The near-infrared companion to HD94660 (=KQ Vel)

TL;DR

This study used interferometry, photometry, and X-ray data to detect and characterize the unseen companion of the Bp star HD94660, ruling out a compact object and suggesting a binary of late F stars.

Contribution

First direct detection of the companion to HD94660 using interferometry, providing new insights into its nature and ruling out a compact object.

Findings

Companion detected at 18.72mas separation with a magnitude difference of 1.8 in H band.

X-ray emission consistent with a magnetically active companion.

Companion unlikely to be a single star or a compact object.

Abstract

The Bp star HD94660 is a single-lined spectroscopic binary. Some authors have suggested that the unseen companion of at least 2M_sun may be a compact object. We intend to study this multiple system in detail, especially to learn more about the so-far unseen companion. We have collected and analyzed PIONIER H-band data from the Very Large Telescope Interferometer, TESS visible photometric data, and X-ray observations with Chandra of HD94660. Using PIONIER, we were able to detect the companion to HD94660, which is absent from high quality spectra at visible wavelengths, with a magnitude difference of 1.8 in the H band at a separation of 18.72mas. The TESS light curve shows variations with a period of 2.1d and also flaring. The Chandra spectrum is well described by emission from hot thermal plasma, yet might include a non-thermal component. The X-ray properties are compatible with a magnetically active companion, while some magnetospheric contribution from the primary is also possible. We can rule out that the companion to HD94660 is a compact source. It is also very unlikely that this companion is a single star, as the estimated mass of more than 2M_sun, the magnitude difference of 1.8 in the H band, and its non-detection in visible spectra are difficult to realize in a single object. One alternative could be a pair of late F stars, which would also be responsible for the detected photometric variations. Interferometric observations over the full binary orbit are necessary to determine the real mass of the companion and to add constraints on the overall geometry of the system.