SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS
A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 12 - JUNE 20, 2006
89 ASTRONOMY
Includes observations of celestial bodies; astronomical instruments and techniques; radio, gamma-ray, x-ray, ultraviolet, and infrared astronomy; and astrometry.
20060013541 NASA Marshall Space Flight Center, Huntsville, AL, USA
X-ray Emission from Millisecond Pulsars
Zavlin, Vyacheslav; January 2006; 1 pp.; In English; Isolated Neutron Stars: from the Interior to the Surface University College London, 24-28 Apr. 2006, London, UK; No Copyright; Avail.: Other Sources; Abstract Only
Isolated (solitary or non-accreting) millisecond pulsars with observed X-ray emission can be divided in two distinct groups: those emitting nonthermal (magnetospheric) radiation and pulsars with the bulk of X-rays of a thermal origin, presumably emitted from small hot spots around the magnetic poles on the neutron star surface (polar caps). I will discuss properties of X-ray emission detected with Chandra and XMM-Newton from a number of millisecond pulsars, with emphasis on those of the thermal component, and compare them with predictions of radio pulsar models. Author
X Rays; Pulsars; Emission; Neutron Stars; Polar Caps
20060013544 National Oceanic and Atmospheric Administration, Rockville, MD USA
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Spectral and Broadband Shortwave Radiometry and Analysis. (Final Report)
Michalsky, J.; Dec. 2005; 10 pp.; In English Report No.(s): DE2006-861172; No Copyright; Avail.: National Technical Information Service (NTIS)
This report includes results for the entire period of this award 9 September 2003 through 14 February 2005. Two contributions were in broadband shortwave irradiance measurements. One included conducting the second diffuse horizontal broadband shortwave irradiance IOP to establish a working standard for diffuse horizontal shortwave irradiance, where none exists. The results are summarized in a paper published in the Journal of Geophysical Research - Atmospheres. Another broadband shortwave effort was in the comparison of clear sky measurements of broadband diffuse and direct irradiance during the May 2003 Aerosol IOP with six radiative transfer models of direct and diffuse irradiance using aerosol and other data inputs carefully measured during the Aerosol IOP. A paper with the results has been submitted to the Journal of Geophysical Research - Atmospheres; it is in review. A third area of research was in spectral radiative transfer model comparisons made using three models and measurements made with the visible rotating shadowband spectroradiometer (RSS) during the first diffuse irradiance IOP in 2001. Besides these contributions that have resulted in papers and/or presentations, the principal investigator (PI) consulted with science team and infrastructure representatives to improve aerosol optical depth measurements and to produce a spectral surface albedo product. NTIS
Broadband; Radiometers; Spectra
20060013548 NASA Marshall Space Flight Center, Huntsville, AL, USA
Evidence for a Binary Companion to the Enigmatic Compact Central Object 1E 1207.4-5209
Woods, P. M.; Zavlin, V. E.; Pavlov, G. G.; January 2006; 1 pp.; In English; Isolated Neutron Stars: From the Interior to the Surface, 24-28 Apr. 2006, London, UK; No Copyright; Avail.: Other Sources; Abstract Only
Located in the supernova remnant G296.5+10.0, 1E 1207.4-5209 is a 0.424 s period X-ray pulsar that exhibits strong absorption lines in its energy spectrum. The physical origin of the spectral features in 1E 1207.4-5209 and more generally, the absence of similar features in other radio-quiet neutron stars remains a mystery. Another, possibly related, anomalous property of 1E 1207.4-5209 is its non-monotonic spin frequency evolution. Zavlin, Pavlov & Sanwal(2004) proposed that the irregular spin-down was caused by either (i) frequent, recurrent glitches, (ii) the presence of a fall-back disk or (iii) a binary companion. Here, we report on a sequence of seven XMM-Newton observations of 1E 1207.4-5209 performed during a 40 day window between 2005 June 22 and July 3 1. Due to unanticipated phase noise, we identified three statistically-acceptable phase-coherent timing solutions with frequency time derivatives of +0.9, -2.6, and +1.6 x 10-12 Hz/s (listed in descending order of significance).We concluded that the local frequency derivative during our XMM-Newton observing campaign differs from the long-term spin-down rate by more than an order of magnitude. This measurement strongly supports the binary interpretation for the observed spin irregularities in 1E 1207.4-5209. We identified a family of orbital solutions that are consistent with our phase-connected solution as well as all archival data. We will discuss possible orbital solutions, prospects for constraining binary parameters with future observations, and consequences for the nature of 1E 1207.4-5209. Author
Energy Spectra; Neutron Stars; Radio Stars; Supernova Remnants; X Rays; Line Spectra; Pulsars
20060014007 NASA Marshall Space Flight Center, Huntsville, AL, USA
A Probable Taurid Impact on the Moon
Cooke, William J.; Suggs, R. M.; Swift, Wesley R.; [2006]; 2 pp.; In English; 2006 Lunar and Planetary Science Conference, 13-17 Mar. 2006, Houston, TX, USA; Copyright; Avail.: CASI: A01, Hardcopy
On November 7, 2005, at 23:41:52 UT, observers located at the Marshall Space Flight Center captured the flash produced by a kilogram-size meteoroid striking the lunar surface. Photometric analysis of the event video, combined with the plausible assumptions of a luminous efficiency of 2x10' and that the meteoroid was a member of the Taurid meteoroid stream, yield a striking power of approximately 640 lbs of TNT and a mass of approximately 3.8 kg. Even though no confirming independent observations are known to exist, there is high confidence in the impact origin of the flash; reasonable attempts have been made to eliminate other possibilities, such as cosmic ray hits on the CCD and glints from satellites that may have crossed the lunar disk near the impact time. Derived from text
Taurid Meteoroids; Lunar Surface; Photometry; Luminosity; Cosmic Rays
20060014587 Naval Observatory, Washington, DC USA
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VLBI Observations of Southern Hemisphere ICRF Sources. II. Astrometric Suitability Based on Intrinsic Structure
Ojha, Roopesh; Fey, Alan L; Charlot, Patrick; Jauncey, David L; Johnston, Kenneth J; Reynolds, John E; Quick, Jonathan F; Ellingsen, Simon P; McCulloch, Peter M; Koyama, Yasuhiro; Dec 2005; 13 pp.; In English Report No.(s): AD-A442534; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA442534; Avail.: Defense Technical Information Center (DTIC)
We present 8.4 GHz very long baseline interferometry (VLBI) observations of 48 southern hemisphere extra-galactic sources from the International Celestial Reference Frame. These are the second in a series of observations intended to image all such sources in the southern hemisphere at milliarcsecond resolution and bring the total number of observed sources to 111. We use these data, together with previously published data, to quantify the magnitude of the expected effect of intrinsic source structure on astrometric bandwidth synthesis VLBI observations by calculating a 'structure index' for the sources; the structure index yields an estimate of their astometric quality. Approximately 35% of sources in our sample have a structure index indicative of compact or very compact structures. The remaining two-thirds of our sources are less compact and should probably be avoided in astrometric and geodetic VLBI experiments requiring the highest accuracy unless intrinsic source structure can be accounted for in the astrometric/geodetic analysis. DTIC
Astrometry; Astronomy; Celestial Reference Systems; Interferometry; Ion Cyclotron Radiation; Plasma Heating; Radio Frequency Heating; Southern Hemisphere; Very Long Base Interferometry
20060014757 New Mexico State Univ., Las Cruces, NM USA
Sound Propagation Through and Scattering by Internal Gravity Waves in a Stably Strategified Atmosphere
Ostashev, Vladimir E; Chunchuzov, Igor P; Wilson, D K; Dec 2005; 11 pp.; In English; Original contains color illustrations Contract(s)/Grant(s): DAAD19-01-1-0640; 03-05-04001 Report No.(s): AD-A442477; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA442477; Avail.: CASI: A03, Hardcopy
A stably stratified atmosphere supports propagation of internal gravity waves (IGW). These waves result in highly anisotropic fluctuations in temperature and wind velocity that are stretched in a horizontal direction. As a result, (IGW) can significantly affect propagation of sound waves in nighttime boundary layers and infrasound waves in the stratosphere. In this paper, a theory of sound propagation through, and scattering by, (IGW) is developed. First, 3D spectra of temperature and wind velocity fluctuations due to (IGW), which were recently derived in the literature for the case of large wave numbers, are generalized to account for small wave numbers. The generalized 3D spectra are then used to calculate the sound scattering cross section in an atmosphere with (IGW). The dependencies of the obtained scattering cross section on the sound frequency, scattering angle, and other parameters of the problem are qualitatively different from those for the case of sound scattering by isotropic turbulence with the von K rm n spectra of temperature and wind velocity fluctuations. Furthermore, the generalized 3D spectra are used to calculate the mean sound field and the transverse coherence function of a plane sound wave propagating through (IGW). The results obtained also significantly differ from those for the case of sound propagation through isotropic turbulence. DTIC
Anisotropy; Gravity Waves; Internal Waves; Scattering; Sound Propagation; Sound Transmission; Sound Waves; Stratosphere; Wave Propagation
20060015630 Jet Propulsion Lab., California Inst. of Tech., Pasadena, CA, USA
Technology Plan for the Terrestrial Planet Finder Interferometer
Lawson, Peter R., Editor; Dooley, Jennifer A., Editor; June 2005; 165 pp.; In English; Original contains color and black and white illustrations Contract(s)/Grant(s): NAS7-03001; 743.01.06.01 Report No.(s): JPL-Publ-05-5; No Copyright; Avail.: CASI: A08, Hardcopy
The technology plan for the Terrestrial Planet Finder Interferometer (TPF-I) describes the breadth of technology development currently envisaged to enable TPF-I to search for habitable worlds around nearby stars. TPF-I is currently in Pre-Phase A (the Advanced Study Phase) of its development. For planning purposes, it is expected to enter into Phase A in 2010 and be launched sometime before 2020. TPF-I is being developed concurrently with the Terrestrial Planet Finder Coronagraph (TPF-C), whose launch is anticipated in 201 6. The missions are being designed with the capability to detect Earth-like planets should they exist in the habitable zones of Sun-like (F,G, and K) stars out to a distance of about 60 light-years. Each mission will have the starlight-suppression and spectroscopic capability to enable the characterization of extrasolar planetary atmospheres, identifying biomarkers and signs of life. TPF-C is designed as a visible-light coronagraph; TPF-I is designed as a mid-infrared formation-flying interferometer. The two missions, working together, promise to yield unambiguous detections and characterizations of Earth-like planets. The challenges of planet detections with mid-infrared formation-flying interferometry are described within this technology plan.
The approach to developing the technology is described through roadmaps that lead from our current state of the art through the different phases of mission development to launch. Technology metrics and milestones are given to measure progress. The emphasis of the plan is development and acquisition of technology during pre-Phase A to establish feasibility of the mission to enter Phase A sometime around 2010. Plans beyond 2010 are outlined. The plan contains descriptions of the development of new component technology as well as testbeds that demonstrate the viability of new techniques and technology required for the mission. Starlight-suppression (nulling) and formation-flying technology are highlighted. Although the techniques are described herein, the descriptions are only at a high-level, and tutorial material is not included. The reader is expected to have some familiarity with the principles of long-baseline mid-infrared interferometry. Selected references to existing literature are given where relevant. Author
Terrestrial Planets; Interferometers; Planetary Atmospheres; K Stars; Light (Visible Radiation)
20060015634 NASA Ames Research Center, Moffett Field, CA, USA
Chemistry and Evolution of Interstellar Clouds
Wooden, D. H.; Charnley, S. B.; Ehrenfreund, P.; [2003]; 1 pp.; In English; Copyright; Avail.: Other Sources; Abstract Only
In this chapter we describe how elements have been and are still being formed in the galaxy and how they are transformed into the reservoir of materials present at the time of formation of our protosolar nebula. We discuss the global cycle of matter, beginning at its formation site in stars, where it is ejected through winds and explosions into the diffuse interstellar medium. In the next stage of the global cycle occurs in cold, dense molecular clouds, where the complexity of molecules and ices increases relative to the diffuse ISM.. When a protostar forms in a dense core within a molecular cloud, it heats the surrounding infalling matter warms and releases molecules from the solid phase into the gas phase in a warm, dense core, sponsoring a rich gas-phase chemistry. Some material from the cold and warm regions within molecular clouds probably survives as interstellar matter in the protostellar disk. For the diffuse ISM, for cold, dense clouds, and for dense-warm cores, the physio-chemical processes that occur within the gas and solid phases are discussed in detail. Author
Molecular Clouds; Interstellar Matter; Solar Nebula; Star Formation; Protostars; Accretion Disks; Interstellar Chemistry
20060015637 NASA Ames Research Center, Moffett Field, CA, USA
Comet Dust: The Story of Planet Formation as Told by the Tiniest of Particles
Wooden, D. H.; [2005]; 1 pp.; In English; No Copyright; Avail.: Other Sources; Abstract Only
Our planetary system formed out of a gas-rich disk-shaped nebula with the early Sun at its center. Many small icy bodieswere consumed by the formation of the giant planets. However, many km-size icy bodies were tossed out of the giant- planet region to the cold, distant reaches of our solar system. Comets remained in their places of cold storage until perturbed into orbits that carry them into the inner solar system where they pass relatively close to the Sun. Comets are warmed by the Sun and shed material from their outer layers. The ices and gases shed by comets reveal simple and complex organic molecules were present at the time and in the region of the formation of the giant planets. Where the Earth was forming was too hot and had too intense sunlight for many of these ices and molecules to survive. The dust shed by comets tells us that some stardust survived unaltered but much of the dust was heated and crystallized before becoming part of the comet. Therefore, comet dust grains tell of large radial migrations from the cold outer reaches near Neptune into the hot regions near the forming Sun, and then back out to the cold regions where icy comets were accreting and forming. On 2005 July 4, the NASA Deep Impact Mission hit a comet and ejected primitive materials fiom its interior. These materials were not released into the comet s coma during normal activity. Despite the many passages of this comet close to the Sun, these primitive volatile gases and dust grains survived in its interior. Comet dust grains show that cold and hot materials were mixed into the same tiny particle very early in the formation of the solar system, and these aggregate dust grains never saw high temperatures again. The survival of primitive materials in comet nuclei suggests comets could have delivered organic molecules and primitive dust grains to early Earth. Author
Cometary Atmospheres; Dust; Planetary Evolution; Comets; Gas Giant Planets; Interplanetary Dust; Comet Nuclei
20060015650 NASA Ames Research Center, Moffett Field, CA, USA
SOFIA'S Challenge: Scheduling Airborne Astronomy Observations
Frank, Jeremy; December 1, 2005; 2 pp.; In English; Space Mission Challenge for Information Technology, 17-21 Jul. 2006, Pasadena, CA, USA; No Copyright; Avail.: Other Sources; Abstract Only
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is NASA's next generation airborne astronomical observatory, and will commence operations in 2005. The facility consists of a 747-SP modified to accommodate a 2.5 meter telescope. SOFIA is expected to fly an average of 140 science flights per year over its 20 year lifetime. Depending on the nature of the instrument used during flight, 5-15 observations per flight are expected. The SOFIA telescope is mounted aft of the wings on the port side of the aircraft and is articulated through a range of 20deg to 60deg of elevation. The telescope has minimal lateral flexibility; thus, the aircraft must turn constantly to maintain the telescope's focus on an object during observations. A significant problem in future SOFIA operations is that of scheduling flights in support of observations. Investigators are expected to propose small numbers of observations, and many observations must be grouped together to make up single flights. Flight planning for the previous generation airborne observatory, the Kuiper Airborne Observatory (KAO), was done by hand; planners had to choose takeoff time, observations to perform, and decide on setup-actions (called 'dead-legs') to position the aircraft prior to observing. This task frequently required between 6-8 hours to plan one flight The scope of the flight planning problem for supporting GI observations with the anticipated flight rate for SOFIA makes the manual approach for flight planning daunting. In response, we have designed an Automated Flight Planner (AFP) that accepts as input a set of requested observations, designated flight days, weather predictions and fuel limitations, and searches automatically for high-quality flight plans that satisfy all relevant aircraft and astronomer specified constraints. The AFP can generate one candidate flight plan in 5-10 minutes, of computation time, a feat beyond the capabilities of human flight planners. The rate at which the AFP can generate flights enables humans to assess and analyze complex tradeoffs between fuel consumption, estimated science quality and the percentage of scheduled observations. Due to the changing nature of SOFIA scheduling problems, this functionality will play a crucial role in optimizing science and minimizing costs during operations.
In the full paper, we will summarize the technical challenges that have been met in order to build this system. These include: design of the search algorithm, design of appropriate heuristics and approximations, and reduction in the size of the search space. We will also describe technical challenges that are currently being addressed, including the extension of the existing approach to handle new solution criteria.
Finally, we will describe a variety of cultural challenges that the astronomical community must address in order to successfully use SOFIA, and describe how the AFT can be used to address some of these challenges. Specifically, many of the intended science users are accustomed to using ground-based or space-based observatories; we will identify some differences that arise due to the nature of airborne observatories, and how the AFT can be extended to provide useful services to ease these cultural differences. Author
SOFIA (Airborne Observatory); Astronomical Observatories; Astronomy; Kuiper Airborne Observatory; Telescopes; Heuristic Methods
20060015659 NASA Ames Research Center, Moffett Field, CA, USA
Spectroscopy of Neutral and Ionized PAHs. From Laboratory Studies to Astronomical Observations
Salama, Farid; [2005]; 1 pp.; In English Contract(s)/Grant(s): 21-188-01-15; No Copyright; Avail.: Other Sources; Abstract Only
Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrochemistry is to reproduce (in a realistic way) the physical conditions that are associated with the emission and absorption interstellar zones. An extensive laboratory program has been developed at NASA Ames to assess the physical and chemical properties of PAHs in such environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. PAHs, neutrals and ions, are expanded through a pulsed discharge nozzle (PDN) and probed with high-sensitivity cavity ringdown spectroscopy (CRDS). These laboratory experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase from the ultraviolet and visible range to the near-infrared range. Intrinsic band profiles and band positions of cold gas-phase PAHs can now be measured with high-sensitivity spectroscopy and directly compared to the astronomical data. Preliminary conclusions from the comparison of the laboratory data with astronomical observations of interstellar and circumstellar environments will also be discussed. Author
Absorption Spectra; Polycyclic Aromatic Hydrocarbons; Carbon; Interstellar Chemistry; Atmospheric Radiation; Ionization; Diffuse Interstellar Bands; Gas-Ion Interactions
20060015660 NASA Ames Research Center, Moffett Field, CA
USA The Second Ring-Moon System of Uranus: Discovery and Dynamics
Showalter, M. R.; Lissauer, J. J.; [2005]; 1 pp.; In English Contract(s)/Grant(s): 459-20-00; No Copyright; Avail.: Other Sources; Abstract Only
Deep exposures of Uranus taken with the Hubble Space Telescope reveal two small moons and two faint rings. All orbit outside of Uranus's previously known (main) ring system, but interior to the large, classical moons. The outer new moon, UXXVI Mab, orbits at roughly twice the radius of the main rings and shares its orbit with a dust ring. The second moon, UXXVII Cupid, orbits just interior to the satellite Belinda. A second ring falls between the orbits of Portia and Rosalind, in a region with no known source bodies. Collectively, these constitute a densely-packed, rapidly varying and possibly unstable dynamica1 system. Author
Astrodynamics; Uranus (Planet); Hubble Space Telescope; Exposure; Dust
20060015679 NASA Ames Research Center, Moffett Field, CA
USA Terrestrial Planet Formation in Binary Star Systems
Lissauer, J. J.; Quintana, E. V.; Adams, F. C.; Chambers, J. E.; January 2006; 1 pp.; In English; American Astronomical Society meeting, 8-12 Jan. 2006, Washington, DC, USA Contract(s)/Grant(s): 344-53-42; No Copyright; Avail.: Other Sources; Abstract Only
Most stars reside in binary/multiple star systems; however, previous models of planet formation have studied growth of bodies orbiting an isolated single star. Disk material has been observed around one or both components of various young close binary star systems. If planets form at the right places within such disks, they can remain dynamically stable for very long times. We have simulated the late stages of growth of terrestrial planets in both circumbinary disks around 'close' binary star systems with stellar separations ($a_B$) in the range 0.05 AU $\le a_B \le$ 0.4 AU and binary eccentricities in the range $0 \le e \le 0.8$ and circumstellar disks around individual stars with binary separations of tens of AU. The initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet growth within our Solar System and around individual stars in the Alpha Centauri system (Quintana et al. 2002, A.J., 576, 982); giant planets analogous to Jupiter and Saturn are included if their orbits are stable. The planetary systems formed around close binaries with stellar apastron distances less than or equal to 0.2AU with small stellar eccentricities are very similar to those formed in the Sun-Jupiter-Saturn, whereas planetary systems formed around binaries with larger maximum separations tend to be sparser, with fewer planets, especially interior to 1 AU. Likewise, when the binary periastron exceeds 10 AU, terrestrial planets can form over essentially the entire range of orbits allowed for single stars with Jupiter-like planets, although fewer terrestrial planets tend to form within high eccentricity binary systems. As the binary periastron decreases, the radial extent of the terrestrial planet systems is reduced accordingly. When the periastron is 5 AU, the formation of Earth-like planets near 1 AU is compromised. Author
Binary Stars; Terrestrial Planets; Planetary Evolution; Star Formation; Stellar Envelopes; Planetary Systems; Gas Giant Planets
20060015683 NASA Ames Research Center, Moffett Field, CA, USA
Hubble Space Telescope NICMOS Polarization Measurements of OMC-1
Simpson, Janet P.; Colgan, Sean W. J.; Erickson, Edwin F.; Burton, Michael G.; Schultz, A. S. B.; January 2006; 36 pp.; In English; Original contains black and white illustrations Contract(s)/Grant(s): NAS5-26555; NCC2-1367; 459-20-1S; Copyright; Avail.: CASI: A03, Hardcopy
We present 2 micrometer polarization measurements of positions in the BN region of the Orion Molecular Cloud (OMC-1) made with NICMOS Camera 2 (0.2' resolution) on Hubble Space Telescope. Our goals are to seek the sources of heating for IRc2, 3, 4, and 7, identify possible young stellar objects (YSOs), and characterize the grain alignment in the dust clouds along the lines-of-sight to the stars. Our results are as follows: BN is approximately 29% polarized by dichroic absorption and appears to be the illuminating source for most of the nebulosity to its north and up to approximately 5' to its south. Although the stars are probably all polarized by dichroic absorption, there are a number of compact, but non-point-source, objects that could be polarized by a combination of both dichroic absorption and local scattering of star light. We identify several candidate YSOs, including an approximately edge-on bipolar YSO 8.7' east of BN, and a deeply-embedded IRc7, all of which are obviously self-luminous at mid-infrared wavelengths and may be YSOs. None of these is a reflection nebula illuminated by a star located near radio source I, as was previously suggested. Other IRc sources are clearly reflection nebulae: IRc3 appears to be illuminated by IRc2-B or a combination of the IRc2 sources, and IRc4 and IRc5 appear to be illuminated by an unseen star in the vicinity of radio source I, or by Star n or IRc2-A. Trends in the magnetic field direction are inferred from the polarization of the 26 stars that are bright enough to be seen as NICMOS point sources. Their polarization ranges from N less than or equal to 1% (all stars with this low polarization are optically visible) to greater than 40%. The most polarized star has a polarization position angle different from its neighbors by approximately 40 degrees, but in agreement with the grain alignment inferred from millimeter polarization measurements of the cold dust cloud in the southern part of OMC-1. The polarization position angle of another highly-polarized, probable star also requires a grain alignment and magnetic field orientation substantially different from the general magnetic field orientation of OMC-1. Author
Molecular Clouds; Hubble Space Telescope; Orion Nebula; Polarization
20060015825 Air Force Research Lab., Hanscom AFB, MA USA
R CrB Candidates in the Small Magellanic Cloud: Observations of Cold Featureless Dust with the Spitzer Infrared Spectrograph
Kraemer, Kathleen E; Sloan, G C; Wood, P R; Price, Stephan D; Egan, Michael P; Sep 13, 2005; 5 pp.; In English Contract(s)/Grant(s): Proj-1010 Report No.(s): AD-A443544; AFRL-VS-HA-TR-2006-1026; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA443544; Avail.: CASI: A01, Hardcopy
We observed 36 evolved stars in the Small Magellanic Cloud (SMC) using the low-resolution mode of the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. Two of these stars, MSX SMC 014 and 155, have nearly featureless spectral energy distributions over the IRS wavelength range (5.2-35 micrometers) and F(sub-nu) peaking at ~8-9 micrometers. The data can be fit by sets of amorphous carbon shells or by single 600-700 K blackbodies. The most similar spectra found in extant spectral databases are of R CrB, although the spectral structure seen in R CrB and similar stars is much weaker or absent in the SMC sources. Both SMC stars show variability in the near-infrared. Ground-based visual spectra confirm that MSX SMC 155 is carbon-rich, as expected for R CrB (RCB) stars, and coincides with an object previously identified as an RCB candidate. The temperature of the underlying star is lower for MSX SMC 155 than for typical RCB stars. The strength of the C(sub-2) Swan bands and the low temperature suggest that it may be a rare DY Per-type star, only the fifth such identified. MSX SMC 014 represents a new RCB candidate in the SMC, bringing the number of RCB candidates in the SMC to six. It is the first RCB candidate discovered with Spitzer and the first identified by its infrared spectral characteristics rather than its visual variability. DTIC
Dust; Infrared Radiation; Infrared Spectrometers; Magellanic Clouds; R Coronae Borealis Stars; Spectrographs
20060015867 Naval Observatory, Flaggstaff, AZ USA
The White Dwarf Luminosity Function from Sloan Digital Sky Survey Imaging Data
Harris, Hugh C; Munn, Jeffrey A; Kilic, Mukremin; Liebert, James; Kleinman, S J; Metcalfe, T S; Fukugita, Masataka; Knapp, G R; Smith, J A; Schneider, Donald P; Jan 2006; 12 pp.; In English Report No.(s): AD-A443601; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA443601; Avail.: CASI: A03, Hardcopy
Asample of white dwarfs is selected from the Sloan Digital Sky Survey (SDSS) Data Release 3 using their reduced proper motions, based on improved proper motions from combined SDSS and USNO-B data. Numerous SDSS and follow-up spectra (Kilic and coworkers) are used to quantify completeness and contamination of the sample; kinematics models are used to understand and correct for velocity-dependent selection biases. A luminosity function is constructed covering the range 7 \h M(sub-bol) \h 16, and its sensitivity to various assumptions and selection limits is discussed. The white dwarf luminosity function based on 6000 stars is remarkably smooth and rises nearly monotonically to M(sub-bol) = 15.3. It then drops abruptly, although the small number of low-luminosity stars in the sample and their unknown atmospheric composition prevent quantitative conclusions about this decline. Stars are identified that may have high tangential velocities, and a preliminary luminosity function is constructed for them. DTIC
Digital Data; Dwarf Stars; Images; Imaging Techniques; Luminosity; Sky Surveys (Astronomy)
20060015939 Aerospace Corp., Los Angeles, CA USA
0.8-13 Micron Spectroscopy of V838 Monocerotis and a Model for Its Emission
Lynch, David K; Venturini, Catherine C; Dimpfl, W; Bernstein, Lawrence S; Sitko, Michael L; Fajardo-Acosta, Sergio; Tokunaga, Alan; Knacke, Roger; Puetter, Richard C; Perry, R B; May 20, 2004; 15 pp.; In English Contract(s)/Grant(s): F4701-00-C-0009 Report No.(s): AD-A443718; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA443718; Avail.: Defense Technical Information Center (DTIC)
We report on the results of a number of infrared spectra (0.8-2.5, 2.1-4.6, and 3-14 microns) of V838 Monocerotis, taken from a short time after discovery in 2002 January to about 14 months later, in early 2003. The spectrum evolved dramatically, changing from a quasi-photospheric stellar spectrum with weak atomic emission lines (some with P Cygni profiles) to onen showing a wide range of deep absorption features indicative of a cool, extended atmosphere with a circumstellar dust shell. The early spectra showed lines of s-process elements, such as Sr II and Ba I. The later spectra showed absorption by gaseous H2O, CO, AlO, TiO, SiO, SO2, OH, VO, and SH, as well as a complex of emission near 10 microns reminiscent of silicate emission, with a central absorbing feature at 10:3 microns. Thus, V838 Mon appears to be oxygen-rich. A simple, spherically symmetric model of the system involving a central star with a two-component expanding circumstellar shell is presented that is able to explain the major molecular features and spectral energy distribution in the object's late stages. The derived shell mass and distance are 0.04 M(circle dot solar) and 9.2 kpc, respectively. DTIC
Emission; Infrared Spectra; Spectroscopy
20060015940 Aerospace Corp., Los Angeles, CA USA
A New Probe of the Planet-Forming Region in T Tauri Disks
Bergin, Edwin; Calvet, Nuria; Sitko, Michael L; Abgrall, Herve; D'Alessio, Paola; Herczeg, Gregory J; Qi, Chunhua; Lynch, David K; Brafford, Suellen M; Perry, R B; Oct 20, 2004; 5 pp.; In English Contract(s)/Grant(s): F4701-00-C-0009 Report No.(s): AD-A443719; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA443719; Avail.: CASI: A01, Hardcopy
We present new observations of the far-ultraviolet (FUV; 1100 2200 A) radiation field and the near- to mid-IR (3-13.5 micron) spectral energy distribution (SED) of a sample of T Tauri stars selected on the basis of bright, molecular disks (GM Aur, DM Tau, and LkCa 15). In each source, we find evidence for Ly-alpha-induced H2 fluorescence and an additional source of FUV continuum emission below 1700 A. Comparison of the FUV spectra to a model of H2 excitation suggests that the strong continuum emission is due to electron impact excitation of H2. The ultimate source of this excitation is likely X-ray irradiation that creates hot photoelectrons mixed in the molecular layer. Analysis of the SED of each object finds the presence of inner disk gaps with sizes of a few AU in each of these young (~1 Myr) stellar systems. We propose that the presence of strong H2 continuum emission and inner disk clearing are related by the increased penetration power of high-energy photons in gas-rich regions with low grain opacity. DTIC
Planets; Space Probes; T Tauri Stars
20060016319 Naval Postgraduate School, Monterey, CA USA
Reachable Sets for Multiple Asteroid Sample Return Missions
Croley, Patrick A; Dec 2005; 145 pp.; In English; Original contains color illustrations Report No.(s): AD-A443432; No Copyright; ONLINE: http://hdl.handle.net/100.2/ADA443432; Avail.: CASI: A07, Hardcopy
In support of future NASA asteroid sample return missions, this thesis examines strategies to reduce the number of feasible asteroid targets. Reachable sets are defined in a reduced classical orbital element space. The boundary of this reduced space is obtained by extremizing a family of convex combinations of orbital elements. The resulting group of optimization problems is solved using a direct collocation pseudospectral technique by a MATLAB application package called DIDO. The reachable sets are examined to narrow the possible valid asteroid choices in order to aid in mission design and analysis of alternative targets. A solar electric propulsion system is modeled with the stay times at each asteroid, Earth departure, and Earth arrival hyperbolic excess velocities implemented as constrained optimization parameters. DTIC
Asteroid Missions; Asteroids; Orbits; Sample Return Missions; Solar Generators; Solar Radiation
20060016362 NASA Marshall Space Flight Center, Huntsville, AL, USA
Chandra Observation of NGC 6822
Tennant, Allyn F.; [2006]; 1 pp.; In English; No Copyright; Avail.: Other Sources; Abstract Only
Chandra observed the nearby dwarf galaxy NGC 6822. There are 70 sources in the Chandra field, two of which are fairly extended and likely background clusters of galaxies. A third source was resolved by Chandra and has the same size and position as a known supernova remnant. The suspected variability detected from this source in previous missions is shown to be in error. The majority of the remaining 67 sources are consistent with background sources. Of the 61 sources detected above a completeness limit of 10 events we estimate that 9+/-4+/-8 are associated with the galaxy including both systematic and statistical errors. We compare the X-ray positions of all sources with various catalogs and HST data'and offer tentative identifications for several. Based on the mass and star formation rate of NGC 6822 we only expect about 10 sources mostly high mass systems. Author
X Ray Astrophysics Facility; Dwarf Galaxies; Galactic Clusters; Star Formation Rate; Supernova Remnants
Source: NASA
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