  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.
