AAS 200th meeting, Albuquerque, NM, June 2002
Session 74. Stellar Atmospheres and Circumstellar Material
Display, Thursday, June 6, 2002, 9:20am-4:00pm, SW Exhibit Hall

## [74.01] The Circumstellar Environments Of 62 Nearby A Stars

J.D. Meiring, J.E. Neff (College of Charleston), K.P. Cheng (Cal State University, Fullerton)

Recent advances in infrared and millimeter-wave imaging have revealed circumstellar dust disks around an ever-growing number of nearby A stars. Among these stars, Beta Pictoris has the most extensive dust disk. Beta Pic also has a dynamic circumstellar gas environment, manifesting itself in narrow and variable absorption features in several ultraviolet and visible spectral lines. Studying stars similar to Beta Pic will help us to understand the linkage between circumstellar gas and dust, which is critical for advancing theories of planetary system formation.

Using high-resolution spectra of the Ca~II~K line, we have searched for circumstellar gas around 62 nearby A stars. Using both the Ca~II~K and the Na~I~D lines as well as ultraviolet spectra, we are able to distinguish between circumstellar and interstellar features. Our K and D-line spectra were obtained using echelle spectrographs at the McMath-Pierce telescope at Kitt Peak, the McDonald 2.7~m telescope, the CTIO 1.5~m telescope, and the Mt. Stromlo 1.9~m telescope. We obtained 271 high-resolution (\lambda/\delta\lambda ~120,000 - 220,000) and high signal-to-noise (200-400) spectra of the 62 stars in our survey. We also analyzed high-dispersion IUE spectra of all these stars. We have detected circumstellar gas in about a dozen stars. Continued monitoring of this smaller sample has revealed a handful (at least 4) with variable circumstellar absorption components. We are using these spectra to determine the physical (column density, temperature, density) and dynamical (e.g., gas flow velocities) properties of the circumstellar and interstellar gas.

This work is being supported by NSF grant number AST-9819737 to the California State University at Fullerton and the College of Charleston.