Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005a%26a...429..993p&link_type=abstract
Astronomy and Astrophysics, v.429, p.993-998 (2005)
Astronomy and Astrophysics
Astrophysics
12
Stars: Binaries: Symbiotic, Stars: Abundances
Scientific paper
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=6200 K and log g=2.4, while AS 201 has Teff=6000 K and log g=2.3. Resulting luminosity and distance estimates are 650 L&sun; and 2.3 kpc for HD 330036, and 700 L&sun; 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.
Based on observations made with the 1.52 m telescope at the European Southern Observatory (La Silla, Chile) under the agreement with the CNPq-Observatório Nacional (Brazil).
Cunha Katia
Pereira Claudio Bastos
Smith Verne V.
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