Y. Pendleton - Academia.edu (original) (raw)
Papers by Y. Pendleton
Science
The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU69) has been larg... more The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU69) has been largely undisturbed since its formation. We study its surface composition using data collected by the New Horizons spacecraft. Methanol ice is present along with organic material, which may have formed through irradiation of simple molecules. H2O ice is not detected. This composition indicates hydrogenation of CO-rich ice and/or energetic processing of CH4+H2O ices in the cold, outer edge of the early Solar System. There are only small regional variations in color and spectra across the surface, suggesting Arrokoth formed from a homogeneous or well-mixed reservoir of solids. Microwave thermal emission from the winter night side is consistent with a mean brightness temperature of 29 ± 5 K.
Symposium - International Astronomical Union
The SETI Institute, the California Academy of Sciences, NASA Ames Research Center, and San Franci... more The SETI Institute, the California Academy of Sciences, NASA Ames Research Center, and San Francisco State University have developed standards-based curriculum materials for a one-year high school integrated science course centered on the unifying theme of evolution. Scientists, teachers, curriculum writers, and media specialists are currently finalizing six modules that integrate astronomical, geological, and biological sciences as well as the history of science and technology. The sequence of lessons in each module is designed to promote students' understanding and skills as defined by the National Science Education Standards and Benchmarks for Science Literacy. The modules cover: Cosmic Evolution, Planetary Evolution, Origin of Life, Evolution of Life, Hominid Evolution, and the Evolution of Technology. The core lessons for all six modules are provided via CD-ROM, including instructional guidelines, science background information, and additional resources (print, audiovisual,...
Symposium - International Astronomical Union
The spectra of objects suffering extinction by diffuse interstellar dust contain a broad feature ... more The spectra of objects suffering extinction by diffuse interstellar dust contain a broad feature centered at ~3300 cm−1 (~3.0 μm), attributed to O-H stretching vibrations, and/or a feature near 2950 cm−1 (3.4 μm) attributed to C-H stretching vibrations. The 2950 cm−1 feature can be attributed to C-H stretching vibrations in the -CH2- and -CH3 groups of a fairly complex carbonaceous material containing aliphatic functional groups.
The Astrophysical Journal
Carbonaceous compounds are a significant component of interstellar dust, and the composition and ... more Carbonaceous compounds are a significant component of interstellar dust, and the composition and structure of such materials is therefore of key importance. We present 1.5-15 m spectra of a plasma-polymerized carbonaceous material produced in radio-frequency discharge under low pressure, using C 2 H 2 as a precursor component. The infrared spectra of the resulting spheroidal carbonaceous nanoparticles reveal a strong aliphatic band (3.4 m feature), weak OH and carbonyl bands, and traces of aromatic compounds, all characteristics identified with dust in the diffuse interstellar medium of our Galaxy. The plasma polymerization process described here provides a convenient way to make carbonaceous interstellar dust analogs under controlled conditions and to compare their characteristics with astronomical observations. Here we focus on a comparison with the IR spectra of interstellar dust. The IR spectrum of carbonaceous dust in the diffuse interstellar medium is characterized by a strong 3.4 m CÀH stretching band and weak 6.8 and 7.2 m CÀH bending bands, with little evidence for the presence of oxygen in the form of carbonyl (C = O) or hydroxide (OH) groups. The plasma polymerization products produced under oxygen-poor conditions compare well with the peak position and profiles of the observed IR spectrum of diffuse dust. In addition, we find that addition of nitrogen to the plasma results in bands at 6.15 m (C = N band) and at 3 m (NH band). We note that, with the addition of nitrogen, the 3.4 m hydrocarbon band diminishes greatly in strength as the NH band grows. This may have implications for the puzzling absence of the 3.4 m hydrocarbon bands in the IR spectra of dust in dense molecular clouds, given that the presence of nitrogen-related bands has been established in dense-cloud dust.
The authors report observations of the B5 core at 160 and 360 mum to further study the environmen... more The authors report observations of the B5 core at 160 and 360 mum to further study the environment of a known star forming region.
The authors have used the KPNO infrared imager at 2.2 mum on the 2.1 meter telescope with 0.78&qu... more The authors have used the KPNO infrared imager at 2.2 mum on the 2.1 meter telescope with 0.78"pixels to produce polarimetric images of the galactic center region. The polarimeter consisted of a rotating half-wave plate, followed by a fixed analyzer, which was placed in the converging beam directly in front of the imager. Images were made of a field centered
Astrophysics and Space Science Library, 1990
ABSTRACT
The Cosmic Dust Connection, 1996
Spectra of objects which lie along several lines of sight through the diffuse interstellar medium... more Spectra of objects which lie along several lines of sight through the diffuse interstellar medium (ISM) all contain an absorption feature near 3.4 mum which has been attributed to saturated aliphatic hydrocarbons on interstellar grains. A remarkable similarity between the spectrum of the diffuse dust and an organic extract from the Murchison meteorite suggests that some of the interstellar organic material may be preserved in primitive solar system bodies. The recent discovery of the 3.4 mum absorption feature in other galaxies has led to comparisons between the extragalactic, galactic, and solar systems organics. The comparisons show strong similarities in position peaks and profile structure between the three spectra. However, the absence, in our own Galaxy, of the aliphatic hydrocarbon signature in the spectra of dense cloud objects is puzzling in the light of the widespread distribution of the aliphatic material throughout the diffuse medium and the short time scales thought to govern the transition of that material back into dense molecular clouds. In an effort to further investigate the 3.4 mum absorption feature in the diffuse ISM, comparisons of the diffuse medium dust to several materials which have been proposed as "fits" to the 3.4 mum feature are presented.
Icarus, 1996
We have measured the spectrum of Titan near 5 micrometers and have found it to be dominated by ab... more We have measured the spectrum of Titan near 5 micrometers and have found it to be dominated by absorption from the carbon monoxide 1-0 vibration-rotation band. The position of the band edge allows us to constrain the abundance of CO in the atmosphere and/or the location of the reflecting layer in the atmosphere. In the most likely case, 5 micrometers radiation is reflected from the surface and the mole fraction of CO in the atmosphere is qCO=10(+10/-5) ppm, significantly lower than previous estimates for tropospheric CO. The albedo of the reflecting layer is approximately 0.07(+0.02/-0.01) in the 5 micrometers continuum outside the CO band. The 5 micrometers albedo is consistent with a surface of mixed ice and silicates similar to the icy Galilean satellites. Organic solids formed in simulated Titan conditions can also produce similar albedos at 5 micrometers.
Nature, Jan 3, 1997
The satellites Rhea and Dione orbit within the magnetosphere of Saturn, where they are exposed to... more The satellites Rhea and Dione orbit within the magnetosphere of Saturn, where they are exposed to particle irradiation from trapped ions. A similar situation applies to the galilean moons Europa, Ganymede and Callisto, which reside within Jupiter's radiation belts. All of these satellites have surfaces rich in water ice. Laboratory studies of the interaction of charged-particle radiation with water ice predicted the tenuous oxygen atmospheres recently found on Europa and Ganymede. However, theoretical investigations did not anticipate the trapping of significantly larger quantities of O2 within the surface ice. The accumulation of detectable abundances of O3, produced by the action of ultraviolet or charged-particle radiation on O2, was also not predicted before being observed on Ganymede. Here we report the identification of O3 in spectra of the saturnian satellites Rhea and Dione. The presence of trapped O3 is thus no longer unique to Ganymede, suggesting that special circumst...
We have detected an absorption feature with a minimum at 260 nm in spectra of Saturn's satell... more We have detected an absorption feature with a minimum at 260 nm in spectra of Saturn's satellites Rhea and Dione obtained with the Hubble Space Telescope's Faint Object Spectrograph (FOS). We have identified this feature as the Hartley continuum of ozone. The feature in Rhea and Dione matches the one identified in ratios of Ganymede's trailing hemisphere to leading hemisphere
The Astronomical journal, 1998
In an attempt to better understand the conditions under which molecules condense onto grains in t... more In an attempt to better understand the conditions under which molecules condense onto grains in the envelopes of evolved stars, we have searched for the presence of H2O ice in the circumstellar envelopes of several evolved (OH/IR) stars. The sample of stars observed was selected on the basis of mass-loss rates, luminosities, and outflow velocities in order to cover a range of physical conditions that might affect the amount of ice present in stellar envelopes. Despite the clear presence of H2O ice around other, previously observed, evolved stars, our search in six OH/IR stars has resulted in only one clear detection, in OH 26.5 + 0.6, and the tentative detection in one other, OH 26.4-1.9. We provide column densities or upper limits for the amount of ice that is present on the grains around these stars and explore the possibility that there could be a relationship between M* or M*/L* and the H2O ice column density to explain the observations.
We present new spectroscopic 2.4 - 5.5 µm observations of the dusty infrared reflection nebula wi... more We present new spectroscopic 2.4 - 5.5 µm observations of the dusty infrared reflection nebula within the Cepheus A molecular cloud located at 730pc in the Cepheus OB3 association. With a spectral resolution of R 1000, we observed the 3.07 µm water ice band, the 3.4 µm long-wavelength water ice wing, the 3.47 µm ''diamond" wing, and the 4.67 µm
Ultra-Luminous Infrared Galaxies (ULIRGs), which emit the bulk of their radiation in the infrared... more Ultra-Luminous Infrared Galaxies (ULIRGs), which emit the bulk of their radiation in the infrared, are intense interacting mergers of two or more galaxies and account for a significant fraction of star formation in the local universe (Sanders & Mirabel 1996). The mid-IR spectra of most ULIRGS are dominated by PAH emission bands at 6.2, 7.7, 8.6, 11.3 and 12.7 microns.
Science
The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU69) has been larg... more The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU69) has been largely undisturbed since its formation. We study its surface composition using data collected by the New Horizons spacecraft. Methanol ice is present along with organic material, which may have formed through irradiation of simple molecules. H2O ice is not detected. This composition indicates hydrogenation of CO-rich ice and/or energetic processing of CH4+H2O ices in the cold, outer edge of the early Solar System. There are only small regional variations in color and spectra across the surface, suggesting Arrokoth formed from a homogeneous or well-mixed reservoir of solids. Microwave thermal emission from the winter night side is consistent with a mean brightness temperature of 29 ± 5 K.
Symposium - International Astronomical Union
The SETI Institute, the California Academy of Sciences, NASA Ames Research Center, and San Franci... more The SETI Institute, the California Academy of Sciences, NASA Ames Research Center, and San Francisco State University have developed standards-based curriculum materials for a one-year high school integrated science course centered on the unifying theme of evolution. Scientists, teachers, curriculum writers, and media specialists are currently finalizing six modules that integrate astronomical, geological, and biological sciences as well as the history of science and technology. The sequence of lessons in each module is designed to promote students' understanding and skills as defined by the National Science Education Standards and Benchmarks for Science Literacy. The modules cover: Cosmic Evolution, Planetary Evolution, Origin of Life, Evolution of Life, Hominid Evolution, and the Evolution of Technology. The core lessons for all six modules are provided via CD-ROM, including instructional guidelines, science background information, and additional resources (print, audiovisual,...
Symposium - International Astronomical Union
The spectra of objects suffering extinction by diffuse interstellar dust contain a broad feature ... more The spectra of objects suffering extinction by diffuse interstellar dust contain a broad feature centered at ~3300 cm−1 (~3.0 μm), attributed to O-H stretching vibrations, and/or a feature near 2950 cm−1 (3.4 μm) attributed to C-H stretching vibrations. The 2950 cm−1 feature can be attributed to C-H stretching vibrations in the -CH2- and -CH3 groups of a fairly complex carbonaceous material containing aliphatic functional groups.
The Astrophysical Journal
Carbonaceous compounds are a significant component of interstellar dust, and the composition and ... more Carbonaceous compounds are a significant component of interstellar dust, and the composition and structure of such materials is therefore of key importance. We present 1.5-15 m spectra of a plasma-polymerized carbonaceous material produced in radio-frequency discharge under low pressure, using C 2 H 2 as a precursor component. The infrared spectra of the resulting spheroidal carbonaceous nanoparticles reveal a strong aliphatic band (3.4 m feature), weak OH and carbonyl bands, and traces of aromatic compounds, all characteristics identified with dust in the diffuse interstellar medium of our Galaxy. The plasma polymerization process described here provides a convenient way to make carbonaceous interstellar dust analogs under controlled conditions and to compare their characteristics with astronomical observations. Here we focus on a comparison with the IR spectra of interstellar dust. The IR spectrum of carbonaceous dust in the diffuse interstellar medium is characterized by a strong 3.4 m CÀH stretching band and weak 6.8 and 7.2 m CÀH bending bands, with little evidence for the presence of oxygen in the form of carbonyl (C = O) or hydroxide (OH) groups. The plasma polymerization products produced under oxygen-poor conditions compare well with the peak position and profiles of the observed IR spectrum of diffuse dust. In addition, we find that addition of nitrogen to the plasma results in bands at 6.15 m (C = N band) and at 3 m (NH band). We note that, with the addition of nitrogen, the 3.4 m hydrocarbon band diminishes greatly in strength as the NH band grows. This may have implications for the puzzling absence of the 3.4 m hydrocarbon bands in the IR spectra of dust in dense molecular clouds, given that the presence of nitrogen-related bands has been established in dense-cloud dust.
The authors report observations of the B5 core at 160 and 360 mum to further study the environmen... more The authors report observations of the B5 core at 160 and 360 mum to further study the environment of a known star forming region.
The authors have used the KPNO infrared imager at 2.2 mum on the 2.1 meter telescope with 0.78&qu... more The authors have used the KPNO infrared imager at 2.2 mum on the 2.1 meter telescope with 0.78"pixels to produce polarimetric images of the galactic center region. The polarimeter consisted of a rotating half-wave plate, followed by a fixed analyzer, which was placed in the converging beam directly in front of the imager. Images were made of a field centered
Astrophysics and Space Science Library, 1990
ABSTRACT
The Cosmic Dust Connection, 1996
Spectra of objects which lie along several lines of sight through the diffuse interstellar medium... more Spectra of objects which lie along several lines of sight through the diffuse interstellar medium (ISM) all contain an absorption feature near 3.4 mum which has been attributed to saturated aliphatic hydrocarbons on interstellar grains. A remarkable similarity between the spectrum of the diffuse dust and an organic extract from the Murchison meteorite suggests that some of the interstellar organic material may be preserved in primitive solar system bodies. The recent discovery of the 3.4 mum absorption feature in other galaxies has led to comparisons between the extragalactic, galactic, and solar systems organics. The comparisons show strong similarities in position peaks and profile structure between the three spectra. However, the absence, in our own Galaxy, of the aliphatic hydrocarbon signature in the spectra of dense cloud objects is puzzling in the light of the widespread distribution of the aliphatic material throughout the diffuse medium and the short time scales thought to govern the transition of that material back into dense molecular clouds. In an effort to further investigate the 3.4 mum absorption feature in the diffuse ISM, comparisons of the diffuse medium dust to several materials which have been proposed as "fits" to the 3.4 mum feature are presented.
Icarus, 1996
We have measured the spectrum of Titan near 5 micrometers and have found it to be dominated by ab... more We have measured the spectrum of Titan near 5 micrometers and have found it to be dominated by absorption from the carbon monoxide 1-0 vibration-rotation band. The position of the band edge allows us to constrain the abundance of CO in the atmosphere and/or the location of the reflecting layer in the atmosphere. In the most likely case, 5 micrometers radiation is reflected from the surface and the mole fraction of CO in the atmosphere is qCO=10(+10/-5) ppm, significantly lower than previous estimates for tropospheric CO. The albedo of the reflecting layer is approximately 0.07(+0.02/-0.01) in the 5 micrometers continuum outside the CO band. The 5 micrometers albedo is consistent with a surface of mixed ice and silicates similar to the icy Galilean satellites. Organic solids formed in simulated Titan conditions can also produce similar albedos at 5 micrometers.
Nature, Jan 3, 1997
The satellites Rhea and Dione orbit within the magnetosphere of Saturn, where they are exposed to... more The satellites Rhea and Dione orbit within the magnetosphere of Saturn, where they are exposed to particle irradiation from trapped ions. A similar situation applies to the galilean moons Europa, Ganymede and Callisto, which reside within Jupiter's radiation belts. All of these satellites have surfaces rich in water ice. Laboratory studies of the interaction of charged-particle radiation with water ice predicted the tenuous oxygen atmospheres recently found on Europa and Ganymede. However, theoretical investigations did not anticipate the trapping of significantly larger quantities of O2 within the surface ice. The accumulation of detectable abundances of O3, produced by the action of ultraviolet or charged-particle radiation on O2, was also not predicted before being observed on Ganymede. Here we report the identification of O3 in spectra of the saturnian satellites Rhea and Dione. The presence of trapped O3 is thus no longer unique to Ganymede, suggesting that special circumst...
We have detected an absorption feature with a minimum at 260 nm in spectra of Saturn's satell... more We have detected an absorption feature with a minimum at 260 nm in spectra of Saturn's satellites Rhea and Dione obtained with the Hubble Space Telescope's Faint Object Spectrograph (FOS). We have identified this feature as the Hartley continuum of ozone. The feature in Rhea and Dione matches the one identified in ratios of Ganymede's trailing hemisphere to leading hemisphere
The Astronomical journal, 1998
In an attempt to better understand the conditions under which molecules condense onto grains in t... more In an attempt to better understand the conditions under which molecules condense onto grains in the envelopes of evolved stars, we have searched for the presence of H2O ice in the circumstellar envelopes of several evolved (OH/IR) stars. The sample of stars observed was selected on the basis of mass-loss rates, luminosities, and outflow velocities in order to cover a range of physical conditions that might affect the amount of ice present in stellar envelopes. Despite the clear presence of H2O ice around other, previously observed, evolved stars, our search in six OH/IR stars has resulted in only one clear detection, in OH 26.5 + 0.6, and the tentative detection in one other, OH 26.4-1.9. We provide column densities or upper limits for the amount of ice that is present on the grains around these stars and explore the possibility that there could be a relationship between M* or M*/L* and the H2O ice column density to explain the observations.
We present new spectroscopic 2.4 - 5.5 µm observations of the dusty infrared reflection nebula wi... more We present new spectroscopic 2.4 - 5.5 µm observations of the dusty infrared reflection nebula within the Cepheus A molecular cloud located at 730pc in the Cepheus OB3 association. With a spectral resolution of R 1000, we observed the 3.07 µm water ice band, the 3.4 µm long-wavelength water ice wing, the 3.47 µm ''diamond" wing, and the 4.67 µm
Ultra-Luminous Infrared Galaxies (ULIRGs), which emit the bulk of their radiation in the infrared... more Ultra-Luminous Infrared Galaxies (ULIRGs), which emit the bulk of their radiation in the infrared, are intense interacting mergers of two or more galaxies and account for a significant fraction of star formation in the local universe (Sanders & Mirabel 1996). The mid-IR spectra of most ULIRGS are dominated by PAH emission bands at 6.2, 7.7, 8.6, 11.3 and 12.7 microns.