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Optical Astronomy Observatories National Optical Astronomy Observatories National Optical Astronomy Observatories Quarterly Report July - September 1989 TABLE OF CONTENTS I. INTRODUCTION j II. SCIENTIFIC HIGHLIGHTS 2 A. Ages of Globular Ousters 2 B. Disk Galaxies in Formation 2 C. Differential Rotation Observed in the Sun as a Star 3 D. Intensity Oscillations in the Far-Infrared 4 E. Supergranular Convection 4 F. Brown Dwarfs: A Detection of Stellar Objects of Subcritical Mass? 5 G. Cooling Flows in Clusters of Galaxies: Where Are All the Stars? 5 III. PERSONNEL 7 A. Visiting Scientists 7 B. New Appointees 7 C. Terminations 7 D. Change of Status ' g E. Summer Research Assistants 8 IV. INSTRUMENTATION, NEW PROJECTS, AND OBSERVATORY ACTIVITIES .... 9 A. Future Telescope Technology Program (FTT) 9 B. Global Oscillation Network Group (GONG) 9 C. Instrumentation Projects ]\ D. Observatory Activities 16 V. PROGRAM SUPPORT !9 A. Director's Office 19 B. Central Administrative Services 20 C. Central Computer Services 20 D. Central Facilities Operations 20 E. Engineering and Technical Services 21 F. Publications and Information Resources 21 Appendices Appendix A: Telescope Usage Statistics Appendix B: Observational Programs I. INTRODUCTION This quarterly report covers scientific highlights for the period of July - September 1989, as well as personnel changes for the period. These highlights emphasize concluded projects rather than work in progress. The report also discusses new technology for telescopes and instrumentation, GONG, instrumentation projects, and observatory activities. The Engineering and Technical Services division now submits reports for the instrumentation projects, with contributions from program scientists, if necessary. The Associate Directors for CTIO and NSO continue to provide the information of efforts at La Serena/Cerro Tololo and Sacramento Peak. Activities of the NOAO units are included, and the appendices list telescope usage statistics and observational programs. II. SCIENTIFIC HIGHLIGHTS A. Ages of Globular Clusters. Charged coupled device (CCD) photometric observations of globular clusters yield the most accurate determination now possible of the ages of galactic globular clusters. These clusters are the oldest easily recognized components of the halo of the Galaxy. Reliable ages of the globular clusters arc of fundamental cosmological importance. The age of the oldest cluster sets a lower limit to the age of the Universe and age differences among the clusters in the galactic halo provide information about the time interval taken by the Galaxy as it, presumably, collapsed from a protogalactic gas mass possessed of angular momentum into the present disk-like galaxy with its large spheroidal halo characterized by the oldest known objects. Two recent studies largely based on observations made at CTIO have provided the most reliable set of ages of globular clusters yet available. The first of these studies was by a group of astronomers headed by P. Stetson of Canada's Dominion Astrophysical Obs. (DAO). Stetson's group relied on observations made with the Canada-France-Hawaii and CTIO 4-m telescopes. Its aim was to determine accurately the age and distance of the cluster Palomar 12, a remote object distant some 15 kiloparsecs from the galactic plane. Surprisingly, this cluster, whose stars are relatively rich in metals, was found to be younger in age than prototype clusters with similar metallicity located in the inner galactic halo. This result suggests that a significant age spread exists among the halo globular clusters. Previous studies, based on less accurate photographic studies, had led to the belief that the halo clusters were practically identical in age. In the other study, M. Bolte (DAO), selected three halo globular clusters, namely NGC 288, NGC 362, and NGC 1261, which have similar well-studied low metal abundances and were presumably formed, according to conventional wisdom, during the early phases of the galactic collapse. The three clusters selected by Bolte are sufficiently close in the sky for observations during the same night with the same instruments and the same calibration standard stars. CTIO's 4-m and 1.5-m telescopes and CCD photometers were used. Reduction procedures were identical for all three clusters. By these precautions observational errors that might obscure the effects of age and distance in the photometric properties of the clusters were minimized. Bolte found an age spread of three billion years among the clusters. Combined with the previous result by Stetson and collaborators, this means that the classic fast collapse model for the formation of the galactic halo is not supported by observational evidence. The 16 billion year age found for NGC 288, the oldest of the three clusters studied by Bolte, appears now to be a reliable lower limit for the age of the Universe. B. Disk Galaxies in Formation. The relationships between the kinematics and chemical composition of the Galaxy's stellar populations are generally regarded as evidence that the Galaxy was formed when a rotating, spherical, gravity-bound, neutral hydrogen-rich gas mass collapsed along its rotation axis. The kinetic energy of the collapse was presumably lost by radiation, and successive stellar generations increased the heavy elements content of the interstellar gas by thermonuclear processing. A significant advance in understanding the Galaxy's formation process would be gained if disk galaxies, similar to our own, could be observed during their early formation stages. This would require observing such galaxies at distances equivalent to look-back times of 5 x 1010 years or longer. Unfortunately, at the corresponding redshifts, namely z > 2, we can only at present identify by direct observation the very luminous giant elliptical galaxies. Nevertheless, a possibility exists of determining the properties of fainter primitive disk galaxies by studying the absorption features they may produce in the light of luminous background quasars. The spectroscopic signatures of such primitive disk galaxies must, however, be differentiated from the numerous absorption lines appearing on the blue side of the Lyman a emission feature shown by distant quasars. Collectively these absorption lines form the so-called "Lyman forest", and most of them are produced by intervening low-column density, highly-ionized gas clouds showing characteristic Doppler-broadened profiles. Some distant quasars, however, show absorption Lyman a lines with a different profile, namely the so-called "damping" profile produced by natural spectral line broadening in relatively cool quiescent gases. A plausible interpretation of such damped absorption lines is that they are produced in foreground disk galaxies. The spectra of very distant quasars showing damped Lyman a lines should therefore be studied in the hope of obtaining direct information about the early history of the galactic disk. In the past several such studies have been attempted with controversial results. K.M. Lanzetta, D.A. Turnshek, and A.M. Wolfe of the U. of Pittsburgh have used the CTIO 4-m and the Smithsonian-Arizona Multiple-Mirror telescopes to study the spectrum of the z = 2.92 quasar Q 1337+113, which shows at z = 2.796 a damped Lyman a absorption feature and at the same redshift a set of unblended low-ionization absorption lines of Fe, Si, C, O, and Al. These features identify Q 1337+113 as a favorable source of information about primitive galactic disks. The U. of Pittsburgh team aimed its study at determining for the z = 2.796 absorber a lower limit of the molecular hydrogen (Hj) abundance, the possible detection of extinction by interstellar dust, and the relative abundance of the elements producing the low-ionization spectral lines. If abundant, H2 would suggest on-going star-formation, while the presence of dust would indicate existence of stars. Relative to atomic hydrogen, the H2 abundance in the Galaxy's massive molecular gas clouds is larger than 5,000 times the abundance found in the z = 2.796 absorber. No evidence of dust extinction was found, although the observations admit an upper limit for the projected dust density of 1/2 the galactic value. The relative abundance ratios suggested by the low-ionization lines appear to be consistent with solar values, but the column density of neutral carbon was found to be at least 200 times less than in a typical galactic gas cloud, a result consistent with a lack of dust extinction in the z = 2.796 absorber. The study was extended by the same investigators and several collaborators to six other large- redshift quasars showing damped Lyman a absorption lines. The same telescopes were again used. The most favorable cases among these other systems support the findings for the z = 2 796 absorber in the foreground of Q 1337+113. These studies have thus probably provided for the first time direct information about the properties of primitive galactic disks, and point the way to future more accurate studies. C. Differential Rotation Observed in the Sun as a Star. The National Solar Observatory/Sacramento Peak (NSO/SP) Calcium K-line data set, which spans the period from November 1976 through the present, has been analyzed by S. Keil (AFGL/NSO/SP) for both differential rotation and for the possibility of using it as a surrogate for much more expensive ultraviolet/extreme ultraviolet (UV/EUV) measurements from space. The data consists of full disk, integrated sunlight, measurements of the Calcium K-line profile from 3900 to 3950 A On observation days, this spectral region is scanned approximately 150 times in 5 mA steps using the Littrow spectrograph at the NSO/SP Evans Facility. These 150 scans are then averaged to form a daily mean. Coverage from 1976 through 1983 was sparse, with only a few measurements each month. These earlier measurements were reported in Astrophys. J. 276, p. 766, (1984). From 1984 to the present, coverage has been over 50% of the days. From the K-line profile, several parameters are deduced: the central intensity, the emission index, line asymmetries, and the position of the emission and absorption features.
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