Chlorine Abundances in Cool Stars

Chlorine abundances are reported in 15 evolved giants and 1 M dwarf in the solar neighborhood. The Cl abundance was measured using the vibration-rotation 1-0 P8 line of H³⁵Cl at 3.69851 μm. The high-resolution L-band spectra were observed using the Phoenix infrared spectrometer on the Kitt Peak Mayall 4 m telescope. The average [³⁵Cl/Fe] abundance in stars with -0.72 < [Fe/H] < 0.20 is [³⁵Cl/Fe] = (-0.10 ± 0.15) dex. The mean difference between the [³⁵Cl/Fe] ratios measured in our stars and chemical evolution model values is (0.16 ± 0.15) dex. The [³⁵Cl/Ca] ratio has an offset of ∼0.35 dex above model predictions, suggesting that chemical evolution models are underproducing Cl at the high metallicity range. Abundances of C, N, O, Si, and Ca were also measured in our spectral region and are consistent with F and G dwarfs. The Cl versus O abundances from our sample match Cl abundances measured in planetary nebula and H II regions. In one star where both H³⁵Cl and H³⁷Cl could be measured, a ³⁵Cl/³⁷Cl isotope ratio of 2.2 ± 0.4 was found, consistent with values found in the Galactic ISM and predicted chemical evolution models.