Astronomy and Astrophysics, volume 429, 993-998 (2005/1-3)
High-resolution spectroscopic observations of the D'-type symbiotic stars HD 330036 and AS 201.
PEREIRA C.B., SMITH V.V. and CUNHA K.
Abstract (from CDS):
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 Teff=6200K and logg=2.4, while AS 201 has Teff=6000K and log g=2.3. Resulting luminosity and distance estimates are 650L☉ and 2.3kpc for HD 330036, and 700L☉ and 4.3kpc 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 +0.9dex for HD 330036 and +1.7dex 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.