Gillian Revill Knapp - US grants

This award supports investigations on the manner in which stars lose mass to the interstellar medium. Topics include observations informing us how red giants generate planetary nebulae, a search for temporal changes of the radio carbon monoxide line emission, and the combination of radio and infrared data to establish the total rate of stellar mass loss to the interstellar medium. There is also a project to map the newly recognized small molecular clouds and to study their composition and radiative properties. Interstellar gases are used to form new stars. Conversely, aging stars return gas to interstellar space. The returned gas is significantly altered in chemical composition and combined into different molecules and dust grains. The gases lost by stars have become observationally accessible only in the last few years. Knapp has identified several well-posed questions designed to learn more about this process. She will use several radio telescopes, in particular the new Submillimeter Observatory in Hawaii.

This study continues Dr. Knapp's creative and respected studies of the intersterllar medium. Recent improvements in observationalsensitivity, leading to the detection of small amounts of cold gas and dust in elliptical galaxies, offer the opprotunity to study the interstellar medium in situations quite different from that in the galactic disk. These observations will be followed up by infrared dust studies, investigations of the fueling of nuclear activity, and studies of the vertical structure of atomic and molecular gas in the disk of our own galaxy.

Under this award, Princeton University will purchase CONVEX mini- supercomputer facilities for theoretical and observational investigations. Primary use will be for large scale simulations in cosmology to test the currently considered theoretical models against the increasingly detailed observations of large scale structure and the background radiation fields. The local facilities will be used both for preliminary modelling and for manipulation and display of the results obtained from NSF supported supercomputer facilities. Also significant will be use for processing of both optical and radio images. For both applications, the C-220 with its speed, large memory (512 Mb), and efficient FFT routines is ideal. Princeton University is providing 50% of the purchase price in a cost-sharing arrangement.

An important area of current astronomical research concerns the study of mass loss of red giant stars as they evolve to white dwarfs through the "planetary nebula" stage. It is now believed that this loss occurs as a wind of atomic particles. The intensity of this wind increases over the course of several thousand years until the envelope of the star is peeled off in a very fast wind at a rapid rate. The Principal Investigator (PI) proposes to continue previous studies of this phenomenon by using a determining the amount of mass lost in this wind in a large sample of red giants from the strength of two carbon monoxide emission lines in the nebular material surrounding them. The amounts of mass loss will be correlated against known stellar parameters such as stellar mass, luminosity, radius, and chemical composition to permit an empirical model to be developed as to how mass is lost during this critical brief stage of evolution.

Dr. Gillian Knapp (Princeton University), Dr. Timothy Beers (Michigan State University), & Dr. Jennifer Johnson (Ohio State University), will identify and analyze up to several thousand carbon-enhanced stars in the Milky Way galaxy, based on medium-resolution stellar spectroscopy and broadband ugriz photometry obtained with the Sloan Digital Sky Survey (SDSS). These data will allow these investigators to derive estimates of both [Fe/H] and [C/Fe] for all stars in this sample. Accurate radial velocities will also enable detailed investigations of the kinematics of these stars. These data will be used to constrain (1) the frequency of carbon enhancement among stars as a function of declining metallicity, which provides information on the nature of the initial mass function for early-generation stars, (2) the distribution of carbon enhancement among low-metallicity stars - e.g., whether it is continuous or multi-modal, and (3) the separation of carbon-enhanced, metal-poor stars into (at least) the two main categories that are presently recognized, those that exhibit the presence of s-process elements, and those that do not, based on the detection (or not) of the strong barium and strontium features that are associated with production in the s-process.

The results of this research will have impact on a wide range of research activities in astronomy, nuclear physics, and chemistry, since knowledge of the astrophysical origins of the elements provides the basis for understanding the chemical evolution of the Milky Way, as well as for detailed investigations of the nature of neutron-capture processes, which are of great interest to the nuclear physics community. This research will provide opportunities for the training of graduate and undergraduate students in the areas of both astronomy and nuclear physics, and will become part of the extensive education and outreach program being undertaken by SDSS-II.