9957( 1) - 04/04/03 10:37 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9957 Version: 1 Check-in Date: 04-Apr-2003 10:37:12 1.Proposal Title: Searching for Astrospheric Lyman-alpha Absorption Detections in the HST Archive ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle AR 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Brian Wood University of Colorado at Boulder CoI: Dr. Jeffrey Linsky University of Colorado at Boulder N CoI: Mr. Seth Redfield University of Colorado at Boulder N CoI: Dr. Hans Mueller Dartmouth College N CoI: Dr. Gary Zank University of California - Riverside N ------------------------------------------------------------------------------------ 5. Abstract The UV spectrometers of HST, first GHRS and now STIS, provide the first opportunity to study the coronal winds of solar-like stars, which were undetectable prior to HST. The interaction regions between these winds and the ISM (i.e., their "astrospheres") often produce enough H I Lyman-alpha absorption to be detectable despite being highly blended with ISM absorption. With the help of hydrodynamic models, mass loss rates can be estimated from the observed astrospheric absorption. The few observations to date suggest that active stars have stronger winds. The activity level of cool main sequence stars decreases with time, so mass loss also decreases with time. To be more precise, the data suggest that mass loss decreases roughly as the inverse square of a star's age. Besides its obvious relevance for solar and stellar astrophysics, this result also has profound implications for the evolution of planetary atmospheres in our solar system. The atmospheres of planets like Mars, which once had a much thicker atmosphere, may have been dramatically affected by solar wind erosion, especially if the solar wind was stronger in the distant past as the astrospheric work suggests. However, the derived mass loss evolution law for solar-like stars is currently based on only 5 astrospheric detections. We propose to improve this situation by searching the HST archive for additional astrospheric detections. In particular, we will analyze all available Lyman-alpha spectra within the HST archive for coronal stars within 100 pc. There are 30 such spectra within the archive that could yield new astrospheric detections and mass loss measurements. ------------------------------------------------------------------------------------ 9957( 1) - 04/04/03 10:37 - [ 2] Summary Form for Proposal 9957 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category AR ------------------------------------------------------------------------------------------------------------------------------------