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EP: Fachverband Extraterrestrische Physik

EP 4: Poster Session

EP 4.4: Poster

Dienstag, 26. Februar 2013, 11:15–12:45, Poster OG

HD 42659: the first spectroscopic binary around a rapidly oscillating Ap star — •Michael Hartmann and Artie Hatzes — Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany

Chemically peculiar Ap stars are main-sequence stars of spectral type B8 – F0 which show large overabundances of some chemical elements (e.g., Si, Sr, Cr, and Eu), especially of rare earth elements, compared to normal A-type stars. Furthermore, they have strong, global magnetic fields and low rotational velocities. Spectra of these stars contain plenty of narrow absorption lines, thus making precise radial velocity (RV) measurements possible. Some Ap stars exhibit high-overtone, low-degree, non-radial p-mode pulsations with periods of 6 – 21 min and are called rapidly oscillating Ap (roAp) stars. Interestingly, no roAp star is known to be a spectroscopic binary (SB), while many non-oscillating Ap (noAp) stars are found in SB systems. One hypothesis to explain this difference is that the pulsations in Ap stars might be inhibited due to tidal interaction in binaries. To find a SB around a roAp star would thus disprove this hypothesis. We observed a sample of noAp and roAp stars with the HARPS spectrograph at the 3.6-m telescope at the European Southern Observatory (La Silla, Chile). We find significant variability with a period of 93 days in the RVs of the roAp star HD 42659 which is caused by a stellar companion with a minimum mass of 0.5 solar masses in a slightly eccentric (e=0.15) orbit. This detection makes HD 42659 the first confirmed SB around a roAp star in a relatively close orbit (a=0.55 AU).