performs well at suppressing spurious precipitation and cloud cover in the model as well as capturing the anvil characteristics of developed storms. Radar data are most effective at resolving the 3D characteristics of the core convection. Assimilating both satellite and radar data generally resulted in the best model analysis and most skillful forecast for this event.

Jones, Thomas A.↗

NASA NTRS1982

OH fluorescence in comets - Fluorescence efficiency of the ultraviolet bands

The present investigation is concerned with the calculation of the fluorescence efficiency of OH over a wide range of heliocentric radial velocities. Three vibrational states in each of the two lowest electronic states are included in these calculations, producing a total of nine vibrational bands in the ultraviolet. The attempt is made to reproduce observed, ultraviolet, cometary spectra of OH by utilizing the Swings fluorescence mechanism. The inclusion of four rotational states within each of the three vibrational states and a detailed solar atlas make it possible to match observations very well, although there remain some discrepancies. This ability to reproduce observations provides confidence that the more general results obtained for the fluorescence efficiency as a function of heliocentric radial velocity can be used in interpreting both previous and future observations of OH in comets.

Schleicher, D. G.↗

NASA NTRS2020

TOI-677b: A Warm Jupiter (P=11.2 days) on an Eccentric Orbit Transiting a Late F-type Star

We report the discovery of TOI-677b,first identified as a candidate in light curves obtained within Sectors 9 and 10 of the Transiting Exoplanet Survey Satellite(TESS)mission and confirmed with radial velocities. TOI-677b has a mass of M(p) = 1.236(+0.069,- 0.067) M(J), a radius of R(P)=1.170 ± 0.03 R(J), and orbits its bright host star (V = 9.8 mag) with an orbital period of 11.23660 ± 0.00011 d, on an eccentric orbit with e = 0.435 ± 0.024. The host star has a mass of M(*) = 1.181 ± 0.058 M(ʘ), a radius of R(*)= 1.28(+0.03,-0.03) R(ʘ), an age of 2.92 (+0.80,-0.73) Gyr and solar metallicity, properties consistent with a main-sequence late-F star with T(eff)=6295 ± 77K. We find evidence in the radial velocity measurements of a secondary long-term signal, which could be due to an outer companion. The TOI-677 b system is a well-suited target for Rossiter–Mclaughlin observations that can constrain migration mechanisms of close-in giant planets.

Andrés Jordán↗

NASA NTRS1997

A search for stars passing close to the sun

Hipparcos proper motion and parallax data are combined for nearby stars with ground-based radial velocity measurements in order to identify stars which may have passed, or will pass, close enough to the sun to perturb the Oort cloud. Close stellar encounters could deflect large numbers of comets into the inner solar system, with possible serious consequences for impact hazards on the earth. Only one star, Gliese 710 is found with a predicted closest approach of less than 0.5 pc, although several stars come within 1 pc during a 8.5 M year interval. In most cases, the uncertainty in closest approach distance is dominated by uncertainties in the barycenter motion of binary systems. A program to obtain new radial velocities for stars in the sample with no previously published values is underway.

Garcia-Sanchez, J.↗

NASA NTRS2021

TOI-431/HIP 26013: a super-Earth and a sub-Neptune transiting a bright, early K dwarf, with a third RV planet

We present the bright (V mag = 9.12), multiplanet system TOI-431, characterized with photometry and radial velocities (RVs). We estimate the stellar rotation period to be 30.5 ± 0.7 d using archival photometry and RVs. Transiting Exoplanet Survey Satellite ( TESS ) objects of Interest (TOI)-431 b is a super-Earth with a period of 0.49 d, a radius of 1.28 ± 0.04 R ⊕ , a mass of 3.07 ± 0.35 M ⊕ , and a density of 8.0 ± 1.0 g cm −3 ; TOI-431 d is a sub-Neptune with a period of 12.46 d, a radius of 3.29 ± 0.09 R ⊕ , a mass of 9.90+1.53 −1.49 M ⊕ , and a density of 1.36 ± 0.25 g cm −3 . We find a third planet, TOI-431 c, in the High Accuracy Radial velocity Planet Searcher RV data, but it is not seen to transit in the TESS light curves. It has an Msin i of 2.83+0.41 −0.34 M ⊕ , and a period of 4.85 d. TOI-431 d likely has an extended atmosphere and is one of the most well-suited TESS discoveries for atmospheric characterization, while the super-Earth TOI-431 b may be a stripped core. These planets straddle the radius gap, presenting an interesting case-study for atmospheric evolution, and TOI-431 b is a prime TESS discovery for the study of rocky planet phase curves.

Ares Osborn↗

NASA NTRS2021

TOI-1231 b: A Temperate, Neptune-sized Planet Transiting the Nearby M3 Dwarf NLTT 24399

We report the discovery of a transiting, temperate, Neptune-sized exoplanet orbiting the nearby (d = 27.5 pc), M3V star TOI-1231 (NLTT 24399, L 248-27, 2MASS J10265947-5228099). The planet was detected using photometric data from the Transiting Exoplanet Survey Satellite and followed up with observations from the Las Cumbres Observatory and the Antarctica Search for Transiting ExoPlanets program. Combining the photometric data sets, we find that the newly discovered planet has a radius of 3.65(+0.16,-0.15)Rꚛ and an orbital period of 24.246 days. Radial velocity measurements obtained with the Planet Finder Spectrograph on the Magellan Clay telescope confirm the existence of the planet and lead to a mass measurement of 15.5 ± 3.3 Mꚛ. With an equilibrium temperature of just 330 K, TOI-1231 b is one of the coolest small planets accessible for atmospheric studies thus far, and its host star's bright near-infrared brightness (J = 8.88, Ks = 8.07) makes it an exciting target for the Hubble Space Telescope and the James Webb Space Telescope. Future atmospheric observations would enable the first comparative planetology efforts in the 250–350 K temperature regime via comparisons with K2-18 b. Furthermore, TOI-1231's high systemic radial velocity (70.5 km/s) may allow for the detection of low-velocity hydrogen atoms escaping the planet by Doppler, shifting the H i Lyα stellar emission away from the geocoronal and interstellar medium absorption features.

Jennifer A. Burt↗

NASA NTRS2001

Short-Term Dynamical Interactions Among Extrasolar Planets

We show that short-term perturbations among massive planets in multiple planet systems can result in radial velocity variations of the central star which differ substantially from velocity variations derived assuming the planets are executing independent Keplerian motions. We discuss two alternate fitting methods which can lead to an improved dynamical description of multiple planet systems. In the first method, the osculating orbital elements are determined via a Levenberg-Marquardt minimization scheme driving an N-body integrator. The second method is an improved analytic model in which orbital elements such as the periods and longitudes of periastron are allowed to vary according to a simple model for resonant interactions between the planets. Both of these methods can potentially determine the true masses for the planets by eliminating the sin(i) degeneracy inherent in fits that assume independent Keplerian motions. As more radial velocity data is accumulated from stars such as GJ876, these methods should allow for unambiguous determination of the planetary masses and relative inclinations.

Laughlin, Gregory↗

NASA NTRS1988

Integrated-light spectroscopy of globular clusters at the infrared Ca II lines

Integrated-light spectroscopy has been obtained for 27 globular clusters at the Ca II IR triplet. Line strengths and radial velocities have been measured from the spectra. For the well-studied clusters in the sample, the strength of the Ca II lines is very well correlated with previous metallicity estimates. Thus, the triplet is useful as a metallicity indicator in globular cluster integrated-light spectra. The greatly reduced effect of interstellar extinction at these wavelengths (compared to the blue region of the spectrum) has permitted observations of some of the most heavily reddened clusters in the Galaxy. For several such clusters, the Ca II triplet metallicities are in poor agreement with metallicity estimates from IR photometry by Malkan (1981). The strength of an interstellar band at 8621A has been used to estimate the amount of extinction towards these clusters. Using the new metallicity and radial-velocity data, the metallicity distribution, kinematics, and spatial distribution of the disk globular cluster system have been analyzed. Results very similar to those of Zinn (1985) have been found. The relation of the disk globulars to the stellar thick disk is discussed.

Armandroff, Taft E.↗

NASA NTRS2018

A Revised Exoplanet Yield from the Transiting Exoplanet Survey Satellite (TESS)

The Transiting Exoplanet Survey Satellite (TESS) has a goal of detecting small planets orbiting stars bright enough for mass determination via ground-based radial velocity observations. Here, we present estimates of how many exoplanets the TESS mission will detect, the physical properties of the detected planets, and the properties of the stars that those planets orbit. This work uses stars drawn from the TESS Input Catalog Candidate Target List and revises yields from prior studies that were based on Galactic models. We modeled the TESS observing strategy to select approximately 200,000 stars at 2-minute cadence, while the remaining stars are observed at 30-minute cadence in full-frame image data. We placed zero or more planets in orbit around each star, with physical properties following measured exoplanet occurrence rates, and used the TESS noise model to predict the derived properties of the detected exoplanets. In the TESS 2-minute cadence mode we estimate that TESS will find 1250 ± 70 exoplanets (90% confidence), including 250 smaller than 2 R(sub ⊕). Furthermore, we predict that an additional 3100 planets will be found in full-frame image data orbiting bright dwarf stars and more than 10,000 around fainter stars. We predict that TESS will find 500 planets orbiting M dwarfs, but the majority of planets will orbit stars larger than the Sun. Our simulated sample of planets contains hundreds of small planets amenable to radial velocity follow-up, potentially more than tripling the number of planets smaller than 4 R(sub ⊕) with mass measurements. This sample of simulated planets is available for use in planning follow-up observations and analyses.

Barclay, Thomas↗

NASA NTRS1974

Interplanetary stream magnetism: Kinematic effects

The particle density, and the magnetic field intensity and direction are calculated in corotating streams of the solar wind, assuming that the solar wind velocity is constant and radial and that its azimuthal variations are not two rapid. The effects of the radial velocity profile in corotating streams on the magnetic fields were examined using kinematic approximation and a variety of field configurations on the inner boundary. Kinematic and dynamic effects are discussed.

Burlaga, L. F.↗

NASA NTRS1978

Copernicus observations of Ly-alpha and Mg II emission from HR 1099 /V711 Tauri/ and UX Ari

Ultraviolet observations of two RS CVn binaries obtained with Copernicus are described. High-resolution (0.05 A) U1 observations indicate that both HR 1099 and UX Ari display broad Ly-alpha emission. The Ly-alpha emission strength from HR 1099 is variable and seems to be correlated with orbital phase, while the UX Ari results indicate no significant variation. Moderate resolution (0.51 A) V2 scans of both systems show variable Mg II h and k emission-line profiles which usually matched the velocity of the more active star in each binary. Additionally, displaced emission components were seen at velocities of up to + or - 250 km/s, indicative of high-velocity gas motions. The radial velocities of these emission features from HR 1099 are marginally correlated with orbital phase. Highly active and variable chromospheric phenomena are found to be the most consistent explanation of these results.

Weiler, E. J.↗

NASA NTRS1979

The effect of a radial rotational velocity gradient on p-mode eigenfrequencies

The splitting of p-mode eigenfrequencies due to a depth-dependent solar rotation rate is considered. It is shown that to a first approximation this splitting can be treated as resulting from the translation of the wave pattern across the field of view with a velocity equal the actual velocity at a depth called the effective depth. The effective depths for a model solar envelope with l/H = 3 are presented as a function of position on the (kh, omega)-plane. The combination of omega near 0.025/s and kh near 0 yields the deepest probe of the solar envelope. For this same combination of kh and omega it is possible to resolve individual groups of eigenmodes in frequency but not in spatial wavenumber. Achievement of this resolution observationally may permit a determination of the lifetime of these particular modes.

Ulrich, R. K.↗

NASA NTRS1993

Pulsed laser Rayleigh scattering diagnostic for hydrogen/oxygen rocket exit plane flowfield velocimetry

A Doppler-resolved, pulsed laser Rayleigh scattering diagnostic has been developed to obtain local flowfield velocity measurements at the exit plane of a low thrust hydrogen/oxygen rocket engine operating in a high-altitude test facility. Fiberoptic signal collection was employed to obtain the forescatter and backscatter Doppler shifts necessary to resolve the axial and radial velocity components. A radial profile was obtained by traversing the collection probes along the beam path at the nozzle exit. The results are compared with theoretical predictions from a full Navier-Stokes model (RK/RPLUS). Significant discrepancies between the measured and predicted axial velocity profiles are observed, in terms of both magnitude and character. Radial velocity measurements exhibit excellent agreement with predictions near the centerline but show some departure off-axis. The discrepancies between theory and experiment are potentially the result of enhanced mixing between the core and fuel-film region beyond that predicted, and/or flow stratification between the hydrogen and oxygen injected into the central core region.

Zupanc, Frank J.↗

NASA NTRS1981

The effect of the charge exchange source on the velocity and 'temperature' distributions and their anisotropies in the earth's exosphere

The velocity distribution of atomic hydrogen in the earth's exosphere is calculated as a function of altitude and direction taking into account both the classic exobase source and the higher-altitude plasmaspheric charge exchange source. Calculations are performed on the basis of a Monte Carlo technique in which random ballistic trajectories of individual atoms are traced through a three-dimensional grid of audit zones, at which relative concentrations and momentum or energy fluxes are obtained. In the case of the classical exobase source alone, the slope of the velocity distribution is constant only for the upward radial velocity component and increases dramatically with altitude for the incoming radial and transverse velocity components, resulting in a temperature decrease. The charge exchange source, which produces the satellite hydrogen component and the hot ballistic and escape components of the exosphere, is found to enhance the wings of the velocity distributions, however this effect is not sufficient to overcome the temperature decreases at altitudes above one earth radius. The resulting global model of the hydrogen exosphere may be used as a realistic basis for radiative transfer calculations.

Hodges, R. R., Jr.↗

NASA NTRS2005

Accurate Realization of GPS Vertical Global Reference Frame

The goal of this project is to improve our current understanding of GPS error sources associated with estimates of radial velocities at global scales. An improvement in the accuracy of radial global velocities would have a very positive impact on a large number of geophysical studies of current general interest such as global sea-level and climate change, coastal hazards, glacial isostatic adjustment, atmospheric and oceanic loading, glaciology and ice mass variability, tectonic deformation and volcanic inflation, and geoid variability. A set of GPS error sources relevant to this project are those related to the combination of the positions and velocities of a set of globally distributed stations as determined &om the analysis of GPS data, including possible methods of combining and defining terrestrial reference frames. This is were our research activities during this reporting period have concentrated. During this reporting period, we have researched two topics: (1) The effect of errors on the GPS satellite antenna models (or lack thereof) on global GPS vertical position and velocity estimates; (2) The effect of reference W e definition and practice on estimates of the geocenter variations.

Elosegui, Pedro↗

NASA NTRS1980

Experimental investigation of reactive turbulent recirculating jet mixing in a dump

A ducted, subsonic, hydrogen air turbulent jet mixing flowfield was investigated, both with and without combustion. The geometric configuration was representative of a sudden expansion or dump combustor, with a central air jet surrounded by a low velocity hydrogen stream at an overall equivalence ratio of 0.12. The ratio of the duct to inner nozzle diameter was 2.5. Radial distributions of mean axial and radial velocity, axial and radial turbulent intensity, velocity cross correlation, gas composition, static temperature and total pressure, as well as axial distributions of wall static pressure, were obtained for axial stations from zero to six duct diameters from the combustor entrance. The data indicate that mixing is slower in the chemically reactive flow field than in the nonreactive flow field, and that the presence of combustion has a significant effect on the size and location of the recirculation zone within the mixing duct.

Smith, G. D.↗

NASA NTRS1992

Structure, rotation, and the peculiar velocity cD galaxy in Abell 2107

The radial velocities of 75 galaxies in the field of Abell 2107 were measured within the framework of a program to study the kinematics of cD clusters of galaxies. Sixty-eight of these galaxies are cluster members. The mean observed velocity of A2107 is 12335 +/- 86 km/s, and the velocity dispersion is 672 +67/-52 km/s. The cD galaxy has a peculiar velocity of 270 km/s with respect to the cluster mean. The distribution of velocities is well fitted by a Gaussian, but the velocities are spatially correlated. Simple two-body subcluster models for A2107 are investigated; they are found to be consistent with the observed data and to account for the peculiar velocity of the cD galaxy. Alternatively, the spatial distribution of the velocities is also consistent with rotation of the single cluster at the 98-percent confidence level.

Oegerle, William R.↗

NASA NTRS1993

Unsteady Flow Simulations in Support of the SSME HEX Turning Vane Cracking Investigation with the ATD HPOTP

Unsteady flow computations are being performed with the P&W (ATD) and the Rocketdyne baseline configurations of the SSME LO2 turbine turnaround duct (TAD) and heat exchanger (HEX). The work is in support of the HEX inner turning vane cracking investigation. Fatigue cracking has occurred during hot firings with the P&W configuration on the HEX inner vane, and it appears the fix will involve changes to the TAD splitter vane position and to the TAD inner wall curvature to reduce the dynamic loading on the inner vane. Unsteady flow computations on the P&W baseline and fix and on the Rocketdyne baseline reference follow steady-flow screening computations done by MSFC/ED32 on several trial configurations arriving at the fix. The P&W TAD inlet velocity profile has a strong radial velocity component that directs the flow toward the inner wall and raises the local velocity a factor of two and the dynamic pressure a factor, of four. The fix is intended to redistribute the flow more evenly across the HEX inner and outer vanes like the Rocketdyne baseline reference. Vane buffeting at frequencies around 4,000 Hz is the leading suspected cause of the problem. Our simulations (work in progress) are being done with the USA 2D axisymmetric code approximating the flow as axisymmetric u+v 2D (axial, u, and radial, v, components only). The HEX coils are included in the model to make sure the fix does not adversely affect the HEX environment. Turbulent kinetic energy, k, levels where k = 1/2 v' rms2 are locally as high as 10,000 ft2/sec2 for the P&W baseline at the engine interface (between the TAD and HEX) at the HEX inner vane location. However, k is less than 8,000 on the HEX outer vane and only about 4,500 on the HEX inner vane for the Rocketdyne baseline. Unsteady turbulence intensity, v'rms/v, and pressure, p', are being computed in the present computations to compare with steady-flow Reynolds-averaged computations where p'rms = const (pk) for overall rms random turbulence from 0.1 to 12,000 Hz frequency. Random overall static, p'rms fluctuations as large as 1.7 psi are estimated from k on the HEX inner vane for the P&W baseline configuration but only about 0.7 psi for the Rocketdyne configuration.

Dougherty, N. S.↗