Dr. Lisa Prato will obtain and analyze high-resolution infrared spectra of very young stellar binaries. The target stars are of the T Tauri type, and represent the early evolutionary phases of stars like the Sun. The goal of the project is to determine dynamical mass ratios down a fraction of the mass of the Sun. Mass is the most fundamental stellar property and, once composition is set, determines all properties of a star's life and death. In spite of its key importance, however, astronomers' knowledge of young star masses, mass ratios, and higher order multiplicity is incomplete because to date no statistically large samples exist. This project will put the T Tauri mass ratio distribution and higher order multiplicity frequency on a sound statistical basis. The resulting mass ratio distribution and sub-distributions, possible with such a large sample, will be compared to theoretical predictions, and to mass ratio distributions for older stars.
These data are anticipated to aid theorists developing models of close binary formation, planet formation, stellar evolutionary models, and cluster formation. Dr. Prato wll also provide "sidewalk astronomy" open night observing and slide shows for senior citizen communities in Flagstaff, Arizona. She will also offer free astronomy mini-courses at Lowell Observatory for seniors. Prato will continue her intensive mentoring activity with students and will encourage them to actively take part in outreach activities associated with this proposal.
A fundamental driver of science which extends broadly across many fields and specialties is human beings' desire to understand our origins. This is manifest in archeological, anthropological, biological, and astronomical research, to name a few. Within astronomy, investigations of the origin of our solar system, planets in general, and Sun-like stars are of particular interest. We strive to understand if our own star, our planetary system, and our home, Earth, are unique, common, easily reproducible, or unusual, in part so that we learn more about our origins as well as about the possibility for the existence of other planets like ours. One way to approach this research is by studying new-born, solar type stars still surrounded by circumstellar material from which planets are likely forming. The most fundamental property of a star is its mass; by determining a young star's mass we can unlock the character and duration of its entire life and the manner of its death, as well as greatly improve our understanding of the potential processes and chronology of planet formation in the system. The most direct way to determine young star masses is to use the orbital motion of two stars in a young binary and apply Kepler's laws of motion to determine the individual masses. Close binary stars, which orbit each other with periods of just a few days to a few months, may be observed in relatively straightforward fashion to measure their mass ratios. Once this is accomplished, additional observations of the stellar pair from the work of other teams which determine the total system mass may be combined with our mass ratio measurements to calculate very precise and accurate young star masses. Comparison between these benchmark objects and young single stars allows astronomers to calibrate all young star masses. My team has obtained dozens of measurements at the world's most powerful observatory using the Keck 2 telescope in order to measure mass ratios in young binary systems. We have calculated these ratios in several dozen systems and, for several of these, have used ancillary data to determine absolute masses. Furthermore, by compiling this large sample of mass ratios we are also providing theoretical astrophysicists with data to improve models for the formation of young binary stars, a common species in the nearby regions of star formation. In addition, we explored the locales of these young binaries to search for very low-mass companion stars to the binary systems. These so-called "tertiaries" are important because they likely play a crucial role in the system dynamics, allowing the binary to form and evolving without breaking up into a small system of individual stars. Most of these close binary stars appear to have nearby companions which likely strongly shaped their evolution. A fundamental outcome of my work with my team has been the training and development of numerous young scientists. For this group of about 6 new astronomers their work with me represents their first experience doing research and many of them have published the results of this work in professional, refereed journals. All of them, undergraduates and masters students during their time at Lowell Observatory under my mentorship, have continued on to pursue Ph.D. degrees at doctoral-granting institutions. Most of these student collaborators were women, a traditionally underrepresented group in STEM fields, three of them were from racially underrepresented populations, and at least three from economically challenged backgrounds.
