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Pendleton, Y.

Publications and source records attributed to Pendleton, Y..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

NASAs Solar System Exploration Research Virtual Institute- Expanded Goals and More Partners

The NASA Solar System Exploration Research Virtual Institute (SSERVI) has been pursuing international partnerships since its inception as the NASA Lunar Science Institute (NLSI), in order to both leverage the science being done by its domestic member institutions as well as to help lunar science and exploration become a greater global endeavor. The international partners of the Institute have pursued a broad program of lunar science stimulated by scientific partnerships enabled by the SSERVI community. Furthermore, regional partnerships have been formed such as the new pan-European lunar science consortium, which promises both new scientific approaches and mission concepts. International partner membership requires long-term commitment from both the partner and SSERVI, together with tangible and specific plans for scientific interaction that will produce results of mutual benefit to both the institute's U.S. Teams and the international partner. International partners are invited to participate in all aspects of the Institute's activities and programs, on a basis of no exchange of funds. Through these activities, SSERVI researchers and international partners participate in sharing ideas, information, and data arising from their respective research efforts, and contribute to the training of young scientists. This talk will present an overview of the Institute and the international nodes. We will also discuss the various processes to become a SSERVI partner as well as the opportunities available for collaborations with the SSERVI national teams.

SSERVI↗
NASA NTRS2006

Ice Chemistry Through Quiescent Dust In IC5146

IC 5146 is a nearby (200pc) dark cloud complex in Cygnus. The lack of star formation activity makes it an excellent laboratory for the study of the chemical complexity in the earliest stages of dense molecular cloud evolution. We have used the Spitzer Infrared Spectrometer (IRS) to probe dust along 10 sight-lines toward K-Giant background stars, sampling a range of visual extinction from 2-20mag. Here we present 5-20micron spectra and correlation studies of the 6.0micron water-ice band and 9.7micron silicate absorption band with Av for a sample of our Spitzer program sources. Our IC5146 Spitzer data indicate grain growth and ice formation occurs early in the history of dense cloud formation. Each sight-line observed reveals the 9.7micron amorphous silicate absorption band. The highest Av sightlines show clear detections of ices at 6.0micron (water-ice mixture), 6.85micron (processed ice) and 15.2micron (CO2). However, sight-lines in the low-to-mid Av range provide intriguing variations. We may have the first example of two objects, one with ice features and one without, seen through the same cloud sightline with similar Av approx. 6 and similar silicate band optical depths. Also, the nominally expected linear correlation of Av with silicate band depth does not appear to hold for this cloud (turnover at Av approx.10-12). Both trends imply complexities in the grain growth at one of the earliest stages of dust and ice interaction ever observed. The highest extinction source in our sample, Av=20, reveals the 6.0micron (water), 6.85micron (processed ice), 9.7micron silicate and 15.2micron CO2 ice bands. Until recently, the 6.85micron band had only been detected towards embedded protostellar objects. Two additional quiescent dust sightlines from the C2D results now also indicate the 6.85micron band (Taurus and Serpens) by Knez et al. 2005, demonstrating the role of energetic processing within pristine ices prior to the onset of star formation.

Ennico, Kimberly↗
NASA NTRS1999

Water Ice on Kuiper Belt Object 1996 TO66

The 1.40-2.40 micron spectrum of Kuiper Belt object (KBO) 1996 TO66 was measured at the Keck Observatory in September 1998. It's spectrum shows the strong absorptions near 1.5 and 2.0 micron characteristic of water ice--the first such detection on a Kuiper Belt object. The depth of the absorption bands and the continuum reflectance of 1996 TO66 also suggest the presence of a black to slightly blue-colored, spectrally featureless particulate material as a minority component mixed with the water ice. In addition, there is evidence that the intensity of the water bands in the spectrum of 1996 TO66 vary with rotational phase suggesting that it has a "patchy" surface.

Brown, R. H.↗
NASA NTRS1998

Identification of water ice on the Centaur 1997 CU26

Spectra of the Centaur 1997 CU26 were obtained at the Keck Observatory on 27 October 1997 (universal time). The data show strong absorptions at 1.52 and 2.03 micrometers attributable to water ice on the surface of 1997 CU26. The reflectance spectrum of 1997 CU26 is matched by the spectrum of a mixture of low-temperature, particulate water ice and spectrally featureless but otherwise red-colored material. Water ice dominates the spectrum of 1997 CU26, whereas methane or methane-like hydrocarbons apparently dominate the spectrum of the Kuiper belt object 1993 SC, perhaps indicating different origins, thermal histories, or both for these two objects.

NASA Discipline Exobiology↗
NASA NTRS1997

Surface composition of Kuiper belt object 1993SC

The 1.42- to 2.40-micrometer spectrum of Kuiper belt object 1993SC was measured at the Keck Observatory in October 1996. It shows a strongly red continuum reflectance and several prominent infrared absorption features. The strongest absorptions in 1993SC's spectrum occur near 1.62, 1.79, 1.95, 2.20, and 2.32 micrometers in wavelength. Features near the same wavelengths in the spectra of Pluto and Neptune's satellite Triton are due to CH4 on their surfaces, suggesting the presence of a simple hydrocarbon ice such as CH4, C2H6, C2H4, or C2H2 on 1993SC. In addition, the red continuum reflectance of 1993SC suggests the presence of more complex hydrocarbons.

NASA Discipline Exobiology↗
NASA NTRS1991

The interstellar C-H stretching band near 3.4 microns - Constraints on the composition of organic material in the diffuse interstellar medium

The composition and history of dust in the diffuse ISM was studied using 3600-2700/cm absorption spectra of objects which have widely varying amounts of visual extinctions along different lines of sight. The 3300/cm and 2950/cm features are attributed to O-H and C-H stretching vibrations, respectively. The O-H feature in OH 32.8-0.3 is suggestive of circumstellar water ice and is probably not due to material in the diffuse ISM. The features in the 3100-2700/cm region are attributed either to C-H vibrations or to M stars. The spectra of the latter show a series of narrow features in this region that are identified with photospheric OH. Objects in which these bands are seen include OH 01-477, T629-5, and the Galactic center source IRS 7. The C-H stretch feature of diffuse ISM dust has subpeaks which fall within 5/cm of C-H stretching vibrations in the -CH2- and -CH3 groups of saturated aliphatic hydrocarbons.

Sandford, S. A.↗
NASA NTRS1990

Can the chirality of the ISM be measured

Many moderately complex carbon-based molecules of the type associated with biological systems can exist in one of two mirror-image forms (left-handed and right-handed), which can be distinguished on the basis of their influence on the state of polarization of a light beam. Both forms are possible in nature; yet in living organisms it is invariably the rule that one of these two species predominates. This gives rise to a net chirality. One possible explanation for the net chirality is that the early earth was somehow seeded from the ISM with an excess of chiral organic compounds which led to the development of life forms which are based on left-handed amino acids and right-handed sugars. Molecular spectroscopy of the interstellar medium (ISM) has revealed a complex variety of molecular species similar to those thought to have been available in the oceans and atmospheres of the earth at the time life formed. The detection of such molecules demonstrates the generality of the chemical processes occurring in both environments. If this generality extends to the processes which produce chirality, it may be possible to detect a net chirality in the ISM. This is of particular interest because determining whether or not net chirality exists elsewhere in the universe is an essential aspect of understanding how life developed on earth and how widely distributed it might be. Researchers report preliminary results of a feasibility study to determine whether or not a net chirality in the ISM can be measured. If laboratory results identify candidate chiral molecules that might exist in the ISM, the next step in this feasibility study will be to estimate the detectability of the chiral signature in astrophysical environments.

Pendleton, Y.↗
NASA NTRS1986

The 3.1 micrometer ice band in infrared reflection nebulae

Recent observations show that infrared reflection nebulae are common phenomena in star forming regions. Extensive observations were made of two nearby infrared reflection nebulae, Orin Molecular Cloud 2 IRS1 (OMC-2/IRS1) and Cepheus A IRS6a (Cep-A/IRS6a). Mie scattering models of ice coated grains were used to study the constraints on the properties and locations of grains that could produce a feature similar to that observed in OMC-2 and Cep-A. It was concluded that scattering by ice particles alone could not be responsible for the 3.1 micron feature observed in infrared reflection nebulae.

Pendleton, Y.↗
NASA NTRS1986

Infrared reflection nebulae in Orion molecular cloud 2

New obervations of Orion Molecular Cloud-2 have been made from 1-100 microns using the NASA Infrared Telescope Facility and the Kuiper Airborne Observatory. An extensive program of polarimetry, photometry and spectrophotometry has shown that the extended emission regions associated with two of the previously known near infrared sources, IRS1 and IRS4, are infrared reflection nebulae, and that the compact sources IRS1 and IRS4 are the main luminosity sources in the cloud. The constraints from the far infrared observations and an analysis of the scattered light from the IRS1 nebula show that OMC-2/IRS1 can be characterized by L less than or equal to 500 Solar luminosities and T approx. 1000 K. The near infrared (1-5) micron albedo of the grains in the IRS1 nebula is greater than 0.08.

Pendleton, Y.↗
NASA NTRS1984

New infrared observations of IRS1, IRS3 and the adjacent nebula in the OMC-2 cluster

Near infrared reflection nebulae are often observed around embedded protostellar objects. New observations of the infrared cluster of low luminosity protostars in Orion Molecular Cloud 2 (OMC2) are reported. The asymmetric distribution of the extended emission seen about IRS1 is in fact another infrared reflection nebulae. Observations of near infrared polarimetry, photometry, and spectrophotometry were carried out.

Pendleton, Y.↗
NASA NTRS1984

New infrared observations of IRS1, IRS3, and the adjacent nebula in the OMC-2 cluster

Observations of the infrared cluster of low luminosity protostars in Orion Molecular Cloud 2 (OMC2) are reported. Results show that the asymmetric distribution of the extended emission seen about IRS1 is another infrared reflection nebula. Energy distributions show that the spectral shape is fairly constant throughout the nebula which indicates there is little internal extinction within this region. Integrated surface brightness values show that the nebula is 5 times brighter than IRS1 at K. Energy distributions show that IRS1 has a more pronounced ice band absorption feature at 3.1 micron; suggesting that there is more extinction along the direct line of sight to IRS1 than along a line from IRS1 to the scattering grains and then to the observer. The distribution of the extended emission around IRS1 is similar to the reflection nebula seen in NGC 7538 (Werner et al. 1979). The asymmetric shapes of the two nebulae are similar and in each case there is excess extinction along line of sight to the illuminating source.

Pendleton, Y.↗