FY1995 Q1 Oct-Dec NO

NATIONAL OPTICAL ASTRONOMY OBSERVATORIES NATIONAL OPTICAL ASTRONOMY OBSERVATORIES QUARTERLY REPORT OCTOBER - DECEMBER 1994 March 6, 1995 TABLE OF CONTENTS I. INTRODUCTION 1 II. SCIENTIFIC HIGHLIGHTS 1 A. Cerro Tololo Inter-American Observatory 1 1. CN and CH Abundance Variations in Globular Cluster Turnoff Stars and Implications for Stellar Evolution and Star Formation 1 2. Detection ofLens Candidates for the Double Quasar Q2345+007 2 3. The Lithium Abundance in M67 and Implications for Stellar Evolution and Cosmology 2 B. Kitt Peak National Observatory 3 1. Color Evolution of Galaxies 3 2. Kinematics ofBrightest Cluster Galaxies 4 3. Evolution ofthe Infrared Spectrum of an ONeMgNova 5 C. National Solar Observatory 6 1. High Temperature Coronal Regions Follow Solar Ring Current 6 2. Scattering ofP-Modes by Localized Inhomogeneities 7 3. Detection of Intrinsically Weak Solar Disk Magnetism 8 III. US GEMINI PROGRAM 9 IV. PERSONNEL AND BUDGET STATISTICS, NOAO 10 A. Visiting Scientists 10 B. Hired 10 C. Completed Employment 10 D. Changed Status 10 E. Gemini 8-m Telescopes Project 11 F. Chilean Economic Statistics 11 G. NSF Foreign Travel Fund 11 Appendices Appendix A: Telescope Usage Statistics Appendix B: Observational Programs Appendix C: Safety Report I. INTRODUCTION This document covers scientific highlights and personnel changes for the period 1 October - 31 December 1994. Highlights emphasize concluded projects rather than work in progress. The NOAO Newsletter Number 41 (March 1995) contains information on major projects, new instrumentation, and operations. The appendices to this report summarize telescope usage statistics and observational programs. H. SCIENTIFIC HIGHLIGHTS A. Cerro Tololo Inter-American Observatory 1. CN and CH Abundance Variations in Globular Cluster Turnoff Stars and Implications for Stellar Evolution and Star Formation Globular clusters are typically characterized by a single abundance of heavy metals: the fraction of heavy elements compared to hydrogen is constant from star to star. This suggests that the cluster formation was rapid, occurring in less than the characteristic time for heavy metal enrichment by Type II supernovae. (In fact, the energetics of these supernovae may have been responsible for clearing the gas from the early clusters, thus ending the star formation process in these systems.) It has long been known, however, that the abundances of light elements, such as carbon (C) and nitrogen (N), vary substantially from star to star within a cluster. These results are based on observations of the bright red giant stars in these clusters. Two scenarios have been put forward to explain these variations. The first involves deep convection, in which material processed by the nuclear reactions near the core of a star is dredged up to the star's surface; the activity of this process varies from star to star, resulting in the light-element abundance variations in stars' spectra. The second possible explanation invokes a "primordial" cause, such as enrichment of the intra-cluster gas and later-forming stars by the stellar winds of the earliest-formed, high-mass stars. Enrichment would have occurred before a cluster was swept clean of gas by supernova detonations. Aluminum (Al) and sodium (Na) abundances also are observed to vary from star to star in some clusters. This was taken as strong evidence for a primordial cause until Langer et al. (1993) showed that nuclear reactions involving Al and Na can take place in the hydrogen-burning shells of some red giant stars. Thus observations of less-evolved stars are required to determine which of the two processes are responsible for the observed C and N variations. During the 1980's, several studies were made of the CN and CH features of main sequence turnoff (MSTO) stars in the nearby globular cluster 47 Tuc. These studies employedsingle-slit spectrographs, however, so the numbers of stars in the samples were small. The studies showed that CN and CH variations do appear at the MSTO, but did not reveal whether the proportions of CN-strong and CN-weak stars mimic those seen among the red giants. M.M. Briley (U. of Texas, Austin), J.E. Hesser (Dominion Astrophys. Obs.), R.A. Bell (U. of Maryland), M. Bolte, and G.H. Smith (UC Santa Cruz) used the Argus multi-fiber spectrograph at the CTIO 4-m telescope to observe 24 stars near the MSTO in 47 Tuc. The work is published in the December, 1994, issue of the Astronomical Journal. The observers obtained spectral indices for the CN feature at 3839 A and for the CH feature at 4300 A. They found a broad range in CN and CH strengths at a given stellar temperature, thus confirming previous studies of MSTO stars. Bycomparing their observed indices with those derived from model atmospheres, they determined that the observed range in CN strengths was larger than could be produced by dredge-up of processed material with C > N, and that a large fraction of the atmosphere must have undergone O > N cycling as well. The range of observed CH strengths also mimics that seen in the red giants, and the dwarf stars show a CN-CH anti-correlation, as do the giants. The observers therefore argue that at least some component of the abundance variations on the giant branch cannot be explained by processes occurring during the giant branch evolutionary phase. They were able to rule out several scenarios for explaining the observed variations: surface accretion of N-rich material ejected from higher-mass cluster members in the past, mass transfer from other more-massive cluster stars during stellar interactions, and mixing via meridional circulation in the stellar interior. They conclude that the abundance variations are most easily explained as having existed from near the time of cluster formation. Perhaps gas enhanced in N and depleted in C was expelled from more- massive stars into the interstellar medium, and then condensed into new stars before the cluster gas was swept out by the first supernovae. 2. Detection of Lens Candidates for the Double Quasar Q2345+007 The object called Q2345+007 AB is actually a pair of quasars that appear to lie about 7" apart on the sky. The two components (A and B) have very similar spectra and redshifts (z = 2.15), raising the possibility that the pair is part of a gravitationally lensed system. Such a system would consist of a single quasar that appears double (or multiple) because an object between Earth and the quasar causes the light from the quasar to be bent. Deep searches have failed to detect the object responsible for the lensing of Q2345+007, however. If the system is not part of a gravitational lens, then the presence of two physically associated quasars at high redshift may indicate that clustering was occurring at this epoch. P. Fischer, J.A. Tyson (Bell Labs), G.M. Bernstein (U. of Arizona), and P. Guhathakurta (STScI) combined images from the CTIO 4-m Prime Focus CCD with images from other telescopes to produce a B-band image of over 13 hours integration time, and an R-band image of nearly 9 hours integration time. They used point-spread- function fitting routines to subtract the light of the quasar pair, and found a faint galaxy (B = 25 mag) about 1.5 arcsec from the B image, nearly on a line between the A and B images. They also detected a large number of faint galaxies scattered over the rest of the image. There were several enhancements in the surface density distribution of these galaxies, one of which lay near the quasar pair. The authors suspect that the latter represents a cluster of galaxies, perhaps at z = 1.5, the redshift at which absorption-line systems are seen in the spectra of the quasars. Assuming that Q2345+007 is a lensing system, Fischer et al. constructed lensing models involving the faint galaxy near component B and the suspected cluster. Though the solution was not uniquely determined, they found several combinations of parameters which reproduced the positions and relative brightnesses of the two quasar components. Thus they suggest that Q2345+007 is an example of a gravitationally lensed system. They further suggest that the slight color difference between components A and B (0.13 mag; a lensing event should be achromatic) might be due to differential reddening along the lines of sight, or to variability of the quasar compounded by the timedelay along the two different light paths. The authors point out that presence of a large cluster (the lens models indicate a mass of 1013 solar masses) at z = 1.5 is less likely in dark matter (Q. = 1) models of the Universe than in open (£2 = 0.2) models. The work is published in the August 20, 1994, issue of the Astrophysical Journal Letters. 3. The Lithium Abundance in M67 and Implications for Stellar Evolution and Cosmology An accurate determination of the primordial abundance of lithium (Li) places important constraints on models of Big Bang nucleosynthesis and on the baryon density of the Universe. Determinations from meteorites suggest A(Li) = 3.31 (on a logarithmic scale where A(hydrogen) = 12), yet observations in stars indicate the primordial value may be lower. Li can be produced or depleted in a variety of ways. In particular, if surface convection in a star is deep enough, Li will be mixed down to a layer where it is burned, and the surface abundance of Li will appear low in that star. Studies of star clusters of different age show that Li is conserved in a narrow range of effective temperatures, thus forming the "Li peak." The Li abundance in stars within the peak slowly drops with age: A(Li) = 3.1 in the Pleiades (80 Myr), 2.9 in the Hyades (700 Myr), and 2.5 in M67 (5 Gyr).

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