Volume 582, October 2015
|Number of page(s)||4|
|Section||Stellar structure and evolution|
|Published online||13 October 2015|
A radial-velocity survey of Ap stars with HARPS⋆
I. HD 42659: The discovery of the first spectroscopic binary around a rapidly oscillating Ap star
Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
Received: 11 November 2014
Accepted: 14 August 2015
Context. Chemically peculiar Ap stars are main-sequence stars of spectral type B8–F3 which show large overabundances of some chemical elements (e.g., Si, Sr, Cr), especially of rare-earth elements, compared to normal A-type stars. Furthermore, they have strong, global magnetic fields and low rotational velocities. Some Ap stars exhibit high-overtone, low-degree, non-radial p-mode pulsations with periods of 6–24 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.
Aims. The goal of this survey was to carry out a systematic search for sub-stellar and stellar companions around Ap stars.
Methods. Between 2004 and 2009, we observed 65 chemically peculiar stars with the HARPS spectrograph at the 3.6-m telescope at the European Southern Observatory (La Silla, Chile). The radial-velocity (RV) measurements were obtained using a new software called HARPS-TERRA which is based on a least-squares matching of each individual spectrum to a high signal-to-noise ratio template for each star.
Results. We find significant variability with a period of 93.2 days and a semi-amplitude of 11.85 km s-1 in the RVs of HD 42659, a star of our sample that belongs to the group of roAp stars. This variability is caused by a stellar companion with a minimum mass of 0.47 M⊙ in a slightly eccentric (e = 0.146) orbit at a separation of 0.55 AU.
Conclusions. This detection makes HD 42659 the first confirmed SB around a roAp star in a relatively close orbit. It shows that tidal interactions in binaries do not necessarily inhibit pulsations in Ap stars.
Key words: techniques: radial velocities / binaries: spectroscopic / stars: chemically peculiar / stars: individual: HD 42659
© ESO, 2015
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.