RESEARCH IN ASTROPHYSICS

Barbara Whitney develops computer codes that simulate the interactions of light as it propagates through various objects. For example, in a forming star, she calculates how much light emerges from the warm "protostar" in the center of a collapsing cloud of gas and dust. By comparing model images to observations, she tests theories for the infalling cloud structure and composition. Barbara uses her model images of a famous evolved star, called Eta Carina, in an attempt to understand the geometry and dust properties of its expanding envelope. In addition to computer modeling, she also enjoys pursuing a few observing projects, mostly related to star formation---searching for supersonic outflows in protostars, and searching for protostars in deeply embedded massive star formation regions (looking at infrared wavelengths that allow you to see into the cloud). Barbara also applies her light propagation studies to planetary science.

Mary Barsony's research interests comprise the detailed study of the formation mechanisms of stars and planetary systems from the tenuous, raw material of the interstellar medium. On the observational front, progress in this field requires data across a broad wavelength range, spanning the near-infrared, mid-infrared, submillimeter, and millimeter wavelengths, because the objects under study are generally deeply embedded in the dust and gas from which they are forming, and their intrinsic radiation is absorbed and re-radiated at wavelengths longer than the visible.

By piecing together data over the near-IR to mm wavelength ranges, astronomers have deduced four general stages in the formation of Sun-like stars over the last fifteen years. The earliest stage lasts only a few tens of thousands of years, during which time the gas which will become part of the newly-born star is dynamically infalling onto a seed protostellar core, even while the system drives powerful bipolar jets of gas into its surroundings. At this early stage, the protostar is only observable at far-IR, sub-mm, and mm wavelengths. The next stage, when the protostar becomes visible at mid-IR, and even near-IR, wavelengths, lasts a few hundred thousand years. By now, the central protostar contains most of the material it will have as a young star, it has formed an accretion disk with enough gas mass to create a planetary sytem, and it is still surrounded by a remnant infall envelope, through which bipolar cavities have been excavated by its outflow. By the third stage, which lasts a few million years, the infall envelope h as been completely dispersed, the accretion disk remains, and the central young object has become optically visible. During the final phase, the disk is dispersed and the young star contracts until its energy source becomes the fusion of hydrogen into helium, at which time it becomes a newborn star.

Although we now have this general overview of the star-formation process, many unanswered questions remain, and are the focus of Mary's current research efforts. Why do stars like to form in groups and associations rather than individually? What drives the protostellar outflows, and what mechanism turns them off? What physical process determines the initial mass a star will have? Most stars are in binary or multiple systems- how do these form? What are the timescales of accretion-disk formation, planetary system formation, and disk dissipation?

Progress toward answering these questions will require data from new or planned satellites and instruments, such as the CHANDRA X-ray observatory, the SIRTF (Space InfraRed Telescope Facility), planned for a December 2001 launch, the SOFIA (Stratospheric Observatory for Far-Infrared Astronomy), planned to begin observations in 2002, and the ALMA (Atacama Large Millimeter Array), planned to start observations in 2007. In the meantime, Mary is analyzing valuable data on the young, embedded protostars gathered with the MIRLIN mid-IR camera at the Palomar 5-m and at the Keck II 10-m telescopes, to answer such questions as: What is the binary frequency amongst the youngest protostars? Are the disks in binary systems aligned or misaligned? Are there disk-disk interactions and how do these affect the evolution of a young system or the formation of planetary systems? What is the distribution of stellar masses upon formation, and does this distribution vary from cloud to cloud?

Mike Wolff's research includes both the study of interstellar dust and the atmosphere/current climate of Mars. He primarily works with spacecraft data (Hubble Space Telescope and the Wisconsin Ultraviolet Photo Polarimeter Experiment), though he still dabbles in the area of ground-based linear spectropolarimetry measurements.

Mike's astrophysical research is generally centered around cosmic dust grains. His studies span the celestial scale from dust (and water ice) aerosols in the Martian atmosphere to interstellar particle in the Small and Large Magellanic Clouds as well as the Andromeda galaxy (M31)! His specific interests are focussed on the scattering properties of nonspherical composite grains and the numerical techniques by which they are calculated (i.e. Discrete Dipole Approximation, T-Matrix, etc.). Mike's current projects include the synthesis of advanced electrodynamical algorithms with the monte carlo radiative transfer technique in studies of star formation processes. In addition, he collaborates very closely with Geoff Clayton's dust group at Louisiana State University, where the analyses are oriented toward dust in extragalactic environments (e.g., starburst galaxies).