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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.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A model for gravity-wave spectra observed by Doppler sounding systems

A model for Mesosphere - Stratosphere - Troposphere (MST) radar spectra is developed following the formalism presented by Pinkel (1981). Expressions for the one-dimensional spectra of radial velocity versus frequency and versus radial wave number are presented. Their dependence on the parameters of the gravity-wave spectrum and on the experimental parameters, radar zenith angle and averaging time are described and the conditions for critical tests of the gravity-wave hypothesis are discussed. The model spectra is compared with spectra observed in the Arctic summer mesosphere by the Poker Flat radar. This model applies to any monostatic Doppler sounding system, including MST radar, Doppler lidar and Doppler sonar in the atmosphere, and Doppler sonar in the ocean.

Vanzandt, T. E.↗
NASA NTRS1984

Dynamics of solar filaments. III - Analysis of steady flows in H-alpha and C IV lines

A statistical analysis of intensities and radial velocities of several solar plage filaments (i.e. prominences seen on the solar disk) observed at disk center is presented. Intensity and radial (= vertical) velocity maps were derived from simultaneous 2D measurements of the H-alpha chromospheric line with the Multichannel Subtractive Double Pass spectrograph operating on the Meudon solar tower, and also obtained from 2D recordings of the C IV transition-zone line (1548 A) with the UV Spectrometer and Polarimeter aboard the Solar Maximum Mission satellite. A good correlation (around 0.5) is found between intensities in both lines, as well as between velocities. Persistent upflows are measured in both lines at the filament location. The mean vertical velocities are respectively 0.5 km/s in H-alpha and 5.6 km/s in C IV. The analysis of mass fluxes suggests that C IV upflows occur in the transition region around prominences rather than below, in the chromosphere-corona transition zone.

Schmieder, B.↗
NASA NTRS1989

The internal velocity dispersions of three young star clusters in the Large Magellanic Cloud

The radial velocities of 11 to 37 stars have been measured in each of three rich young star clusters in the LMC: NGC 1866, NGC 2164, and NGC 2214. A thorough analysis of the observational errors and contamination by field stars is presented along with a new method to assign confidence limits to the velocity dispersions. Limits are set to the central densities, total masses, and mass-to-light ratios of the clusters, and the question of whether they have unbound halos is addressed. From the small velocity dispersion and large radial extent of NGC 1866, it is inferred that the cluster is not yet tidally limited by the LMC.

Lupton, Robert H.↗
NASA NTRS1989

Stellar kinematics in the galactic centre

The observations of the stellar kinematics in the central 8 pc of the Galaxy are presented. It is shown that the spectroscopy of the 2.3 microns CO absorption feature, in late type stars, yields the stellar velocity dispersion and the average stellar radial velocity as a function of galactocentric distance. A sample spectra that illustrates the observed velocity shifrs and velocity dispersion is given. The analysis shows that the velocity dispersion of the stars is large, and that it dominates the stellar kinematics. The use of these kinematic data, to probe the mass distribution in the Galactic center, is considered.

Mcginn, M. T.↗
NASA NTRS1990

Imaging and two-dimensional spectra of the IR-bright galaxy NGC 2146 - A recent low-energy merger?

New data are presented on the IR-luminous galaxy NGC 2146 from several sources: direct imaging in B, R, and H-alpha; IR imaging in the J, H, and K bands; long-slit spectroscopy at optical and IR wavelengths; and scanning etalon observations in H-alpha. The results allow measurement of the interstellar extinction in the dust lane, and estimation of the true luminosity of the galaxy and nuclear regions. The spectra indicate that there is no active nucleus, and measure the changing ratio of forbidden to permitted lines across the galaxy. IR images and colors indicate the existence of a significant population of hot young stars in the central regions of the system. The H-alpha velocity maps show the full radial-velocity pattern, and suggest that the system consists of a disturbed disk and a merging or interacting arm which connects to the inner dust and radio structures. Outer H-alpha and H I structures appear to be the earlier remnants of this spiraling merger.

Hutchings, J. B.↗
NASA NTRS1986

Milky Way halo gas kinematics

Measurements of high resolution, short wavelength absorption data taken by IUE toward high latitude O and B stars are presented in a discussion of the large scale kinematic properties of Milky Way Halo gas. An analysis of these data demonstrates that: (1) the obsrved absorption widths (FWHM) of Si II are very large, ranging up to 150 Km/s for the most distant halo star; this is much larger than is generally appreciated from optical data; (2) the absorption is observed to be systematically negative in radial velocity, indicating that cool material is, on the whole, flowing toward the disk of the galaxy; (3) there is some evidence for asymmetry between the northern and southern galactic hemispheres, in accordance with the HI 21 cm data toward the galactic poles; (4) low column density gas with highly negative radial LSR velocity (V less than -70 km/s) can be found toward stars beyond 1-3 kpc in the northern galactic hemisphere in all four quadrants of galactic longitude; and (5) only the profiles toward stars in the direction of known high velocity HI features show a clear two component structure.

Danly, L.↗
NASA NTRS1979

Recent developments at JPL in the application of image processing to astronomy

Four applications of image processing to astronomy, automated location and analysis of star and galaxy images, geometric and radiometric decalibration of vidicon spectra, display of multiband radio images, and generation of high resolution polarization direction and magnitude maps from images are presented with illustrative examples. The technique by which a digital image can be analyzed automatically to locate and segregate between stars and galaxies and the steps performed by the classifier to determine the nature of each object are outlined. The classification program executed on a 48 inch Schmidt plate of the cluster of galaxies 655 is described. The calibration and decalibration steps to remove geometric and radiometric distortions from a silicon vidicon camera digital spectra are discussed. Three methods of displaying multispectral radio data, generating a mosaic of each image, producing a color coded image to depict radio velocity, and producing a stereo pair with radial velocity as depth are described. The generation of polarization information from images obtained through linear polarizing filters is illustrated, and it is concluded that in each case information was displayed using digital techniques which could not readily have been provided visually.

Lorre, J. J.↗
NASA NTRS1992

Flow diagnostics of an arcjet using laser-induced fluorescence

A diagnostic has been developed to measure velocity and translational temperature in the plume of an arcjet thruster. Laser induced fluorescence with a narrowband CW laser is used to probe the Balmer alpha transition of excited atomic hydrogen. The velocity is determined from the Doppler shift of the fluorescence excitation spectrum while temperature is inferred from its shape. Analysis shows that while Doppler broadening is the only significant broadening mechanism, the fine structure of the transition must be accounted for. Near the exit plane, axial velocities vary from 4 to 14 km/s; radial velocities vary from 0 to 4 km/s; and swirl velocities are shown to be relatively small. Temperatures from 1000 to 5000 K indicate high dissociation fractions.

Liebeskind, John G.↗
NASA NTRS1994

On the ellipticity of the Galactic disk

We investigate two kinds of constraints on the ellipticity of the Galactic disk: local constraints, based on the kinematics of the solar neighborhood (such as the Oort constants, the axis ratio of the velocity ellipsoid, the vertex deviation, and the radial velocity of the local standard of rest relative to the Galactic center), and global constraints (H I tangent point velocities, the velocity fields of distant carbon stars, Cepheids and H II regions, and the kinematics of distant H I). Local and global constraints independently suggest that the Sun lies near the minor axis of the potential of an elliptical Galactic disk, with equipotential axis ratio 0.9. The kinematic data are consistent with a flat rotation curve of constant ellipticity, with a mean rotation speed of 200 km/s. In this model, the present velocity of the local standard of rest is 180 km/s.

Kuijken, Konrad↗
NASA NTRS2012

Dual-Doppler Feasibility Study

When two or more Doppler weather radar systems are monitoring the same region, the Doppler velocities can be combined to form a three-dimensional (3-D) wind vector field thus providing for a more intuitive analysis of the wind field. A real-time display of the 3-D winds can assist forecasters in predicting the onset of convection and severe weather. The data can also be used to initialize local numerical weather prediction models. Two operational Doppler Radar systems are in the vicinity of Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS); these systems are operated by the 45th Space Wing (45 SW) and the National Weather Service Melbourne, Fla. (NWS MLB). Dual-Doppler applications were considered by the 45 SW in choosing the site for the new radar. Accordingly, the 45th Weather Squadron (45 WS), NWS MLB and the National Aeronautics and Space Administration tasked the Applied Meteorology Unit (AMU) to investigate the feasibility of establishing dual-Doppler capability using the two existing systems. This study investigated technical, hardware, and software requirements necessary to enable the establishment of a dual-Doppler capability. Review of the available literature pertaining to the dual-Doppler technique and consultation with experts revealed that the physical locations and resulting beam crossing angles of the 45 SW and NWS MLB radars make them ideally suited for a dual-Doppler capability. The dual-Doppler equations were derived to facilitate complete understanding of dual-Doppler synthesis; to determine the technical information requirements; and to determine the components of wind velocity from the equation of continuity and radial velocity data collected by the two Doppler radars. Analysis confirmed the suitability of the existing systems to provide the desired capability. In addition, it is possible that both 45 SW radar data and Terminal Doppler Weather Radar data from Orlando International Airport could be used to alleviate any radar geometry issues at the NWS MLB radar, such as the "cone of silence" or beam blockage. In the event of a radar outage at one of the sites, the multi-radar algorithms would provide continuing coverage of the area through use of the data from the remaining operational radar sites. There are several options to collect, edit, synthesize and display dual-Doppler data sets. These options include commercial packages available for purchase and a variety of freeware packages available from the National Center for Atmospheric Research (NCAR) for processing raw radar data. However, evaluation of the freeware packages revealed that they do not have sufficient documentation and configuration control to be certified for 45 SW use. Additionally, a TI data line must be installed/leased from the NWS MLB office and CCAFS to enable the receipt of NWS MLB raw radar data to use in the dual-Doppler synthesis. Integration of the TI data line into the Eastern Range infrastructure that will meet the security requirements necessary for 45 SW use is time-consuming and costly. Overall evaluation indicates that establishment of the dual-Doppler capability using the existing operational radar systems is desirable and feasible with no technical concerns. Installation of such a system represents a significant enhancement to forecasting capabilities at the 45 WS and at NWS MLB. However, data security and cost considerations must be evaluated in light of current budgetary constraints. In any case, gaining the dual-Doppler capability will provide opportunities for better visualization of the wind field and better forecasting of the onset of convection and severe weather events to support space launch operations at KSC and CCAFS.

Huddleston, Lisa L.↗
NASA NTRS1976

Measurements in the mixing region of a turbulent jet in a coflowing airstream

The mixing region of a turbulent jet is an important example of an intermittent turbulent shear flow. There are a great deal of interest in this region because of interest in jet noise and STOL aircraft which use upper surface blowing or externally blown flap configurations to increase lift. A detailed study of the one point statistical properties of a smoke laden jet was made using a combination of a laser velocimeter and a light scattering system. The jet, with a 14 to 1 contraction, was placed inside a wind tunnel where the ratio of the jet exit velocity to free stream was 5.1 to 1. All measurements are made for a jet Reynolds number of 22,600. Among the quantities measured are mean axial and radial velocities, axial and radial intensities, power spectra, mean smoke concentration, concentration intensities, concentration spectra, intermittencies and velocity-concentration correlations. The results are compared with hot-wire data where available.

Morton, J. B.↗
NASA NTRS2000

The Effect of Companions on the SIM Reference Frame

The Space Interferometry Mission (SIM) is a 10-m Michelson space-based optical interferometer designed for precision astrometry (4 microarcseconds, 3 microarcseconds/year) with better accuracy than before over a narrow field of view. One of the primary objectives of the SIM instrument is to determine accurately the directions to a grid of stars, together with their proper motions and parallax, improving a priori knowledge by nearly three orders of magnitude over Hipparcos and one order of magnitude over FAME's planned accuracy (Johnston, 2000). The instrument does not measure directly the angular separation between stars, but rather it measures the projection of each star's direction vector onto the interferometer baseline vector by measuring the pathlength delay of starlight as it passes through the two arms of the interferometer. The accuracy and stability of SIM's celestial reference frame is subject to degradation over the 5-year mission from the reflex motion induced by massive companions of the objects used to construct the celestial reference frame. The authors present the results of simulations that show the sensitivity of reference frame accuracy to companions as a function of mass and period. They assume that pre-launch ground surveys will eliminate all objects with RMS radial velocity greater than 10 m/s. They further assume that the standard astrometric parameters of position, parallax, and proper motion plus acceleration terms in right ascension and declination will be allowed to absorb reflex motion.

ASTROMETRY↗
NASA NTRS2003

Long baseline interferometric observations of HD 195019: no K dwarf companion detected

Radial velocity measurements of the G3V/IV star HD 195019 revealed the presence of an orbiting companion with m sin(i) = 3.5 Jupiter masses and a period of 18 days. Here we present new visability measurements obtained at the Palomar Testbed Interferometer which rule out any companion in an orbit consistent with the spectroscopic data and having more than 1% of the flux of the primary star in the near-infrared K band.

extrasolar planets interferometry radial velocity↗
NASA NTRS2015

Composition, Structure and Formation of Low-Density Planets Within 0.5 AU of Their Star

Kepler has discovered that tens of percent of sunlike stars possess one or more planets larger than Earth within 0.5 AU. Masses of dozens of small and mid-sized exoplanets have been measured using radial velocity or transit timing variations. Few transiting planets larger than 1.6 Earth radii are rocky. Rather, the planetary mass-radius diagram for planetary radius between 1.6 and 8 times that of Earth shows a tendency for mass to increase slowly with size. The scatter is larger than can be explained by observational errors and correlations with temperature, implying that the population is heterogeneous. Many Neptune-size planets have very low densities and must have a substantial fraction of their volumes occupied by hydrogen and/or helium. Models of the structure, growth and evolution of planets made of mixtures of rock and light gases will be presented and compared with observations of both individual bodies and of the characteristics of the population as a whole.

radial velocity↗
NASA NTRS2022

A Super-Earth Orbiting Near the Inner Edge of the Habitable Zone Around the M4.5 Dwarf Ross 508

We report the near-infrared radial velocity (RV) discovery of a super-Earth planet on a 10.77 d orbit around the M4.5 dwarf Ross 508 (J mag = 9.1). Using precision RVs from the Subaru Telescope IRD (InfraRed Doppler) instrument, we derive a semi-amplitude of 3.92 +0.60 −0.58 ms −1 , corresponding to a planet with a minimum mass m sin i = 4.00 +0.53 −0.55 M ⊕ . We find no evidence of significant signals at the detected period in spectroscopic stellar activity indicators orMEarth photometry. The planet, Ross 508 b, has a semi-major axis of 0.05366 +0.00056 −0.00049 au. This gives an orbit-averaged insolation of ≈1.4 times the Earth’s value, placing Ross 508 b near the inner edge of its star’s habitable zone. We have explored the possibility that the planet has a high eccentricity and its host is accompanied by an additional unconfirmed companion on a wide orbit. Our discovery demonstrates that the near-infrared RV search can play a crucial role in finding a low-mass planet around cool M dwarfs like Ross 508.

Techniques↗
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 NTRS2020

TOI 564 b and TOI 905 b: Grazing and Fully Transiting Hot Jupiters Discovered by TESS

We report the discovery and confirmation of two new hot Jupiters discovered by the Transiting Exoplanet Survey Satellite(TESS): TOI 564 b and TOI 905 b. The transits of these two planets were initially observed by TESS with orbital periods of 1.651 and 3.739 days, respectively. We conducted follow-up observations of each system from the ground, including photometry in multiple filters, speckle interferometry, and radial velocity measurements. For TOI 564 b, our global fitting revealed a classical hot Jupiter with a mass of-+1.4630.0960.10MJand a radius of-+1.020.290.71RJ. Also a classical hot Jupiter, TOI 905 b has a mass of-+0.6670.0410.042MJand radius of-+1.1710.0510.053RJ. Both planets orbit Sun-like, moderately bright, mid-G dwarf stars with V11. While TOI 905 b fully transits its star, we found that TOI 564 b has a very high transit impact parameter of-+0.9940.0490.083, making it one of only∼20 known systems to exhibit a grazing transit and one of the brightest host stars among them. Therefore, TOI 564 b is one of the most attractive systems to search for additional nontransiting, smaller planets by exploiting the sensitivity of grazing transits to small changes in inclination and transit duration over a timescale of several years.

Exoplanet astronomy↗