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| Paper: |
Extinction and Mass Loss in AGB Stars from Optical Emission Lines and Mid-IR Imaging |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
1630 |
| Authors: |
Origlia, L.; Busso, M.; Silvestro, G.; Marengo, M.; Persi, P.; Lagage, P. O. |
| Abstract: |
We observed a number of partially obscured AGB stars, as part of a larger sample for which we are studying evolution, mass loss, circumstellar dust emission and emission in optical lines. Medium-resolution spectroscopy allows us to derive the flux in the Balmer lines and to estimate the optical extinction through line ratios. This extinction is compared with the outcome of mid-IR imaging. The results point out that O-rich envelopes easily reach appreciable extinctions, even in the presence of moderate mass loss, while C-rich envelopes develop higher mass loss rates, but with lower (on average) circumstellar extinction. This bimodal relation between wind intensity and optical depth should be taken into account in any observational study of AGB evolution. Optical data qualitatively confirm this finding: O-rich stars have high extinctions, to the point that generally a flux ratio for Balmer lines cannot be derived; on the contrary, for C-rich stars A_V values can easily be derived and are well correlated with mass loss rates. |
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