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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Einstein Observatory survey of X-ray emission from solar-type stars - The late F and G dwarf stars

Results of a volume-limited X-ray survey of stars of luminosity classes IV and V in the spectral range F7-G9 observed with the Einstein Observatory are presented. Using survival analysis techniques, the stellar X-ray luminosity function in the 0.15-4.0 keV energy band for both single and multiple sources. It is shown that the difference in X-ray luminosity between these two classes of sources is consistent with the superposition of individual components in multiple-component systems, whose X-ray properties are similar to those of the single-component sources. The X-ray emission of the stars in our sample is well correlated with their chromospheric CA II H-K line emission and with their projected equatorial rotational velocity. Comparison of the X-ray luminosity function constructed for the sample of the dG stars of the local population with the corresponding functions derived elsewhere for the Hyades, the Pleiades, and the Orion Ic open cluster confirms that the level of X-ray emission decreases with stellar age.

Maggio, A.↗
NASA NTRS1987

Near-infrared imaging of Comet Halley: Discovery of a color gradient in the inner coma

Near-infrared images of Comet Halley were obtained in the standard J, H, and K bandpasses, on 3.5 Nov. 1985 with an HgCdTe camera at a 1.54 m telescope. Each image covers 38.4 arcsec on the side. A well defined gradient in the J-H and H-K colors within 5000 km of the nucleus is discovered with the bluest colors at the photocenter. Surface brightness profiles steeper than the canonical 1/rho are observed in the same region. Analysis indicates that the color gradient and the brightness profiles can both be explained by the presence of volatile (dirty ice) grains in the inner coma. An outburst of very small (Rayleigh scattering) dust particles could also account for the observations, however, this model is not supported by the spacecraft measurements. No obvious jets or other structures are observed.

Rieke, M. J.↗
NASA NTRS1988

The NASA Infrared Telescope Facility Comet Halley monitoring program 2: Post-perihelion results

The post perihelion results of a 1 to 20 micrometer infrared monitoring program of Comet Halley are presented. These results complement previous observations of the pre-perihelion passages of Halley. The observations cover the time period of Mar. 1986 to the present time. During the time the comet was observable, two or more observations were obtained per month. The most interesting results were: (1) a detectable change in the J-H and H-K colors of Halley, and (2) a search for a nucleus rotation at J during 20 Feb. to 10 Mar. was unsuccessful. The perihelion J-H and K-K colors were constant at 0.48 + or - 0.01 and 0.17, respectively. A preliminary reduction of the data is given. It is concluded that the colors were at first similar to pre-perihelion and then changed from July onward to be bluer and more similar to the solar colors. This suggests that a change may have occurred in the composition of the dust coma of Halley in July 1986.

Tokunaga, Alan T.↗
NASA NTRS1988

The absence of a color-distance trend in comets

New near-IR J-H and H-K observations of 23 comets have been obtained in the heliocentric distance range of 1 to 6 AU. No evidence is found for a color-distance trend in the present sample. Significant differences between the grain populations in different comets are pointed out. The results indicate that the color distributions are unimodal, and that, unlike asteroids, the comets cannot be classified into distinct color-defined groups.

Jewitt, D.↗
NASA NTRS1988

The NASA Infrared Telescope Facility Comet Halley monitoring program. II - Postperihelion results

Postperihelion 1-20-micron magnitudes of Comet Halley obtained at the NASA Infrared Telescope Facility are presented. These magnitudes complement the preperihelion magnitudes published earlier by Tokunaga et al.(1986). The time period covered in this program was March 1986 through June 1987. While no systematic near-infrared color change was found during the preperihelion passage, a distinct J-H, H-K color change occurred during the postperihelion passage after July 1986. This indicates that there was a change in either the composition or particle size of the cometary dust, or both.

Tokunaga, A. T.↗
NASA NTRS1989

Evaluation of transport conditions during physical vapor transport growth of opto-electronic crystals

Transport conditions were evaluated during the vapor phase growth of mercurous chloride crystals in a closed tube. Experimentally observed growth rates were much smaller than those calculated by the Hertz-Knudsen (H-K) equation. The Arrhenius behavior of growth rate with the temperature was used to derive the sticking coefficient. A one-dimensional diffusion model was used to calculate the total mass flux and was compared with the condensing flux. It was predicted that growth occurred in the convecto-diffusive range.

Singh, N. B.↗
NASA NTRS1989

An infrared color gradient in the inner coma of Comet Halley

A well-defined gradient is noted in the J-H and H-K colors of near-IR images obtained for Comet Halley in November, 1985, within about 8000 km of the nucleus; the bluest colors are at the photocenter, in conjunction with surface brightness profiles that are steeper than those expected. The color gradient and the brightness profiles are both explainable by the present analysis in terms of the presence of volatile, dirty-ice grains in the inner coma. An outburst of Rayleigh-scattering dust particles (unsupported by spacecraft measurements obtained to date) may also account for the observational data.

Campins, H.↗
NASA NTRS1990

Near-infrared mapping of spiral barred galaxies

In external galaxies, near-infrared emission originates from stellar populations, hot dust, free-free emission from H+ regions, gaseous emission, non-thermal nucleus if any. Because of the low extinction compared to the visible, infrared wavelengths are useful to probe regions obscured by dust such as central parts where starburst phenomena can occur because of the large quantity of matter. The results presented were obtained with a 32 x 32 InSb charge injection device (CID) array cooled at 4K, at the f/36 cassegrain focus of the 3m60 Canada-France-Hawaii telescope with a spatial resolution of 0.5 inches per pixel. The objects presented are spiral barred galaxies mapped at J(1.25 microns), H(1.65 microns) and K(2.2 microns). The non-axisymetric potential due to the presence of a bar induces dynamical processes leading to the confinement of matter and peculiar morphologies. Infrared imaging is used to study the link between various components. Correlations with other wavelengths ranges and 2-colors diagrams ((J-H), (H-K)) lead to the identification of star forming regions, nucleus. Maps show structures connected to the central core. The question is, are they flowing away or toward the nucleus. Observations of M83 lead to several conclusions. The star forming region, detected in the visible and the infrared cannot be very compact and must extend to the edge of the matter concentration. The general shape of the near-infrared emission and the location of radio and 10 micron peaks suggest the confinement of matter between the inner Linblad resonances localized from CO measurements about 100 and 400 pc. The distribution of color indices in the arc from southern part to the star forming region suggests an increasing amount of gas and a time evolution eventually triggered by supernova explosions. Close to the direction of the bar, a bridge-like structure connects the arc to the nucleus with peculiar color indices. Perhaps, this structure can be linked to a height velocity component seen in UV and we can attribute it to a jet and/or a matter flow along the bar toward the nucleus, fuelling it. NGC 1068 is the nearest Seyfert 2 galaxy. It has been a subject of many studies at all wavelengths. This object was mapped at J, H, K, L and M, and in polaro-imagery. Results are given.

Gallais, P.↗
NASA NTRS1993

Bright near-infrared sources within 1 deg of the Galactic center. I - Survey and 1-20 micron photometry

Results of a near-IR survey of 0.55 sq deg toward the Galactic center are reported. Additional IR photometry of 50 objects found in this survey was made in order to investigate the nature of luminous stars in the central region of the Milky Way including all sources with K less than 7.6 and H-K not less than 1.4. In addition to candidates for normal M-type stars and long-period variables, four objects whose energy spectra peak at about 5 microns have been detected in a small region around (l, b) = (0.15, 0.0 deg), near the crossing of the 6-cm radio arc with the Galactic plane. These four might be young stellar objects near the Galactic center. It is suggested that the relative depth change in the silicate absorption is localized to a fairly small region around the Galactic center.

Nagata, Tetsuya↗
NASA NTRS1993

Infrared luminosity functions for the young stellar population associated with the L1641 molecular cloud

Results are reported of a deep near-IR imaging survey which samples 0.77 sq deg of the L1641 star-forming complex and reaches 5 sigma limits at J (1.25 micron,), H (1.65 micron), and K (2.2 microns) of 16.8, 15.8, and 14.7 mag, respectively. A population of about 1500 stars spread throughout the cloud, seven small aggregates comprised of 10-50 stars whose typical projected surface densities exceed that of the distributed population by factors of 4-10, and a heretofore unknown, partially embedded dense cluster comprised of about 150 stars are identified. Analysis of the distribution of (J-H), (H-K), and (R-I) colors for these groups suggest that, in all cases, the stellar populations are dominated by solar-type PMS stars which appear to contain a mix of objects analogous to weak-line T Tauri stars. The present observed luminosity functions are based on reddening-corrected J-band magnitude.

Strom, Karen M.↗
NASA NTRS1993

The embedded young stars in the Taurus-Auriga molecular cloud. II - Models for scattered light images

We describe NIR imaging observations of embedded young stars in the Taurus-Auriga molecular cloud. We find a large range in J-K and H-K colors for these class I sources. The bluest objects have colors similar to the reddest T Tauri stars in the cloud; redder objects lie slightly above the reddening line for standard ISM dust and have apparent K extinctions of up to 5 mag. Most of these sources also show extended NIR emission on scales of 10-20 arcsec which corresponds to linear sizes of 1500-3000 AU. The NIR colors and nebular morphologies for this sample and the magnitude of linear polarization in several sources suggest scattered light produces most of the NIR emission in these objects. We present modeling results that suggest mass infall rates that agree with predictions for cold clouds and are generally consistent with rates estimated from radiative equilibrium models. For reasonable dust grain parameters, the range of colors and extinctions require flattened density distributions with polar cavities evacuated by bipolar outflows. These results support the idea that infall and outflow occur simultaneously in deeply embedded bipolar outflow sources. The data also indicate fairly large centrifugal radii and large inclinations to the rotational axis for a typical source.

Kenyon, Scott J.↗
NASA NTRS1994

Dust extinction and molecular gas in the dark cloud IC 5146

In this paper we describe a powerful method for mapping the distribution of dust through a molecular cloud using data obtained in large-scale, multiwavelength, infrared imaging surveys. This method combines direct measurements of near-infrared color excess and certain techniques of star counting to derive mean extinctions and map the dust column density distribution through a cloud at higher angular resolutions and greater optical depths than those achieved previously by optical star counting. We report the initial results of the application of this method to a dark cloud complex near the cluster IC 5146, where we have performed coordinated, near-infrared, JHK imaging and (13)CO, C(18)O, and CS millimeter-wave, molecular-line surveys of a large portion of the complex. More than 4000 stars were detected in our JHK survey of the cloud. Of these, all but about a dozen appear to be field stars not associated with the cloud. Star count maps at J band show a striking and detailed anticorrelation between the surface density of J-band sources and CO and CS molecular-line emission. We used the (H-K) colors and positions of nearly 1300 sources to directly measure and map the extinction and thus trace the dust column density through the cloud at an effective angular resolution of 1 min .5. We report an interesting correlation between the measured dispersion in our extinction determinations and the extinction. Modeling this relation indicates that effects of small-scale cloud structure dominate the uncertainties in our measurements. Moreover, we demonstrate that such observations can be used to place constraints on the nature of the spatial distribution of extinction on scales smaller than our resolution. In particular, we show that models in which the dust is distributed uniformly or in discrete high-extinction clumps on scales smaller than (1 min .5) are inconsistent with the observations. We have derived extinctions at the same positions and at the same angular resolution (1 min .7) as our molecular-line observations. This enabled a direct comparison of (13)CO, C(18)O, and CS integrated intensities and column densities with A(sub V) for more than 500 positions in the cloud, corresponding to a range in A(sub V) between 0 to 32 mag of extinction. We found the integrated intensities of (13)CO, C(18)O, and CS to be roughly linearly correlated with extinction over different ranges of extinction. However, for all three molecules we find the scatter in the observed relations to be larger than can be accounted for by instrumental error, suggesting that there are large intrinsic variations in the abundances or excitation of the molecules through the cloud. Mean abundances for all the molecules relative to hydrogen were directly derived from the data. The ratio of (13)CO to C(18)O abundances was found to be significantly higher than the terrestrial ratio in regions where extinction is less than 10 mag. In the same region, the dispersion in the abundance ratio is also found to be very large, suggesting that the abundances of one or both molecules are very unstable even at relatively large cloud optical depths. Beyond 10 mag of extinction the abundances of both species appear very stable with their ratio close to the terrestrial value.

Lada, Charles J.↗
DOE OSTI2020

Materials Data on KH by Materials Project

HK1 is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. K1+ is bonded to six equivalent H1- atoms to form a mixture of corner and edge-sharing KH6 octahedra. The corner-sharing octahedral tilt angles are 0°. All K–H bond lengths are 2.85 Å. H1- is bonded to six equivalent K1+ atoms to form a mixture of corner and edge-sharing HK6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KH3 by Materials Project

KH3 is alpha bismuth trifluoride structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. K1+ is bonded in a distorted body-centered cubic geometry to twelve H+0.33- atoms. There are eight shorter (2.61 Å) and four longer (2.93 Å) K–H bond lengths. There are two inequivalent H+0.33- sites. In the first H+0.33- site, H+0.33- is bonded to four equivalent K1+ atoms to form a mixture of corner and edge-sharing HK4 tetrahedra. In the second H+0.33- site, H+0.33- is bonded in a square co-planar geometry to four equivalent K1+ atoms.

36 MATERIALS SCIENCE↗