Binarity and multiperiodicity in high-amplitude δ Scuti stars

Abstract

We have carried out a photometric and spectroscopic survey of bright high‐amplitude δ Scuti (HADS) stars. The aim was to detect binarity and multiperiodicity (or both) in order to explore the possibility of combining binary star astrophysics with stellar oscillations. Here, we present the first results for 10, predominantly southern, HADS variables. We detected the orbital motion of RS Gru with a semi‐amplitude of ∼6.5 km s−1 and 11.5 d period. The companion is inferred to be a low‐mass dwarf star in a close orbit around RS Gru. We found multiperiodicity in RY Lep from both photometric and radial velocity data and detected orbital motion in the radial velocities with hints of a possible period of 500–700 d. The data also revealed that the amplitude of the secondary frequency is variable on the time‐scale of a few years, whereas the dominant mode is stable. Radial velocities of AD CMi revealed cycle‐to‐cycle variations, which might be due to non‐radial pulsations. We confirmed the multiperiodic nature of BQ Ind, while we obtained the first radial velocity curves of ZZ Mic and BE Lyn. The radial velocity curve and the O–C diagram of CY Aqr are consistent with the long‐period binary hypothesis. We took new time series photometry on XX Cyg, DY Her and DY Peg, with which we updated their O–C diagrams.

Chemical Composition and Photometry of BE Lyncis

“…Szakats et al (2008) suggested that the phase of the maximum brightness varies slightly and that the nature of the amplitude variation is not periodic. Derekas et al (2009) performed radial velocity measurements for BE Lyn for three nights to detect possible binarity or additional pulsational frequencies, and they could not detect any nonradial mode pulsation in the RV curve. Recently, Boonyarak et al (2011) got 156 times of maximum light after adding their own observations, and they argued that BE Lyn is a binary or multiple system.…”

Metal-rich SX Phe stars in theKeplerfield

“…The last of these papers identified 25 EBs containing low-amplitude (0.007 to 0.02 mag) δ Sct stars. Derekas et al (2009)…”

Kepler observations of the high-amplitude δ Scuti star V2367 Cyg

“…From the ground, HADS stars typically have only one or two dominant frequencies which are most probably radial modes. Some stars, for example, AI Vel (Walraven, Walraven & Balona 1992), RY Lep (Rodríguez et al 2004; Derekas et al 2009) and V974 Oph (Poretti 2003), appear to have low‐amplitude non‐radial modes in addition to the dominant radial mode(s). Recently, a HADS star observed by the CoRoT spacecraft was discovered to have many non‐radial modes as well as small but very clear amplitude modulation of the fundamental radial mode (Poretti et al 2011).…”

“…The distinction is mostly in the large light amplitude, which one may expect of radial modes. Some HADS stars are members of spectroscopic binaries (Derekas et al 2009).…”