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Carol Winifred Ambruster, specialist in coronal and chromospheric activity in late-type dwarf stars and, later in her career, in archaeoastronomy of the American Southwest, died on 9 December 2013 during a robbery in her Germantown, Pennsylvania, apartment. Born on 25 December 1943, Ambruster grew up in New York City. She received her bachelor’s degree in physics from Northeastern University in 1971 and her doctorate in astronomy from the University of Pennsylvania in 1984. Her thesis, “A Survey of Fast X-Ray Transients Using the HEAO A-1 Sky Survey Experiment,” was completed under the supervision of Kent Wood at the Naval Research Laboratory in Washington, D.C. She conducted post-doctoral research on cool stars at the Joint Institute for Laboratory Astrophysics (now JILA), in Boulder, Colorado, until 1987, when she joined the astronomy faculty at Villanova University.
Ambruster’s life as an astronomer, colleague, and friend is memorialized in the following tributes by three of her former associates:
Tony Hull, Adjunct Professor of Physics & Astronomy, University of New Mexico
I had known Carol since graduate school, when we both studied astronomy at the University of Pennsylvania. We immediately became good friends when she arrived at Penn about 1970, and remained so throughout her life. The two of us collaborated during that period on observations made with the Pierce-Blitzstein Pulse Counting Dual Channel Photometer at Penn’s Flower and Cook Observatory, from which we published several joint papers in the 1970s. Later we did historical reports on that fine instrument.
Carol went on to do a dissertation in X-ray astronomy under Kent Woods at the Naval Research Laboratory, and a post-doctoral appointment at JILA, where she began her studies of cool stars. She received observing time on both the International Ultraviolet Explorer and the Hubble Space Telescope, and supplemented these with large blocks of observing time at Kitt Peak. I would join her and assist at the latter. Carol was among the most careful observers I have known, and looked at data from every angle.
While in graduate school at U Penn, we both became acquainted with cultural astronomy, and both followed through with extended work in that field later in our careers. While at JILA, Carol spent considerable time at Southwest U. S. sites, including Chaco Canyon, Hovenweep, and Chimney Rock, working with Ray Williamson, Von del Chamberlain, Kim Malville and GB Cornucopia. In the early 1990s, I started to join her at Hovenweep and Chaco Canyon, and we began to publish papers, especially on a remarkable site in Eastern Chaco Canyon with evidence of early Navajo habitation. Archaeologist and friend Elizabeth Jewell joined us in these studies, which continue to the present.
Carol was very inclusive: she always sought input from the Navajo (the team’s discoveries of early Navajo solstice recognition extended knowledge of the culture), including Navajo scholar David Brugge. Her level of scholarship was high. Always a critical thinker, whether on astrophysics or archaeology, Carol pushed hard not to settle for easy conclusions, but to also include proofs of everything she studied. We presented several papers on Monte Carlo methods to aid in research design and evaluation of results in cultural astronomy. Carol believed it paramount to discriminate between likely cultural meaning of observations and random occurrence of alignments. She was part of raising the bar for research standards in the field.
Tragically, in December 2013, as she, Beth Jewell and I were preparing a paper to be read at the January 2014 HAD meeting of the AAS, we lost Carol. Everything Carol did, she wanted to do to the highest standards. The paper was read, and Dr. Ed Guinan arranged for a minor planet to be named after Carol. This was perfect for her!
Edward Guinan, Professor of Astronomy & Astrophysics, Villanova University
Carol arrived at Villanova University in 1987 as an Assistant Professor and retired in Fall 2011. She died tragically in December 2013. During much of her astronomical career, Carol specialized in the study of red dwarf and related stars. Red dwarfs are small, cool, low mass stars that make up about 75% of all stars in the Galaxy. These ubiquitous little stars have robust magnetic dynamos that produce strong coronal X-ray and chromospheric ultraviolet emissions. These stars also have strong, frequent optical flares and often show light variations from the presence of large starspots. Red dwarfs are more active than solar-type stars of the same age, mainly because of their deep outer (magnetic field generating) convective zones.
Carol’s interest in red dwarfs started with her PhD thesis (1984, University of Pennsylvania) in which she did pioneering work on fast X-ray transients using the HEAO A-1 Sky Survey Experiment. It turned out that most of these fast X-ray transients in the all-sky survey are red dwarf flare stars. Carol’s research focused on mainly the youngest, most active red dwarfs, and she carried out X-ray and ultraviolet observations of many of them. She “adopted” several especially-active red dwarfs as her “hyperactive children.” Her two favorites were the young active red dwarf flare stars EV Lac and AT Mic. For her work, she utilized a host of astronomical resources, including the Einstein X-ray Observatory, International Ultraviolet Explorer (IUE) satellite, Extreme Ultraviolet Explorer (EUVE), and the Hubble Space Telescope (HST). Over her career, Carol collaborated with large number of people that include, among others: Alexander Brown, Frank Fekel, Brian Wood, Rachel Osten, Suzanne Hawley, and Jeff Linsky.
In addition to studying red dwarfs, Carol also was interested in chromospherically-active K dwarfs and giants. I had the pleasure to work with Carol on several projects during the late 1980s to 1990s. In one of the programs, she and her collaborators studied and developed relations between rotation and activity for young red and orange dwarfs (Ambruster et al. 1989). She was fun to work with, and from her strong X-ray background, she had excellent insights in the underlying physics of these active stars. It was also good working with Carol on the extremely active and heavily spotted K giant star 1E 1751+7046 – now known as ET Draconis. This rapidly rotating, apparently single K giant star, has strong X-ray and UV emissions and also shows periodic light variations presumably arising from starspots. The most likely explanation (Carol’s idea) was that this star evolved from the merger with a former binary companion and thus could be related to FK Comae variables. Carol was enthusiastic about this research and her enthusiasm was contagious to me and our students.
Carol was also a pioneer and a passionate researcher in the field of archaeoastronomy. Her interests were primarily in the study of astronomical references left behind by the ancestral Pueblo peoples who inhabited Chaco Canyon in northwest New Mexico about 1000 years ago, and the subsequent early Navajo presence in the Southwest. She was so fascinated by this area of research that archaeoastronomy became her main research field over the last decade of her life. She was an active member of the Society for Cultural Astronomy in the American Southwest (SCAAS) and published a number of interesting papers mainly with Tony Hull and Elizabeth Jewell. She loved the Southwest and spent much time in Chaco Canyon around the times of equinoxes and solstices, studying astronomical alignments with the Sun and stars. She also used this time to study and analyze rock art. During her many visits to New Mexico, she had accumulated a beautiful collection of native baskets, fabrics, art and jewelry. She also was an avid bird watcher who found time during her trips to build her bird-spotting inventory.
It is noteworthy that during her tenure at Villanova, Carol was a conscientious teacher and a caring mentor to our students. She took a great deal of time mentoring and advising our female undergraduate students, in particular. She left her office door open for students, and I frequently saw students waiting their turn at her door. Carol is deeply missed by her friends and colleagues as well as her former students.
Alexander Brown, Senior Research Associate/Fellow, Center for Astrophysics and Space Astronomy, University of Colorado at Boulder
Early in her career, using the HEAO 1 and Einstein spacecraft, Carol was among the first to recognize the dramatic effects on stellar X-ray emission produced by the strong magnetic activity of young, low-mass, flare stars and close binaries. Over many years — even before the plethora of young local moving groups were well known — she worked to understand the population of nearby young stars that were revealed by their anomalously bright X-ray and ultraviolet emissions, as detected by a wide variety of space-based X-ray and UV observatories. While at JILA, her UV work started with IUE and later continued with HST.
Carol had a great appreciation for the beauty of the natural world. She was an accomplished birder and observer of other natural phenomena. She enjoyed the special moments that nature offers, whether it be finding a sought-after bird or viewing a fine sunrise/sunset over mountains or the ocean. She had a particular love for the desert landscapes of the Southwest U.S.
The Society for Cultural Astronomy in the American Southwest (SCAAS) has established the Carol Ambruster Memorial Fund, to provide research grants to support further study of the Chaco Canyon and other Southwest U.S. sites (http://www.scaas.org). The SCAAS website states that “Carol was the most thorough note taker one could imagine. Throughout her career, Carol took a profound interest in students, and often worked individually with them, helping their understanding, while always keeping the academic standards high. Carol’s scholarship and love of cultural astronomy will be missed, but her influence will continue through this fund.”
— Edward Guinan, Tony Hull, Alexander Brown, and friends of Carol Ambruster
Obituary written by: Edward Guinan (Villanova), Tony Hull (UNM), Alexander Brown (U Colorado Boulder)
BAAS Citation: BAAS, 2017, 49, 019