Multiplicity of rapidly oscillating Ap stars

Abstract

Rapidly oscillating Ap (roAp) stars have rarely been found in binary or higher order multiple systems. This might have implications for their origin. We intend to study the multiplicity of this type of chemically peculiar stars, looking for visual companions in the range of angular separation between 0.05" and 8". We carried out a survey of 28 roAp stars using diffraction-limited near-infrared imaging with NAOS-CONICA at the VLT. Additionally, we observed three non-oscillating magnetic Ap stars. We detected a total of six companion candidates with low chance projection probabilities. Four of these are new detections, the other two are confirmations. An additional 39 companion candidates are very likely chance projections. We also found one binary system among the non-oscillating magnetic Ap stars. The detected companion candidates have apparent K magnitudes between 6.8 and 19.5 and angular separations ranging from 0.23" to 8.9", corresponding to linear projected separations of 30-2400AU. While our study confirms that roAp stars are indeed not very often members of binary or multiple systems, we have found four new companion candidates that are likely physical companions. A confirmation of their status will help understanding the origin of the roAp stars.

9 pages, 4 figures, 3 tables, accepted for publication in A&A. arXiv admin note: substantial text overlap with arXiv:1010.3643

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• K2 space photometry reveals rotational modulation and stellar pulsations in chemically peculiar A and B stars
• On the first $\delta$ Sct--roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars
• KIC 7582608: A new Kepler roAp star with frequency variability
• Six new rapidly oscillating Ap stars in the Kepler long-cadence data using super-Nyquist asteroseismology
• Long-period Ap stars discovered with TESS data: The northern ecliptic hemisphere
• HD 213258: a new rapidly oscillating, super-slowly rotating, strongly magnetic Ap star in a spectroscopic binary
• Magnetic field measurements of sharp-lined Ap stars