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An Assessment of Ground-Based Techniques for Detecting Other Planetary Systems Volume II: Position Papers

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An Assessment of Ground-Based Techniques for Detecting Other Planetary Systems Volume II: Position Papers NASA Conference Publication 2124 --•--.- (HASA-CP-2124) AN ASSESSMENT OF N80-25224 GEOUND-BASED TECHNIQUES FOB DETECTING GTHES PLANETA8Y SYSTEMS. VOLUflE 2: POSITION PAPESS (NASA) 253 p EC A12/BF A01 , CSCL 03A Onclas G3/89 20984 An Assessment of Ground-Based Techniques for Detecting Other Planetary Systems Volume II: Position Papers March 1980 REPRODUCED BY NATIONAL TECHNICAL INFORMATION SERVICE U.S. DEPARTMENT Of COMMERCE SPRINGFIELD, VA. 22161 NASA National Aeronautics and Space Administration NOTICE THIS DOCUMENT HAS BEEN REPRODUCED FROM THE BEST COPY FURNISHED US BY THE SPONSORING AGENCY. ALTHOUGH IT IS RECOGNIZED THAT CERTAIN PORTIONS ARE ILLEGIBLE, IT IS BEING RELEASED IN THE INTEREST OF MAKING AVAILABLE AS MUCH INFORMATION AS POSSIBLE. 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. NASA CP-2124, Volume II 4. Title and Subtitle 5. Report Date AN ASSESSMENT OF GROUND-BASED TECHNIQUES FOR DETECTING OTHER PLANETARY SYSTEMS. VOLUME II: POSITION PAPERS 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Edited by David C. Black and William E. Brunk* A-8114 10. Work Unit No. 9. Performing Organization Name and Address 196-41-68-01 Ames Research Center, NASA, Moffett Field, Calif, 11. Contract or Grant No. and *NASA Headquarters, Washington, D.C. 13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Conference Publication National Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, D.C. 20546 15. Supplementary Notes 16. Abstract One of the oldest unanswered questions in astronomy is "how did the solar system form?" Recent studies of the solar system using telescopes and spacecraft have provided exciting new discoveries as well as valuable information on the present state and evolution of planets in the solar system. However, the processes involved in planetary evolution tend to obscure vital clues as to how the planets formed, and even if we could unravel the natural record to reveal how Earth and her sister planets formed, it remains unclear whether we would understand how the solar system itself formed. One way to obtain valuable and probably essential data for an understanding of the origin of the solar system is to discover and study planetary systems revolving around stars other than the Sun: there is currently no unequivocal observational evidence for other planetary systems In an attempt to examine whether it is feasible to use ground-based astronomical techniques to search for other planetary systems, two scientific workshops were held during the interval October 1978 to January 1979. The workshop participants, experts in various branches of astronomy and instrumentation, addressed the questions of whether the accuracy of existing techniques (e.g., astrometry and spectroscopy) could be improved to the level required for such a demanding observa- tional effort, what the factors are that limit the achievable accuracy, and whether the achievable accuracies were sufficiently good to permit strong scientific interferences in the presence of negative results from a search. Volume I of this report is an overview of the workshop findings; volume II contains technical position papers authored by workshop members on major aspects of the workshop deliberations. 17. Key Words (Suggested by Auttior(s)) 18. Distribution Statement Origin of solar system Unlimited Detection of planetary systems Astronomical techniques STAR Category - 89 19. Security Qassif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 253 Unclassified Unclassified 'For sale by the National Technical Information Service. Springfield, Virginia 22161 \ 5- U. S. GOVERNMENT PRINTING OFFICE: NASA Conference Publication 2124 An Assessment of Ground-Based Techniques for Detecting Other Planetary Systems Volume II: Position Papers Edited by David C. Black, Ames Research Center, Moffett Field, California William E. Brunk, NASA Headquarters, Washington, D.C. NASA National Aeronautics and Space Administration Ames Research Center ' Moffett Field, California 94035 PREFACE The material contained in Volume I of this document is an overview of the Workshop deliberations and findings. The general scientific and technical basis that underlies the High-Priority Program outlined in that Volume is presented in Chapter 3. We felt that many readers of these proceedings would have no desire to plumb the more detailed considerations that were developed by the Workshop members and their collaborators in support of the general discussion given in Chapter 3. However, recognizing that some readers may wish to examine these details, and that it would be useful to have these wide-ranging consid- erations localized in a single document, we provide in this volume ten position papers concerning key elements to the Workshop study. These papers are referred to in Volume I as PI, P2, etc. We extend our thanks to the authors for their efforts. David C. Black William E. Brunk Ames Research Center NASA Headquarters preceding page blank] iii TABLE OF CONTENTS Page Preface iii Paper 1 - Using Small Aperture Interferometry to Detect Planets in Nearby Binary Star Systems - Douglas G. Currie, Harold A. McAlister, Timothy J. Schneeberger, and Simon P. Worden ... 1 Paper 2 - Limit Posed for Astrometry by Earth's Atmosphere - C. KenKnight 55 Paper 3 - A Proposed Ground-Based Narrow Field Astrometric System - Pierre Connes 61 Paper 4 - On the Astrometric Detection of Neighboring Planetary Systems, II - George Gatewood, Lee Breakiron, Ronald Goebel, Steven Kipp, Jane Russell, and John Stein 77 Paper 5 - Detection of Extra Solar Planets Using Optical Amplitude Interferometry - Douglas G. Currie 119 Paper 6 - Optical Interferometers in Astrometry - Michael Shao .... 127 Paper 7 - Precision Stellar Catalogs and the Role of Anomalous Refraction - Douglas G. Currie 143 Paper 8 - The University of Arizona Radial Velocity Spectrometer - K. Serkowski, J. E. Frecker, W. D. Heacox, and E. H. Roland 175 Paper 9 - A Proposed System for Spectroscopic Detection of Dark Companions - Pierre Connes 197 Paper 10 - Sites for Future Dedicated Telescopes - M. F. Walker .... 239 Preceding page blank PAPER 1 USING SMALL APERTURE INTERFEROMETRY TO DETECT PLANETS IN NEARBY BINARY STAR SYSTEMS Douglas G. Currie Dept. of Physics and Astronomy The University of Maryland, College Park, MD 20742 Harold A. McAlister Dept. of Physics Georgia State University, University Plaza, Atlanta, GA 30303 Timothy'J. Schneeberger and Simon P. Worden Air Force Geophysics Laboratory Sacramento Peak Observatory, Sunspot, NM 88349 ABSTRACT If suitably accurate binary star orbits can be observed, the effects of planets in the binary star system may be detectable in the reflex motion of the component binary stars. We show that interferometric measurements of binary star systems will provide this information. We discuss the effects of the atmosphere on degrading images and how interferometry will remove these effects to provide very accurate binary star positions relative to the other components in the binary system. Two systems, amplitude interferometry and speckle interferometry, can accomplish this using existing telescopes and techniques. With these methods, mearly accuracies of 2 x 10"^ arc second are possible for binaries of 1 arc second separation and 10~4 arc second for a 5 arc second binary. These accuracies are more than enough to detect planets in orbits like Jupiter's out to over 20 pc. There are 188 observable systems within 20 pc, in most of which it is possible to have stable planetary orbits similar to solar system orbits. With advanced data recording systems it is possible to observe binary systems where the components are as faint as +16 stellar magnitudes. A dedicated 2-meter interferometric telescope to monitor binary stars could be built for about 1.4 million dollars. I. INTRODUCTION . ' Lowmassand non-luminous companions of nearby stars may be detected in several ways. Among the most promising methods are indirect methods; that is detecting the effects of an invisible object on its visible companion. Spectroscopic methods may be used to observe radial velocity fluctuations in the visible star caused by the orbital reflex motion relative to the invisible companion. Astrometric detection involves obser.v-i.ng—the-po.s-i-t-iona-l—per-tur-ba-t-ion-caused-by—the-orb-i-t—o-f—the-unseen— object. Astrometry therefore requires establishing the position of the center of light in a stellar image and referencing this center to a fixed frame. Astrometry is limited by the'ability to establish the center of a star image and uncertainties in the reference frame. Star images, perturbed by seeing, are roughly gaussian. The accuracy for finding the center of the gaussian is obviously dependent on the stability of the gaussian profile. Long exposures are therefore used to: 1) collect enough photons to accur- ately define the center of each star image and 2) to average out seeing for image motion. The reference frame of these measurements may in principle be established by the centers of three or more other star images. Since the proper motions of these stars may influence the coordinate frame, the reference stars are chosen to be distant background stars. The Earth's atmosphere can also distort the reference frame as a function of atmos- pheric conditions and colors of the reference stars. These uncertainties may be reduced by using a relatively large number of reference stars in conjunction with sophisticated mathematical error analysis schemes. In spite of such difficulties conventional astrometry may now reach positional accuracies of ± ".05 for a single exposure, this may be improved to better than ± ".001 (Gatewood, 1976) for the results of one year's observation. Astrometric accuracy could be improved by getting smaller star images. The problem of finding a star image center is clearly easier the smaller the image is. If images were improved to the diffraction limit the increase is substantial. The task of finding the center of a 2 meter telescope diffraction limited spot of ".05 may be done with much higher precision than finding the center of a 1 arc-second seeing disk with the same number of photons.
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