High-resolution spectroscopic observations of the D-type symbiotic stars HD 330036 and AS 201*
Observatório Nacional, Rua José Cristino, 77, CEP 20921-400, São Cristóvão, Rio de Janeiro-RJ, Brazil e-mail: email@example.com
2 University of Texas at El Paso, El Paso, TX 79968, USA
Accepted: 10 August 2004
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 K and log , while AS 201 has K and log . Resulting luminosity and distance estimates are 650 and 2.3 kpc for HD 330036, and 700 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 traits are signatures of these rare binary systems.
Key words: stars: binaries: symbiotic / stars: abundances
© ESO, 2005