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  • 1
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    Advanced Telescopes and Observatories Capability Roadmap Presentation to the NRC (2005)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: This viewgraph presentation provides an overview of the NASA Advanced Planning and Integration Office (APIO) roadmap for developing technological capabilities for telescopes and observatories in the following areas: Optics; Wavefront Sensing and Control and Interferometry; Distributed and Advanced Spacecraft; Large Precision Structures; Cryogenic and Thermal Control Systems; Infrastructure.
    Keywords: Astronomy
    Type: Capabilities Roadmap Briefings to the National Research Council
    Format: application/pdf
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  • 2
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    Variability of Disk Emission in Pre-main-sequence and Related Stars. I. HD 31648 and HD 163296: Isolated Herbig Ae Stars Driving Herbig-Haro Flows (2008)
    In:  Other Sources
    Details
    Publication Date: 2019-08-26
    Description: Infrared photometry and spectroscopy covering a time span of a quarter-century are presented for HD 31648 (MWC 480) and HD 163296 (MWC 275). Both are isolated Herbig Ae stars that exhibit signs of active accretion, including driving bipolar flows with embedded Herbig-Haro (HH) objects. HD 163296 was found to be relatively quiescent photometrically in its inner disk region, with the exception of a major increase in emitted flux in a broad wavelength region centered near 3 micron in 2002. In contrast, HD 31648 has exhibited sporadic changes in the entire 3-13 micron region throughout this span of time. In both stars, the changes in the 1-5 micron flux indicate structural changes in the region of the disk near the dust sublimation zone, possibly causing its distance from the star to vary with time. Repeated thermal cycling through this region will result in the preferential survival of large grains, and an increase in the degree of crystallinity. The variability observed in these objects has important consequences for the interpretation of other types of observations. For example, source variability will compromise models based on interferometry measurements unless the interferometry observations are accompanied by nearly simultaneous photometric data.
    Keywords: Astronomy
    Type: The Astrophysical Journal; 678; 1070-1078
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  • 3
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    Time Variability of the Dust Sublimation Zones in Pre-Main Sequence Disk Systems (2007)
    In:  Other Sources
    Details
    Publication Date: 2019-08-26
    Description: The dust sublimation zone (DSZ) is the region of pre-main sequence (PMS) disks where dust grains most easily anneal, sublime, and condense out of the gas. Because of this, it is a location where crystalline material may be enhanced and redistributed throughout the rest of the disk. A decade-long program to monitor the thermal emission of the grains located in this region demonstrates that large changes in emitted flux occur in many systems. Changes in the thermal emission between 3 and 13.5 microns were observed in HD 31648 (MWC 480), HD 163296 (MWC 275), and DG Tau. This emission is consistent with it being produced at the DSZ, where the transition from a disk of gas to one of gas+dust occurs. In the case of DG Tau, the outbursts were accompanied by increased emission on the 10 micron silicate band on one occasion, while on another occasion it went into absorption. This requires lofting of the material above the disk into the line of sight. Such changes will affect the determination of the inner disk structure obtained through interferometry measurements, and this has been confirmed in the case of HD 163296. Cyclic variations in the heating of the DSZ will lead to the annealing of large grains, the sublimation of smaller grains, possibly followed by re-condensation as the zone enters a cooling phase. Lofting of dust above the disk plane, and outward acceleration by stellar winds and radiation pressure, can re-distribute the processed material to cooler regions of the disk, where cometesimals form. This processing is consistent with the detection of the preferential concentration of large crystalline grains in the inner few AU of PMS disks using interferometric spectroscopy with the VLTI.
    Keywords: Astronomy
    Type: 39th Annual DPS meeting; Oct 07, 2007 - Oct 12, 2007; Orlando, FL; United States
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  • 4
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    Star Confusion Effect on SIM PlanetQuest Astrometric Performance (2007)
    In:  Other Sources
    Details
    Publication Date: 2019-08-26
    Description: SIM PlanetQuest will measure star positions to an accuracy of a few microarcseconds using precise white light fringe measurements. One challenge for SIM observation scenario is "star confusion," where multiple stars are present in the instrument field of view. This is especially relevant for observing dim science targets because the density of number of stars increases rapidly with star magnitude. We study the effect of star confusion on the SIM astrometric performance due to systematic fringe errors caused by the extra photons from the confusion star(s}. Since star confusion from multiple stars may be analyzed as a linear superposition of the effect from single star confusion, we quantify the astrometric errors due to single star confusion surveying over many spectral types, including AOV, FOV, K5III, and MOV, and for various visual magnitude differences. To the leading order, the star confusion effect is characterized by the magnitude difference, spectral difference, and the angular separation between the target and confusion stars.Strategies for dealing with star confusion are presented. For example, since the presence of additional sources in the field of view leads to inconsistent delay estimates from different channels, with sufficient signal to noise ratio, the star confusion can be detected using chi-square statistics of fringe measurements from multiple spectral channels. An interesting result is that the star confusion can be detected even though the interferometer cannot resolve the separation between the target and confusion stars when their spectra are sufficiently different. Other strategies for mitigating the star confusion effect are also discussed.
    Keywords: Astronomy
    Type: 2007 SPIE Optics and Photonics Conference; Aug 26, 2007 - Aug 30, 2007; San Diego, CA; United States
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  • 5
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    Astronautics and Aeronautics: A Chronology, 1996-2000 (2009)
    In:  Other Sources
    Details
    Publication Date: 2019-08-26
    Description: This report is a chronological compilation of narrative summaries of news reports and government documents highlighting significant events and developments in United States and foreign aeronautics and astronautics. It covers the years 1996 through 2000. These summaries provide a day-by-day recounting of major activities, such as administrative developments, awards, launches, scientific discoveries, corporate and government research results, and other events in countries with aeronautics and astronautics programs. Researchers used the archives and files housed in the NASA History Division, as well as reports and databases on the NASA Web site.
    Keywords: Astronomy
    Type: PB2009-106797 , NASA SP-2009-4030
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  • 6
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    The Nature of the X-Ray Binary IGR J19294+1816 from INTEGRAL, RXTE, and Swift Observations (2009)
    In:  Other Sources
    Details
    Publication Date: 2019-08-26
    Description: We report the results of a high-energy multi-instrumental campaign with INTEGRAL, RXTE, and Swift of the recently discovered INTEGRAL source IGR J19294+ 1816. The Swift/XRT data allow us to refine the position of the source to R.A. (J2000) = 19h 29m 55.9s, Decl. (J2000) = +18 deg 18 feet 38 inches . 4 (+/- 3 inches .5), which in turn permits us to identify a candidate infrared counterpart. The Swift and RXTE spectra are well fitted with absorbed power laws with hard (Gamma approx 1) photon indices. During the longest Swift observation, we obtained evidence of absorption in true excess to the Galactic value, which may indicate some intrinsic absorption in this source. We detected a strong (P = 40%) pulsations at 12.43781 (+/- 0.00003) s that we interpret as the spin period of a pulsar. All these results, coupled with the possible 117 day orbital period, point to IGR J19294+ 1816 being an high-mass X-ray binary (HMXB) with a Be companion star. However, while the long-term INTEGRAL/IBIS/ISGRI 18-40 keV light curve shows that the source spends most of its time in an undetectable state, we detect occurrences of short (2000-3000 s) and intense flares that are more typical of supergiant fast X-ray transients. We therefore cannot make firm conclusions on the type of system, and we discuss the possible implication of IGR J19294+1816 being an Supergiant Fast X-ray Transient (SFXT).
    Keywords: Astronomy
    Type: Astronomy and Astrophysics; er 2; 2; 889-894
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  • 7
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    Starlight Nulling Technology at the Jet Propulsion Laboratory (2007)
    In:  Other Sources
    Details
    Publication Date: 2019-08-26
    Description: The current interests in extra-solar planet detection and space-based and ground-based interferometry for astronomical observations has led to the development of a number of nulling instrument designs at the Jet Propulsion Laboratory (JPL) and elsewhere. This paper summarizes briefly JPL's efforts in nulling interferometry to date and consists of illustrations of some key nulling activities. Basic layouts of nulling testbeds are described and key applications discussed.
    Keywords: Astronomy
    Type: IEEE Aerospace Conference - Interferometry and Large Optical Systems; Mar 03, 2007 - Mar 10, 2007; Big Sky, MT; United States
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  • 8
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    V3885 Sagittarius: A Comparison With a Range of Standard Model Accretion Disks (2009)
    In:  Other Sources
    Details
    Publication Date: 2019-08-26
    Description: A chi-squared analysis of standard model accretion disk synthetic spectrum fits to combined Far Ultraviolet Spectroscopic Explorer and Space Telescope Imaging Spectrograph spectra of V3885 Sagittarius, on an absolute flux basis, selects a model that accurately represents the observed spectral energy distribution. Calculation of the synthetic spectrum requires the following system parameters. The cataclysmic variable secondary star period-mass relation calibrated by Knigge in 2006 and 2007 sets the secondary component mass. A mean white dwarf (WD) mass from the same study, which is consistent with an observationally determined mass ratio, sets the adopted WD mass of 0.7M(solar mass), and the WD radius follows from standard theoretical models. The adopted inclination, i = 65 deg, is a literature consensus, and is subsequently supported by chi-squared analysis. The mass transfer rate is the remaining parameter to set the accretion disk T(sub eff) profile, and the Hipparcos parallax constrains that parameter to mas transfer = (5.0 +/- 2.0) x 10(exp -9) M(solar mass)/yr by a comparison with observed spectra. The fit to the observed spectra adopts the contribution of a 57,000 +/- 5000 K WD. The model thus provides realistic constraints on mass transfer and T(sub eff) for a large mass transfer system above the period gap.
    Keywords: Astronomy
    Type: AD-A513043 , The Astrophysical Journal; 703; 1839-1850
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  • 9
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    1393 Ring Bus at JPL: Description and Status (2007)
    In:  Other Sources
    Details
    Publication Date: 2019-08-24
    Description: Completed Ring Bus IC V&V Phase - Ring Bus Test Plan Completed for SIM Project - Applicable to Other Projects Implemented a Avionics Bus Based upon the IEEE 1393 Standard - Excellent Starting Point for a General Purpose High-Speed Spacecraft Bus - Designed to Meet SIM Requirements for - Real-time deterministic, distributed systems. - Control system requirements - Fault detection and recovery Other JPL Projects Considering Implementation F'light Software Ring Bus Driver Module Began in 2006, Continues Participating in Standard Revision. Search for Earth-like planets orbiting nearby stars and measure the masses and orbits of the planets it finds. Survey 2000 nearby stars for planetary systems to learn whether our Solar System is unusual, or typical. Make a new catalog of star position 100 times more accurate than current measurements. Learn how our galaxy formed and will evolve by studying the dynamics of its stars. Critically test models of exactly how stars shine, including exotic objects like black holes, neutron stars and white dwarfs.
    Keywords: Astronomy
    Type: Advanced Microelectronics and Photonics for Satellites Conference (AMAPS); Jun 26, 2007 - Jun 28, 2007; Fayetteville, Arkansas; United States
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  • 10
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    X-Ray and Infrared Observations of Embedded Young Stars in NGC 2264 (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-08-17
    Description: Images of the NGC 2264 star-forming region, which we have acquired with the XMM-Newton spacecraft, reveal strong X-ray emission from three deeply embedded (Av 〉 10 mag) young stellar objects in the vicinity of Allen's infrared source (AFGL 989 = IRS 1) and Castelaz & Grasdalen s infrared source (RNO-EW = IRS 2). Thermal plasma models for the brightest source in X-rays, located 11 southwest of Allen's star, yield a quasi-steady luminosity of Lx = 10 ergs s-1 and an extraordinarily high X-ray temperature of 100 MK. The high temperature is consistent with the presence of emission lines of Fe xxv and Fe xxvi at photon energies of 6.7 and 6.9 keV, respectively. An even higher temperature of nearly 140 MK was observed during the rise phase of a powerful impulsive X-ray flare of another young star in the IRS 2 region. Moderate-resolution near-infrared (1-4 um) spectra of the embedded objects, obtained at the NASA Infrared Telescope Facility, exhibit deep water ice absorption bands, as well as a variety of emission and absorption features of H I, CO, and both neutral and ionized metals.
    Keywords: Astronomy
    Type: Astrophysical Journal; 618; 795-809
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