Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010a%26a...509a..21c&link_type=abstract
Astronomy and Astrophysics, Volume 509, id.A21
Astronomy and Astrophysics
Astrophysics
1
Stars: Individual: Β Scorpii, Binaries: Spectroscopic, Stars: Abundances, Stars: Chemically Peculiar
Scientific paper
Context. The multiple system β Scorpii consists of five components and two suspected members forming a total of seven stars. In the past, this system acquired much interest because of a series of occultation by the planet Jupiter and one of its satellites (Io). The study of this phenomena allowed us to ascertain the principal components of the system and the possible nature of each component. Aims: By using optical spectroscopy, we derive radial velocities, T_eff, log g, abundances L/L_&sun;, M/M_&sun;, and R/R_&sun; for β Sco C and E. We also refine previously published values of L/L_&sun;, M/M_&sun;, and R/R_&sun; of β Sco Aa + Ab to obtain a clear understanding of the evolutionary state of the β Sco system. Methods: We convert Doppler shifts in wavelength into radial velocities. Atmospheric parameters and abundances are computed by assuming the local thermodynamic equilibrium using model atmospheres and the spectral synthesis codes ATLAS and SYNTHE. Results: We solve the orbit of β Sco E and provide information about the motion of β Sco C. By fitting four Balmer lines, we determine that: T_effC =24 000 ± 500 K, log gC = 3.8 ± 0.2, and T_eff^Ea = 13 000 ± 800 K, log g^Ea = 4.2 ± 0.2. Rotational velocities are derived by modeling the profiles of metallic lines: v sin i C = 55 ± 3 km s-1 and v sin i ^Ea = 5 ± 1 km s-1. As for the abundances, we find that β Sco C is more or less of solar abundance, while β Sco Ea has a significant overabundance of manganese, followed by those of strontium, phosphorous, and titanium. The most underabundant element is magnesium, followed by silicon, aluminum, sulfur, iron, and nickel. Other light elements, such as carbon, nitrogen, oxygen, and neon, are found to be normal. From the derived values of luminosities and temperatures, we infer that these stars have an age of ≈ 6.3 ± 3.0 Myr. Conclusions: We explain the observed variability in velocity of β Sco E in terms of a close companion. Thus, we observe a triple system composed by β Sco C and β Sco Ea + Eb. While β Sco C is a normal star, β Sco Ea is probably a mercury-manganese (HgMn) star. The line-profile variability observed for β Sco C could be explained by assuming its membership to the class of slow pulsating B stars. According to the position of β Sco Ab in the HR diagram, we exclude the possibility that this star could be a β Cephei class pulsator.
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