"CAREER: The Stellar Phase Space and Abundance Distributions of the Stars of the Milky Way"

点击翻译按钮获取中文摘要

Abstract - Majewski The research to be carried out involves the creation of the deepest survey of positions, absolute proper motions, multi-color charged-coupled-device (CCD) photometry, and spectroscopy for a complete, magnitude limited survey of Galactic stars. The study builds upon the results from earlier work in a single field at the North Galactic Pole (NGP) to assemble high quality proper motions, photometric parallaxes, photometric abundances and radical velocities as a means to explore the combined dimensional phase space and metallicity distribution of stars in the Galactic halo, disk, and Intermediate Population II thick disk. Among the discoveries of this earlier, high precision proper motion survey at the NGP were: (1), the large scale height and local normalization of the ubiquitous Intermediate Population II (IPII) thick disk stars; (2), an apparently smooth kinematical gradient between the population I disk and IPII field stars; and (3), a retrograde rotation for the Galactic halo stars. The addition of spectroscopy data to the deep proper motions has confirmed the additional discovery of a retrograde moving group of halo stars 4.5 kpc above the Galactic plane, and this result has allowed the elucidation of this kinematical structure as just one of several large scale, stellar streams in this part of the sky. The implications of these findings are: (1) the halo is not a dynamically relaxed system, but rather seems to contain streams of coherently moving debris from the break-up of stellar agglomerations, (2) differences among halo survey results might be attributable to differences in lines of sight, each characterized by local streaming motions rather than by global descriptions, and (3) the bulk of the halo field star population appears to be derived from the accretion of stellar systems, most likely Galactic satellites. This conclusion has apparently been confirmed with the discovery of the Sagittarius dwarf spheroidal galaxy, a Galactic satellit e in the process of tidal disruption by the Milky Way. The aim is to carry out similar astrometric, photometric and spectroscopic analyses in nine other fields that lie along two orthogonal, meridional planes of the Galaxy. Photographic plates from the Kitt Peak 4-m telescope will be scanned with the University of Virginia PDS microdensitometer to construct stellar catalogues and for the measurement of proper motions. Multifiber spectroscopy with the HYDRA system on the WIYN 3.5-m telescope will provide the third dimension of velocity as well as spectroscopic abundances. This survey, the deepest in situ study of field dwarf stars ever carried out, will allow systematic probing of the thin disk, Intermediate population II and halo without the selection biases that affect other types of Galactic structure surveys. By mapping the halo phase space distribution along the two meridional planes, it will be possible to (a) constrain the halo stream angular correlation scale, by looking for similar structures in adjacent fields, (b) measure the volume overfilling factor of streams (found to be ~3 in the NGP field) in the halo, and c look for correlations between the field star streams and Galactic satellites, globular clusters, and the alignment planes of these objects. The research program involves extensive involvement of both undergraduate and graduate students, who are involved, indeed critical, to all phases of the astrometric, photometric and spectroscopic analysis. To increase understanding Galactic structure and astrometric research that has been conducted at the University of Virginia throughout its long history in these endeavors, three additional efforts of educational outreach will be initiated for the benefit of both University students and the general public. Each effort centers on conversion of the McCormick Observatory to a unique, first class educational facility: (1) New instrumentation for the historic 26" Clark refractor telescope will provide a quick c onversion from eyepiece to CCD observation, as a means to broaden the scope of both course- related and "Open to the Public" night instruction with the astrometric telescope. The CCD will increase the efficiency of telescope viewing by large groups of visitors, provide the basis for new kinds of undergraduate laboratory exercises, demonstrate modern methods in astronomy, allow classroom instruction via computer display of live telescope images, and provide easier access to telescope viewing for elderly, disabled or very young visitors. (2) The addition of a teaching spectrograph will fill an important gap in the present astronomy majors program. (3) Finally, we will take advantage of McCormick's long tradition of astrometry to create a one of a kind museum of astronomical measuring devices. On the order of 5,000 people per year will take advantage of these improvements to the McCormick Observatory.