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Hodge, P. W.

Publications and source records attributed to Hodge, P. W..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

ISO Mid-Infrared Observations of Giant HII Regions in M33

We present Infrared Space Observatory Camera (ISOCAM) Circular Variable Filter scans of three giant HII regions in M33. IC 133, NGC 595, and CC 93 span a wide range of metallicity, luminosity, nebular excitation, and infrared excess; three other emission regions (CC 43, CC 99, and a region to the northeast of the core of NGC 595) are luminous enough in the mid-infrared to be detected in the observed fields. ISOCAM CVF observations provide spatially resolved observations (5'') of 151 wavelengths between 5.1 and 16.5 microns with a spectral resolution R = 35 to 50. We observe atomic emission lines ([Ne II], [Ne III], and [S IV]), several "unidentified infrared bands" (UIBs; 6.2, 7.7, 8.6, 11.3, 12.0, and 12.7 microns), and in some cases a continuum which rises steeply at longer wavelengths. We conclude that the spectra of these three GHRs are well explained by combinations of ionized gas, PAHs, and very small grains in various proportions and with different spatial distributions. Comparisons between observed ratios of the various UIBs with model ratios indicate that the PAHs in all three of the GHRs are dehydrogenated and that the small PAHs have been destroyed in IC 133 but have survived in NGC 595 and CC 93. The [Ne III]/[Ne II] ratios observed in IC 133 and NGC 595 are consistent with their ages of 5 and 4.5 Myr, respectively; the deduced ionization parameter is higher in IC 133, consistent with its more compact region of emission.

Skelton, B. P.↗
NASA NTRS1987

Giant H II regions in M81

H-alpha and VLA radio continuum observations at wavelengths of 6 and 20 cm are used to study the distribution of extinction and the distribution of giant radio H II regions along the spiral arms in M81. The radial distribution of visual extinction Av in the plane of M81 shows no trend, with an upper limit 0.1 mag/kpc for the radial extinction gradient and a mean Av of 1.1 + or - 0.4 mag. Nearly all the giant radio H II regions lie along the spiral arms or the inner H I ring. The radial distribution of the set of giant radio H II regions exhibits a strong maximum at a galactocentric distance R roughly 300 arcsec. Unless molecular hydrogen in M81 is also concentrated near R roughly 300 arcsec, the data disagree with Visser's (1980) model for star formation associated with a density wave. Some suggestions are made about how to change the ballistic particle model of Leisawitz and Bash to agree with the observed radial distribution of giant radio H II regions.

Kaufman, Michele↗
NASA NTRS1984

Blue clusters, populous clusters, and globulars

The introduction of new photometric techniques for faint objects has tremendously increased our understanding of the MC clusters, especially at the old end of the age spectrum. Many of the well-studied clusters of the past have gone through several transformations, starting as true globulars in 1960, becoming intermediate-age objects in the 1970's, but now returning to the true globular classification in the 1980's. LW 868 is an example of a cluster with such a history. Better photometric accuracy is also greatly improving our understanding of younger clusters, allowing detailed comparisons with theoretical evolutionary models, and a more reliable determination of the age-abundance relationship. The dynamical history of MC clusters can also be examined from the new data. The cluster formation rate, as well as the destruction rate, can be reconstructed from modern, deep cluster surveys.

Hodge, P. W.↗
NASA NTRS1980

Meteoroid ablation spheres from deep-sea sediments

The paper deals with an examination of spheres that are magnetically extracted from mid-Pacific abyssal clays that are up to half a million years old. The spheres are divided into three groups using their dominant mineralogy - namely, iron, glassy, and silicate. Most spheres were formed from particles that completely melted as they separated from their parent meteoroids during the ablation process. It is concluded that the mineralogy and composition of the deep-sea spheres are identical in many respects to the meteorite fusion crusts, laboratory-created ablation debris, and the ablated interplanetary dust particles in the stratospheric collection.

Blanchard, M. B.↗
NASA NTRS1980

Analysis of interplanetary dust collections

Interplanetary dust particles collected in the form of micrometeorites in the stratosphere and meteor ablation spherules in deep sea sediments are possibly a relatively unbiased sample of the micrometeoroid complex near 1 AU. Detailed laboratory analysis of the particles has provided information on physical properties which may be useful in modeling a variety of aspects of interplanetary dust.

Brownlee, D. E.↗
NASA NTRS1978

Silicate spherules from deep-sea sediments - Confirmation of extraterrestrial origin

Silicate spherules larger than 100 microns were extracted from 100 kg of box core samples of Pacific red clay taken in the mid-Pacific at a depth of 5 km, and the concentration of nonvolatile trace elements was determined for three spheres. One of the spheres shows excellent resemblance to C1 chondrite nonvolatile trace-element abundance patterns, and the relative abundances of the other two spheres are also very similar to those of C1 chondrites. One of these two spheres is depleted in Ir and Ru, while the other is depleted for Ni and Cr; possible explanations for the depletions are considered. Since the elemental abundances of the third sphere match the abundances of C1 chondrites, it is suggested that this sphere must be of extraterrestrial origin.

Ganapathy, R.↗
NASA NTRS1978

Meteor ablation spheres from deep-sea sediments

Spheres from mid-Pacific abyssal clays (0 to 500,000 yrs old), formed from particles that completely melted and subsequently recrystallized as they separated from their meteoroid bodies, or containing relict grains of parent meteoroids that did not experience any melting were analyzed. The spheres were readily divided into three groups using their dominant mineralogy. The Fe-rich spheres were produced during ablation of Fe and metal-rich silicate meteoroids. The glassy spheres are considerably more Fe-rich than the silicate spheres. They consist of magnetite and an Fe glass which is relatively low in Si. Bulk compositions and relict grains are useful for determining the parent meteoroid types for the silicate spheres. Bulk analyses of recrystallized spheres show that nonvolatile elemental abundances are similar to chondrite abundances. Analysis of relict grains identified high temperature minerals associated with a fine-grained, low temperature, volatile-rich matrix. The obvious candidates for parent meteoroids of this type of silicate sphere is a carbonaceous chondrite.

Blanchard, M. B.↗
NASA NTRS1977

Analyses of atmospheric extinction data obtained by astronomers. II - Seasonal variations in astronomical extinction

Archival astronomical atmospheric extinction records obtained from fifteen observatory sites were analyzed by not strictly rigorous statistical averaging procedures in order to obtain sufficiently reliable pictures of the trends and variations in atmospheric transparency for the period 1956-1972. While the northern hemisphere sites reveal definite seasonal variations with maxima occurring during local summer, the southern hemisphere displays little such effect. The only southern hemisphere sites with any variation were in South Africa, where a late winter maximum was observed.

Laulainen, N. S.↗
NASA NTRS1976

Physical properties of interplanetary grains

Morphological analyses of micrometeorite craters found on lunar rocks and laboratory simulation experiments are used to formulate a meteoritic interplanetary dust particle for optical scattering calculations that is roughly spherical and has a density of 2g cm/3. The model particle has chondritic elemental abundances and also contains a high content of finely dispersed carbon.

Brownlee, D. E.↗
NASA NTRS1974

Elemental abundances in interplanetary dust

The paper reports on measurements taken of elemental abundances in two interplanetary dust grains. Meteoroidal residue found inside micrometeoritic craters was discovered by optically scanning the 800 sq cm aluminum surface of the S-228 transuranic cosmic-ray experiment exposed to space for 67d during the Skylab-IV mission. Crater analyses for two randomly sampled meteoroids showed a composition consistent with troilite in the 9 micron-minute particle. Chondritic abundances were found in the 30 micron-minute particle. Particles of similar size and chemistry were common in carbonaceous chondrite meteorites. The inferred grain sizes within the 30 micron-minute particle provided evidence for the similarity to carbonaceous chondrites rather than to other meteorite types.

Brownlee, D. E.↗
NASA NTRS1973

Lunar and terrestrial impact crater spherules.

Comparisons between the chemistry of impact debris, especially spherical droplets of impact-formed material, are made for lunar samples and for soil samples taken from terrestrial impact sites. Differences are assigned to differences in the chemistry of impacting bodies and in the surface rocks, and to the influence of the atmosphere in the terrestrial cases.

Hodge, P. W.↗
NASA NTRS1973

Ablation debris and primary micrometeoroids in the stratosphere.

Analysis of micrometer-sized stratospheric particulates suggests that the majority of extraterrestrial material in the atmosphere is the product of ablation of larger bodies. Ablation debris is of considerable interest because of the possibility that much of it may have originated from classes of easily fragmented meteoroids that are incapable of surviving atmospheric entry to become meteorites. Comparison is made between the elemental abundance patterns found in stratospheric particulates and that found in fusion crusts of primitive meteorite types. Also discussed are criteria for distinguishing ablation products from primary unablated micrometeoroids.

Brownlee, D. E.↗
NASA NTRS1973

The physical nature of interplanetary dust as inferred by particles collected at 35 km

Particles were collected at an altitude of 35 km by two flights of a volume sampling micrometeorite collector. The collection scheme is very sensitive and is capable of collecting a significant number of particles. Many of the particles collected have chemical compositions similar to solar or to iron meteorites. Morphology of collected particles indicates that both true micrometeorites and ablation products were collected.

Brownlee, D. E.↗
NASA NTRS1972

Program management aid for redundancy selection and operational guidelines

Although this criterion was developed specifically for use on the shuttle program, it has application to many other multi-missions programs (i.e. aircraft or mechanisms). The methodology employed is directly applicable even if the tools (nomographs and equations) are for mission peculiar cases. The redundancy selection criterion was developed to insure that both the design and operational cost impacts (life cycle costs) were considered in the selection of the quantity of operational redundancy. These tools were developed as aids in expediting the decision process and not intended as the automatic decision maker. This approach to redundancy selection is unique in that it enables a pseudo systems analysis to be performed on an equipment basis without waiting for all designs to be hardened.

Hodge, P. W.↗