RUI: A Detailed Study of the Circumstellar Environment Around Neaby A-Type Stars: Possible Planet Construction Zones

点击翻译按钮获取中文摘要

Abstract K. P. Chang AST 98-19737The objectives of this research project are to assess the frequency of the "Beta Pictoris phenomenon" in our solar neighborhood, and to gain more insight into the "planetary system formation process" through detailed spectroscopic studies of Beta Pictoris-like systems.For years, astronomers have been searching for other planets outside our Solar System. They especially want to study systems that are undergoing the process of planet formation so that they can gain insight into the origin of our own Solar System. The best candidate is Beta Pictoris, a nearby A type star surrounded by a huge dust disk and a very dynamic circumstellar gas environment. It has been suggested that the short-term variations of circumstellar gas absorption components in the Beta Pictoris system could be due to the evaporation of comet-size bodies. It also has been suggested that the huge dust disk around Beta Pictoris could be an analog of our Kuiper Belt, a region past the orbit of the planet Neptune that is now considered to be the source of short-period comets.A detailed, spectroscopic study of the circumstellar environments of nearby A-type stars has been carried out. The program stars are young A-type stars that could serve as laboratories for the study of gas accretion during the clearing phase of planetary disks. The goal has been to characterize the debris disks around these stars. A sky volume-limited search for Beta Pictoris-like systems among the 62 A-stars within 25 parsecs of the Sun has been completed. The preliminary search consisted of two independent studies: one to obtain data on circumstellar dust using the IRAS satellite data and the second one for data on the circumstellar gas using high-resolution visual and ultraviolet spectra. It was found that more than 18% of the stars have circumstellar dust, and more than a dozen stars with circumstellar gas have been identified. Further monitoring of the stars has revealed that at least four of these have Beta Pictoris-like variable spectral signatures indicating gaseous infall. One of the four stars is identified to have variable circumstellar gas features and has no dust signature at the IRAS Faint Source Survey detection limit. More studies of Beta Pictoris-like systems will be carried out to provide important constraints for our understanding of planetary system formation.Analyzing high signal-to-noise and high-resolution visual and ultraviolet wavelength spectra will identify more nearby A-stars that have circumstellar gas similar to Beta Pictoris. A study of the dynamics in all the Beta Pictoris-like systems will be carried out by monitoring the temporal and variable circumstellar absorption line components observable in high-resolution Calcium II K and Sodium I D wavelength spectra. This study will lead to a better understanding of the inter-relationship between the circumstellar gas and dust. Ultimately, an atlas will be compiled of the circumstellar dust and gas properties; namely mass, density, temperature distributions, velocity fields, and chemical gradients for all the nearby A-type stars. These physical conditions, especially those in the Beta Pictoris-like systems, will provide valuable constraints for models of accretion and planetary system formation. This atlas will be the first thorough compilation of the properties of circumstellar dust and gas around all the nearby A-type stars using data from the IRAS, HST, IUE satellite data, in addition to ground-based data. The atlas will be available to the general astronomical community through journal publications, and the ground-based data (150 plus nights of observations obtained at Kitt Peak National Astronomy Observatory, Cerro Tololo International Observatory, McDonald Observatory, and Mt. Stromlo Observatory) will be made available via the Internet.