NATIONAL OPTICAL ASTRONOMY OBSERVATORIES NATIONAL OPTICAL ASTRONOMY OBSERVATORIES Cerro Tololo Inter-American Observatory Kitt Peak National Observatory National Solar Observatory La Serena, Chile Tucson, Arizona 85726 Sunspot, New Mexico 88349 ANNUAL REPORT October 1995 - September 1996 October 31,1996 TABLE OF CONTENTS I. INTRODUCTION II. AURA BOARD III. SCIENTIFIC PROGRAM A. Cerro Tololo Inter-American Observatory (CTIO) 1. The Binary-Star Content of Globular Clusters 2. White Dwarfs and the Age of the Milky-Way Disk 2 3. A Census of the Outer Solar System 3 B. Kitt Peak National Observatory (KPNO) 3 1. Dynamical Processes in Giant H II Regions 3 2. Large-Scale Streaming in the Galactic Halo 4 3. Structure and Dynamics of the Coma Cluster of Galaxies 5 C. National Solar Observatory (NSO) 6 1. First Results from GONG 6 2. Acoustical Events as Source of the Global P-mode Energy 8 3. Chromospheric He I Observations: Looking for Solar Wind and Coronal Rain 8 IV. DIVISION OPERATIONS 9 A. Cerro Tololo Inter-American Observatory 9 1. CTIO Telescope Upgrades and Instrumentation 9 2. Facilities Operations 15 B. Kitt Peak National Observatory 17 1. New KPNO Programs in FY 1996 17 2. KPNO Observing Improvements 18 3. KPNO Instrumentation Improvements 19 C. National Solar Observatory 20 1. Kitt Peak 20 2. Sac Peak 23 D. US Gemini Program 25 E. NOAO Instrumentation Program 27 V. MAJOR PROJECTS 30 A. Global Oscillation Network Group 30 B. Precision Solar Photometric Telescope 32 C. SOLIS 32 D. CLEAR Feasibility Study 33 VI. CENTRAL COMPUTER SERVICES 34 Vn. SCIENTIFIC STAFF 38 A. CTIO Scientific Staff Changes 38 B. KPNO Scientific Staff Changes 38 C. NSO Scientific Staff Changes 39 VIII. DIRECTOR'S OFFICE 39 EX. NOAO STATISTICS 40 A. CTIO Statistics 40 B. KPNO Statistics 41 C. NSO Statistics 42 D. NOAO Tucson Headquarters Building Statistics 42 APPENDICES Appendix A NOAO Technical Reports List Appendix B CTIO Publications List Appendix C KPNO Publications List Appendix D NSO Publications List I. INTRODUCTION This report covers the period 1 October 1995 - 30 September 1996. The National Optical Astronomy Observatories (NOAO) are operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for the National Science Foundation (NSF). The four divisions of the NOAO are: the Cerro Tololo Inter-American Observatory (CTIO) in northern Chile; the Kitt Peak National Observatory (KPNO) near Tucson; the National Solar Observatory (NSO) with facilities on Kitt Peak and at Sacramento Peak, New Mexico; and the US Gemini Program (USGP) based in Tucson. NOAO observing and data reduction facilities are available to the entire astronomical community. The NOAO Home Page contains on-line information about NOAO services, including telescope schedules and instrument availability, and information abouthow to apply for telescope time. The NOAO Home Pagecan be accessed through the World Wide Web at http://www.noao.edu/. II. AURA BOARD The NOAO is an operating center managed by AURA, a private, non-profit corporation. There are twenty-eight AURA member institutions, including three international affiliates. The member institutional representatives elect a governing Board of Directors, consisting of thirteen directors (including the President, ex-officio). In addition to NOAO, AURA operates and manages the Space Telescope Science Institute under contract with NASA, and the international Gemini Project under cooperative agreement with the NSF. III. SCIENTIFIC PROGRAM The following paragraphs describe only a few of the many ongoing programs of research carried out at the National Optical Astronomy Observatories. The programs described here are representative of the important contributions to scientific research made by NOAO astronomers and NOAO facilities. A. Cerro Tololo Inter-American Observatory (CTIO) 1. The Binary-Star Content of Globular Clusters The fraction of binary stars is a basic parameter of any stellar population. The number and types of binary stars are potentially important indicators of the mechanisms by which the stars formed. For dense stellar systems such as globular clusters, the dynamical evolution of the system is intimately tied to the number and type of binary stars present. Perhaps the most dramatic consequence of a population of primordial binaries is their tendency to delay the onset of core collapse. While initial studies suggested that globular clusters were deficient in the fraction of binaries compared to field stars, a number of more recent results all conclude that the fraction of binaries in globular clusters is roughly comparable to that in the field population. While the current fraction of binaries in globular clusters seems now to be well established, the exact distribution of periods for globular-cluster binaries is still not well known; as we shall see, this could have a bearing on our conclusions concerning the primordial population of binaries. In two studies, Patrick Cote (DAO) and his collaborators address the question of binaries in globular clusters in very different regimes of orbital period. Using the Argus multi-object spectrograph on the Blanco 4-m telescope, Cote and Philippe Fischer (Michigan U.) have searched for main-sequence binaries with very short periods, between 2 days and 3 years, in the cluster M4. In a sample of 33 main-sequence stars, two show velocity differences of greater than 10 km/s in observations separated by 11 months. Including the efficiency for discovering binaries with different periods and orbital parameters, Cote and Fischer's result yields a binary fraction of 15% in M4. In a companion study, Cote, Carlton Pryor (Rutgers U.), Robert McClure, J.M. Fletcher and James Hesser (DAO) search for long-period binaries by combining observations of the velocities of red giants in the globular cluster M22 taken over a period of 22 years at Palomar, CFHT, MMT and CTIO. The complete data set, which consists of 333 repeat velocity measurements for 109 stars, does not contain a single star that shows a velocity difference greater than 7 km/s. These observations lead to a binary fraction of < 1% assuming circular orbits; a binary fraction of < 3% results if the assumption of circular orbits is relaxed. A possible explanation for the difference in the binary fraction between the short-period, close binaries in M4 and the long-period, wide binaries in M22 is that loosely bound, wide binaries are more easily disrupted by encounters with other stars than are tightly bound, short-period binaries. Thus, a primordial population of long-period binaries could be destroyed over the life of the cluster. 2. White Dwarfs and the Age of the Milky-Way Disk White dwarfs are the remnants of low-to-moderate-mass stars after they have completely exhausted their nuclear fuels; our Sun will eventually become a white dwarf in another five billion years. An important result which has come from surveys for faint white dwarfs in the vicinity of the Sun is the absence of low-luminosity, cool white dwarfs. With no internal energy sources, white dwarfs simply cool and grow fainter as they age. Thus the temperatures and luminosities of a white dwarf serve as a cosmic clock, recording the time which has passed since the white dwarf formed. The lack of white dwarfs below a certain critical luminosity indicates that insufficient time has elapsed for these oldest white dwarfs to cool beyond this limiting luminosity. Thus, the ages of the least luminous white dwarfs that can be found provide a lower limit for the age of the disk of the Galaxy. A necessary step in establishing the age of a white dwarf is to derive quantities such as the temperature, composition and surface gravity of the star from the available observations. Pierre Bergeron (U. of Montreal), Maria Teresa Ruiz (U. de Chile), and S.K. Leggett (U. of Hawaii) have recently completed an extensive study which used the colors and spectra from a large sample of cool white dwarfs to calibrate a state-of-the-art sequence of model atmospheres. The model atmospheres provide the transformation from observed quantities into physical quantities such as the temperature and surface gravity. Observations were made of 110 white dwarfs, primarily using the telescopes at CTIO. These observations included optical spectroscopy with the CTIO 4-m, infrared photometry with the CTIO 4-m and 1.5-m, and optical photometry with the CTIO 1.5-m and 0.9-m. The principal result of this work is a calibrated and verified set of model atmospheres that describe the observable properties of the coolest white dwarfs. These model atmospheres can be used to derive the temperatures, masses and luminosities for faint white dwarfs found in present and future surveys. When combined with models for how the temperature and luminosity of white dwarfs change with time as these stars cool, refinements to the model atmospheres should improve the accuracy with which the white dwarf luminosity function may be used to reconstruct the star formation history in the disk of the Galaxy. The oldest white dwarfs in the sample used to calibrate the model atmospheres have ages in the range of 6.5 to 10 billion years. Since this sample is not a complete sample of stars, these ages are strictly a lower limit to the age of the Galactic disk. 3. A Census of the Outer Solar System Much closer to home, the number and sizes of small, icy bodies in the outer solar system is still poorly known. It is only within the last twenty years that the first of the Centaurs, 100 km-sized objects with orbits between Saturn and Neptune, was found. And it has only been within the past few years that similar objects orbiting beyond Neptune, the Kuiper belt objects, have been discovered. In an effort to improve our knowledge of the contents of the solar system beyond the orbit of Saturn, David Jewitt (U.