NATIONAL OPTICAL ASTRONOMY OBSERVATORIES NATIONAL OPTICAL ASTRONOMY OBSERVATORIES QUARTERLY REPORT JULY-SEPTEMBER 1995 July 16, 1996 TABLE OF CONTENTS I. INTRODUCTION II. SCIENTIFIC HIGHLIGHTS. A. Cerro Tololo Inter-American Observatory 1. The Southern Nearby Star Campaign—Identifying the Nearest and Least Luminous Stars 2. The Transparency of Galaxy Disks 3. Absorption in the Quasar Pair Tol 1037-2704/Tol 1038-2712: A Supercluster at z = 2? 2 B. Kitt Peak National Observatory 2 1. The Smallest Galaxies 2 2. Disk Accretion and Mass Loss from Young Stars 3 3. Massive Stars in Milky Way Clusters and Associations 4 C. National Solar Observatory 5 1. Imaging Coronal Emission Lines 5 2. The Infrared Coronal Spectrum 6 3. Local Helioseismology 7 m. PERSONNEL AND BUDGET STATISTICS, NOAO 8 A. Visiting Scientists 8 B. Hired 8 C. Completed Employment 8 D. Changed Status 8 E. 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 July - 30 September 1995. Highlights emphasize concluded projects rather than work in progress. The December 1995 NOAO Newsletter Number 44 contains information on major projects, new instrumentation, and operations. The appendices to this report summarizetelescope usage statisticsand observational programs. II. SCIENTIFIC HIGHLIGHTS A. Cerro Tololo Inter-American Observatory 1. The Southern Nearby Star Campaign—Identifying the Nearest and Least Luminous Stars M dwarfs are the dominant population of stars in the solar neighborhood, accounting for at least 70% of all stars and comprising nearly half of the Galaxy's total stellar mass, yet many of the closest M dwarfs to the sun still remain unrecognized due to their very low luminosity. This is especially true in the southern hemisphere where few follow-up observations of candidates have been done. T. Henry (STScI), J.D. Kirkpatrick (JPL/TPAC) and P. Ianna (U. of Virginia) are involved in an effort to discover new stars within 10 pc of the sun and to identify the reddest dwarfs known. At CTIO they are conducting a systematic campaign to discover and characterize nearby stars and ultra-cool dwarfs through a combination of infrared photometry using the 1.5-m with infrared imager and red spectroscopy using the 4-m with RC spectrograph. In August 1995, they verified 13 additional stars to be within 10 pc, increasing the census of nearby stars by 4% in a single observing run. The nearest of these is a previously unnoticed M dwarf at a distance of 3.7 pc, which ranks it 20th among the nearest star systems. Henry, Kirkpatrick and Ianna have also classified eight more dwarfs to have spectral types similar to or even cooler than VB 8, which has a type of M7 V. This boosts the sample of these feebly shining dwarfs by 40%. It is especially important to build this sample of coolest dwarfs because there is some evidence that these ultra-cool dwarfs may not even be stars, but a young population of brown dwarfs. The more examples we have to study, the better we will understand their nature. Ianna has a successful parallax program continuing at Mt. Stromlo and Siding Spring Observatories in Australia, and will be observing all of these new targets to determine distances. These exciting results are a fundamental contribution to stellar astronomy. As the nearby and ultra-cool samples become more robust, it will be possible to determine the luminosity and mass functions for the Sun's neighbors to unprecedented accuracy, and evaluate the character of the least luminous stars known. 2. The Transparency of Galaxy Disks How is dust distributed within the disks of spiral galaxies and how much internal extinction results from this dust? In addition to an improved understanding of galaxy dynamics and evolution, the answers to these questions have implications for diverse areas of extragalactic astronomy that range from the evolution of QSOs (through the obscuration of high redshift QSOs by dust in intervening spiral galaxies), to large scale bulk motions and the value of the Hubble constant (through the proper choice for the inclination corrections to apply when using the Tully-Fisher method to measure distances). In a program of CCD imaging using the CTIO 1.5-m (coupled with observations of northern objects at Lowell Obs. and KPNO) W. Keel, R.E. White HI and C. Conselice (U. Alabama) have produced the most direct measurements of where and how much light is absorbed by dust in spirals. For most spirals, they find that absorption by dust is strongly concentrated in spiral arms and similar structures such as resonance rings, with much less absorption between the arms. This finding contradicts conclusions based on the statistics of integrated galaxy properties, and these new observations also show how these previous conclusions erred — the assumption of axisymmetric galaxies is far too crude. 3. Absorption in the Quasar Pair Tol 1037-2704/ToI 1038-2712: A Supercluster at z = 2? The population of narrow absorption lines due to heavy elements in the spectra of high redshift quasars provides a powerful method for sampling the distribution of matter in the early universe. There exists a substantial body of evidence associating these metal lines with intervening galaxies. Thus, observations of the spatial distribution of metal line absorption systems have the potential to reveal when and how clusters of galaxies formed. Because of the difficulty of locating and observing high redshift galaxies directly, quasar absorption lines are, at present, the best technique for studying such processes. N. Dinshaw and C. Impey (U. of Arizona) have analyzed high resolution (30 km/s) spectra, obtained with the CTIO 4-m and echelle spectrograph, of the wide quasar pair Tol 1037-2704 and Tol 1038-2712 as well as two neighboring quasars. These quasars exhibit a large number of apparently correlated CTV absorption systems over a narrow redshift range 1.48 < z < 2.15 that are thought to be produced by an intervening supercluster. The two-point velocity correlation function of CIV absorbers distributed among the four lines of sight shows significant clustering signal on comoving scales out to -30 Mpc at redshift z ~ 2. The spatial correlation function shows a marginally significant peak on scales of < 18 Mpc. The clustering amplitude on these scales is larger than that predicted by current theories of the formation of large scale structure. B. Kitt Peak National Observatory 1. The Smallest Galaxies Understanding the process of galaxy formation remains elusive. A fundamental parameter is the ratio of the number of small galaxies to the number of massive giant galaxies. That ratio could be a function of environment and evolve with time through encounters. There may also be differences between low- density groups and high-density clusters. Galaxies with very low luminosities, such as dwarf ellipticals, are relatively easy to study within the Local Group (although difficult to identify near the Galactic plane). Faint galaxy surveys in the field tend to be dominated by distant giant galaxies rather than nearby dwarfs. Dwarf galaxies are very faint even in nearby clusters, and require extremely deep imaging over substantial fields of view to establish the population characteristics. Very deep images of the core of the Coma Cluster of galaxies were recently analyzed to produce the distribution of luminosities of the faintest identifiable galaxies. The team consisted of G.M. Bernstein (U. of Michigan), R.C. Nichol (U. of Chicago), J.A. Tyson (AT&T Bell Labs), M.P. Ulmer (Northwestern U.), and D. Wittman (U. of Arizona). They report in the October 1995, Astronomical Journal on CCD images from the PrimeFocus of the Mayall 4-meter Telescope, providing 135 minutes of exposure on the cluster core, and images of five control fields taken to similar depth. Bernstein and colleagues went to extraordinary means to flatten the CCD response, remove the extended profiles of the 23 brightest galaxies in the image, account for the real background gradient from the cD galaxy NGC 4874, and match the resolution and noise characteristics of the control fields to that of the target field to remove the field galaxy background. They employed the image analyzing software package, FOCAS, to identify and measure all the faintest galaxies in the image. They derived accurate galaxy counts to R = 25.5 mag, or absolute R magnitude -9.4. Bernstein and collaborators determined the luminosity distribution of galaxies in the Coma core by parameterizing the relative differential number of objects per unit luminosity as a power-law function of luminosity. They found that the value of the power-law index was -1.42 ± 0.05 for galaxies with absolute magnitudes between -19.4 and -11.4, approximately the range from the Magellanic Clouds to the brightest globular clusters. This power-law index is in good agreement with that found for the faint galaxies in the Virgo Cluster, but is much more heavily weighted toward the faintest objects than the values determined for the field, which are typically in the range -1.0 to -1.2. At fainter absolute magnitudes, the relative number of objects rises very steeply. Since they are unresolved in ground-based seeing and have a distribution shape consistent with that of the M 87 globular clusters shifted to the distance of the Coma Cluster, the faintest population is probably dominated by globular clusters. The very faint galaxies in Coma are concentrated toward the central cD galaxy NGC 4874, with a radial power-law distribution similar to that of the diffuse light and the globular clusters. Since the survey is sensitive to isophotes as faint as R = 27.6 mag / sq arcsec, Bernstein et al.