High-resolution spectroscopic observations of the D′-type symbiotic stars HD 330036 and as 201

We present high-resolution spectroscopic analyses of two stars classified as D′-type symbiotic stars, HD 330036 and AS 201. These two stars display both rapid rotation and enhancements of the s-process elements that are synthesized via slow neutron captures during stellar evolution along the asymptotic giant branch (AGB). Both characterisitics of rapid rotation and s-process overabundances have also been discovered recently in another D′-type symbiotic, S190. The stellar parameters derived here for HD 330036 are T_eff= 6200 K and log g = 2.4, while AS 201 has T _eff = 6000 K and log g = 2.3. Resulting luminosity and distance estimates arc 650 L_⊙ and 2.3 kpc for HD 330036, and 700 L _⊙ and 4.3 kpc for AS 201. Both HD 330036 and AS 201 have evolved away from the main sequence and are approaching the base of the red-giant branch. These stars have near-solar abundances of iron and calcium, but substanial enhancements (by about +0.9 dex for HD 330036 and +1.7 dex for AS 201) of the s-process element barium. The observed barium overabundances in the current cool-star members of these two binary systems probably resulted from mass-transfer when the current white dwarf was an AGB star. The rapid rotation found in the cool stars may also be due to mass-transfer, with the mass-gaining stars being spun up with the transfer of angular momentum from the AGB winds. As only a few (six) D′-type symbiotics are known, the fact that the 3 studied to date at high-spectral resolution all display rapid rotation and s-process elemental overabundances may indicate that these two trails are signatures of these rare binary systems.