Multiplicity of rapidly oscillating Ap stars

TL;DR

This study investigates the multiplicity of rapidly oscillating Ap stars using high-resolution near-infrared imaging, finding that they are rarely in binary systems but identifying new potential companions that could shed light on their origins.

Contribution

The paper presents the first high-resolution imaging survey of 28 roAp stars, discovering four new likely physical companions and providing insights into their binary nature.

Findings

Few roAp stars are in binary systems.

Four new companion candidates likely to be physical companions.

Detected companions have separations of 30-2400AU.

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.