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National Optical Astronomy Observatories NATIONAL OPTICAL ASTRONOMY OBSERVATORIES NATIONAL OPTICAL ASTRONOMY OBSERVATORIES QUARTERLY REPORT APRIL-JUNE 1993 August 15,1993 TABLE OF CONTENTS I. INTRODUCTION 1 II. SCIENTIFIC HIGHLIGHTS 1 A. Cerro Tololo Inter-American Observatory 1 1. Halo Masses of Spiral Galaxies 1 2. Detection of [Fe II] Emission in the Galactic Center 2 3. Southern Spectrophotometry Standards 2 B. Kitt Peak National Observatory 3 1. Primordial Lithium in Very Old, Very Metal Poor Stars 3 2. NGC 6611: A New Star Cluster Caught in the Act of Formation 3 3. Dusty Emission Filaments in M87: Probing the History of the Intracluster Medium ... 4 C. National Solar Observatory 5 1. Solar Oscillations and Atmospheric Structures 5 2. Flare-like Phenomena in High Coronal Loops 6 3. Research in Local Helioseismology 6 III. PERSONNEL AND BUDGET STATISTICS, NOAO 7 A. Visiting Scientists 7 B. New Hires 7 C. Change in Status 8 D. Terminations 8 E. Summer Research Assistants 8 F. Gemini 8-m Telescopes Project 8 G. Chilean Economic Statistics 9 H. NSF Foreign Travel Fund 9 Appendices Appendix A: Telescope Usage Statistics Appendix B: Observational Programs I. INTRODUCTION This document covers scientific highlights and personnel changes for the period 1 April - 30 June 1993. Highlights emphasize concluded projects rather than work in progress. The NOAO Newsletter No. 35 (September 1993) contains information on major projects, new instrumentation, and operations. The appendices to this report summarize telescope usage statistics and observational programs. II. SCIENTIFIC HIGHLIGHTS A. Cerro Tololo Inter-American Observatory 1. Halo Masses of Spiral Galaxies Galaxy formation is an essential test of any cosmological theory. Despite many efforts to investigate the subject over the past decade, it remains very poorly understood. The cosmological theory that has received the most attention in the last several years is the cold dark matter (CDM) model, which assumes that most of the mass in the Universe is made of nonluminous matter. Great support for this assumption comes from the study of galactic rotation curves, which indicate that spiral galaxies are embedded in massive dark halos. Rotation curves, however, can probe the halo mass distribution only out to the maximum radius of luminous material (stars and ionized gas) in a galaxy. It is clear that the dark matter extends further out than this, but how far is unknown. A rough estimate that this distance was relatively small (-50 kpc) with a commensurably small mass (2 x 1011 solar masses) was made based upon analyses of ten satellite galaxies around the Milky Way; this estimate was corroborated by less extensive studies of several nearby spiral galaxies. Such truncated halos would be difficult to reconcile with the standard CDM model. The discovery of several new satellites of the Galaxy caused the mass estimate for the Milky Way to go up by a factor offive, contributing to mounting evidence from independent methods that the Galaxy is indeed surrounded by a massive halo. In order to extend greatly the radius and accuracy at which halos of galaxies like the Milky Way can be probed directly, D. Zaritsky (Steward Obs./Carnegie Inst, of Washington), R. Smith (U. of Wales, UK), C. Frenk (U. of Durham, UK) and S. White (U. of Cambridge, UK) surveyed satellite galaxies around a homogeneous set of spiral galaxies (1993, ApJ, 405, 464). They took most of their data with the CTIO 4-m telescope and the Argus multifiber spectrograph, with additional data taken with the Steward Observatory 2.3-m, AAT, WHT, and from published catalogues, in order to determine radial velocities of faint galaxies around isolated bright spirals. This enabled them to separate true satellites from coincidental pairings. Isolated spirals of similar absolute magnitude, morphology, and distance were used as targets for the study in order to avoid complicating effects from the gravity of neighboring large galaxies and to minimize variations in supposed halo structure with galaxy characteristics (which are suggested by rotation curve studies). Thirty-five new satellite galaxies were discovered, over half of them resulting from CTIO data. Treating the sample of satellites as an ensemble around a typical spiral galaxy, it is found that the more diffuse satellites tend to be at larger separations from their primaries, as though tidal effects extend only out to a certain distance. Their result indicates that halos of galaxies like the Milky Way characteristically extend out to -200 kpc, with total masses of 2 x 1012 solar masses, and is the first evidence that typical spiral galaxies have massive extended dark halos. 2. Detection of [Fe II] Emission in the Galactic Center The center of our own Galaxy provides a unique opportunity to study the dynamics and physical conditions of the region around a galactic nucleus in detail. However, due to the vast amounts of dust and gas between us and the Galactic center, optical radiation from the center cannot reach us. Studies at other wavelengths, particularly in the infrared and radio, have revealed a highly complex environment. Some studies have produced evidence for high velocity gas and stellar motions, supporting the idea that there may be a massive compact object, such as a black hole, buried in the center of our Galaxy. Other studies have found evidence of gas streamers, which may be indicative of shocks and other violent processes. While radio studies have measured electron temperatures from 7000 K to 40,000 K, no complementary electron density measurements have been available to complete the picture. Using the CTIO 1.5-m telescope and CTIO's infrared spectrometer (IRS), D. DePoy (now at Ohio State U.) obtained spectra of the Galactic center covering the emission of ionized iron, [Fe II] at 1.64 and 1.53 u.m, as well as the infrared emission from hydrogen, Bry, at 2.17 (im. [Fe II] emission has been widely used as a tracer of shocked gas. The ratio of the two [Fe II] lines can be used to derive electron densities. DePoy found emission from both of the [Fe II] lines (1992, ApJ, 398, 512). The measured ratio of [Fe II] 1.64 (im to Bry is similar to that seen in galaxies with active nuclei. This result is intriguing, as it may point to a similarity between the center of our supposedly "normal" Galaxy and the centers of active galaxies. With the detection of both [Fe II] lines, DePoy was able to derive a density of > 10 cm"3, a density much greater than that of 10 to 100 cm"3 found in the disk of our galaxy. DePoy found that the source of the [Fe II] emission could be either shock excitation or photoionization by nonthermal radiation, such as that produced by accretion onto compact objects. Observation of additional lines of [Fe II] may provide information to clarify this ambiguity and give additional information about the centers of active galaxies, where we cannot see the details we can see in the center of our own Galaxy. 3. Southern Spectrophotometric Standards Standard stars with accurate energy fluxes are essential for the absolute determination of fluxes, temperatures, luminosities and surface gravities of celestial objects. The primary (defining) standard for calibrations is the bright star Vega in the northern hemisphere. Several observers have transferred the flux calibration of Vega to a set of secondary spectrophotometric standards, most of which are bright stars in the northern hemisphere. These bright stars are generally too bright for modern detectors on large telescopes, so a tertiary set of standard stars has been in wide use for the past decade. The Stone-Baldwin spectrophotometric standards, measured at CTIO in the early 1980s, have been the standards of choice in the southern hemisphere. Recent advances in detector technology (charge coupled devices or CCDs) have made more accurate calibrations possible. In addition, an updated fundamental calibration of Vega was published by Hayes in 1985. For these reasons, CTIO staff members M. Hamuy, A. Walker, N. Suntzeff, P. Gigoux, S. Heathcote, and M. Phillips (1992, PASP, 104, 533 for first results) have been working for the past six years on a revision of the calibration of the Stone-Baldwin spectrophotometric standards. These new measurements cover almost all optical wavelengths observable from the ground (3300 to 10,000 A) at moderate (50 A) steps. The calibrations are accurate to better than 1%, allowing accurate spectrophotometry of program objects for southern hemisphere observers. Ten of the bright secondary standards have also been recalibrated based on the newfundamental calibrationand sampledat sufficiently small regular intervals (16 A) to be useful for high-dispersion spectroscopy. Both ofthese sets ofstandards will be of great use for a wide variety of spectroscopic observing programs done from the southern hemisphere. B. Kitt Peak National Observatory 1. Primordial Lithium in Very Old, Very Metal Poor Stars The abundances of the light elements D, 3He, 4He, Li, Be, and B provide one of the few direct, observational tests of cosmological models. The amounts of these elements produced in the Big Bang not only test the consistency of the standard model for primordial nucleosynthesis, but also may constrain the cosmic baryon to photon ratio, the mass density of baryons in the Universe, and the number of lepton families permitted in particle physics. The determination of the abundances of these species is, however, a difficult observational problem. Many of the species (D, Li, Be, and B) are easily destroyed in the hot, dense environment of a stellar interior; other species (3He and 4He) can be observed only in hot stars. All of these species (except D) may also be produced through spallation or fusion reactions in the interstellar medium, in normal stars undergoing main sequence hydrogen burning or double shell burning, or in supemovae.
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