AAS 197, January 2001
Session 8. Circumstellar Matter and Winds
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

## [8.27] Large, cold dust grains orbiting stars in the TW Hydrae Association

R. A. Webb (NASA - Ames), B. Zuckerman (UCLA), J. S. Greaves, W. S. Holland (JAC)

Submillimeter observations of late-type stars in the nearest region of recent star formation, the TW Hydrae Association, indicate roughly Earth-mass quantities of cold, particulate matter not detected at far-infrared wavelengths by IRAS. Most of the detected mass at TW Hya, HD 98800, Hen3-600 and TWA 7 is carried by large particles of size ~ few hundred microns whose number density (n) may be less steeply peaked toward smaller radii (a) than would be the case for the popular fragmentation spectrum dn \alpha a-3.5 da. In the multiple systems HD 98800 and Hen3-600, the cold dust is probably orbiting outside of the orbits of the visual binaries at > 100 AU. At the apparently single star TW Hya, the preponderance of the dust is likely located in the same general region as the Kuiper cometary belt of our solar system. TWA 7 is probably the first Vega-like star whose dusty circumstellar disk is detected in the submillimeter without first being detected in the far infrared by IRAS.