Chlorine Abundances in the Disk and Cl Isotope Ratios in Carbon Stars

The odd-Z element chlorine is thought to be primarily produced in core collapse supernovae (CCSNe), with some contributions from Type Ia supernovae and AGB stars. The two stable Cl isotopes are also predicted to be made in different sites. ³⁵Cl may be created by neutrino spallation during a CCSNe while ³⁷Cl may be made through the s-process. However, Cl is difficult to measure in stars due to a lack of atomic or molecular features in the optical spectral range. We report the results from a survey of ³⁵Cl abundances in 52 M giants and in a dozen carbon/SC stars measured using HCl lines at 3.7 microns. We find ³⁵Cl abundances are consistent with chemical evolution models and nebular Cl abundances in H II regions and planetary nebulae, with an assumed solar Cl isotope ratio. [Cl/Fe] and [Cl/Ti] ratios suggest ³⁵Cl is primarily made from CCSNe with some Type Ia contributions with no other sources needed. To investigate the s-process contribution, we measured the ³⁵Cl/³⁷Cl isotope ratio in carbon stars spanning 0.99 < C/O < 1.2.