Search NASA⌕ Search

SEARCH · Search NASA

Results for “galactic dust”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

The capability of the ultraviolet imaging telescope for observing interstellar dust

The Ultraviolet Imaging Telescope (UIT) was designed to be able to obtain deep images of nearby galaxies with a single frame. This ability makes it ideal for many imaging problems of the interstellar dust. The instrument has a forty arc-minute field of view with two arc-second resolution. It has 11 ultraviolet filters and a grating which is used as a grism for full field spectroscopy. In a thirty minute exposure (one orbital night) the limiting magnitude for hot objects is V = 25, or a UV mag of 22 for point sources and a UV mag of 26 for extended sources. Programs are planned for the observation of dust in reflection nebulae H II regions, planetaries, dark nebulae, the diffuse galactic light, and dust in other galaxies are planned. The UIT was integrated into the Astro Spacelab Payload and is scheduled to be launched on the Columbia in Nov. 1989.

Stecher, Theodore P.↗
NASA NTRS1988

Investigation of the diffuse ultraviolet background with DE data

The imaging instrumentation on the Dynamics Explorer 1 satellite is used to measure the intensity of the diffused ultraviolet radiation on two great circles about the sky. It was found that the extragalactic component of the diffuse ultraviolet radiation has an intensity of 530 + or - 15 units (a unit is one photon/(sq cm s A sr) at a wavelength of 150 nm. The galactic component of the diffuse ultraviolet radiation has a dependence on galactic latitude which requires strongly forward scattering particles if it is produced by dust above the galactic plane.

Fix, John D.↗
NASA NTRS1989

Measurements of the diffuse ultraviolet radiation

The imaging instrumentation on the Dynamics Explorer 1 satellite has been used to measure the intensity of the diffuse ultraviolet radiation on two great circles about the sky. It is found that the isotropic component of the diffuse ultraviolet radiation (possibly of extragalactic origin) has an intensity of 530 + or - 80 units (a unit is 1 photon per sq cm s A sr) at a wavelength of 150 nm. The Galactic component of the diffuse ultraviolet radiation has a dependence on Galactic latitude which requires strongly forward scattering particles if it is produced by dust above the Galactic plane.

Fix, John D.↗
DOE OSTI2021

The Atacama Cosmology Telescope: Microwave Intensity and Polarization Maps of the Galactic Center

Herein we present arcminute-resolution intensity and polarization maps of the Galactic center made with the Atacama Cosmology Telescope. The maps cover a 32 deg 2 field at 98, 150, and 224 GHz with |l| ≤ 4°, |b| ≤ 2°. We combine these data with Planck observations at similar frequencies to create coadded maps with increased sensitivity at large angular scales. With the coadded maps, we are able to resolve many known features of the Central Molecular Zone (CMZ) in both total intensity and polarization. We map the orientation of the plane-of-sky component of the Galactic magnetic field inferred from the polarization angle in the CMZ, finding significant changes in morphology in the three frequency bands as the underlying dominant emission mechanism changes from synchrotron to dust emission. Selected Galactic center sources, including Sgr A*, the Brick molecular cloud (G0.253+0.016), the Mouse pulsar wind nebula (G359.23-0.82), and the Tornado supernova remnant candidate (G357.7-0.1), are examined in detail. These data illustrate the potential for leveraging ground-based cosmic microwave background polarization experiments for Galactic science.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1982

Far-ultraviolet studies. VI - Further limits on diffuse galactic light scattered at large angles by dust

The Apollo 17 wide-field far-ultraviolet spectrometer was used to scan six large bands of the sky during trans-earth coast. After accounting for internal scattered light and the light expected from stars in the field of view, no significant residual flux remains. This imposes important constraints on the scattering properties of the interstellar dust grains: either the grains are extremely strongly forward scattering, or the albedo of the grains is low. The absence of a scattered light signal from dusty, moderate galactic latitude regions of the sky indicates that the high galactic latitude flux reported by Henry et al. (1977) and by Anderson et al. (1979) does not represent starlight backscattered by dust.

Anderson, R. C.↗
NASA NTRS1990

On planetary nebulae as sources of carbon dust: Infrared emission from planetary nebulae of the galactic halo

Planetary nebulae of the galactic disk are generally seen to emit a thermal continuum due to dust grains heated by stellar and nebular photons. This continuum typically peaks between 25 and 60 micron m, so that the total power emitted by the dust is sampled well by the broad-band measurements made by IRAS. Researchers examine here the characteristics of the infrared emission from the four planetary nebulae which are believed on the basis of their low overall metallicities to belong to the halo population. These nebulae are of particular interest because they are the most metal-poor ionized nebulae known in our Galaxy, and offer the opportunity to probe possible dependences of the dust properties on nebular composition. Researchers present fluxes extracted from co-addition of the IRAS data, as well as ground-based near infrared measurements. Each of the four halo objects, including the planetary nebula in the globular cluster M15, is detected in at least one infrared band. Researchers compare the estimated infrared excesses of these nebulae (IRE, the ratio of measured infrared power to the power available in the form of resonantly-trapped Lyman alpha photons) to those of disk planetary nebulae with similar densities but more normal abundances. Three of the halo planetaries have IRE values similar to those of the disk nebulae, despite the fact that their Fe- and Si-peak gas phase abundances are factors of 10 to 100 lower. However, these halo nebulae have normal or elevated C/H ratios, due to nuclear processing and mixing in their red giant progenitors. Unlike the other halo planetaries, DDDM1 is deficient in carbon as well as in the other light metals. This nebula has a substantially lower IRE than the other halo planetaries, and may be truly dust efficient. Researchers suggest that the deficiency is due to a lack of the raw material for producing carbon-based grains, and that the main bulk constituent of the dust in these planetary nebulae is carbon.

Dinerstein, Harriet L.↗
NASA NTRS1982

Large beam observations of the galactic center at 150, 200, and 300 microns

Observations with 10 arcmin resolution of a 2 sq deg portion of the galactic plane around the galactic center at 150, 200, and 300 microns are presented, obtained as part of a galactic plane survey. In the galactic center region the mean dust temperature is about 30 K. Both the temperature and the dust-to-gas mass ratio in the galactic center region are typical of a large portion of the galactic plane. Three main emission peaks, Sgr A, B, and C, are detected; these peaks appear as dust column density enhancements rather than temperature enhancements. The dust responsible for the FIR emission may only be a fraction of the dust responsible for the visual extinction toward the galactic center.

Stier, M. T.↗
NASA NTRS1995

Star formation in the Galactic Center GMC cores: Sagittarius B2 and the dust ridge

The total far-infrared luminosity and the ionizing flux inferred from radio continuum observations of the Galactic center region imply a rate of star formation per unit mass of molecular material comparable to that in the Galactic disk. However, H2O and OH masers commonly found in sites of high-mass star formation are relatively rare in the nuclear disk. Far-infrared studies suggest that the formation rate of stars with masses greater than approximately 20 Solar Mass is reduced in the central region compared to the Galactic disk. Star formation might be suppressed currently in the central region as a result of the different geometry and strength of the magnetic fields there, which arguably might tend to inhibit cloud collapse. High gas pressures implied by observations of the diffuse X-ray emission suggest that giant molecular clouds (GMCs) in the nuclear disk may be held together by external pressure rather than self-gravity. The gravitational collapse leading to the formation of high density cores may thus be suppressed in all but the most massive clouds.

Lis, D. C.↗
NASA NTRS1987

Star Formation in Galaxies

Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

Source record↗
NASA NTRS1972

A 100-micrometer (100-micron)map of the galactic center

The results of a survey made of the galactic center by a balloon-borne telescope are reported. The telescope mapped far infrared emission over a 5 degree portion of the sky with overlapping scans perpendicular to the plane. Data show emission is a continuous band along the galactic plane and emission perpendicular to the plane is on the order of 2 degrees. The map covers, for the first time, the distribution of dust in the galactic plane.

Hoffman, W.↗
NASA NTRS1981

Dust-sensitive forbidden line ratios

The paper studies observations of certain pairs of forbidden emission lines in the redshifted spectra of intrinsically bright objects, which may make possible the study of dust at large distances. The forbidden line pairs most likely to be useful in detecting dust in both galactic and extragalactic objects are presented, and forbidden O III 2322, 4364 A, which is the best line pair for the ground-based detection of dust intermediate-redshift quasars is discussed. Spectrophotometric observations at 1-2 microns could permit the study of dust toward highly luminous quasars at redshifts as large as 5, and quasars brighter than visual magnitude 17 are presented as candidates for studying dust with forbidden O III 2322, 4364 A.

Draine, B. T.↗
NASA NTRS1980

The diffuse UV background

The diffuse radiation field in the UV (900-3,000 A) affects the structure of galactic molecular clouds and conveys important information concerning the physical characteristics and spatial distribution of gas and dust in the universe. Continuum emission in this range is probably dominated by interstellar dust scattering in our galaxy. For view directions and angular resolutions allowing observations in the rifts between galactic dust clouds, the background due to the integrated light of spiral galaxies may be detected, providing important information on their structure and evolution. The redshifted emission from an intergalactic medium may be observable in the regions between nearby bright galaxies. Present observations provide weak constraints on the radiation field required to ionize the intergalactic medium at the level required by the Gunn-Peterson test.

Paresce, F.↗
NASA NTRS1993

Dust near luminous ultraviolet stars

This report describes research activities related to the Infrared Astronomical Satellite (IRAS) sky survey. About 745 luminous stars were examined for the presence of interstellar dust heated by a nearby star. The 'cirrus' discovered by IRAS is thermal radiation from interstellar dust at moderate and high galactic latitudes. The IRAS locates the dust which must (at some level) scatter ultraviolet starlight, although it was expected that thermal emission would be found around virtually every star, most stars shown no detectable emission. And the emission found is not uniform. It is not that the star is embedded in 'an interstellar medium', but rather what is found are discrete clouds that are heated by starlight. An exception is the dearth of clouds near the very hottest stars, implying that the very hottest stars play an active role with respect to destroying or substantially modifying the dust clouds over time. The other possibility is simply that the hottest stars are located in regions lacking in dust, which is counter-intuitive. A bibliography of related journal articles is attached.

Henry, Richard C.↗
NASA NTRS1992

The remarkable twisted disk of NGC 4753 and the shapes of galactic halos

The complex dust lanes in the S0 galaxy NGC 4753 are shown to be consistent with a disk that is strongly twisted by differential precession. Yet another peculiar S0 can therefore be explained as the result of an accretion event. An evolving disk model is fitted to the observed distribution. This disk is inclined by 15 deg relative to the galaxy's equatorial plane and twisted such that its line of nodes changes smoothly by 3.8 pi over a factor of seven in radius. The model indicates that most of the galaxy's mass is unseen, is nearly spherically distributed, and has a nearly scale-free spatial distribution. The ellipticity of the total galactic mass distribution must be constant to within 20 percent over the radial extent of the twisted disk - a conclusion which may significantly constrain galaxy formation mechanisms.

Steiman-Cameron, Thomas Y.↗
NASA NTRS2004

Final Summary of Research Report to the National Aeronautics and Space Administration Cosmochemistry Program

The discovery of presolar grains in meteorites is one of the most exciting recent developments in meteoritics. Six types of presolar grain have been discovered: diamond, Sic, graphite, Si3N4, Al2O3 and MgAl2O4. These grains have been identified as presolar because their isotopic compositions are very different from those of Solar System materials. Comparison of their isotopic compositions with astronomical observations and theoretical models indicates most of the grains formed in the envelopes of highly evolved stars. They are, therefore, a new source of information with which to test astrophysical models of the evolution of these stars. In fact, because several elements can often be measured in the same grain, including elements that are not measurable spectroscopically in stars, the grain data provide some very stringent constraints for these models. Our primary goal is to create large, unbiased, multi-isotope databases of single presolar Sic, Si,N,, oxide and graphite grains in meteorites, as well as any new presolar grain types that are identified in the future. These will be used to: (i) test stellar and nucleosynthetic models, (ii) constrain the galactic chemical evolution (GCE) paths of the isotopes of Si, Ti, 0 and Mg, (iii) establish how many stellar sources contributed to the Solar System, (iv) constrain relative dust production rates of various stellar types and (v) assess how representative of galactic dust production the record in meteorites is. The primary tool for this project is a highly automated grain analysis system we have developed for the Carnegie 6f ion probe.

O'D.Alexander, Conel↗
NASA NTRS2003

Final Summary of Research Report to the National Aeronautics and Space Administration Cosmochemistry Program

The discovery of presolar grains in meteorites is one of the most exciting recent developments in meteoritics. Six types of presolar grain have been discovered: diamond, Sic, graphite, Si3N4, Al2O3 and MgAl2O4. These grains have been identified as presolar because their isotopic compositions are very different from those of Solar System materials. Comparison of their isotopic compositions with astronomical observations and theoretical models indicates most of the grains formed in the envelopes of highly evolved stars. They are, therefore, a new source of information with which to test astrophysical models of the evolution of these stars. In fact, because several elements can often be measured in the same grain, including elements that are not measurable spectroscopically in stars, the grain data provide some very stringent constraints for these models. Our primary goal is to create large, unbiased, multi-isotope databases of single presolar Sic, Si,N,, oxide and graphite grains in meteorites, as well as any new presolar grain types that are identified in the future. These will be used to: (i) test stellar and nucleosynthetic models, (ii) constrain the galactic chemical evolution (GCE) paths of the isotopes of Si, Ti, O and Mg, (iii) establish how many stellar sources contributed to the Solar System, (iv) constrain relative dust production rates of various stellar types and (v) assess how representative of galactic dust production the record in meteorites is. The primary tool for this project is a highly automated grain analysis system on the Carnegie 6f ion probe.

O'D. Alexander, Conel↗
NASA NTRS2004

Research Report to the National Aeronautics and Space Administration Cosmochemistry Program

The discovery of presolar grains in meteorites is one of the most exciting recent developments in meteoritics. Six types of presolar grain have been discovered: diamond, Sic, graphite, Si3N4, Al2O3 and MgAl2O4 (NIITLER, 2003). These grains have been identified as presolar because their isotopic compositions are very different from those of Solar System materials. Comparison of their isotopic compositions with astronomical observations and theoretical models indicates that most of the grains formed in the envelopes of highly evolved stars. They are, therefore, a new source of information with which to test astrophysical models of the evolution of these stars. In fact, because several elements can often be measured in the same grain, including elements that are not measurable spectroscopically in stars, the grain data provide some very stringent constraints for these models. Our primary goal is to create large, unbiased, multi-isotope databases of single presolar Sic, Si3N4, oxide and graphite grains in meteorites, as well as any new presolar grain types that are identified in the future. These will be used to: (i) test stellar and nucleosynthetic models, (ii) constrain the galactic chemical evolution (GCE) paths of the isotopes of Si, Ti, O and Mg, (iii) establish how many stellar sources contributed to the Solar System, (iv) constrain relative dust production rates of various stellar types and (v) assess how representative of galactic dust production the record in meteorites is. The primary tool for this project is a highly automated grain analysis system on the Carnegie 6f ion probe. This proposal was part of a long-standing research effort that is still ongoing.

Alexander, Conel O'D.↗
NASA NTRS2010

The Origin of Dust in the Early Universe: Probing the Star Formation History of Galaxies by Their Dust Content

Two distinct scenarios for the origin of the approximately 4 x 10(exp 8) Solar Mass of dust observed in the high-redshift (z = 6.4) quasar J1148+5251 have been proposed. The first assumes that this galaxy is much younger than the age of the universe at that epoch so that only supernovae, could have produced this dust. The second scenario assumes a significantly older galactic age, so that the dust could have formed in lower-mass AGB stars. Presenting new integral solutions for the chemical evolution of metals and dust in galaxies, we offer a critical evaluation of these two scenarios. ^N;"(,, show that the AGB scenario is sensitive to the details of the galaxy's star formation history (SFH), which must consist of an early intense starburst followed by a period of low stellar activity. The presence or absence of massive amounts of dust in high-redshift galaxies can therefore be used to infer their SFH. However, a problem with the AGB scenario is that it produces a stellar mass that is significantly larger than the inferred dynamical mass of J1148+5251, an yet unresolved discrepancy. If this problem persists, then additional sites for the growth or formation of dust, such as molecular clouds or dense clouds around active galactic nuclei, must be considered.

Dwek, Eli↗