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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

A high resolution UV spectrograph for sounding rocket measurement of planetary emission line profiles

We have constructed a high resolution imaging spectrograph for use as a payload in a sounding rocket experiment. The spectrograph employs a modified Ebert-Fastie design using a LiF predispersing prism and a replica of the E1 echelle grating developed for the Space Telescope Imaging Spectrograph. The spectrograph is used as a focal plane instrument of the Jupiter Telescope, a Cassegrain telescope constructed exclusively for use as a sounding rocket payload. The telescope and spectrograph were launched from the White Sands Missile Range on May 4, 1991 to observe the H Ly-alpha line profile spatially resolved across the disk of Jupiter in the north-south and east-west directions, and to measure the H Ly-alpha emission line profile from interplanetary hydrogen associated with the local interstellar medium.

Harris, Walter↗
NASA NTRS2016

En Route to Destruction: the Evolution in Composition of Ices in Comet D 2012 S1 (ISON) Between 1.2 and 0.34 Au from the Sun as Revealed at Infrared Wavelengths

We report production rates for H2O and eight trace molecules (CO, C2H6, CH4, CH3OH, NH3, H2CO, HCN, C2H2) in the dynamically new, Sun-grazing Comet C2012 S1 (ISON), using high-resolution spectroscopy at Keck II and the NASA IRTF on 10pre-perihelion dates encompassing heliocentric distances Rh1.210.34 AU. Measured water production rates spanned two orders of magnitude, consistent with a long-term heliocentric power law Q(H2O) Rh-3.10.1). Abundance ratios for CO, C2H6, and CH4 with respect to H2O remained constant with Rh and below their corresponding mean values measured among a dominant sample of Oort Cloud comets. CH3OH was also depleted for Rh 0.5 AU, but was closer to its mean value for Rh0.5 AU. The remaining four molecules exhibited higher abundance ratios within 0.5 AU: for Rh 0.8 AU, NH3 and C2H2 were consistent with their mean values while H2CO and HCN were depleted. For Rh 0.5 AU, all four were enriched, with NH3, H2CO, and HCN increasing most. Spatial profiles of gas emission in ISON consistently peaked sunward of the dust continuum, which was asymmetric antisunward and remained singly peaked for all observations. NH3 within 0.5 AU showed a broad spatial distribution, possibly indicating its release in the coma provided that optical depth effects were unimportant. The column abundance ratio NH2H2O at 0.83 AU was close to the typical NHOH from optical wavelengths, but was higher within 0.5 AU. Establishing its production rate and testing its parentage (e.g., NH3) require modeling of coma outflow.

Disanti, M. A.↗
NASA NTRS2021

Probing Galaxy Evolution in Massive Clusters Using ACT and DES: Splashback as a Cosmic Clock

We measure the projected number density profiles of galaxies and the splashback feature in clusters selected by the Sunyaev–Zel'dovich effect from the Advanced Atacama Cosmology Telescope (AdvACT) survey using galaxies observed by the Dark Energy Survey (DES). The splashback radius is consistent with CDM-only simulations and is located at-+-h2.4 Mpc0.40.31. We split the galaxies on color and find significant differences in their profile shapes. Red and green-valley galaxies show a splashback-like minimum in their slope profile consistent with theory, while the bluest galaxies show a weak feature at a smaller radius. We develop a mapping of galaxies to subhalos in simulations and assign colors based on infall time onto their hosts. We find that the shift in location of the steepest slope and different profile shapes can be mapped to the average time of infall of galaxies of different colors. The steepest slope traces a discontinuity in the phase space of dark matter halos. By relating spatial profiles to infall time, we can use splashback as a clock to understand galaxy quenching. We find that red galaxies have on average been in clusters over 3.2 Gyr, green galaxies about 2.2 Gyr, while blue galaxies have been accreted most recently and have not reached apocenter. Using the full radial profiles, we fit a simple quenching model and find that the onset of galaxy quenching occurs after a delay of about a gigayear and that galaxies quench rapidly thereafter with an exponential timescale of 0.6 Gyr.

Galaxy clusters↗
NASA NTRS1993

Plasma dynamics driven by finite-width current filament and KV potential drops in ionosphere-magnetosphere coupling

We have simulated the plasma dynamics of a quasi-two-dimensional current filament in ionosphere-magnetosphere coupling. The simulation consists of a set of one-dimensional flux tube simulations with different imposed time-dependent, field-aligned currents. The dynamical interactions of the individual current filaments with the ionospheric and magnetospheric plasma generate kV field-aligned potential drops along the field lines, and the side-by-side display exhibits the evolution of the implied potential structure in the horizontal direction. The primary cross-field motion produced by the horizontal E-field (ExB drift) is perpendicular to both of the significant spatial directions, and is thus ignorable in this geometry. The effects of other cross-field drict processes are discussed. The simulation thus provides insight into the dynamical evolution of 2D potential structures driven by an imposed finite-width field-aligned current profile. Spatial and temporal variation of other plasma parameters (temperatures, density, etc.) that are determined primarily by parallel transport effects are also displayed.

Ganguli, Supriya B.↗
NASA NTRS2020

An Algorithm to Derive Temperature and Humidity Profile Changes Using Spatially and Temporally Averaged Spectral Radiance Differences

A linear inversion algorithm to derive changes of surface skin temperature and atmospheric temperature and specific humidity vertical profiles using spatially and temporally averaged spectral radiance differences is developed. The algorithm uses spectral radiative kernels, which is the top-of-atmosphere spectral radiance change caused by perturbations of skin temperature and air temperature and specific humidity in the atmosphere, and is an improved version of the algorithm used in earlier studies. Two improvements are the inclusion of the residual and cloud spectral kernels in the form of eigenvectors of principal components. Three and six eigenvectors are used for, respectively, the residual and cloud spectral kernels. An underlying assumption is that the spectral shape of the principal components is constant and their magnitude varies temporally and spatially. The algorithm is tested using synthetic spectral radiances with the spectral range of the Atmospheric Infrared Sounder averaged over 16 days and over a 10° × 10° grid box. Changes of skin temperature, air temperature, and specific humidity vertical profiles are derived from the difference of nadir-view all-sky spectral radiances. The root-mean-square difference of retrieved and true skin temperature differences is 0.59 K. The median of absolute errors in the air temperature change is less than 0.5 K above 925 hPa. The median of absolute errors in the relative specific humidity changes is less than 10% above 825 hPa.

Fang Pan↗
NASA NTRS2022

Volatile Abundances, Extended Coma Sources, and Nucleus Ice Associations in Comet C/2014 Q2 (Lovejoy)

High-resolution infrared spectra of comet C/2014 Q2 Lovejoy were acquired with NIRSPEC at the W. M. Keck Observatory on two post-perihelion dates(UT 2015 February 2 and 3).H2O was measured simultaneously with CO,CH3OH, H2CO, CH4, C2H6,C2H4, C2H2, HCN, and NH3 on both dates, and rotational temperatures, production rates, relative abundances, H2O ortho-to-para ratios, and spatial distributions in the coma were determined. The first detection of C2H4in a comet from ground-based observations is reported. Abundances relative to H2O for all species were found to be in the typical range compared with values for other comets in the overall population to date. There is evidence of variability in rotational temperatures and production rates on timescales that are small compared with the rotational period of the comet. Spatial distributions of volatiles in the coma suggest complex outgassing behavior.CH3OH, HCN, C2H6, and CH4 spatial distributions in the coma are consistent with direct release from associated ices in the nucleus and are peaked in a more sunward direction compared with co-measured dust. H2O spatial profiles are clearly distinct from these other four species, likely due to a sizable coma contribution from icy grain sublimation.Spatial distributions for C2H2,H2CO, and NH3suggest substantial contributions from extended coma sources, providing further evidence for distinct origins and associations for these species in comets. CO shows a different spatial distribution compared with other volatiles, consistent with jet activity from discrete nucleus ice sources.

Neil Dello Russo↗
NASA NTRS1985

Acoustic Gaussian Far-Field Pattern

Gaussian profile achieved by using annular electrodes. Transducer constructed by deposting circularly symmetric metallic multielectrode array on 12.7 mm diameter X-cut quartz disk. Each electrode independently connected to impedance network optimized to produce Gaussian distribution with less than 2 percent error. Ultrasonic transducer produces far field beam with Gaussian spatial profile for materials evaluation applications.

Claus, R. O.↗
NASA NTRS1999

Quantitative Species Measurements in Microgravity Combustion Flames using Near-Infrared Diode Lasers

Understanding the physical phenomena controlling the ignition and spread of flames in microgravity has importance for space safety as well as for characterizing dynamical and chemical combustion processes which are normally masked by buoyancy and other gravity-related effects. Unfortunately, combustion is highly complicated by fluid mechanical and chemical kinetic processes, requiring the use of numerical modeling to compare with carefully designed experiments. More sophisticated diagnostic methods are needed to provide the kind of quantitative data necessary to characterize the properties of microgravity combustion as well as provide accurate feedback to improve the predictive capabilities of the models. Diode lasers are a natural choice for use under the severe conditions of low gravity experiments. Reliable, simple solid state operation at low power satisfies the operational restrictions imposed by drop towers, aircraft and space-based studies. Modulation wavelength absorption spectroscopy (WMS) provides a means to make highly sensitive and quantitative measurements of local gas concentration and, in certain cases, temperature. With near-infrared diode lasers, detection of virtually all major combustion species with extremely rapid response time is possible in an inexpensive package. Advancements in near-infrared diode laser fabrication technology and concurrent development of optical fibers for these lasers led to their use in drop towers. Since near-infrared absorption line strengths for overtone and combination vibrational transitions are weaker than the mid-infrared fundamental bands, WMS techniques are applied to increase detection sensitivity and allow measurement of the major combustion gases. In the first microgravity species measurement, Silver et al. mounted a fiber-coupled laser at the top of the NASA 2.2-sec drop tower and piped the light through a single-mode fiber to the drop rig. A fiber splitter divided the light into eight channels that directed the laser beam across a methane or propane diffusion jet flame. The light beams were recaptured by a set of gradient index lenses, coupled back into separate fiber optic lines, and transmitted back to detectors and electronics in the instrument package. In these experiments a 6-mm od fiber cable (containing the nine optical fibers) fell with the drop rig. Using separate detection and demodulation channels, spatial and temporal (up to 20 Hz) maps of water vapor and methane concentrations were obtained at differing heights in the flames. While this apparatus was useful from a demonstration standpoint, several drawbacks needed attention before useful scientific measurements could be obtained. First, eight lines of sight are somewhat insufficient for detailing the spatial profiles of the gas. Second, multiple detection channels operating in parallel are both expensive and present a challenge for accurate calibration. As a result, a newer scanning system was developed in our first contract under this program. The primary characteristic of this system is that it contains a single detection channel and achieves "continuous" spatial resolution by scanning the laser beam across the flame region, then directing this beam onto a single detector. Thus spatial measurements are converted to a temporal series of data. The true spatial resolution is limited only by the beam diameter and width of the sweep. In these experiments the beam is focused to about 1-mm diameter and scans across a region up to 4-cm wide.

Silver, Joel A.↗
NASA NTRS1990

IUE and Einstein observations of the LINER galaxy NGC 4579

Results of International Ultraviolet Explorer (IUE) and Einstein observations of the LINER galaxy NGC 4579 are reported. Spatial profiles of the long wavelength IUE emission show a two component structure, with an unresolved core superimposed on broader underlying emission. The core spectrum shows strong C II lambda 2326 and broad Mg II lambda 2800 emission, and perhaps emission due to blends of Fe II multiplets (2300 to 23600 angstrom). The short wavelength emission is spatially unresolved, and shows C II lambda 1335, C III lambda 1909 broad C IV lambda 1550 emission, and a broad feature at approximately 1360 angstrom which may be due to 0.1 lambda 1356. Contrary to previous reports no evidence for He II lambda 1640 is found in the spectrum. An unresolved x ray source is detected at the location of the nucleus; its spectrum is well fitted by a power law of energy slope alpha approximately -0.5. These results further support the idea that NGC 4579 may contain a dwarf Seyfert nucleus.

Reichert, G. A.↗
NASA NTRS1986

A test of Lee's quasi-linear theory of ion acceleration by interplanetary traveling shocks

Lee's (1983) quasi-linear theory of ion acceleration is tested using ISEE-3 measurements of the November 12, 1978 quasi-parallel interplanetary shock. His theory accounts with varying degrees of precision for the energetic proton spatial profiles; the dependence of the spectral index of the power law proton velocity distribution upon the shock compression ratio; the power law dependence of the upstream proton scalelength upon energy; the absolute magnitude of the upstream proton scale length; the behavior of the energetic proton anisotropy upstream and downstream of the shock; the behavior of the alpha-particle proton ratio upstream; the equality of the spatial scale lengths at the shock of the upstream waves and of the protons that resonate with them; and the dependence of the integrated wave energy density upon the proton energy density at the shock. However, the trace magnetic field frequency spectra disagree with his theory in two ways. The part of the spectrum that can resonate with the observed protons via first-order cyclotron resonance is flat, whereas Lee's theory predicts an f exp - 7/4 frequency dependence for the November 12 shock. Higher frequency waves, which could not resonate with the observed upstream protons, increased in amplitude as the shock approached, suggesting that they too were generated by the shock.

Kennel, C. F.↗
NASA NTRS1984

Luminosity and spatial distribution of the forbidden O I 6300-A emission in comets

The Tuttle, Stephan-Oterna, and Brooks 2 comets have been subjected to CCD observations of the 6300 and 6364 A forbidden oxygen lines, in order to determine the spatial profiles and absolute luminosities of the cometary forbidden O I lines. Analysis indicates the source of the observed O I photons to be direct photodissociation of water vapor. O 1D production by dissociation of OH becomes dominant at larger distances from the nucleus, and the water vapor production rates derived from O I emissions are found to be in good agreement with those determined from forbidden line OH by the IUE spacecraft, as well as ground-based photometry. It is demonstrated that analysis of cometary O 1D emission allows the determination of the spatial distribution of the parent molecule water vapor.

Fink, U.↗
NASA NTRS1982

Spectroscopic observations of comets

Development of a spectrograph using a microchannel plate intensifier for observing faint comets is described. The spectrograph is capable of obtaining useful spectra of objects as faint as M(2) = 18. The increased guiding efficiency achieved by the optical coupling of the ISIT vidicon of the 154 cm telescope has resulted in a better signal to noise ratio. The ability to take a direct image of the comet aids in the interpretation of the spatial profile of the emissions. Spectra of comets Schwassmann-Wachmann 1, Bradfield, Encke, Tuttle, and Stephen-Oterma are discussed.

Source record↗
NASA NTRS1981

Use of MAGSAT anomaly data for crustal structure and mineral resources in the US Midcontinent

The analysis and preliminary interpretation of investigator-B MAGSAT data are addressed. The data processing included: (1) removal of spurious data points; (2) statistical smoothing along individual data tracks, to reduce the effect of geomagnetic transient disturbances; (3) comparison of data profiles spatially coincident in track location but acquired at different times; (4) reduction of data by weighted averaging to a grid with 1 deg xl deg latitude/longitude spacing, and with elevations interpolated and weighted to a common datum of 400 km; (5) wavelength filtering; and (6) reduction of the anomaly map to the magnetic pole. Agreement was found between a magnitude data anomaly map and a reduce-to-the-pole map supporting the general assumption that, on a large scale (long wavelength), it is induced crustal magnetization which is responsible for major anamalies. Anomalous features are identified and explanations are suggested with regard to crustal structure, petrologic characteristics, and Curie temperature isotherms.

Carmichael, R. S.↗
NASA NTRS1983

The discovery of S2 in comet IRAS-Araki-Alcock 1983d

Ultraviolet spectra of comet IRAS-Araki-Alcock 1983d, obtained with the International Ultraviolet Explorer spacecraft when the comet was only 0.032 AU from earth, show strong emission bands due to S2, the first detection of this species in an astronomical object. The spatial profiles imply that the S2 is released directly from the nucleus and has a lifetime of the order of 450 s. The derived production rate of S2 was 2 x 10 to the 25th per s. It is suggested that the S2 can be formed by cosmic-ray irradiation of other sulfurous compounds in the ices and that it need not be primordial. It has been also determined that the scale length of the parent of CS (presumably CS2) is 300 km and that the CS production is approximately equal to that of S2, both near 5 x 10 to the -4th that of OH and comparable to that of other trace species observed in comets.

Ahearn, M. F.↗
NASA NTRS1985

Images in the rocket ultraviolet - The stellar population in the central bulge of M31

Imagery of the bulge of M31 obtained with a rocket-borne telescope in two broad bands centered at 1460 A and 2380 A is discussed. The UV spatial profiles over a region about 200 arcsec wide are identical with those at visible wavelengths. The absence of detectable point sources indicates that main-sequence stars hotter than B0 V are not present in the bulge. It is suggested that the far-UV flux in old stellar populations originates in post-AGB stars. The UV flux from such stars is extremely sensitive to age and the physics of their previous mass loss.

Bohlin, R. C.↗
NASA NTRS1987

EX56a study of extended X-ray emission around isolated galaxies EX56b identification and spectra of bright X-ray sources at high galactic latitude

The EXOSAT observations confirmed the identification and extended nature of PKS 2345-35. It gave a good 2 to 10 keV X-ray spectrum and a detailed spatial profile indicating asymmetry of the structure. In the high galactic latitidue investigation, the BL Lac object identified with the HEAO-1 source 1430+423 was detected, and the first X-ray spectrum was obtained. Several simulataneous observations of H0323+022 were obtained over a broad range of electromagnetic spectrum. Studies of luminous active galactic nuclei have given significant information on the spectrum of the quasar PKS 0558-504. In a study of Southern sky cataclysmic variables, the EXOSAT was used to determine the X-ray spectrum and search for periodicities in two objects. Studies of complete identifications have revealed that X-ray sources in two high galactic latitude fields are stars, and therefore are to be excluded from the Piccinotti extragalactic sample. Only one Piccinotti source remains to be identified.

Schwartz, Daniel A.↗
NASA NTRS1986

The ionospheric extent of P/Halley from ground based operations during the 1985-1986 apparition

Spatial profiles of H2O(+) emission in the inner coma of P/Halley on 8 dates during the 1985 to 1986 apparition are presented. The profiles are derived from two dimensional CCD spectrograms taken with the spectrograph slit oriented along the cometary radius vector. The observations cover the range from 16 Oct. 1985 (r = 2.14 AU preperihelion) to 6 June 1986 (r = 2.14 AU postperihelion). The surface brightness profile of the 6198A H2O(+) emission line is calibrated in terms of the column density of H2O(+) ions. The profile from 14.4 Mar. 1986 is compared with the Giotto Ion Composition Experiment measurement of the shape of the H2O(+) space density profile. The ionosphere becomes larger and steeper in the sunward direction with an increasing water production rate.

Mccarthy, Patrick J.↗
NASA NTRS1986

Plasma wave turbulence in the strong coupling region at comet Giacobini-Zinner

Within 100,000 km of comet Giacobini-Zinner's nucleus, strong plasma wave turbulence was detected by the ICE electric and magnetic field wave instruments. The spatial profiles of the wave amplitudes are compared with measurements of the heavy ion fluxes of cometary origin, the plasma electron density, and the magnetic field strength. The general similarity of the wave and heavy ion profiles suggest that the waves might be generated by free energy in the pick-up ion distribution function. However, the expected parallel streaming instability of electrostatic modes generates waves with frequencies that are too low to explain the observations. The observed low frequency magnetic turbulence is plausibly explained by the lower hybrid loss-cone instability of heavy ions.

Coroniti, F. V.↗