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  • 1
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    Measuring Extended Structure in Stars Using the Keck Interferometer Nuller (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Keck Interferometer Nuller is designed to detect faint off-axis mid-infrared light a few tens to a few hundreds of milliarcseconds from a bright central star. The starlight is suppressed by destructive combination along the long (85 m) baseline, which produces a fringe spacing of 25 mas at a wavelength of 10 m, with the central null crossing the position of the star. The strong, variable mid-infrared background is subtracted using interferometric phase chopping along the short (5 m) baseline. This paper presents an overview of the observing and data reduction strategies used to produce a calibrated measurement of the off-axis light. During the observations, the instrument cycles rapidly through several calibration and measurement steps, in order to monitor and stabilize the phases of the fringes produced by the various baselines, and to derive the fringe intensity at the constructive peak and destructive null along the long baseline. The data analysis involves removing biases and coherently demodulating the short-baseline fringe with the long-baseline fringe tuned to alternate between constructive and destructive phases, combining the results of many measurements to improve the sensitivity, and estimating the part of the null leakage signal which is associated with the finite angular size of the central star. Comparison of the results of null measurements on science target and calibrator stars permits the instrumental leakage - the "system null leakage" - to be removed and the off-axis light to be measured.
    Keywords: Astronomy
    Type: SPIE Astronomical Telescopes and Instrumentation; May 24, 2006 - May 31, 2006; Orlando, FL; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Baseline Monitoring for Astrometry in Interferometry (2004)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: One of the science goals of NASA's Navigator program is ground-based narrow-angle astrometry for extra-solar planet detection, which could be done as part of the proposed Outrigger Telescopes Project. The narrow-angle measurement process, which would use the outrigger telescopes, starts with the determination of the conventional interferometer astrometric baseline, determined from wide-angle astrometry of Hipparcos stars. A baseline monitor system would be employed at each outrigger telescope. This system monitors the pivot point of each telescope - the end point of the astrometric baseline - to measure telescope imperfections that would cause the baseline to vary with telescope rotation. The baseline monitor includes azimuth and elevation cameras that monitor runout along the azimuth and elevation axes of the telescopes. In conjunction with the baseline monitor system, a pivot monitor camera in the dual-star module is used to register the laser metrology corner-cube reflector to the telescope pivot, tying the narrow-angle baseline, which applies to the narrow-angle astrometric measurement, to the wide-angle baseline. In this paper we present the proposed designs for the baseline monitor and pivot-point camera.
    Keywords: Astronomy
    Type: SPIE Conference on Astronomical Telescopes and Instrumentation; Jun 21, 2004 - Jun 25, 2004; Glasgow, Scotland; United Kingdom
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Adverse Effects in Dual-Star Interferometry (2008)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Narrow-angle dual-star interferometric astrometry can provide very high accuracy in the presence of the Earth's turbulent atmosphere. However, to exploit the high atmospherically-limited accuracy requires control of systematic errors in measurement of the interferometer baseline, internal OPDs, and fringe phase. In addition, as high photometric SNR is required, care must be taken to maximize throughput and coherence to obtain high accuracy on faint stars. This article reviews: the keys aspects of the dual-star approach and implementation; the main contributors to the
    Keywords: Astronomy
    Type: Astrometry and Imaging with the Very Large Telescope Interferometer; Jun 02, 2008 - Jun 13, 2008; Keszthely; Hungary
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
    Electronic Resource
    Electronic Resource
    Cooperation in a deep helical energy well (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 3 (1991), S. 285-291 
    Details
    ISSN: 0899-0042
    Keywords: macromolecular ; optical activity ; polyisocyanate ; deuterium ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In contrast to random coil polymers, polyisocyanates maintain a highly extended helical conformation in solution. This structural characteristic causes unusually large chiral optical properties to arise from copolymerization of tiny proportions of optically active monomer isocyanates with achiral isocyanates or even from stereospecific placement of deuterium in the side chain of poly(n-hexyl isocyanate). These effects can be understood as phenomenologically related to the optical activity amplification properties of vinyl polymers studied by Pino and his co-workers and ascribed to breaking the energetic degeneracy of the otherwise equally populated left- and right-handed helical states of the backbone. Statistical thermodynamic calculations, based on this model, and analogous to those carried out earlier on the vinyl polymers, allow matching the temperature and molecular weight dependence of the optical activity in poly((R)-1-deuterio-1-hexyl isocyanate) to the approximate responsible energy terms.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530030412
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  • 5
    Electronic Resource
    Electronic Resource
    The road to chiral amplification in polymers originated in Italy (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 424-427 
    Details
    ISSN: 0899-0042
    Keywords: polymers ; chiral amplification ; Italy ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fact that stereoregular polymers produced by Ziegler-Natta polymerization methods could be crystallized and studied by X-ray diffraction methods lead to the discovery that these polymers adopted helical conformations in the crystalline solid. In addition to the nearly perfect asymmetric synthesis demonstrated by the highly isotactic stereoregularity produced by the catalyst, the conformation adopted in the crystalline state also involves chirality. The large number of units polymerized produced though gives rise to a cryptochiral material in which the mirror helical conformations are necessarily equally populated and therefore the measurement of optical activity can never be a consideration in these experiments. At that time though Natta's students began to prepare stereoregular vinyl polymers with chiral nonracemic pendant groups and discovered that the optical activities of such materials in solution showed nonlinear relationships between enantiomeric content and optical activity. This phenomenon arising from the effect of the chiral pendants on the population of the helical senses of the polymer backbone, acted to demonstrate that these stereoregular polymers adopted helical conformations in solution comparable to those investigated in the solid state. In recent times this effect has reached an extreme in the polyisocyanates which show a much larger sensitivity to chiral effects than found for the vinyl polymers although the underlying forces at work are identical to those studied earlier by the Italian School. Chirality 9:424-427, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 6
    Electronic Resource
    Electronic Resource
    A chiral polymeric analogy to a one-dimensional paramagnetic materialFigure 2 is reprinted with permission from Green MM, Peterson NC, Sato T, Teramoto A, Cook R, Lifson S. A helical polymer with a cooperative response to chiral information. Science 1995;268:1860. Copyright 1995 American Association for the Advancement of Science. Readers may view, browse, and/or download this material for temporary copying purposes only, provided these uses are for noncommerical personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or in part, without prior written permission from AAAS. (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 41-45 
    Details
    ISSN: 0899-0042
    Keywords: polymers ; polyisocyanates ; helical conformation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A class of polymers synthesized at DuPont in the late 1950's, the polyisocyanates, are the simplest analogs of the Nylons and have proven valuable as experimental models for theories of wormlike macromolecules. The macromolecular dimensional properties associated with all wormlike polymers arise from a strongly preferred local conformation of the chain and in the polyisocyanates this conformation is helical with an interesting additional property in that the mirror helical senses are of equal probability. Recent experiments have shown that discrimination between the helical senses can be accomplished with surprisingly small chiral influences indicating high cooperativity which arises from a conformational state in which long sections of one helical sense are separated from the other sense by infrequent helical reversals. This can be seen to be analogous to theoretical ideas about one-dimensional paramagnetic materials in which the spin states and the domain boundaries are analogs to the helical sense and the helical reversals in the polyisocyanates. The mathematical formalisms of the one-dimensional magnetic materials precisely describe the chiral properties of the polyisocyanates. Chirality 10:41-45, 1998. © 1998 Wiley-Liss,Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.8
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  • 7
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    Water Vapor Measurement and Compensation in the Near and Mid-infrared with the Keck Interferometer Nuller (2006)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A viewgraph presentation describing the methods, motivation and methods for water vapor measurement with the Keck interferometer near and mid infrared radiation band is shown. The topics include: 1) Motivation: Why measure H2O?; 2) Method: How do we measure H2O?; 3) Data: Phase and Group Delays for the K and N Bands; 4) Predicted and Actual Nband Phase and Dispersion; and 5) Validation of Atmospheric Turbulence Models with KI Data.
    Keywords: Astronomy
    Type: SPIE 50th Annual Conference; Jul 31, 2006 - Aug 04, 2006; San Diego, CA; United States
    Format: text
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    NASA TECHNICAL REPORTS
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