G. Donald Penrod

G. Donald Penrod passed away on October 23, 1998 in Portales, New Mexico. During his brief career in astronomy, Don left a lasting mark on contemporary research on active OB stars. I enjoyed working with him on the first IUE campaign on 28 Cyg in 1985. In response to one of my queries on his interpretation of the optical spectra, he wrote me a concise two page summary on NRP in B stars, of course including his characteristic small, light printing, that I still refer to today. I remember the excitement when he discovered the lines from the secondary star in the CX Dra system. Below are some personal reminiscences from his Ph.D. dissertation adviser, an early colleague, and a researcher who comments on the scientific contributions from his work.

Gerrie Peters

In memory of Don Penrod...

I had the good fortune of working with Don, both as a friend and as a colleague from about 1980 to 1989. Don came to Lick as a graduate student from Cal Tech and subsequently chose to work with me as his research supervisor. Don was much more of a colleague than a student, and I probably learned more from him than he from me. Don was clearly one of the most intelligent people I have ever known. He had an almost photographic memory, and an uncanny ability to grasp difficult concepts with ease. I remember how well he did in my graduate Stellar Atmospheres course. On homework problems where many students would go on for pages with their mathematical solutions, Don would often do it in the space of one line; cleanly, clearly, and always correctly. I used to challenge him in a "human calculator" game, giving him complex division or multiplication problems to do in his head, while I did them on a calculator. To 3 significant figures, he would always beat me!

Don did most of his theoretical work with a few basic tools, a #4 pencil, a pad of unlined paper, a 40-step programmable HP calculator, and a giant "Pink Pearl" eraser. He carried these simple tools around always, and with them could crack most any problem. He once programmed a simple stellar model on that little calculator! His #4 pencil left barely visible, spidery lines in his precise, micro-font hand. These writings were almost not reproducible on a xerox machine as they were so faint. I used to have to jack up the contrast and darkness settings to near max, just to make the copies legible. But those spidery lines wove a rich web of wisdom and insight which have left a lasting mark on todays' fields of non-radial pulsations of OB stars, and Doppler Imaging.

Don worked mostly alone, apart from the graduate students. He often worked all evening, and slept during the day. Since I was 180 degrees out of phase with this schedule, he communicated mostly by little yellow "Post-It" notes left on my desk, again in that spidery micro-font hand. He was ever the gentlemen, with nothing but kind things to say about everyone, and a positive attitude always. He had a wonderful sense of humor. Once, as we were deep in the development of the maximum entropy Doppler Imaging technique, Don and Tod Lauer decided to make a model of a spotted star for my office. They purchased an 8-foot diameter weather balloon and inflated it in my office one night. I came in the next morning to find much of the office occupied by this giant sphere with a huge polar spot and several smaller equatorial spots. Only later did I learn that their first attempt had failed, ending in explosion of the balloon on a previous night, and hours of frantic pre-dawn cleaning to get all the spot paint off my office walls!

Don contributed mightily to several areas of research. He helped to develop the methods for modelling NRP's of OB stars, and started a whole new paradigm in our thinking about the Be phenomenon. He observed and characterized the NRP properties of several dozen OB stars, though unfortunately he had to leave Astronomy before these were published and they have never made it into the literature. Some day I hope to free up enough time to revisit this field and get his results out. He went on from the NRP modelling research to write much of the underlying code which became the Maxent Doppler Imaging tool that Don, Artie Hatzes and I used throughout the 80's and 90's to derive images of spotted late-type stars, and Ap stars. He helped me in the early stages of conceptualizing the HIRES spectrometer at Keck, and was the most prolific member of the HIRES science advisory team. It was a great loss to Astronomy that he had to leave the field abruptly in early 1988, though he certainly left a lasting mark from his graduate career at Lick. I was profoundly saddened to learn of his passing. He was an extraordinary individual and I feel very lucky to have known and worked with him for those few years.

Steve Vogt - UCO/Lick Observatory

Astronomers outside the fields of Doppler imaging or Be stars probably will not recognize the name G. Donald Penrod, but for those of us who work in these areas we are well aware of the impact he had in these fields in spite of his short career. Don played a major role in laying out the foundations of Doppler imaging and established that Be stars oscillate in high degree nonradial modes, which may be responsible for the Be outburst phenomenon. Today NRP pulsations in B stars is taken as a given and whole conferences are now devoted to Doppler imaging. The fact that he did all this in a career that spanned approximately 7 years, all in graduate school, is nothing short of amazing. Many of us struggle for a full career to make contributions that pale in comparison to Don's. Of all the astronomers I have met in my life, Don still ranks up there as one of the most gifted and I am sure that given a full career he would have established himself as one of the great stellar astrophysicists of the last 20 years. Instead, we are left to ponder "what if".

My relationship with Don dates back to 1976 when we were both undergraduates at Caltech living in the same dormitory (Ricketts House). It did not take long for us to become good friends and we spent many an hour in the astrophysics library reading the journals (I for class work, Don just for the sheer love of it.) Don was a voracious reader and virtually lived in the library. In fact, he read ApJs to the detriment of his classwork and often would have to cram over the last week of the trimester to catch up before final exams. I have fond memories of him pacing up and down outside his room the night before a physics final chanting "Woe is me, woe is me, I'm doomed, I'm doomed!". (As a testament to his brilliance, he still managed to do far better in classes than those of us who toiled on the classwork for the whole trimester). It was during his readings as an undergraduate that he was greatly influenced by Myron Smith's work on nonradial pulsations and their effect on the line profile variations in B stars. This was largely the reason he pursued this work as a graduate student.

After Caltech I followed Don to U.C. Santa Cruz, became his roommate, and eventually had the same thesis advisor, Steve Vogt. This was the smartest move of my career for I learned as much astronomy from my late-night discussion with Don at home and on observing runs than I did from graduate courses. His impact on astronomy began immediately upon his arrival in Santa Cruz. He started by laying down the foundations of Doppler imaging and was one of the first to realize that dark spots on rapidly rotating stars would produce pseudo-emission features in the line core, something that is not at first intuitively obvious. This was one of Don's strongest traits, a keen physical intuition that enabled him to see things quicker than most people. After choosing Steve Vogt as my advisor, Don and I began work on putting Doppler imaging on a firmer mathematical foundation and employing the principles of Maximum Entropy. Don's contribution in this effort was indispensable and without him I doubt that we could have developed our Doppler imaging technique as quickly as we did. To this day we still employ the software he developed. Many of Don's ideas came while sitting in a beanbag chair in our apartment and we often would joke about his "Institute for Beanbag Astrophysics."

Don's largest contribution was arguably in the field of nonradial pulsations in Be stars. I will not go into the details of this work, since it is familiar to those of you who read this newsletter and others are more qualified to comment on this than I. I do know that Don had amassed a large body of observational data on Be stars and most was already analyzed. In fact, he was in the midst of writing his Ph.D. thesis when, for medical reasons, he dropped out of the graduate program, forever. This was a great tragedy for Be star research.

Don's interests were not confined to just astronomy. He was incredibly well-read in a wide field of subjects and could carry on high-level conversations in subjects ranging from literature to military history (WWII in particular). In fact, his initial ambition was to be a literature professor like his father, but this was derailed after reading a book on astronomy by Fred Hoyle (Thank you Fred).

I will leave you with one more related anecdote about Don. Don could write the most turgid fortran code that would somehow run efficiently. Embedded in this morass of code one could find genuine jewels that could only come from the mind of Don Penrod. Don had written some code to display Doppler images to a monitor and as part of that code a "ghoststar" image was generated. This was a globe consisting of latitude and longitude lines which showed the inclination of the star. The code that generated this globe was only about 10 lines long. Several years after Don left astronomy, graduate Steve Allen was left with the task of converting this fortran code to C. Steve could look at a code, understand its workings immediately, tear it apart, and reconstruct it so that it ran more efficiently. Never had he been baffled by anyone's computer code. On a visit back to Santa Cruz shortly after I graduated I happened to encounter Steve walking down the hall with a dazed look in his eyes and shaking his head. He stopped me and said "Do you remember that Penrod code that creates the ghoststar? I have been staring at it for hours trying to understand how it works. It works; I don't know why it works, but it does. And I can't imagine anyone accomplishing the same task in as few lines as Penrod used.... It is a gem." He then continued to walk on down the hall with his dazed look. I couldn't help but think that Salieri had just had his first encounter with Mozart!

The last contact I had from Don was via e-mail about a year before he died. His e-mail sounded very upbeat and full of the Penrodian humor that I loved so well. His mother sent me a letter after his death and told me that we should be comforted in the fact that the last few years for Don were by far the happiest of his life.

In 1987 when Don left astronomy the field truly lost one of it most gifted practitioners. When Don left us in 1998 the world lost a truly wonderful human being, and that is the far greater loss. We will all miss him dearly. Don's favorite Shakespeare play was Hamlet and these words from that play are indeed appropriate: "Now cracks a noble heart. Good night sweet prince and flights of angels sing thee to thy rest!"

Artie Hatzes - University of Texas, Austin

I want to thank the editor for asking me to round out this short collection of remembrances on Don Penrod. Steve and Artie have spoken eloquently, so I will attempt only to put some of Don's work into a history of science perspective.

I can think of three effects in line profile analysis that are counter-intuitive, and for this very reason they all have far-reaching implications. Two of these effects were discovered by Don and announced in two remarkable papers by Vogt and Penrod, 1983. The first is the result that a spot on a rotating star's surface which appears black both in an absorption line and the continuum produces an integrated flux line profile with an apparent emission bump (line emission caused by a different kind of spot can produce a similar effect, so one must be careful!). The second is that a high-degree nonradial mode can produce bumps and wiggles in a line profile of a rotating star. In the modeling I had done before Don entered the picture I had made the mistake of testing the effects of rotation or NRP-degree alone. I thus came to the wrong conclusion on this second effect that high degree modes in rapidly rotating stars were not yet worth pursuing. It took a brilliant intuition to understand that problems involving vectorial addition cannot be handled in a controlled environment of looking at the effects of a single parameter at a time. Don's two discoveries each mark key points in the history of spectoscopic analysis of active stars. Each of these counter-intuitive effects has produced a new technique-oriented subfield: the diagnosis of high-degree NRPs from line profiles and the "Doppler imaging" of surface spots (a term Steve coined). It is not an exaggeration to say that he permanently changed the course of two substellar subfields of stellar astronomy. One day, perhaps in our lifetimes, the information we are learning from these techniques will be supplemented by interferometric imaging. I suspect Don could have had a hand in hastening the opening of this frontier.

My last contact with Don was an exchange of letters in which he apologized for "letting Steve and you down" for leaving astronomy for health reasons, but to the contrary it was we whose lives and professional interests he had enriched. It is impossible to know what would have happened had Don not been born with a flaw in one key gene. At the time Don was forced to halt his studies, a postdoc position had been prepared for him at Los Alamos. Certainly he would have also pursued a theoretical study of nonradial pulsations and integrated his results with an observer's understanding. I would like to hope that he might have become one of the all too rare players with one foot securely in each of the cool and hot star communities and who likewise might have become a rare member of his generation to become a leader in complementary disciplines of theoretical and observational astrophysics.

Whether we might have known Don as a junior colleague or of him by his reputation, let us acknowledge our appreciation to his family, friends and teachers for enabling him to become a pathfinder to discovery and to delight in life.

Myron Smith - CSC/STScI