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University of Texas McDonald Observatory and Department of Astronomy Austin, Texas 78712

This report covers the period 1 September 1994 31 August Academic 1995. Named Professors: Frank N. Bash ͑Frank N. Edmonds Regents Professor in Astronomy͒;Ge´rard H. de Vau- couleurs ͑Jane and Roland Blumberg Professor Emeritus in 1. ORGANIZATION, STAFF, AND ACTIVITIES Astronomy͒; David S. Evans ͑Jack S. Josey Centennial Pro- fessor Emeritus in Astronomy͒; Neal J. Evans II ͑Edward 1.1 Description of Facilities Randall, Jr. Centennial Professor͒, William H. Jefferys ͑Har- The astronomical components of the University of Texas lan J. Smith Centennial Professor in Astronomy͒; David L. at Austin are the Department of Astronomy, the Center for Lambert ͑Isabel McCutcheon Harte Centennial Chair in As- Advanced Studies in Astronomy, and McDonald Observatory tronomy͒; R. Edward Nather ͑Rex G. Baker, Jr. and Mc- at Mount Locke. Faculty, research, and administrative staff Donald Observatory Centennial Research Professor in As- offices of all components are located on the campus in Aus- tronomy͒; Edward L. Robinson ͑William B. Blakemore II tin. The Department of Astronomy operates a 23-cm refrac- Regents Professor in Astronomy͒; John M. Scalo ͑Jack S. tor and a 41-cm reflector on the Austin campus for instruc- Josey Centennial Professor in Astronomy͒; Gregory A. tional, test, and research purposes. Shields ͑Jane and Roland Blumberg Centennial Professor in McDonald Observatory is in West Texas, near Fort Davis, Astronomy͒; Steven Weinberg ͑Regents Professor and Jack on Mount Locke and Mount Fowlkes. The primary instru- S. Josey–Welch Foundation Chair in Science͒; and J. Craig ments are 2.7-m, 2.1-m, 91-cm, and 76-cm reflecting tele- Wheeler ͑Samuel T. and Fern Yanagisawa Regents Profes- scopes and a 76-cm telescope dedicated to laser ranging to sorship in Astronomy͒. the moon and artificial satellites. Professors: Michel Breger ͑adjunct͒, James N. Douglas, McDonald Observatory is also a partner in the Caltech Roman Smoluchowski ͑emeritus͒, Paul Shapiro, Chris Submillimeter Observatory on Mauna Kea, Hawaii. Sneden, Paul A. Vanden Bout ͑adjunct͒, Ethan Vishniac, Derek Wills, and Don Winget. Associate Professors: Harriet Dinerstein, Paul M. Har- 1.2 Administration vey, Dan Jaffe, John Lacy, and R. Robert Robbins,Jr.As- sistant Professors: Beverley Wills. William H. Jefferys is Chair of the Department of As- tronomy, with Ethan Vishniac as Assistant Chair. Frank N. Non-Academic Bash is the Director of McDonald Observatory and the Cen- ter for Advanced Studies in Astronomy, Thomas G. Barnes Senior Research Scientists: Thomas G. Barnes III, Robert III is Associate Director, Chris Sneden was Associate Direc- G. Tull, Laurence M. Trafton. tor for the Hobby-Eberly Telescope, and Phillip W. Kelton is Research Scientists: Edwin S. Barker, George F. Bene- Assistant Director. Mark Adams is the resident Superinten- dict, Anita L. Cochran, William D. Cochran, Artie P. dent. Hatzes, Paul D. Hemenway, Gary Hill, Daniel F. Lester, Bill Block was Chair of the McDonald Observatory and Frank Ray, Peter J. Shelus, Verne Smith, Jocelyn Tomkin, Department of Astronomy Board of Visitors, with George and Arthur L. Whipple. Christian Vice Chair and Lucy Alexander Secretary. Research Associates: Mark Cornell, Robert Duncan, Members of the Board of Visitors: Lucy Alexander, Mark Mary Kay Hemenway, Victor Krabbendam, Alexei Bivins, William Block, Malcolm Brachman, Wm. Terry Khokhlov, Larry Long, Hugo Martel, Alvin L. Mitchell, Bray, J.P. Bryan, Clifton Caldwell, George Christian, Jo- Phillip MacQueen,EdNelan, Darrell Story, and Er-Ho seph Cialone, Anne Dickson, Marshall Doke, George Fin- Zhang. ley, David Graeber, William Guest, Paul Hobby, Elizabeth Postdoctoral Research Associates and Other Visiting ´ ´ ´ Hutchinson, Katherine Johnson, Herbert Kelleher, Garland Staff: Eric Bakker, Beth Clark, Ramon GarcıaLopez, ´ Lasater, Thomas Link, Paul Meek, Arthur Miller, Bradford Guillermo Gonzalez, Christopher Johns-Krull, Inger Moody, Lillian Murray, Judy Newton, Pike Powers, Will- Jo”rgensen, Doug Kelly, Soon-Wook Kim, Jeremy King, iam Ratz, Carl Ryan, Marshall Steves, Robert Strauser, Chris Koresko,M.Kusunose, Alex Lazarian, Zong-Wei Li, ¨ Curtis Vaughan, David Weeks, Gene Wiggins, Francis Matt Richter, Judit Gyorgyey Ries, Yaron Sheffer, Keith L. Wright, and Samuel Yanagisawa. Thompson, and Lifan Wang.

1.4 Senior Research Support and Administration 1.3 Teaching and Research Personnel HET Project Manager:TomSebring. ͑In the lists that follow, asterisks denote Mount Locke resi- Special Assistant to the Director: Joyce C. Sampson ͑De- dents.͒ velopment͒. 638 ANNUAL REPORT

Associated member of another department: Raynor L. Anita Cochran was elected Vice Chair of the Division for Duncombe, Professor of Aerospace Engineering and Engi- Planetary Sciences of the AAS. neering Mechanics. Art Whipple served his fourth year as secretary of the Director of the McDonald Public Information Office: San- AAS Division on Dynamical Astronomy. Peter Shelus dra L. Barnes. served his 17th year as treasurer of the AAS Division on McDonald Supervisors: Gordon Wesley ͑mechanical en- Dynamical Astronomy. Judit Ries is a member of the Com- gineering͒, Edward Dutchover,Jr.*͑administrative support͒, mittee of the Division on Dynamical Astronomy. Earl Green* ͑observing support͒, George E. Grubb* ͑physi- Anita Cochran served on the National Research Coun- cal plant͒, Mark Cornell ͑computing systems͒, Phillip Mac- cil’s Task Group on the BMDO New Technology Orbital Queen ͑CCD Development͒, Alvin L. Mitchell ͑engineering Observatory. support͒, and Jerry R. Wiant* ͑MLRS͒. Craig Wheeler served on the NASA Long-Term Space Administrative Services Officer: Cecilio Martinez Astrophysics Review Panel, the NASA Hubble Fellows Se- lection Panel, and the NASA Astrophysics Advanced Mis- 1.5 Visitors and Affiliations sion Concepts Review Panel. William Cochran served on the NASA Origins of Solar Systems Program Management Dr. Rob Kennicutt, of the University of Arizona, visited Operations Working Group. Anita Cochran served on the in the fall as the Beatrice M. Tinsley Visiting Professor. He Solar System Exploration Subcommittee. gave a series of lectures on extragalactic astronomy. Bev Wills is a member of the STScI–NASA–ESA Space The Antoinette de Vaucouleurs Medal for this year was Telescope Users’ Committee. Art Whipple served on the So- awarded to Dr. Don Osterbrock, Lick Observatory. He gave lar System Panel of the Hubble Space Telescope Cycle 5 the medal lecture entitled ‘‘The Nature and Structure of Ac- Time Allocation Committee. tive Galactic Nuclei.’’ In addition, he gave the public lecture Paul Shapiro was co-Chair of the Scientific Organizing ‘‘Active Galaxies in the Universe.’’ Committee of ‘‘The Physics of the Interstellar Medium and In addition to these visitors whose visits were funded by the Intergalactic Medium,’’ Elba, Italy, June 1994. named programs, the following people were visitors to the Greg Shields served on the Scientific Organizing Com- department for periods of one week or longer: mittee for the Fifth Mexico–Texas Conference on Astrophys- ics held in Tequesquitengo, Mexico, April 2–5, 1995. M. de Fatima Saraiva, University of Brazil Tom Barnes served on the Organizing Committee for H. Dekker, European Southern Observatory IAU Commission 27 ͑Variable Stars͒. P. Diener, University of Copenhagen Robert Robbins was on the Organizing Committee for J. Laird, Bowling Green State University I. Lichtenstadt, IAU Commission 46. Hebrew University of Jerusalem Craig Wheeler was on the International Organizing Com- B. Milvang-Jensen, Copenhagen University Observatory mittee for the Texas Symposium on Relativistic Astrophysics I. Novikov, Theoretical Astrophysics Center, University of and the Organizing Committee for IAU Commission 42 Copenhagen ͑Close Binary Systems͒. K. Oliveria Filho, University of Brazil Paul Shapiro was a visiting member of the Institute for E. Oran, Naval Research Laboratory Theoretical Physics, University of California at Santa Bar- J.M. Owen, Ohio State University bara, for one week in March 1995 and on May 15–June 15 J. Stein, Hebrew University of Jerusalem quotation as a participant in the 1995 Workshop on Galaxy Formation and Radiation Backgrounds at the ITP. 1.6 Awards, Honors, and Special Activities Craig Wheeler was on the Executive Committee of the Board of Trustees for the Aspen Center for Physics. He was Inger Jorgensen was awarded a Hubble Space Telescope ” also on the Admission Committee for this center. Postdoctoral Fellowship. She will use her fellowship at the Robert Robbins designed and presented a four-day ar- University of Texas at Austin. chaeoastronomy workshop for college teachers under the John Lacy was selected by his peers as the recipient of auspices of the NSF-Chautauqua program. the 1995 Board of Visitors’ Teaching Award. Larry Trafton continues to serve as an Associate Editor of Anita Cochran was a Councilor for the American Astro- Icarus. nomical Society. Mary Kay Hemenway continued to serve Greg Shields spent the spring 1995 semester on leave at as Education Officer for the AAS, on the American Institute the Department of Space Physics and Astronomy at Rice of Physics Committee on Physics Education, as a liaison to University. At Rice, he worked with Dr. R. Dufour on the National Committee on Science Standards and Assess- Hubble Space Telescope observations of dwarf irregular gal- ment of the National Research Council, and on the Steering axies and delivered the Marlar Graduate Lectures on ‘‘Topics Committee of the UT Women’s Faculty Organization. She is in Active Galactic Nuclei’’ ͑May 1995͒. on the national Steering Committee of the Coalition for Earth Science Education. She also serves as Associate Director of 2. ACADEMIC AND EDUCATIONAL PROGRAM the University of Texas Institute for Science and Mathemat- ics Education. Craig Wheeler was the Chair of the AAS 2.1 Graduate Program Nominations Committee and was on the Tinsley Prize Com- The Graduate Studies Committee Chair was Ethan Vish- mittee. niac with Graduate Advisor Neal Evans. UNIVERSITY OF TEXAS 639

The Fred T. Goetting, Jr. Memorial Endowed Presidential r-Process Element Europium in F and G Disk Dwarf Scholarship was awarded to Michael Montgomery, who was Stars’’ studying asteroseismology of white dwarf stars. The Board • Luke Keller ͑Supervisor D. Jaffe͒: ‘‘The Large Scale of Visitors Graduate Student Endowment Fund was also Distribution of H-Alpha and ͓FeII͔ 1.6435 Micron awarded to Michael Montgomery. The David Alan Benfield Emission in IC 443’’ Memorial Fellowship was awarded to Chuck Claver, who studied the age of the Milky Way using white dwarf chro- 2.2 Undergraduate Program ´ nometry. Rene Plume won the first prize in the URSI student Derek Wills is the chair of the Undergraduate Studies essay contest, for his paper ‘‘The World’s Smallest Ten- Committee. There were 39 astronomy majors this year, and Meter Submillimeter Telescope.’’ URSI is a international or- two students received BAs. Dan Jaffe served as Undergradu- ganization of radio and millimeter-wave engineers, and the ate Advisor. Eric Berger was awarded the Outstanding prize included a $1000 cash award and a trip to Boulder, Graduating Senior Award. He is going on to graduate school Colorado, where the award was presented. in science journalism at the University of Missouri. Graduate students in 1994–1995 were Robert Benjamin, Jay Boisseau, Michael Brotherton, David Chappell, 2.3 Educational Services Jungyeon Cho, Minho Choi, Charles Claver, Alejandro Clocchiatti, Cecilia Colome´, James DiFrancesco, Cynthia Operation of the nine-inch refractor ͑Painter Hall Obser- Froning, Niall Gaffney, Youxin Gao, Erik Gregersen, Jim vatory͒ was directed by Antoˆnio Kanaan-Neto. The Painter Heath, Daniel Hiltgen, Antoˆnio Kanaan-Neto, Luke Hall Observatory hosts public star parties every Saturday Keller, Soon-Wook Kim, Scot Kleinman, Eric Klumpe, night. From September ’94 until September ’95, we had 24 Paul Kornreich, Anand Kudari, Wenbin Li, Zhiqing Li, star parties receiving a total of 617 visitors. Star parties for Yingming Lou, Michael Luhman, Shan Luo, Feng Ma, By- UT students were held every Monday night, and we had 27 ron Mattingly, Rebecca McQuitty, Michael Montgomery, of them bringing a total of 107 visitors. The Observatory also Michael Moscoso, Atsuko Nitta, Fred Ortiz, Soojong Pak, gives tours to school groups; during this year we gave 11 Rene´ Plume, Divas Sanwal, Susan Trammell, Joe Wang, group tours with a total of 165 visitors. Qiangguo Wang, Yangsheng Wang, Lance Wobus, Vincent Judit Ries, as Education Services Office manager, has Woolf, Changsong Zhang, and Eric Zink. compiled and installed an electronically accessible informa- Doctoral Dissertations: Nine Ph.D. degrees in astronomy tion system about the department. Thus, the Department of were awarded in 1994–1995: Astronomy is the first of the departments to appear on the • Robert Benjamin ͑Supervisor P. Shapiro͒: ‘‘The Origin University-wide ITower system. and Evolution of Galactic Halo Gas’’ A World Wide Web home page ͑currently http:// • Minho Choi ͑Supervisor N. Evans͒: ‘‘Study of Massive www.as.utexas.edu/͒ was established for the Department and Star Formation Regions With a Monte Carlo Radiative Observatory. In addition, a WWW abstract server for pre- Transfer Method’’ prints was created ͑currently http://abstract.as.utexas.edu/ • Chuck Claver ͑Supervisor E. Nather͒: ‘‘The Age of the abstracts.html͒. Milky Way Galaxy From White Dwarf Chronometry’’ The Educational Services Office hosted star parties every • Alejandro Clocchiatti ͑Supervisor C. Wheeler͒: ‘‘Su- Wednesday while UT was in session on the 14th floor ob- pernova Spectroscopy’’ serving deck of RLM. About 400 people attended in total. • Soon-Wook Kim ͑Supervisor C. Wheeler͒: ‘‘Topics in On July 19th, the NASA documentary ‘‘A Time of Apollo’’ Accretion Disk Instabilities: ͑1.͒ Magnetized Disks in was shown to commemorate the National Space Week. Spe- Intermediate Polars and GK Per, and ͑2.͒ Irradiated cial solar tours are also arranged through the ESO for stu- Disks in Black Hole X-Ray Novae’’ dents ranging from second grade to eighth grade ͑attendance about 700 total . • Michael Luhman ͑Supervisor D. Jaffe͒: ‘‘Near-Infrared ͒ Molecular Hydrogen Emission as a Probe of the Struc- Judit Ries, Derek Wills, and Lara Eakins, with the help of astronomy graduate students, hosted a special stargazing ture of Photodissociation Regions?’’ party on July 28th at the 16-inch telescope on the top of the • Rene´ Plume ͑Supervisor D. Jaffe͒: ‘‘A Study of Warm, RLM building for 60 high school honors students. Atomic Gas in the Interstellar Medium’’ The department also participated in the Texas Energy • Susan Trammell ͑Supervisor H. Dinerstein͒: ‘‘The Symposium for high school students and teachers, where Ju- Structure of Objects in Transition from the AGB to dit Ries gave a talk on energy production in the stars. Planetary Nebula’’ • Yangsheng Wang ͑Supervisor N. Evans͒: ‘‘From Dense 2.4 Public Information Office Cores to Protostars’’ Master’s Theses: Four Master’s degrees in astronomy The Public Information Office moved from 2601 Univer- were earned in 1994–1995: sity to 2609 University and added 2,000 square feet of office • Michael Montgomery ͑Supervisor D. Winget͒: ‘‘The space. The W.L. Moody, Jr. Visitors’ Information Center was Asteroseismology of White Dwarf Stars’’ renovated to add 400 square feet of gift shop floor space, a • Divas Sanwal ͑Supervisor E. Robinson͒: ‘‘Optical partition to the theater area, and office space. Study of Pulsars’’ Funding totaling $180,000 was received from the Abell • Vincent Woolf ͑Supervisor D. Lambert͒: ‘‘The Hanger Foundation to build the George T. Abell Visitors’ 640 ANNUAL REPORT

Gallery. This will be adjacent to the Hobby-Eberly Tele- ber, with Orbital Sciences Corporation the winner. In January scope. Conceptual drawings for a 7,000-square-foot expan- 1995, Eastman Kodak completed a redesign of the spherical sion to the Visitors’ Center were developed. Plans for an aberration corrector to achieve better optical performance. outdoor expansion which adds an amphitheater, pavilion, and The new design featured four reflective elements in contrast the Rebecca Gale Astronomical Park were also developed. to the original design’s two. At this point, structural steel Universo, the new Spanish language version of the Star- erection at the facility was nearly complete, and 36 mirror Date radio program, was launched. The series exceeded its segments were in fabrication at Eastman Kodak. first major milestone in August by adding over 60 radio sta- In February, Mero Structures of Wurzburg, Germany oc- tions that are airing the program in Spanish. The program is cupied a portion of the site to assemble the primary mirror produced at KXCR studios in El Paso and is also marketed truss. This 11-meter truss utilizes more than 1700 structural out of those studios. Teresa Fendi de la Cruz is the announcer members to support the primary mirror segments. Its design for Universo, Arturo Vasquez is the co-producer, Armando de is such that manufacturing tolerances alone control node po- la Fuente assisted with the marketing, and Rosario H. Torres sition to within 4 mm, allowing simple, bolt-together assem- is the translator. Technical editors include Jorge Lopez, As- bly at the site. sistant Professor of Physics, UT El Paso; Carmen Pantoja, Erection of the enclosure dome began in March. At this Arecibo Observatory; and Celia Colome´, UT Austin. The point, the initial phase of construction was nearing comple- Universo series is made possible with grant funding from the tion, with the control and service building and telescope en- National Science Foundation and NASA. closure enclosed and ready for the installation of the tele- Funds from NASA Astrophysics Grants to Supplement scope structure. A layer of finely finished concrete, flat to Education funded the Guide to the Solar System. Ethan Vish- 0.010 inch, had been applied to the telescope pier for the niac is PI on the grant, and the production is being done by structure azimuth rotation air bearings to run on. the Public Information Office. In April, Comsat/Radiation Systems, Inc. occupied the A new 16-inch Meade telescope and CCD camera were site to commence installation of the telescope structure. The added at the Visitors’ Center. They are housed in a 20-foot base portion of the structure was assembled in place, and the dome that previously housed the 30-inch telescope. The completed primary mirror truss was lifted into place. This dome has been refurbished at the Visitors’ Center site. truss sits on kinematic mounts which prevent any deforma- The StarDate radio program continues to broadcast to an tion of the telescope structure from affecting primary mirror audience of 2.5 million daily on over 200 radio stations in figure. On 28 June, the HET structure rotated in azimuth for the U.S. Sternzeit, StarDate’s German counterpart, continues the first time. The framework for the dome was very nearly to broadcast on Deutschland Radio in Cologne, Germany to completed adjacent to the telescope enclosure. an audience of 20 million daily. Sternzeit is produced by By June, twelve shipments of zerodur primary mirror Axel Scheibchen and directed by Edgar Forschbach; the an- blanks from Schott had been received, and 65 of the total 95 ¨ nouncer is Gunther Dybus. Forschbach also heads up ‘‘For- mirror blanks were at Eastman Kodak. The first two mirror schung Aktuell’’ ͑Current Research͒, a daily half-hour infor- blanks were completed and met optical and dimensional re- mation program that incorporates Sternzeit. quirements. Mirrors are being fabricated using a continuous StarDate magazine added an 800 number to increase cir- planetary polishing process with final ion figuring. Testing of culation and over 80,000 copies were circulated. The Visi- the mirror support prototype was completed at Kodak, and it tors’ Center served over 130,000 visitors and continued to met requirements for repeatability and positioning accuracy. provide the astronomy curriculum for the Prude Ranch envi- In July, the structure had been completely assembled and ronmental education program and the Elderhostel program. the enclosure dome was lifted into place atop the enclosure walls. The first two mirrors were transported to Denton 3. RESEARCH PROGRAM Vacuum for use in development of the protected silver coat- ing process. In August, the dome was made weather tight, 3.1 Future Plans: The Hobby-Eberly Telescope and Phase II of construction began. Between August and The Hobby-Eberly Telescope project is a joint effort of January 1996, the interior and exterior finishes of the facility the Univerisity of Texas, Penn State University, Stanford will be applied, all electrical wiring and plumbing com- University, the Ludwig Maximilian University in Munich, pleted, and the environmental controls completed. The dome and the Georg-August University in Go¨ttingen. will then be completed and the HET Project Team will com- Substantial progress has been made in the construction of mence installation of the computers and equipment which the Hobby-Eberly Telescope during this reporting period. make up the telescope control system. Ground was broken in May of 1994. By September, progress First light is expected in the summer of 1996, with a had been realized in the pouring of foundations, in the de- partially filled primary mirror array and using a temporary tailed design of the telescope structure and dome, and in the two-element surrogate corrector. At first light it is expected development of a process for manufacturing the mirrors. that the telescope will acquire, track, form images, and allow In November, final acceptance testing was performed on assessment of the expected optical performance to be real- the Center of Curvature Alignment Sensor, the polarization ized. Completion of the telescope and dedication to full time shearing interferometer to be used to sense the relative posi- operations is planned for mid-1997. The Hobby-Eberly Tele- tions of the 91 one-meter mirrors which make up the pri- scope is unique in that it features the largest primary mirror mary. Bids were received for the tracker system in Decem- in the world, utilizes a 9-meter pupil in its Arecibo-type con- UNIVERSITY OF TEXAS 641

figuration, and yet is being constructed for a total cost of which connects Mount Locke into the UT System network $13.5 million, including all labor and materials. via the UT Permian Basin campus in Odessa. The T1 line has been extended from Mount Locke to the adjacent Mount 3.2 Observing Conditions at McDonald Observatory Fowlkes, where it will connect to the Hobby-Eberly Tele- scope facility now under construction. A summary of the hours scheduled, hours lost to poor There has been a great deal of excitement among astrono- weather, hours lost to telescope/instrument problems, and mers the last few years as technological improvements have hours assigned to maintenance is given below. Scheduled made it possible to obtain high-resolution visual and near- hours are measured from civil twilight to civil twilight, plus infrared images from ground-based telescopes. P. Harvey, C. any especially scheduled daytime hours. ͑The daytime hours Koresko, and D. Sill began work in January 1994 on a new for all four telescopes together total only 52 hours.͒ Category near-infrared camera optimized for taking images at the ‘‘Other’’ is comprised primarily of time when the telescope highest possible resolution. The new camera, named D-LITE was not scheduled or no program object was available. ͑Diffraction-Limited Infrared Telescope Experiment͒,isde- Since the 2.7-m telescope is used almost exclusively for signed to be used for speckle interferometry at the Casseg- spectrometry, a reasonable estimate of the spectrometric rain focus of McDonald Observatory’s 2.7-m telescope and weather can be obtained from its records. After correcting for on the U.S. Air Force Starfire 1.5-m adaptive-optics tele- downtime due to maintenance, equipment, etc., the spectro- scope, which has recently been declassified and made avail- metric time is estimated as 65% for the last fiscal year. This able to university astronomers. The new camera saw first value can be compared with 63% for the previous year, and light at McDonald in January 1995. In May, they joined J. 62.1% for a fourteen-year mean. Until fiscal year 1992–93 Christou and R. Fugate at Starfire to demonstrate the advan- the 0.9-m telescope was used predominately for photometry, tages of adaptive optics and speckle interferometry over or- so its usage can be used to infer the photometric weather dinary direct imaging and the greater advantage which can statistic. ͑Since 1992–93 the 0.9-m telescope has been used be had when the two techniques are used together to perform mostly for programs not requiring photometric weather.͒ ‘‘compensated speckle.’’ They are preparing for a second From the 0.9-m telescope statistics for 1981–1992, the pho- Starfire trip in late October, when they hope to use the new tometric weather at McDonald Observatory averaged 39.8% instrument to study the young stars in the Taurus Dark Cloud of the available hours. with a superb combination of resolution and sensitivity. TABLE 1. Utilization Statistics for McDonald Observatory Optical Telescopes ͑1994–1995͒͑Hours͒ R. Plume and D. Jaffe have modified their re-imaging device for the Caltech Submillimeter Observatory to accom- modate the new telescope secondary. Plume has used the 2.7-m 2.1-m 0.9-m 0.8-m device to observe large-scale emission in neutral carbon and in several CO lines and has now used the device to complete a͒* 4022 4019 4031 4011 his Ph.D. thesis. b͒ 2383 ͑62%͒ 2395 ͑60%͒ 1296 ͑32%͒ 1160 ͑29%͒ Following their initial work on front-surface microma- chined gratings, L. Keller, T. Benedict, and D. Jaffe have c͒ 1305 ͑33%͒ 1330 ͑33%͒ 1287 ͑32%͒ 758 ͑19%͒ fabricated an IR immersion diffraction grating on a silicon prism using standard photolithographic chemical etching d͒ 42 ͑1%͒ 48 ͑1%͒ 27 ͑1%͒ 107 ͑3%͒ ͑ ͒ techniques. They are currently working on improving the e͒ 52 ͑1%͒ 55 ͑1%͒ 56 ͑1%͒ 140 ͑3%͒ process to minimize surface defects and improve grating ef- ficiency. The final product will be an echelle grating which f͒ 139 ͑3%͒ 191 ͑5%͒ 1365 ͑34%͒ 1846 ͑46%͒ has Ӎ 3.5 times the resolving power of a front surface grat- *a͒ Scheduled; b͒ Observed; c͒ Lost to weather; ing with identical size. d͒ Lost to telescope/instrument problems; P. MacQueen, J. Graw, and G. Hansen have designed and e͒ Scheduled maintenance; f͒ Other prototyped an 18-bit Analog Signal Processor ͑ASP͒ to re- place present and future McDonald analog modules. It uses three integrators for constant-gain readouts at 20, 50, and Ϫ1 3.3 Scientific Results 100 kpixels s . A checksum generator confirms data trans- mission integrity. A versatile synthetic waveform generator 3.3.1 Instrumentation: and a power supply monitor provide detailed diagnostics. Several significant developments occurred last year in The prototype delivers a signal-to-noise ratio of over computing systems at McDonald. Control of all of the major 200,000:1 and is linear to at least 30,000:1 peak-to-peak. instruments which use CCDs was transferred from VAXsta- P. MacQueen, G. Wesley, J. Graw, G. Hansen, J. Welborn, tion systems to Sun systems. The Sun systems use Sbus- and D. Edmonston commissioned a CCD detector system based interfaces, developed by P. MacQueen’s CCD group, called TK3 with a Tektronix 2Kϫ2K, grade 1, thin CCD. It and new software which runs under the IRAF Control Envi- uses a new 150-mm-diameter detector housing with a CCD ronment ͑ICE͒, developed by M. Cornell’s computing group. mount that flexes less than 0.1 ␮m between any two orien- A major upgrade of the computing network to the mountain tations while leaking only 220 mW of heat. TK3 uses a pro- was also implemented. The old 9600-baud leased line system totype ASP to provide a 180,000 eϪ dynamic range with a between Austin and Mount Locke was replaced by a T1 line 3.5 eϪ readout noise. 642 ANNUAL REPORT

P. MacQueen, D. Edmonston, and J. Welborn upgraded contributions plus University of Texas matching funds. Many the TK2 CCD system from use of a thin Tektronix 512 of the major optical components have been ordered. The ϫ512 CCD to a SITe 1Kϫ1K, thin, grade 1 CCD system needed CCDs for a mosaic of two 2048ϫ4096 chips with 15 called TK4. ␮m pixels were recently produced at ORBIT Semiconductor P. MacQueen and D. Edmonston upgraded the analog in collaboration with the Lick Observatory CCD Lab. A pro- electronics of the RA2 CCD system which uses an EG&G posal has been prepared to seek the remaining funding from Reticon 1200ϫ400, thin CCD. MacQueen and J.F. Harvey NSF. Completion is planned for 1998. have implemented a new lamp for efficient UV flooding of G. Hill is leading the design team for the HET low- RA2. resolution spectrograph ͑LRS͒. The design is an efficient P. MacQueen and C. Claver developed a new collimation grism spectrograph covering 0.4 to 1.4 ␮mat technique for the 0.76-m Prime Focus Corrector ͑PFC͒.An Rϭ500–4000. Hill has assisted Larry Ramsey ͑HET Project image quality of 24 ␮m FWHM can be achieved which is a Scientist͒ with the design of the tracker optical package limit set by errors in the manufacture of the optics. The null ͑TOP͒ for the HET, which will provide acquisition, guiding, lens for the tertiary mirror was found to be misfigured, and fiber-feed control, and interface to prime-focus instruments has been reworked to allow the corrector optics to be refig- for the telescope. Hill was also a member of the HET Tech- ured. nical Steering Committee. W. Wren and C. Wheeler have constructed and dedicated a novel new telescope to be used for a visual search for 3.3.2 Solar System: nearby supernovae. This telescope sits on an optical bench A. Cochran, H. Levison, A. Stern ͑SwRI͒, and M. Duncan with a fixed 18-inch primary mounted with its optical axis ͑Queen’s University͒ announced their detection of 5–10 km- horizontal. The only moving part is a flat at the opposite end sized bodies in the Kuiper Belt. The observations were ob- of the optical bench. The light path from the flat to the pri- tained with the WFPC2 on the Hubble Space Telescope. The mary is brought to focus through a hole in the center of the detected population of 29 objects in less than 4 arcmin2 im- flat to a fixed eyepiece. This configuration will strongly re- plies a population of 2ϫ108 objects of 5–10 km in a region duce the observer fatigue involved from chasing the eyepiece of the Kuiper Belt with inclinations less than 12° and dis- in a normal equatorial mount telescope. Wren has observed tances from the Sun of less than 40 AU. This population of several hundred galaxies a night with orthodox telescopes objects is sufficient to supply the known short-period comets. and has discovered SN 1992H and SN 1994Y. This new in- Observations obtained by the McDonald Observatory strument should make his work more efficient. Comet Impact Science Team during the R, U, and V impacts G. Hill, B. Wills, and K. Thompson have been continuing of Shoemaker-Levy 9 on Jupiter were analyzed. Light curves construction of the dual-beam spectrograph for the Mc- were derived from images obtained at 2.12 ␮m ͑pressure- Donald 2.7-m. The spectrograph will cover 3150 Å to induced H2) and 0.89 ␮m ͑CH4) with the 2.7-m and 0.76-m 11,000 Å at Rϭ700 simultaneously through use of a dich- telescopes at McDonald Observatory, respectively. The first roic beamsplitter. Optimized red and UV-blue coatings will precursor flash and the main event were clearly seen in the yield high throughput over the entire wavelength range. Con- 2.12 ␮m data for the R impact, but this impact produced no struction of the red arm of the spectrograph will be com- flash at 0.89 ␮m. From the upper limit on the flux increase at pleted in early 1996, and it will be used on the 2.7-m as an CH4 and the detection at H2 , the team derived an upper limit efficient red spectrograph while the custom CCD camera for temperature for the main event of the R impact of 1300 K. the blue arm is constructed. The U impact produced a very small flash at 2.12 ␮m, cor- G. Hill upgraded the ROKCAM IR imager with new op- responding to the main event. No impact flash was detected tics and mechanical design. Gordon Wesley assisted in the from the V impact. mechanical design. The upgraded instrument has improved Follow-up observations of the long-term effects of the imaging and is parfocal over the J, H, and K bands. Darren impact of Comet D/Shoemaker-Levy 9 on the atmosphere of DePoy ͑Ohio State University͒ designed the optics. The in- Jupiter were obtained by A. Cochran, W. Cochran, E. Barker strument will reenter service in December. Hill completed ͑NASA HQ͒, W. Pryor ͑LASP͒, and C. Na ͑LASP͒. These the optical design for Coolspec, an innovative cooled IR data included CCD images, and low- and high-resolution spectrometer to mate with the ROKCAM IR imager on the spectroscopy. By the time of the last observations in June 2.7-m telescope. The instrument has a simple modified 1995, the obvious prominent southern hemisphere features Czerny-Turner design and a 50-mm beam size. Construction ͑dark in the continuum and bright in CH4 bands͒ had faded of Coolspec is continuing, and the instrument is expected to significantly. see first light in 1996. L. Trafton participated in the reduction and analysis of R. Tull and colleagues are planning a high-resolution spectroscopic data taken during the impact of Comet SL-9 broad-band optical spectrometer for the HET. The local team with Jupiter last year at the UKIRT and HST. Information on includes P. MacQueen, C. Sneden, W. Cochran, D. Lambert, the composition and distribution of impact-generated debris and A. Hatzes. The international team also includes members was extracted and published. This included information on at the HET member organizations at Penn State University Jupiter, the comet, and the chemical processes taking place and the Universities of Munich and Go¨ttingen. More than during the impact. Sulfur-bearing compounds and enhanced half the needed funding has been raised through private gifts NH3 were detected. to the University together with state of Texas and NASA M. Brown ͑LPL͒, A. Bouchez ͑UC Berkeley͒, H. Spinrad UNIVERSITY OF TEXAS 643

͑UC Berkeley͒, and C. Johns-Krull analyzed high-resolution companions, these data will still have great value as a ‘con- spectra of the comet P/Swift-Tuttle for the presence of emis- trol’ in the Proxima Cen ‘experiment.’ Systematics intro- sion in the OH Meinel system. The high resolution (RϷ duced by HST or the FGS are present in the data for both 60,000͒ of the spectra and the large heliocentric velocity of stars. the comet permit easy separation of these lines from nearby Anything detected in the Proxima data not in the Barnard OH sky lines. No OH Meinel lines were detected in the data becomes less likely instrumental, and more likely astro- comet, consistent with theoretical calculations of prompt and nomical. The intrinsic value of additional Barnard observa- fluorescent cometary emission and contrary to reports based tions prompted the Astrometry Science Team to dedicate 10 on low-resolution work. Cycle 5 GTO orbits to continued monitoring of Barnard’s Observations of the distribution of OH in the comae of Star. Benedict secured 10 additional orbits of HST GO time comets were continued as part of a program by A. Cochran to continue monitoring Proxima Cen. They have determined, and D. Schleicher ͑Lowell Observatory͒ to understand the with the HST data, that Barnard’s Star is a periodic photo- photodissociation of H2O as a function of changing solar metric variable, and can report that the period is clearly dif- activity. An excellent set of observations of comets with he- ferent than that found for Proxima Centauri. Benedict ͑as- liocentric distances from 1–2 AU were obtained while the sisted by P. Shelus, A. Whipple, and D. Cornell͒ has Sun was at a minimum of activity. Observations obtained on instigated a ground-based photometric monitoring program different comets on the same night showed that the scale to confirm or refute the period indicated by HST for Barnard. lengths of the OH gas in the comae were different for differ- They are using the McDonald Observatory Prime Focus ent comets. Since the observations were the same night, the Camera. photodissociation lifetimes must be the same. This implies L. Trafton participated in an HST study of Io’s SO2 UV that the outflow velocities are quite different for different spectrum with J. Caldwell, C. Cunningham ͑both York Uni- comets and that the scale lengths are also dependent on the versity͒, and C. Barnet ͑GSFC͒. They found new, larger, density of gas in the coma. Work continues on this project. lower limits to the portions of Io’s leading and trailing hemi- The McDonald Observatory Planetary Search ͑MOPS͒ sphere covered by the gas. Io’s atmosphere is too thin for it program ͑W. Cochran and A. Hatzes͒ continued survey ob- to envelope Io; it resides near sunlit ices and volcanic servations designed to detect planetary systems in orbit sources. They also further constrained the maximum SO2 around nearby solar type stars. Extremely high-precision column abundance and argued that the UV results differ from measurements are obtained of radial velocity variations of a the mm-wave results because the latter technique samples sample of 36 dwarfs and subgiants of spectral types F, G, and essentially only the hot gas over volcanoes, which is more K. A time series of such observations will reveal the orbital abundant than elsewhere. motion of the star around the star–planet barycenter. An I2 L. Trafton extended his ‘‘Detailed Balancing Model’’ gas absorption cell placed in front of the 2.7-m telescope ͑DBM͒ of the interaction between the vapor pressure of sur- coude´ spectrograph allows velocity precision of about face ices, the relative composition of ice volatiles, and the 5–10 m sϪ1 to be achieved. A companion southern- atmospheric composition he developed for Pluto’s methane- hemisphere survey is being conducted at the European nitrogen atmosphere to Triton. He showed that the model can Southern Observatory in collaboration with M. Ku¨rster, K. explain Triton’s atmospheric methane/ nitrogen ratio ob- Dennerl, and S. Do¨bereiner ͑MPI Garching͒. The ESO sur- served by the Voyager EUV experiment. This has been prob- vey uses an I2 absorption cell at the 1.4-m CAT. Three years lematical because this ratio is close to the value expected for of data from ESO have demonstrated a long-term precision the pure ices but should be orders of magnitude smaller ow- of better than 10 m sϪ1. ing to the observed solution of solid methane in solid nitro- The Hubble Space Telescope Astrometry Science Team gen. Henry’s ͑or Raoult’s͒ law predicts that the vapor pres- continues to monitor the nearby stars Proxima Centauri and sure of the minor constituent ͑methane͒ should be Barnard’s Star for low-mass companions ͑investigation lead proportional to its mole fraction in the ice. The DBM re- by G.F. Benedict͒. No new data for Proxima Centauri were solves the conflict by invoking a compositional discontinuity acquired this year with which to either confirm or refute the at the surface of the ice above which a thin methane-rich weak perturbation detected at Pϳ80 days. With 25 observa- layer is maintained by interaction with the atmosphere. The tion sets acquired over two years, there are no obvious com- DBM is an alternative to the ‘‘Hot Methane Patch Model’’ of panions to Barnard’s Star. Monte Carlo and Bayesian analy- Stansberry for explaining Pluto’s enhanced atmospheric ses ͑D. Chappell͒ yielded present companion mass detection methane content. limits for both Proxima Cen and Barnard’s Star at or below A. Whipple and P. Shelus performed long-term numerical one Jupiter mass for periods ranging from 100 to 600 days. integrations of the orbits of the Near Earth Asteroid Rendez- Re-application of their continually evolving and improving vous mission targets to determine the dynamical context for astrometry reduction procedures have resulted in a signifi- the physical observations that will be made of these asteroids cant increase in the precision with which the team deter- by the spacecraft. They found that the rendezvous target, 433 mines the parallax and proper motion of Barnard’s Star. A Eros, is on a fairly chaotic orbit and that its proximity to time-dependent version of their master calibration ͑OFAD͒ Mars (aӍ1.46 AU͒ places it in the middle of the very high and a correction of an obvious systematic signature in their order mean motion resonances associated with the 1:1 mean calibration residuals reduced by nearly a factor of two the motion resonance with Mars. They also found that the flyby formal uncertainties. Should Barnard have no detectable target, 253 Mathilde, is located in a dynamically unusual part 644 ANNUAL REPORT of the asteroid belt. It is located just inside of the 11:4 mean rotation. Recent theoretical investigations predict large levels motion resonance with Jupiter and near the gϪ2g6ϩg5 of differential rotation in these stars which can be discerned secular resonance. These resonances have caused significant in the shape changes produced in the absorption line profiles. depletion of the asteroid belt in the vicinity of Mathilde. Analysis of line profiles in the above stars show that the A. Whipple calculated the Lyapunov times for all num- large levels of differential rotation are not present. The pro- bered asteroids whose current perihelion distance is less than files suggest that modest levels of ‘‘anti-solar’’ ͑poleward 1.6 AU to investigate the structure of chaos in the inner acceleration͒ differential rotation may exist in these stars asteroid belt. He found that the planet-crossing asteroids which if true could falsify the detection of polar spots in have extraordinarily short Lyapunov times, virtually all less many late-type stars using Doppler imaging techniques. than 5000 years. The Lyapunov time was found to depend C. Johns-Krull and J. Valenti ͑JILA͒ have begun using the very strongly on perihelion distance. These results support high-resolution (Rϭ 120,000͒ mode of the cross-dispersed the conclusion that the predominant cause of the extreme echelle spectrometer on the 2.7-m telescope to look for Zee- chaos among the planet-crossing asteroids is their close en- man splitting in the gϭ2.5 FeI line at 8468.4 Å in dMe counters with the terrestrial planets rather than mean motion flare stars. To date, strong splitting has been detected in two and secular resonances. The magnitude of the chaos found in stars ͑EV Lacerta and Gliese 729͒ indicating large magnetic these asteroids severely limits the ability to predict their mo- fields (Ͼ3kG͒covering substantial amounts of the stellar tions for even centuries. surface (Ͼ50%). J. Ries and W. Jefferys carried out a preliminary study on G. Basri ͑UC Berkeley͒, K. Stassun ͑Wisconsin͒,R. the application of Bayesian method for lunar data analysis. Mathieu ͑Wisconsin͒, C. Johns-Krull, G. Marcy ͑SFSU͒, and According to the study, identification of lunar returns and J. Valenti ͑JILA͒ have analyzed several high-resolution spec- recovery of earth orientation parameters is promising using tra of the T Tauri star DQ Tau and found it to be an eccentric this technique. (Ϸ0.6) double-lined spectroscopic binary system. This is the latest spectral-type T Tauri binary discovered. Photometric 3.3.3 Stars and Stellar Systems: monitoring of this system also indicates that the accretion T. Barnes with T. Moffett ͑Purdue University͒ examined rate of material from the disk to the primary increases dra- the uncertainties ͑random and systematic͒ in the visual sur- matically just before periasteron. face brightness technique ͑Baade-Wesselink method͒ as ap- C. Johns-Krull, S. Hawley ͑Michigan State͒, G. Basri ͑UC plied to Galactic Cepheid variables. Gieren, Barnes, and Berkeley͒, and J. Valenti ͑JILA͒ are currently analyzing Moffett had used this technique to establish the most exten- high-resolution echelle spectra of a solar flare obtained at sive Galactic Cepheid period–luminosity relation to date, so Lick Observatory in 1993. Initial results show that the it is important to understand the uncertainties in it. They Balmer decrement in solar flares is substantially steeper than showed that the random error in a single Cepheid distance in flare on dMe flare stars. In addition, comparison of these measurement is Ϯ8% and that an upper limit to the system- spectra with the flare models of Hawley and G. Fisher ͑UC atic uncertainty in the surface brightness PL relation is Berkeley͒ indicate that the coronal pressure in flare loops is Ϯ6% in distance. These combine, for a single Cepheid, to a higher than previously thought. typical uncertainty of Ϯ10% and, for samples larger than ten V. Woolf, J. Tomkin, and D.L. Lambert completed a study Cepheids appropriate to studies of other galaxies, to a typical of the abundances of the r-process element Eu in 81 nearby uncertainty of less than Ϯ6% in distance. field F and G disk dwarfs. In comparison with the solar J. Fernley ͑ESA-Vilspa͒ and T. Barnes completed most of abundance ratio, the stars’ Eu/Fe ratio increases by a factor the observations of the Hipparcos RR Lyrae stars for mean of three as their Fe abundance decreases from approximately radial velocity and for metallicity. These data will be com- twice the solar Fe abundance to approximately one-tenth so- bined with Hipparcos proper motions for a new study of the lar. The relative increase of the Eu abundance in the metal- mean absolute magnitudes of RR Lyraes. This work is in deficient stars, which are also the older stars, points to Type collaboration with D.W. Evans ͑RGO͒ and Suzanne Hawley II supernovae as the site of the r-process. Although this trend ͑Michigan State University͒. has been seen before, the new Eu abundances correlate more T. Moffett ͑Purdue University͒, T. Barnes, and W. Gieren closely with predictions based on models of Type II super- ͑Catholic University, Santiago͒ completed their observational novae than previous data have. program to determine high-quality BVRI photometry of those J. Tomkin and D.L. Lambert completed high-resolution LMC/SMC Cepheids with existing, precise radial velocities. observations of the 7800 Å RbI line in metal-deficient These 22 stars are also being investigated for metallicities dwarfs and giants. Reduction and analysis of the observa- using the CTIO 4-m telescope in the fall 1995 Magellanic tions are in progress and show that the RbI line can be de- Cloud season. When the data are complete, Barnes and col- tected down to metallicities as small as 1/30 of the solar laborators will be able to check the metallicity pattern found metallicity. Rb abundances are of interest as a monitor of the by Luck and Lambert for Magellanic Cloud Cepheids and neutron density at the s-process site. will do a surface brightness analysis for the LMC/SMC dis- G. Gonza´lez, in collaboration with D. Lambert and S. tances. Giridhar ͑Bangalore, India͒, has been working on a long- C. Johns-Krull examined three rapidly rotating T Tauri term project to estimate abundances for RV Tau variable stars ͑HDE 283572, RY Tau, and SU Aur͒ and a half-dozen stars. The observations are being obtained at McDonald Ob- rapidly rotating Pleiades F stars for evidence of differential servatory. RV Tau’s are highly evolved low- or intermediate- UNIVERSITY OF TEXAS 645 mass stars considered to be in a post-AGB phase of their sity͒, and C. Wheeler have begun a new program to obtain evolution. The results of this study should reveal something routine photometric and spectropolarimetric observations of new about the chemical enrichment histories of these stars. bright supernovae. They have observed 6 supernovae in the P. Ho¨ flich ͑Harvard͒ and A. Khokhlov analyzed Type Ia first two trimesters of this program, thereby increasing the light curves and compared them with observations of numer- total sample of supernova with polarization data by over 50 ous individual observed supernovae. They concluded that percent. Combining the new data with results from the litera- H0 ϭ 69 Ϯ 10. The Pskovskii–Branch–Phillips relation be- ture reveals a potentially critical dichotomy. Of the events tween the brightness and post-maximum decline of Type Ia with reliable ͑multi-wavelength, multi-epoch͒ data for which supernovae light curves was interpreted and explained in the the effect of the ISM can be corrected, it appears that all framework of the delayed detonation scenario by M. Hamuy, Type II supernovae are polarized at about the 1 percent level M. Phillips, N. Suntzeff ͑all CTIO͒,Ho¨flich, Khokhlov, and and that Type Ia supernovae are unpolarized with an upper C. Wheeler. limit of about 0.2 percent. The Imaging Grating Instrument For his Ph.D. dissertation, A. Clocchiatti showed that has been adapted to do imaging or spectopolarimetry. This some supernovae classified from their maximum light spec- will be much more effective for background subtraction than tra as helium-deficient Type Ic nevertheless have late-time the instrument used in the preliminary program. light curves very similar to some helium-rich, hydrogen-poor P. Ho¨ flich ͑Harvard͒, C. Wheeler, D. Hines ͑Arizona͒, and Type Ib and to the peculiar Type II SN 1993J. The fact that S. Trammell ͑Chicago͒ have analyzed the spectropolarimetry these supernovae display a range in ejecta velocities and of SN 1993J more thoroughly. The observations seem to hence presumably ejecta mass suggests that some of the ra- show that the intrinsic polarization did not change substan- dioactive matter that powers the light curve is not participat- tially while the photosphere receded down through the hy- ing in the overall homologous expansion. If that were the drogen envelope and into the helium mantle. The polariza- case, the events with smaller mass would trap gamma rays tion can be modeled by an ellipsoidal electron-scattering from radioactive decay less efficiently and have steeper light envelope with an axis ratio of about 1.6 to 1. The data are curves. Some Type Ic events do, in fact, have steeply decay- consistent with a geometry in which the ellipsoid is viewed ing late-time light curves so that the spectral classification nearly edge on and which does not display a very steep den- alone is not sufficient to characterize these events. Clocchi- sity gradient just after the second maximum of the light atti also showed that all Type Ic plausibly show weak evi- curve. The constancy of the polarization may, however, be dence for helium in the optical, so that they are not com- more consistent with a deeply buried off-center source of pletely helium deficient. luminosity, perhaps a bubble of radioactive nickel, in a mass M. Adams, W. Wren, M. Ward, L. Wang, and C. Wheeler distribution with smaller geometrical distortion. have begun a search program for supernovae in clusters with Z. Li ͑Beijing Normal University͒ and C. Wheeler re- redshift in the range Z ϭ 0.03–0.15. This search will take examined the dependence of Type Ia supernovae on the H advantage of the wide field of view of the Prime Focus Cam- band luminosity in galaxies of varying Hubble type. They era on the 0.76-m telescope to survey entire Abell clusters in confirm the earlier study by van den Bergh that spirals have a single image. The McDonald program will help elucidate a much higher rate per unit H band luminosity than do ellip- the dependence of the variation of properties of Type Ia su- ticals. This suggests that Type Ia have progenitors that are pernovae, especially the light curve amplitude/shape, on the not associated with old, red companion stars and perhaps that morphological type of the host galaxy. This will strengthen some younger population is providing the higher rate in spi- the ability to use Type Ia supernovae as ‘‘calibrated candles’’ rals. to determine the distance scale. They will specifically survey the Abell clusters analyzed by Lauer and Postman which 3.3.4 Interstellar Medium, Compact Regions, Protostellar showed a velocity dipole with different orientation from the Disks, Star-Forming Regions: cosmic background radiation and from samples of Type Ia H. Dinerstein, C. Sneden, and J. Uglum ͑Stanford͒ pub- supernovae. They will apply the Type Ia supernovae tech- lished results from a survey of planetary nebulae observed at nique directly to the Lauer–Postman clusters. high spectral resolution in the NaI D resonance lines. More L. Wang and C. Wheeler, in collaboration with the Hubble than half of their sample of 21 nebulae showed evidence for Space Telescope Supernova Intensive Study Team headed by NaI lines associated with the nebula, in addition to interstel- R. Kirshner ͑Harvard͒, have analyzed the very late time lar features. They interpret this as strong evidence that neu- spectra of SN 1987A obtained with HST. The spectra of the tral circumnebular envelopes are prevalent among planetary ejecta show that the gas is very cold despite being heated by nebulae; even in cases where there is no molecular compo- gamma rays. A feature in the blue is identified as the Balmer nent, there is often neutral, atomic material. Dinerstein, continuum and its profile used to determine that the tempera- Sneden, and K. Volk ͑University of Calgary͒ are following ture in the ejecta nebula is 400–500 K. The doublet ͓OI͔ this up with a new study using the 2.7-m ‘‘2-d coude’’ spec- ␭␭ 6300, 6364 still does not display the ratio of three to one trometer to obtain broader wavelength coverage and higher expected of optically thin emission. The argument is made spectral resolution. This new survey will not only examine that the lines are optically thin, but that the observed inten- other resonance lines that might arise in the neutral enve- sity ratio is altered because the line profiles are non- lopes of planetary nebulae ͑such as CaII, CaI, and KI, but Gaussian. will also provide information on the expansion velocities and L. Wang, A. Clocchiatti, Z. Li ͑Beijing Normal Univer- line profiles in the ionized and neutral layers. 646 ANNUAL REPORT

S. Trammell defended her Ph.D. dissertation on spec- Class 0 sources ͑molecular cloud cores thought to be at a tropolarimetry, spectroscopy, and imaging polarimetry of ob- very early stage of star formation͒ in HCOϩ J ϭ 4–3 and jects undergoing the transition between the late red giant 3–2 lines and have found several new candidates for protos- ͑post-AGB͒ and planetary nebula phases of stellar evolution. tellar collapse. Using optical spectropolarimetry, she ͑together with H. Din- S. Zhou, N. Evans, and Y. Wang have submitted a paper erstein, and R. Goodrich, STScI͒ established that more than reporting observations with BIMA of 13CO and C18O J ϭ 50% of a sample of 31 stellar objects identified as being 1–0 emission from two protostellar collapse candidates, ‘‘post-AGB’’ stars show evidence for large-scale spatial L1527 and CB54. asymmetries, manifested as intrinsic linear polarization. With J. DiFrancesco and collaborators have completed large G. Hill, Trammell studied several more evolved ‘‘bipolar scale maps in the J ϭ 1–0 line of C18O of five cores in the nebulae,’’ including Gl 618, M 2-9, M 1-91, and M 1-92, Taurus molecular cloud, which will allow them to study the with a new imaging polarimeter, obtaining polarimetric in- process which separates one star-forming core from another. formation for images taken in both emission lines and con- N. Evans has published the results of combined submilli- tinuum. The polarized ͑reflected͒ component shows a ten- meter and infrared spectroscopy of GL2591. dency for ‘‘flattening’’ of the position angles which contains K. Tatematsu and co-workers have submitted a study of clues about the geometry of these nebulae; now at University structure in the outer parts of the Orion cloud using molecu- of Chicago, Trammell is currently attempting to model the lar line observations from the CSO. Tatematsu et al. find that reflection process, together with J. Kartje ͑University of Chi- UV radiation affects the isotopic chemistry in the clumps cago͒. The unpolarized component of the line emission in outside the cloud core. these nebulae, which arises from shocks, reveals compact M. Choi et al. have published a paper with lower limits structures such as knots, ‘‘bars,’’ and arc-like structures. on emission of neutral carbon in the extremely-high-velocity J. DiFrancesco, N.J. Evans, and co-workers have contin- wings in molecular outflows, constraining the chemical state ued to observe several Herbig Ae/Be stars at 2.7 mm to of the stellar wind. search for direct evidence of circumstellar disks, most re- R. Plume and D. Jaffe have completed a survey of CI cently with the IRAM interferometer. Of the 3 stars observed emission from three nearby dark clouds, using the re- so far this year, only Elias 1 appears to have emission that imaging device on the CSO. Plume and Jaffe have also com- may unambiguously be from a disk. In addition to the 5 pleted a study of CI emission from four molecular clouds of sources observed earlier, AB Aur and MWC 1080 were not intermediate size and have obtained a map of CI emission detected, indicating any 2.7-mm emission is far below that from a strip covering 2 degrees in galactic longitude about predicted by disk models. the galactic center. The CI emission most likely arises from In another attempt to determine the nature of their pos- PDRs distributed throughout the galactic center region. sible circumstellar disks, J. DiFrancesco and S.R. Trammell M. Luhman and colleagues have detected degree-scale ͑University of Chicago͒ have observed 30 Herbig Ae/Be emission in the near-IR emission lines of molecular hydro- stars with the IGI spectropolarimeter at McDonald. Interest- gen in the Orion clouds. Analysis of the line strengths indi- ingly, about one third of the objects surveyed have emission cates that the emission arises in gas at the surface of the lines that are polarized differently than the continuum, sug- cloud which is excited by ultraviolet photons. gesting different sources of scattering within their circum- S. Pak and collaborators have detected large-scale mo- stellar environments. lecular hydrogen emission from the inner 400 pc of the Y. Wang and co-workers have published his work on Milky Way, using the University of Texas Near-IR Fabry- high-frequency line calibration standards for the CSO. Perot Spectrometer. This emission is excited by ultraviolet M. Choi and collaborators have published a re-analysis of radiation from young stars and is similar to the H2 emission the CS and H2CO emission lines toward the best protostellar in the nuclei of many other galaxies. collapse candidate, B335, using a new, more accurate radia- S. Pak et al. have observed the Magellanic Clouds with tive transfer code. Choi and Evans developed this code using the University of Texas Near-IR Fabry-Perot Spectrometer. the Monte Carlo method to be more flexible and self- They detected H2 emission toward regions where no CO J ϭ consistent than previous codes. 1–0 emission has been detected. Strong UV-fields may dis- M. Choi has developed a 2-D Monte Carlo code, which sociate CO molecules in low-metallicity regions like dwarf will allow analysis of aspherical clouds, including rotation, galaxies. In these regions, near-IR H2 emission is a very as well as collapse and turbulence, in a self-consistent way. important tracer for the molecular gas. The first application of this code has been to model the emis- M. Luhman and D. Jaffe have compared large-scale emis- ϩ sion of a large number of molecular lines in the Mon R2 sion from H2 , CO, and C to the far-infrared emission from molecular cloud. dust toward four clouds. The H2 emission is excited by ul- Y. Wang et al. have identified several more collapse can- traviolet light and extends beyond the boundaries of the CO didates in a sample of Bok globules, by comparing the line emission. Over the entire cloud, there is a significant corre- 18 profiles of C O and H2CO lines at wavelengths around 1 lation between the emission from H2 and from dust. mm. Wang and Evans have completed a complementary M. Miesch ͑University of Colorado͒ and J. Scalo have study of CS emission from globules, which they are prepar- completed a study of the one-point probability distribution of ing for publication. central radial velocities in star-forming gas using the densely E. Gregersen and N. Evans have surveyed most of the sampled Bell Labs CO data for a number of molecular UNIVERSITY OF TEXAS 647 clouds with active star formation. The results show strong and by variations in mean ages and metal content. This com- evidence for non-Gaussian velocity distributions in some re- plicates the use of the FP as a distance indicator. To further gions, with the tails of the distributions being nearly expo- understand the effects of age, metal content, and disks, nential. Although they examined a number of possible physi- Jo”rgensen and B. Milvang-Jensen ͑Copenhagen University, cal explanations, none of them seem to explain the Denmark͒ are investigating the FP for a magnitude-limited exponential nature of the tails. Work using this dataset is sample of galaxies in the Hydra cluster. continuing. They have found that the probability distribu- I. Jo”rgensen, M. Franx ͑Kapteyn Institute͒, and J. Hjorth tions of linewidths appear uniformly exponential or possibly ͑Cambridge, UK͒ have obtained observations of two galaxy lognormal, an unexpected and unexplained result. Interpreta- clusters at z ϭ 0.2, which will allow investigation of these tions in terms of physical mechanisms are underway in col- clusters in similar detail as previously done for low redshift laboration with groups performing numerical simulations of clusters. The observations will make it possible for the first coupled star formation-hydrodynamics. time to establish the FP for high redshift clusters. Thus, one may study galaxy evolution using this tight relation. In the 3.3.5 Extragalactic: course of these observations a previously unknown galaxy G.F. Benedict, in collaboration with B.J. Smith ͑IPAC͒ cluster was discovered at a redshift of 0.7. and J. Kenney ͑Yale͒, has obtained, reduced, and analyzed M. Brotherton obtained moderate-resolution spectra of the CO interferometry of NGC 4314. These data were obtained H␤ –͓OIII͔␭5007 region for 41 radio-loud quasars using the at Owens Valley Radio Observatory. These CO͑1–0͒ inter- LCS on McDonald Observatory’s 2.7-m telescope. Spectra ferometer data provide 2.3Љϫ2.2Љ spatial resolution and 13 from the literature were also used to form a data set of 60 km sϪ1 velocity resolution. The data reveal a clumpy cir- radio-loud quasars in order to investigate relationships cumnuclear ring of gas. They also find a central peak of CO among quasars’ broad- and narrow-line profiles, radio struc- within 2 of the optical center. Deviations from circular mo- tures, and X-ray properties. Statistical analyses identified tion areЉ seen where the dust lanes along the leading edge of several strong, related trends: the FWHM, equivalent width, the primary stellar bar intersect the nuclear ring, consistent and degree of redward asymmetry of H␤ increase with de- with gas inflow along the bar. This is the clearest evidence creasing radio core dominance ͑an orientation indicator͒, for inflow along a stellar bar observed in any galaxy. H␣ whereas the FWHM of ͓OIII͔␭5007 increases with luminos- maps of this galaxy show bright HII regions near the ends of ity and ␣ox . this inflow region, perhaps indicating triggering of star for- B. Wills and D. Hines ͑Steward Observatory͒ continued mation by the inflow. polarimetric investigations of the Low et al. sample of IRAS G. Shields, R. Dufour ͑Rice University͒, D. Garnett ͑Uni- QSOs. Using spectropolarimetry of the Broad Absorption versity of Minnesota͒, and several collaborators completed a Line ͑BAL͒ QSO IRAS 07598ϩ6508, they showed it had study of silicon abundances in dwarf irregular galaxies, find- unpolarized broad emission lines and a polarized continuum. ing that silicon is not depleted by more than about a factor of The continuum consists of two components: an unpolarized, two by dust formation. Si/O remains fairly constant at reddened continuum that passes through low-ionization BAL Ϫ1.59Ϯ0.07 over an oxygen abundance range ͑NaI͒ gas, and a polarized ͑scattered͒ continuum that is much Ϫ1.6ϽlogO/HϽϪ3.4. less reddened and is not absorbed by the BAL gas. This G. Shields completed the second phase of a study of the provides direct evidence that the BAL gas does not com- chemical abundances of Virgo spiral galaxies with E. Skill- pletely cover the QSO continuum source, consistent with the man ͑University of Minnesota͒, R. Kennicutt ͑University of presence of BAL gas in all QSOs with the BAL phenomenon Arizona͒, and D. Zaritsky ͑UCSC͒. New spectrophotometric being simply a line-of-sight effect. With S. Young, J. Hough observations of HII regions were combined with earlier mea- ͑University of Hertfordshire͒, and collaborators, B. Wills dis- surements to study the interstellar oxygen abundances in the covered and investigated scattered light polarization arising disks of nine Virgo spirals. The results show that the HI from buried QSOs in a sample of warm infrared and Seyfert deficient spirals closest to the cluster core have O/H values 2 galaxies. ϳ0.5 dex higher than in comparable field spirals, whereas B. Wills and M. Brotherton investigated a different way of the spirals in the outskirts of the Virgo cluster, with normal measuring the dominance of a compact radio core in lumi- HI contents, have normal abundances. Simple theoretical nous quasars, using the rest-frame ratio of flux densities in models of the chemical evolution of the Virgo galaxies sug- the radio-core to that in the optical continuum. They showed gests that a cutoff of infall of primordial gas several billion that this measure correlates well with orientation angle de- years ago in the Virgo spirals could account for much of the rived from observations of superluminal motion and limits effect observed. on inverse-Compton scattered X-ray flux. The good anticor- I. Jo”rgensen, M. Franx ͑Kapteyn Institute, Holland͒, and relation between the new core-dominance measure and the P. Kjæ rgaard ͑Copenhagen University, Denmark͒ have stud- width of the broad H␤ emission line suggests that orienta- ied the Fundamental Plane ͑FP͒ for a large sample of low tion significantly affects our view of the broad emission line redshift elliptical and lenticular galaxies. The FP is a tight region. relation between effective radius, surface brightness, and ve- The HST team ͑B. Wills, D. Wills, K. Thompson, M. locity dispersion for the galaxies. The existence of the FP has Brotherton; J. Baldwin ͑CTIO͒; H. Netzer ͑Tel Aviv Univer- implications for galaxy formation and evolution. They have sity͒; G. Ferland ͑University of Kentucky͒; I Browne ͑Uni- found that the FP is affected by both the cluster environment versity of Manchester͒; and R. Carswell ͑Institute of As- 648 ANNUAL REPORT tronomy, Cambridge University͒͒ have now completed ward at speeds ϳ0.3c, explaining the observed blueshift of quasi-simultaneous spectroscopy using HST’s faint-object the polarization rise relative to the expected wavelength of spectrograph in the ultraviolet and ground-based spectra for the Lyman edge. the optical and infrared, for a sample of radio-loud quasars. P. Shapiro and H. Martel continued their development of a Using archival HST spectra, the sample contains about 60 new and improved version of the numerical gas dynamics objects. Reduction of the thousands of spectra are almost method known as Smoothed Particles Hydrodynamics complete, as well as new VLA radio maps. Clear, important ͑SPH͒, with application to cosmology. As a Lagrangian trends among continuum and emission line shapes, radio method, SPH is well-suited to the simulation of galaxy for- core-dominance, and radio loudness are emerging within the mation by the growth of cosmological density fluctuations sample and by comparison with, e.g., radio-quiet QSOs. since it uses particles which move with the flow as centers of Netzer et al. show that reddening intrinsic to the QSO affects interpolation which replace the fixed grid points of finite- both emission lines and continuum, and possibly the line difference codes, thereby increasing its resolving power in wings more than their cores. In conjunction with this spec- high-density regions as density contrasts arise. The standard trophotometry, ground-based photometric monitoring shows version of SPH, however, suffers from two deficiencies trends of flux variability with luminosity. which are particularly acute in cosmology simulations: ͑1͒ G. Hill studied the rest-frame optical and UV spectra of the smoothing, or interpolation, of particle data, which is at high-redshift quasars, redshifted in to infrared, in collabora- the heart of the method, uses an isotropic interpolation kernel tion with R. Elston ͑CTIO͒ and K. Thompson. J, H, and K which is parametrized by a scalar smoothing length, even band spectra were obtained with the cryogenic spectrometer at the KPNO 4-m and with the IRS Spectrometer at the though the gravitational collapse and shock waves which CTIO 4-m. Rest-frame optical FeII emission line complexes dominate the flows involve highly anisotropic volume near H-beta and MgII were detected in QSOs with redshifts changes; and ͑2͒ shocks are handled by artificial viscosity, up to z ϭ 4.8, confirming their earlier result and indicating which causes widespread, spurious viscous heating of com- that the nuclear environment of QSOs was highly enriched pressing regions far from any shocks. The new method — even at a very early epoch. Observations of objects at the Adaptive SPH ͑ASPH͒ — solves these problems by intro- highest redshift can constrain the geometry of the universe as ducing an anisotropic interpolation kernel and a tensor iron takes ϳ1 Gyr to enrich to above solar abundance. These smoothing length which automatically adjust the resolving power in time, in space, and in direction by tracking the data indicate a low value of q0 . G. Hill continued the Texas Large-Scale Structure Survey mean particle spacing along different directions around each ͑TLSS͒ using the Prime Focus Camera on the McDonald particle in the flow. In addition, shock-tracking is accom- 0.76-m reflector. The aim of the survey is to select clusters of plished using the tensor smoothing lengths to predict the galaxies from a 100 sq. deg. area with redshifts out to z ϭ occurrence of density caustics and thereby to restrict viscous 0.5, using UBVRI photometry. This project shares the dataset heating to gas encountering a shock. As a result, the new of the Texas Deep Sky Survey ͑TDSS͒ of C. Claver, Hill, and ASPH method has at least an order of magnitude better re- P. MacQueen. Spectroscopic redshifts of clusters in the re- solving power than standard SPH. Collaborators include M. sulting catalog will provide a map of the largest-scale struc- Owen ͑Ohio State University͒ and J. Villumsen ͑Max Planck ture in the universe, using clusters rather than galaxies as the Institute for Theoretical Astrophysics, Munich, Germany͒. tracers. Claver, I. Jo”rgensen, D. Cornell, and F. Ma were P. Shapiro, H. Martel, A. Valinia ͑Physics Department͒, involved in obtaining data for the TDSS/TLSS, and the cur- and J. Villumsen ͑MPITA͒ applied their new ASPH numeri- rent area coverage stands at about 25 sq. deg., in spite of cal gas dynamics method to simulate the formation of large- relatively poor weather. scale structure and the evolution of the intergalactic medium ͑IGM͒ in cosmology models including Cold Dark Matter 3.3.6 Theory: ͑CDM͒, Cold-plus-Hot Dark Matter ͑CHDM͒, and Hot Dark G. Shields and L. Wobus continued work on the polariza- Matter ͑HDM͒, with high resolution in 2D. Their results in- tion of thermal emission from an accretion disk around a dicate that dense regions tend to be anti-biased ͑gas concen- supermassive black hole in a quasar. Preliminary results in- trates less tightly than does dark matter͒. Observed X-ray dicate that the polarization of the disk continuum changes surface brightness profiles of galaxy clusters have been used little across the Lyman edge and can remain significant to recently to measure the cluster total mass and the baryonic infrared wavelengths. This result differs from previous re- gas fraction, by assuming the cluster is an isothermal sphere sults because the current work uses a model for the vertical in hydrostatic equilibrium. This has led to claims of a so- density profile in the disk. The photospheric density is much called ‘‘baryon catastrophe,’’ since the results indicate that lower than the midplane density, which had been used in the the cluster baryon mass fraction is significantly higher than earlier work, and the lower density causes electron scattering the mean value allowed by Big Bang nucleosynthesis abun- to remain the dominant opacity source over a wider range of dance constraints if the total universal mean density is wavelength. Shields began a theoretical investigation of the enough to make the Universe flat. Shapiro et al. have used origin of the recently observed abrupt increase of the polar- their simulations of flat models of cosmology to test the as- ization of QSO continua at wavelengths shorter than the Ly- sumptions underlying the analysis which leads to the baryon man edge. He is considering a model in which the polarized catastrophe. Their results confirm that the high baryonic continuum component is emitted by an axial jet moving out- mass fraction inside clusters found by X-ray observers can- UNIVERSITY OF TEXAS 649 not be explained by flat universe models like CDM, CHDM, plained by such a Galactic fountain flow, when the self- and HDM. illumination of the cooling gas by the radiation emitted by P. Shapiro has continued his study of the re-ionization of the hotter part of the flow is properly taken into account. the intergalactic medium ͑IGM͒ and quasar absorption line These calculations have been generalized to describe steady- clouds ͑QALCs͒. With M. Giroux ͑University of Colorado͒, state, radiative MHD shocks. They have also been applied he modeled the ionization and thermal history of the IGM successfully to predict and explain the metal lines observed numerically, by a space-averaged approach which takes ac- in quasar Lyman-limit absorption-line systems, believed to count of the ionization and heating due to photons from qua- originate in galactic halos over a range of earlier redshifts. sars and stars and bulk heating by hydrodynamical processes, A. Valinia, P. Shapiro, H. Martel, E. Vishniac, and J. Vil- radiative and Compton cooling, cosmological expansion, lumsen ͑MPITA͒ have studied the gravitational instability of non-equilibrium ionization and recombination, and radiative cosmological pancakes. They have modeled these pancakes transfer, including the continuum opacity of the observed as 1D, plane-wave density fluctuations in a collisionless gas, QALCs. Their results include predictions of widespread which collapse into sheets along the planes of each density metal production prior to redshift 3 if stars are responsible maximum, and have subjected the pancakes to transverse for producing the metagalactic UV background and the HeII perturbations which are either symmetric ͑density͒ or anti- Lyman alpha resonance absorption troughs in quasar spectra symmetric ͑bending͒ modes. They have shown by high- at high redshift ͑HeII Gunn-Peterson effect͒. Recently, HST resolution 2D, gravitational N-body simulations by the and the Hopkins UV Telescope ͑HUT͒ detected such HeII Particle-Mesh ͑PM͒ method that pancakes are unstable to the Lyman alpha absorption in quasar spectra at redshift 3 due formation of clumps for a substantial range of perturbation either to unresolved HeII lines associated with low-column wavelengths from roughly equal to the pancake mode wave- density QALCs or to the diffuse IGM or both. Together with length to smaller wavelengths. results like those of Giroux and Shapiro, these detections The antisymmetric modes also lead to significant genera- constrain the nature of the IGM and the QALCs and the tion of vorticity. Numerical gas dynamical simulations using origin of the metagalactic UV radiation background. the new ASPH method developed here have also been per- P. Shapiro and M. Giroux considered the feedback on the formed, revealing similar instabilities when a gaseous com- IGM and on the rate of formation of new objects out of the ponent is included. IGM due to the ionizing energy released by the first genera- H. Martel studied analytically the non-linear growth of tion of bound objects to form by condensing out of the IGM. cosmological perturbations for flat cosmological models with They demonstrated that, if energy is released at a rate high a uniform component that can be either a non-zero cosmo- enough to re-ionize the IGM, this reheats and raises the Jeans logical constant, domain walls, cosmic strings, massive neu- mass of the uncollapsed IGM, which suppresses and delays trinos, or radiation. The semi-analytical solutions obtained the growth of the collapsed fraction. In a model like the Cold show that the relationship between the present density con- Dark Matter ͑CDM͒ model in a flat universe, the maximal trast and peculiar velocity field is a sensitive function of the efficiency for energy release associated with stellar nucleo- density parameter, but it is very insensitive to the presence or synthesis is enough to re-ionize the IGM as early as a red- nature of the uniform component. This rules out any hope of shift of about 50. In order to investigate the importance of determining the presence of a uniform component by study- the feedback effect of this re-ionization and reheating of the ing the dynamics of the local universe. Only redshift- IGM on the rate of formation of galaxies and QALCs out of dependent tests might reveal the presence of this component. the IGM, Shapiro and H. Martel have applied their ASPH This generalizes the results obtained previously by various method to simulate the gas dynamical response of the IGM authors for models with a non-zero cosmological constant. to such reheating and the consequences for the rate of for- A. Khokhlov proposed a scaling law for buoyancy-driven mation of galaxy-sized and subgalactic gas clouds. Their re- turbulent pre-mixed flames and confirmed it by means of sults indicate that the observed amount of baryonic mass three-dimensional simulations. This regime of burning is rel- already formed into QALCs by redshift 3 is too high to be evant both for supernovae and for lean hydrocarbon terres- consistent with predictions of the CHDM model, while the trial flames in vertical tubes. For such flames, the scaling law CDM model is consistent if either photoheating alone re- has been recently confirmed experimentally. Khokhlov, E. heats the IGM or if explosive heating occurs as well, but this Oran, and C. Wheeler proposed that terrestrial experiments heating is accompanied by very efficient radiative cooling. can be used to calibrate thermonuclear models of Type Ia R. Benjamin ͑University of Texas and University of Min- supernova explosions. nesota͒ and P. Shapiro continued their modeling of hot gas A. Khokhlov also performed the first three-dimensional which cools radiatively in the Galactic halo as in the Galactic simulations of the explosion of a massive carbon oxygen fountain model. Their calculations of a steady-state, 1D flow white dwarf as a Type Ia supernova. The results show a of gas cooling from close to 106K to below 104K, including substantial decrease of the burning rate due to expansion non-equilibrium ionization, radiative cooling and radiative effects and sphericity. The results were consistent with a par- transfer, make detailed predictions for comparison with Ga- tial burning of a central portion of the star which leads to an lactic halo ISM observations. They show that UV emission expansion and recontraction. A detonation may occur at that and absorption lines observed from highly ionized species in point. our Galactic halo by IUE, HST, and various other space- Three-dimensional simulations of relativistic tidal interac- borne detectors, for example, can be self-consistently ex- tions of a star with a supermassive Kerr black hole were 650 ANNUAL REPORT carried out for the regimes of weak interaction to complete S.-W. Kim completed his dissertation research on time- disruption to ultra-strong compression of the star by A. dependent, irradiated accretion disk models for black hole Khokhlov, P. Deiner, and I. Novikov. A general relation be- X-ray transients. He found that self-shadowing by the disk tween the tidal tensor and the energy and momentum depos- can lead to phenomena like the secondary reflare which char- ited into a star has been found which covers both weak, acterizes many black hole candidate systems. Models that strong, relativistic, and non-relativistic regimes. For ultra- reproduce the observed light curves reasonably well have close encounters, material is ejected from the vicinity of the very little irradiation of the companion. The models tend to black hole in a large solid angle and can interact with inter- have a central portion near the black hole that remains hot stellar matter effectively. Sgr A East in the Galactic Center and ionized even in quiescence, when most of the disk is may be a result of the disruption of a solar-like star by a predicted to be cold, and an accretion rate down the black 6 black hole of 10 solar masses at a distance of several hole that is in approximate accord with X-ray observations. Schwarzschild radii. M. Moscoso has continued work in collaboration with M. The development of the multi-energy, multi-dimensional Kusunose to develop a code that can compute the radiation- neutrino transport and fluid dynamics model, ALLA-C, for induced pair wind expected to be driven from a pair- Type II supernova explosions was completed by I. Lichten- dominated corona around a black hole. stadt and A. Khokhlov. Preliminary results show a phase of M. Della Valle, S. Benetti ͑Asiago Observatory͒, and C. turbulent boiling before the explosion. Wheeler are writing a paper on the black hole candidate J. Boisseau completed his Ph.D. dissertation on the study X-ray transient Nova Vel 1993. This system is only the sec- of the stability of carbon detonation fronts with two- ond known to have experienced multiple outbursts over dimensional models. In analogy to terrestrial detonations, he times of hundreds of days after the main outburst. found that the detonation front fragments on the scale of the P. Kornreich and J. Scalo completed one phase of their post-shock carbon burning length into unburned pockets with investigation of the production of vortical internal motions in a size characterized by the equation of state and nuclear re- interstellar clouds by shock waves produced by stellar explo- action dynamics. This effect increases with decreasing den- sions and winds. Analytical methods, supported by numerical sity and may dominate for the low-density detonations that simulations, have been used to study the vorticity generated are thought to characterize delayed detonation models of as an initially planar shock propagates through irregular den- Type Ia supernovae. This may affect the detonation propaga- sity and velocity fields. A general analytic result for the im- tion and the resultant distribution of burning products. mediate post-shock vorticity and the downstream vorticity J. Wang has continued to construct a computer code ca- was derived. It was found that the passage of a shock through pable of simulating the principle features of multi- a cloud with a density gradient should generate strong inter- dimensional gravitational collapse models of supernovae. nal vortical motions, which should eventually be converted Such a code will allow a study of a broader range of param- by vortical-compressible interactions into density fluctua- eter space than full multi-dimensional models. Wang has implemented a ‘‘two-stream’’ formalism to simulate the ef- tions. These calculations suggest a physically plausible fects of convection and overshoot. mechanism for sustaining the supersonic linewidths observed C. Wheeler, Research Assistant R. Gearhart, and D. in interstellar clouds, provide a means of generating internal Swartz ͑Marshall Space Flight Center͒ are re-examining the density and velocity structure in clouds without any source production of carbon monoxide in SN 1987A. They are using of instabilities, and are also relevant to observations of cloud the distribution of composition, ionization, and ionizing flux rotation and initial protostellar angular momentum. from complete radiative transfer models in contrast to earlier D. Chappell and J. Scalo continued their study of models one-zone models. They find that the CO velocity distribution for collective spatial and temporal behavior of star formation is better reproduced in models in which the composition is in galaxies. The models operate on a lattice and include ab- substantially macroscopically unmixed. stracted implementations of threshold star formation, propa- M. Kusunose worked on hot accretion disks with non- gating star formation, fluid advection, heating by stellar pro- thermal particles and on particle acceleration around black cesses, radiative cooling, and turbulent dissipation. Because holes. With S. Mineshige ͑Kyoto University͒, he studied the of its abstracted nature, the model calculations are extremely structure of accretion disks around black holes and examined fast compared to conventional hydrodynamic simulations the condition where electron–positron annihilation emission and allow us to examine a wide range of parameter space and is observed from accretion disks. He applied this model to initial conditions. Most of the work this year has been de- Galactic black hole candidates such as Cyg X-1 and voted to a model that simulates the physics of the interaction GX339-4 to determine model parameters. With this model, between non-linear fluid advection and expanding shells he further examined a mechanism to explain the two differ- driven by threshold star formation. Besides the ability of the ent states of X-ray emission from Galactic black hole candi- models to generate extremely interesting structure as a result dates, i.e., the low state and the high state. Kusunose, H. Li, of advection alone interacting with the motions driven by and E. Liang ͑Rice University͒ constructed a model to cal- star formation, a particularly interesting result is that the glo- culate particle acceleration and radiation transfer self- bal star formation rate becomes ‘‘bursty’’ if the adopted stel- consistently, by which gamma-ray spectra from non-thermal lar initial mass function is steep enough. The models should plasmas near black holes are calculated and compared with eventually provide an observational test for whether star for- observations. mation primarily excites or inhibits further star formation UNIVERSITY OF TEXAS 651 and whether burst/lull behavior should be expected in non- areas: solar system ephemeris development, general relativ- interacting galaxies. ity and gravitational physics, lunar science, and geodynam- E. Vazquez-Semadeni ͑UNAM͒ and J. Scalo are collabo- ics. rating on a summary of observational and numerical simula- Laser ranging observations were obtained with the MLRS tion evidence that interstellar clouds may for the most part be at record-setting levels for the sixth straight year as person- transient entities that are usually far from equilibrium. They nel cooperated with colleagues around the world, making calculated the probability distribution for interstellar gas to maximum use of the data type in earth, moon, and solar be subjected to shocks from supernovae and winds/bubbles. system-related dynamics. For the first time ever with the Coupled with a study of the numerical simulations, this MLRS, the group is reaching lunar data densities approach- shows that clouds are probably disturbed by external shock ing those obtained in the mid-1970s with the 2.7-m system, waves and advective interactions with larger scales which act but at levels of accuracy and precision almost five times on timescales smaller than the time required to attain equi- better. Principal research activity includes monitoring the ex- librium. These results suggest that the entrenched view of change of angular momentum between the solid earth and its clouds in a state of virial equilibrium, and the concept of atmosphere, the principal geopotential terms, plate tectonic external confinement by turbulent pressure, may be invalid. activity, tidal dissipation in the lunar orbit, the lunar free J. Scalo began an investigation of a range of theoretical libration, and the equivalence principle of general relativity. models for the stellar initial mass function ͑IMF͒, with an In a service capacity the project serves as Observing Center emphasis on models that couple the IMF to the nature of the and Analysis Center in the International Earth Rotation Ser- velocity field in the clouds from which the stars form, such vice, obtaining millisecond accuracy estimates of the con- as velocity fields dominated by stellar winds, externally- stant of precession and coefficients of nutation, polar motion, driven shock waves, or some sort of more traditional ‘‘tur- and Earth rotation. This constitutes the only near-real-time bulence.’’ The properties of other models are also being ex- source of this information that includes the lunar laser rang- amined. The goal is to understand how different assumptions ing data type. about the dominant physics affect the predicted IMF, espe- The MLRS Auto-Guiding and Imaging System ͑AGIS͒ is cially on the issue of universality, and to question whether approaching full integration in all facets of the laser ranging meaningful choices between theories can presently be made, operation. The AGIS is an integrated hardware and software given that the range of possible physical scenarios is so great system that accepts real-time video signals as input, e.g., and the observational constraints so weak. The availability of highly magnified images of a small portion of the lunar sur- data from HST on deep star counts in various environments face, or stellar or artificial satellite point-source images. It and from accumulating spectroscopy of massive star popula- performs real-time image processing and allows a user to tions plays a key role in answering these questions. select among various levels and types of image enhance- ment. Further, the AGIS produces raw and filtered tracking 3.3.7 Laser Ranging: error signals that under user selection are communicated to a Lunar and artificial satellite laser ranging, with Project control computer for guiding control. At this time, most use Director P. Shelus and staff members R. Ricklefs, J. Ries, A. of the AGIS is applied to the lunar effort, producing a Whipple, and J. Wiant, continues under the support of the marked increase in the volume of LLR data. National Aeronautics and Space Administration. The Mc- A second, improved Avalanche Photo-Diode ͑APD͒ was Donald Laser Ranging Station ͑MLRS͒ is a fundamental sta- delivered to the MLRS this summer by German colleagues in tion in the world-wide laser ranging network. It consists of a Wettzell in the effort to replace the MLRS Varian high quan- 0.76-m reflecting telescope and a very short pulse, tum efficiency photomultiplier tube in lunar laser ranging frequency-doubled, 532-nm-wavelength, neodymium-YAG operations. Such an APD detector, now in use at the French laser, with associated computer, electronic, and timing hard- LLR station, has exhibited a significant increase in sensitiv- ware. The station is located on Mt. Fowlkes, to the northeast ity and improved accuracy and precision. A similar device is of Mt. Locke, and shares the mountaintop with the new used for artificial satellite laser ranging operations in the Hobby-Eberly Telescope. With a two-crew observing opera- United Kingdom and elsewhere in Europe. The first unit that tion, laser ranging is carried on to a host of artificial satellites the team received exhibited intolerable noise characteristics ͑Fizeau, ERS-1, ERS-2, Starlette, Stella, Meteor-3, Ajisai, and marginal sensitivity when installed in the MLRS ranging TOPEX/Poseidon, LAGEOS-1, LAGEOS-2, Etalon-1, system. The second unit appears to possess much improved Etalon-2, GPS-35, GPS-36, GLONASS, and Meteosat P-2͒ noise characteristics and greater sensitivity. The first test re- plus the moon. The MLRS is the only lunar-capable station sults on the moon have been very encouraging. in the United States and only one of two lunar-capable sta- Finally, the team has replaced the MLRS’s 15-year-old tions in the entire world. By measuring the time it takes for a Data General NOVA control computer system with a laser pulse to leave a ground station, bounce off a targeted LynxOS-based, X-windows, real-time Unix system running reflector array, and return to the ground station, one can mea- on PC hardware. This has been coordinated with similar up- sure very precisely the distance between the station and the grades at other NASA- based laser ranging systems. It has reflector array. Comparing a series of measurements ͑almost created a system having highly compatible, transportable, 30 years of lunar laser ranging observations have now been and transferable hardware and software architecture in an accumulated, together with more than 10 years of artificial open-systems ͑POSIX͒ environment. The approach has al- satellite data͒, scientific results are obtained in four broad lowed a maximum amount of software portability and shar- 652 ANNUAL REPORT ing. All MLRS data, both lunar and artificial satellite, are Saturn, and Neptune, and of many selected asteroids. Most now being obtained with this system. of these objects have, been grossly underobserved in the past, and orbit refinements require that a continuous set of 3.3.8 Astrometry: precise and accurate positional observations be maintained. Positions of all interesting objects are determined in a stan- The Hubble Space Telescope Astrometry Science Team is dard reference frame. based at the University of Texas. Local members include G. Benedict ͑Deputy P.I.͒, R. Duncombe ͑Aerospace Engineer- ing͒, W. Jefferys ͑P.I.͒, B. McArthur, P. Hemenway, E. Nelan PUBLICATIONS ͑STScI͒, P. Shelus, and D. Story ͑Goddard Spaceflight Cen- Achtermann, J.M. & Lacy, J.H. 1995, ‘‘Structure and Kine- ter͒. The team continued reducing and analyzing data bearing matics Within the Starburst Nucleus of M82: Searching on planet searches, HIPPARCOS-quasar reference frame tie- for a Bar,’’ ApJ, 439, 163 in, and parallaxes of astrophysically interesting objects (␦ Armosky, B.J., Sneden, C., Langer, G.E. & Kraft, R.P. 1994, Cephei, RR Lyrae, Feige 24, planetary nebulae central stars, ‘‘Abundance Trends Among Neutron Capture Elements in the Hyades, low-mass M-dwarfs͒. All data are obtained with Giants of Globular Clusters M5, M3, M13, M92, and Fine Guidance Sensor 3 aboard HST. They continue to ob- M15,’’ AJ, 108, 1364 tain milliarcsecond or better precision for parallax values. Atreya, S.K., Edgington, S.G., Trafton, L.M., Caldwell, J.J., Much future science will come from nearly simultaneous Noll K.S., & Weaver, H.A. 1995, ‘‘Abundances of NH3 transfer scan and position mode astrometry with FGS 3 to and CS2 in the Jovian Stratosphere Following the Impact obtain precise orbits, parallaxes, and masses for close binary of Comet Shoemaker–Levy 9,’’ GRL, 22, 1625 stars difficult or impossible to study from the ground. Barnes, T.G. & Moffett, T.J., 1995, ‘‘Uncertainties in the This year the team carried out two remaining calibrations, Galactic Cepheid Distance Scale,’’ in Astrophysical Appli- lateral color and cross-filter. Shelus’ analysis of the most cations of Stellar Pulsation, ASP Conference Series 83, recent HST lateral color observations was finished with no 363 substantive effect being detected. 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