Search NASA⌕ Search

SEARCH · Search NASA

Results for “Interstellar scattering”

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.

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

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Illuminating a red supergiant wind around SN 1987A

A recently discovered light echo at a radius of about 9 arcsec from SN 1987A is interpreted as the result of a circumstellar shell at a radius of 4.5 pc from the SN. The shell may have its origin in the deceleration of the pre-SN red supergiant wind by the pressure of the surrounding medium. The required pressure is p/k = about 1000 per cu cm K. The echo is predicted to expand and contract over the next 30 yr with a declining surface brightness and a broadening of its width. Colors of the echo compared to those of the larger echoes may show differences in the wavelength dependence of scattering of the circumstellar grains compared to interstellar grains.

Chevalier, Roger A.↗
NASA NTRS2003

A New Method to Use Chandra Data to Resolve the X-Ray Halos Around Point Sources and Its Application to Cygnus X-1

The excellent angular resolution, good energy resolution and broad energy band make Chandra ACIS the best instrument for studying the X-ray halos around some galactic x-ray point sources caused by the dust scattering of X-rays in the interstellar medium, but direct images of bright sources of b r i g h t sources obtained with ACIS usually from severe pile- UP - Making use of the fact that an isotropic image could be reconstructed from it's projection on any direction, we can reconstruct the images of the X-ray halos from data obtained with the regular HETGS and/or the CC mode. With the reconstructed high resolution images, we can probe the X-ray halos as close as 1 arcsecond to their associated point sources.

Yao, Y.↗
NASA NTRS2003

A New Method to Resolve X-Ray Halos around Point Sources with Chandra Data and Its Application to Cygnus X-1

With excellent angular resolution, good energy resolution, and a broad energy band, the Chandra Advanced CCD Imaging Spectrometer (ACIS) is the best instrument for studying the X-ray halos around some Galactic X-ray point sources caused by the dust scattering of X-rays in the interstellar medium. However, the direct images of bright sources obtained with the ACIS usually suffer from severe pileup. Making use of the fact that an isotropic image could be reconstructed from its projection in to any direction, we can reconstruct the images of the X-ray halos from the data obtained with the High Energy Transition Grating Spectrometer (HETGS) and/or in continuos clocking (CC) mode. These data have no or less serious pileup and enable us to take full advantage of the excellent angular resolution of Chandra. With the reconstructed high-resolution images, we can probe the X-ray halos as close as 1" to their associated point sources. Applying this method to Cygnus X-1 observed with the Chandra HETGS in CC mode, we derived an energy-dependent radial halo flux distribution and concluded that in a circular region (2' in radius) centered a the point source: (1) relative to the total intensity, the fractional halo intensity is about 15% at keV and drops to aboout 5% at approximately 6 keV (2) about 50% of the halo photons are within the region of a radius less than 40 inches and (3) the spectrum of the pooint source is slightly distorted by the halo contamination.

Yao, Yangsen↗
NASA NTRS2015

Measurement and Modeling of Electromagnetic Scattering by Particles and Particle Groups

Small particles forming clouds of interstellar and circumstellar dust, regolith surfaces of many solar system bodies, and cometary atmospheres have a strong and often controlling effect on many ambient physical and chemical processes. Similarly, aerosol and cloud particles exert a strong influence on the regional and global climates of the Earth, other planets of the solar system, and exoplanets. Therefore, detailed and accurate knowledge of physical and chemical characteristics of such particles has the utmost scientific importance.

Interstellar matter↗
NASA NTRS1977

Consequences of using nonlinear particle trajectories to compute spatial diffusion coefficients

In a study of cosmic ray propagation in interstellar and interplanetary space, a perturbed orbit resonant scattering theory for pitch angle diffusion in a slab model of magnetostatic turbulence is slightly generalized and used to compute the diffusion coefficient for spatial propagation parallel to the mean magnetic field. This diffusion coefficient has been useful for describing the solar modulation of the galactic cosmic rays, and for explaining the diffusive phase in solar flares in which the initial anisotropy of the particle distribution decays to isotropy.

Goldstein, M. L.↗
NASA NTRS1993

Heliospheric hydrogen beyond 15 AU - Evidence for a termination shock

The Voyager and Pioneer 10 spacecraft are moving upstream and downstream into the local interstellar flow, monitoring H Lyman alpha radiation resonantly scattered from heliospheric hydrogen. Voyager Cruise Maneuver observations obtained between 15 and 35 AU reveal that H Lyman alpha intensities in the upstream direction fall as r exp -0.75+/-0.05. Beyond 15 AU downstream, Pioneer 10 intensities fall as r exp -1.07+/-0.1. These trends cannot be simultaneously reproduced using a hot H distribution model that does not include termination shock structure. The Voyager H Lyman alpha intensities also show a distinctive trend to decrease less rapidly with increasing heliocentric distance. Between 15 and 20 AU, Voyager intensities fall as r exp -1, whereas between 30 and 35 AU they fall as r exp -0.35. This flattening trend implies that the upstream H density is increasing rapidly with heliocentric distance beyond about 25 AU. This steepening trend is significant because similar H density gradients are predicted in models which include the effects of the termination shock. Taken together, the Voyager and Pioneer 10 H Lyman alpha observations beyond 15 AU imply the existence of a solar wind termination shock, suggesting that it lies between 70 and 105 AU in the upstream direction.

Hall, D. T.↗
NASA NTRS1992

Interstellar dust from the Milky Way to the Magellanic Clouds

Interstellar dust in the Magellanic Clouds, with a weak or nearly absent 2175 A extinction feature, may be of interest in studies of galaxies in early stages of chemical evolution. To this inquiry, we extend the graphite-silicate grain model, introduced by Mathis, Rumpl, and Nordsieck and developed by Draine and Lee (1984) from the Milky Way to the Magellanic Clouds. We find that the empirical extinction curves in the Large and Small Magellanic Clouds can be reproduced by adjusting only the relative abundances of graphite and silicate grains, while leaving all other model properties fixed to those appropriate for the Galactic extinction curve. Using the graphite-silicate models, we calculate the absorption and scattering optical depths, the mass-density ratio of interstellar dust to neutral hydrogen, and the Kramers-Kronig relation for all three galaxies. We also present a fitting function for the three extinction curves, valid not only over the observed range of wavelengths but also over the full range as predicted by the models. All the quantities we derived here are independent of the dust-to-gas ratios in the Milky Way and the Magellanic Clouds, and can be applied to other galaxies if they contain Galactic or Magellanic-type dust.

Pei, Yichuan C.↗
NASA NTRS1978

Ultraviolet photometry from the orbiting astronomical observatory. XXX - The Orion reflection nebulosity

Surface-brightness measurements are presented that cover the region of Orion in nine intermediate-width bandpasses ranging from 4250 to 1550 A. The existence of an extended ultraviolet reflection nebulosity in this area is confirmed, and the characteristics of its spectrum and spatial distribution are derived. The observations are consistent with a model in which the dense molecular cloud complex in Orion is illuminated by the foreground Orion aggregate of early-type stars. The interpretation is complicated by the fact that foreground dust may contribute to the observed scattered light. The scattering particles in the cloud appear to exhibit a wavelength-dependent albedo similar to that found for interstellar grains in general, with a strong indication that the phase function changes to a less forward-scattering form in the ultraviolet.

Witt, A. N.↗
NASA NTRS1981

A search for interplanetary He II, 304-A emission

A survey of a region of the sky around the antisolar direction in the earth's shadow was surveyed by the extreme ultraviolet telescope on the Apollo-Soyuz mission, whose 170-620 A channel is primarily sensitive to the H II, 304-A and He I, 584-A resonance. A sharp decrease in intensity was found as the line of sight sweeps into the shadow region. Once the line of sight is contained within the shadow, a residual signal above instrumental background was observed that was independent of view direction and spacecraft position. An upper limit at the 2sigma confidence level to a possible He II, 304-A component that can escape detection by the instrument corresponds to 0.002 R, or to a column density of 10 to the 9th ions/sq cm scattering at line center. The brightest possible sources for such emissions are multiple scattering from plasmaspheric He(+) in the shadow and scattering from He(+) created by the photoionization of the interstellar wind neutral helium.

Paresce, F.↗
NASA NTRS1990

A comparison of H-alpha intensity and radio wave scattering on eight low-latitude lines of sight

Radio scattering and H-alpha measurements for eight sources in Cygnus are compared. The diameter of the radio scattering disk at 1 GHz is found to be correlated with emission measure as determined from the H-alpha measurements, and that strong radio scattering characterized by a diameter of about 30 milliarcsec is produced in regions with emission measures of about 100/cm exp 6 pc or less. The slope of diameter-emission measure correlation is steeper than would be the case if all lines of sight were characterized by the same turbulent outer scale and modulation index. It is suggested that the lines of sight to unscattered or lightly scattered sources traverse only a diffuse medium which is revealed by H-alpha observations at high latitudes. Heavily scattered sources are viewed through an additional component of interstellar H II which has turbulence with different properties.

Spangler, Steven R.↗
NASA NTRS1972

Preliminary results on interstellar reddening as deduced from filter photometry

Filter photometry has been used to derive the interstellar reddening law from stars through the study of a single spectral type, B0. The deficiency in the far ultraviolet flux of a supergiant relative to a main sequence star is compared with the difference in the flux distribution due to a change of one spectral class. Individual interstellar reddening curves show the general feature reported by Stecher (1969) and by Bless and Savage (1970). There is a large amount of scatter in the far ultraviolet which may be partially due to a real difference in interstellar extinction and partially due to observational inaccuracy.

Laget, M.↗
NASA NTRS1995

High Resolution IRAS Maps and IR Emission of M31 -- II. Diffuse Component and Interstellar Dust

Large-scale dust heating and cooling in the diffuse medium of M31 is studied using the high resolution (HiRes) IRAS maps in conjunction with UV, optical (UBV), and the HI maps. A dust heating/cooling model is developed based on a radiative transfer model which assumes a 'Sandwich' configuration of dust and stars takes account of the effect of dust grain scattering.

infrared astronomy galaxies interstellar grains ph↗
NASA NTRS2008

SWCX Emission from the Helium Focusing Cone - Preliminary Results

Preliminary results from an XMM-Newton campaign to study solar wind charge exchange (SWCX) emission from the heliospheric focusing cone of interstellar helium are presented. The detections of enhanced O VII and O VIII emission from the cone are at the 2(sigma) and 4(sigma) levels. The solar wind charge exchange (SWCX) emission in the heliosphere not associated with distinct objects (e.g., comets and planets including exospheric material in and near Earth s magnetosheath) is proportional to the flux of the solar wind and the space density of neutral material. The neutral material originates in the interstellar medium (ISM) and passes through the solar system due to the relative motion of the Sun and the ISM. The flow of the neutral material through the solar system is strongly perturbed by the Sun both by gravity and by radiation pressure. Because of the relative radiative scattering cross sections and the effect of solar gravitation the density of interstellar hydrogen near the Sun is reduced while interstellar helium is gravitationally focused. This creates a helium focusing cone downstream of the Sun [e.g., 1, and references therein].

Snowden, S. L.↗
DOE OSTI2021

Cherenkov Telescope Array sensitivity to the putative millisecond pulsar population responsible for the Galactic Centre excess

ABSTRACT The leading explanation of the Fermi Galactic Centre γ-ray excess is the extended emission from an unresolved population of millisecond pulsars (MSPs) in the Galactic bulge. Such a population would, along with the prompt γ-rays, also inject large quantities of electrons/positrons (e±) into the interstellar medium. These e± could potentially inverse-Compton (IC) scatter ambient photons into γ-rays that fall within the sensitivity range of the upcoming Cherenkov Telescope Array (CTA). In this article, we examine the detection potential of CTA to this signature by making a realistic estimation of the systematic uncertainties on the Galactic diffuse emission model at TeV-scale γ-ray energies. We forecast that, in the event that e± injection spectra are harder than E−2, CTA has the potential to robustly discover the IC signature of a putative Galactic bulge MSP population sufficient to explain the Galactic Centre excess for e± injection efficiencies in the range of ≈2.9–74.1 per cent, or higher, depending on the level of mismodelling of the Galactic diffuse emission components. On the other hand, for spectra softer than E−2.5, a reliable CTA detection would require an unphysically large e± injection efficiency of ${\gtrsim} 158{{\ \rm per\ cent}}$. However, even this pessimistic conclusion may be avoided in the plausible event that MSP observational and/or modelling uncertainties can be reduced. We further find that, in the event that an IC signal were detected, CTA can successfully discriminate between an MSP and a dark matter origin for the radiating e±.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1973

Interplanetary Lyman-beta emissions

Derivation of the intensity of the diffuse hydrogen Lyman-beta glow at 1025 A which is due to resonance scattering of the solar H I 1025 A line by interstellar and interplanetary hydrogen. Two sources of neutral hydrogen are considered: the local interstellar medium interacting with the solar system, and the dust deionization of the H(+) component of the solar wind. It is shown that if the dust geometrical factor is less than or equal to five quintillionths per cm, observations of backscattered Lyman-beta radiation will provide a unique determination of the density and temperature of the local interstellar medium.

Paresce, F.↗
NASA NTRS1978

Interpretation of tails of X-ray bursts

Four reasons for ruling out the Alcock and Hatchett (1978) proposal concerning the tails of X-ray bursts are advanced. This proposal suggests that the tails of X-ray bursts observed during burst decay are due to the small-angle scattering of the original pulse of X-rays on interstellar dust grains; grains with a typical size of approximately 3 microns are assumed. The arguments against this theory involve differences in burst tail sizes sometimes observed for bursts from the same source; the different kinds of bursts emitted by MXB 1730-335 (rapid burster); an indication that MXB 1730-335 bursts have tails less than 2 s long; and the lack of correlation between relative strength of burst tails and the interstellar absorption.

Van Paradijs, J.↗