Wendy Hagen Bauer - Infrared, optical and ultraviolet observations of cool stars, and binaries containing one hot and one cool component.
I have been studying mass loss from luminous cool stars through observations of circumstellar (CS) matter surrounding the stars. CS gas is observed via high-dispersion spectroscopy where the expanding shell is detected through asymmetries in the profiles of spectral lines. CS dust (mostly silicate grains in the stars I observe) is detected through an excess of radiation at wavelengths of 10 microns and longer. The stars appear to be losing mass at a rate significant enough to affect their evolution, and no correlation is seen between the quantities of CS gas and dust, indicating that the mechanism for mass loss is not entirely radiation pressure on the grains.
Work published in the Astrophysical Journal 274, 286 (1983) with R.E. Stencel and D.F. Dickinson has shown that a high CS gas-to-dust ratio is strongly correlated with the presence of chromospheric calcium emission and with the absence of hydrogen Balmer emission and molecular maser emission. Two colleagues and I have used the International Ultraviolet Explorer Satellite to look for chromospheric emission from other elements than calcium and have found it, indicating that these stars do, after all have chromospheres (Astrophysical Journal 308, 859 (1986), with R.E. Stencel and K.G. Carpenter.)
I have used observations of cool stars made by the Infrared Astronomy Satellite. For a number of these objects, the spatial extent of the CS dust shell is great enough to have been resolved by IRAS. The binaries VV Cep and 31 Cyg consist of a cool supergiant with an extended atmosphere and a much smaller hot companion star. The systems are eclipsing binaries, and as the hot star passes behind the extended atmosphere of the cool star, its orbital motion can be used as a probe to study the structure of the cool star atmosphere. This is being done with observations from the International Ultraviolet Explorer satellite and with ground-based observations from Kitt Peak National Observatory.
Student Projects: A 370 project was done by Deborah Crocker searching for water vapor masers at radio wavelengths in previously known infrared sources. Our observations continued during her first year in graduate school, and the results appear in the Astronomy and Astrophysics Supplement Series 54, 405 (1983). Two students have worked with me on circumstellar gas and dust, and two on the eclipsing binary project.
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Richard G. French - Planetary Astronomy, especially the study of planetary rings and atmospheres, using both earth-based and spacecraft observations.
Fifteen years ago, astronomers were trying to understand why Saturn was the only planet known to have rings. Since then, ring systems have been discovered around Jupiter and Uranus, and even Neptune has a bizarre set of incomplete rings, or "arcs". I am interested in using earth-based and spacecraft observations to study the properties of these ring systems.
One especially effective technique is to observe the passage of the rings and planet in front of a star. The rings cast shadows on the earth, and from accurate timing of the arrival of the shadows at a given observatory, we can determine the orbits of the rings with remarkable precision. The radial distribution of material in the ring can be determined from variations in the darkness of the shadows.
Over the last few years, I have organized and taken part in several world-wide expeditions to observe such stellar "occultations" using large optical telescopes. I have also been involved in planning the observations of the outer planets by the Voyager spacecraft, now on its way out of the solar system, and in combining the earth-based and spacecraft observations to investigate the dynamics and structure of the Uranian and Saturnian rings. I am a member of a science team on NASA's Cassini Mission to Saturn, which will be launched in 1997.
Student Projects:
I have directed student theses, summer projects, and independent study courses on such things as Neptune's atmosphere, variable stars, occultations of stars by the moon, and mathematical models of planetary rings. Each year, two or three students have worked with me on projects related to my own professional research interests. I am particularly interested in developing observing projects with students, using Whitin Observatory for photometry of asteroids and variable stars, and in using computers for automated data analysis. I am also planning to incorporate computer graphics into the advanced astronomy courses, and I invite students to work with me on the Astronomy Department's advanced color workstations.
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Research:
My current research centers on investigating the role of nuclear activity in the evolution of galaxies. I have been using the Hubble Space Telescope and ground-based telescopes in Arizona to obtain infrared images of the galaxies in which quasars and active nuclei live. These images indicate a "luminosity/host-mass limit" in which the bigger black holes must be found in bigger galaxies. This discovery has become especially exciting in light of recent observations by others that normal galaxies like our Milky Way satisfy a similar relation. Together, these results suggest that the formation of a central black hole is a fundamental part of the evolution of all galaxies. Other past research interests include: an observational study of the archetypal starburst galaxy M82 using a suite of cameras and infrared spectrometers; observations of the continuum emission from quasars with the ISO satellite; predictions of properties of the lens galaxy for the gravitationally lensed quasar Q1208+1011; a successful search in polarized visible light for a hidden AGN in the famous megamaser galaxy NGC 4258; tests of the use of fibers for infrared spectroscopy; theoretical predictions of effects of infrared pumping on CO and HCN molecules in protostars and young stellar objects. Most recently, I have begun a feasibility test to determine whether Wellesley's 24-inch telescope can be used to search for planets around other stars. The idea is to monitor the brightnesses of thousands of stars to watch for slight dimmings as planets traverse the line-of-sight between the stars and Earth.
Student Projects:
I have advised several student projects over the past few years. One summer student used the Digitized Sky Survey data to constrain the amount and location of dust along the planes of Seyfert galaxies. Another compiled data to examine the energy distributions of quasars from x-ray to radio wavelengths. A third summer student assisted me in reducing our quasar host galaxy images from the Hubble. I have also advised two independent research projects for students who are not physics oriented. One student carried out a historical study of the instruments in the Observatory, and another tested the capabilities of our 24-inch telescope's spectrometer. I have recently submitted a proposal to do a one-year feasibility test to use our 24-inch telescope to search for extrasolar planets by the transit method. I am tremendously excited about this possibility and hope that it will keep me and many Wellesley students engaged in research for many years to come.