The near-infrared companion to HD 94660 (=KQ Vel)

Abstract

Context. The Bp star HD 94660 is a single-lined spectroscopic binary. Some authors have suggested that the unseen companion of at least 2 M⊙ may be a compact object. Aims. We intend to study this multiple system in detail, especially to learn more about the thus far unseen companion. Methods. We have collected and analyzed PIONIER (Precision Integrated-Optics Near-infrared Imaging ExpeRiment) H-band data from the Very Large Telescope Interferometer, TESS (Transiting Exoplanet Survey Satellite) visible photometric data, and X-ray observations with Chandra of HD 94660. Results. Using PIONIER, we were able to detect the companion to HD 94660, 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 18.72 mas. The TESS light curve shows variations with a period of 2.1 d and also flaring. The Chandra spectrum is well described by emission from hot thermal plasma, yet it might include a nonthermal component. The X-ray properties are compatible with a magnetically active companion, while it is also possible that there might be some magnetospheric contributions from the primary. Conclusions. We can rule out that the companion to HD 94660 is a compact source. It is also very unlikely that this companion is a single star, as the estimated mass of more than 2 M⊙, the magnitude difference of 1.8 in the H band, and its nondetection 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.

Discovery and origin of the radio emission from the multiple stellar system KQVel

“…Further, the TESS (Transiting Exoplanet Survey Satellite) 2 light curve showed clear photometric variability, compatible with a period of ≈ 2.1 days, and two flare-like features (Schöller et al 2020). On the other hand, the highly sensitive visible spectra of KQ Vel show spectral features related to the Ap star only (Bailey et al 2015;Schöller et al 2020). On the basis of the expected spectral line detection level, Schöller et al (2020) concluded that the spectral signature of a couple of main sequence F8 type stars (or later) might be unseen.…”

“…As expected, the stellar rotation periods are not affected by their large orbital separation, hence, the dynamo mechanism of the two stars does not seem to be amplified. KQ Vel evidenced photometric variability with a period of 2.1 days, much shorter than the 2800 d rotation period of the bright Ap star (Schöller et al 2020). The observed periodicity is likely of rotational origin.…”

“…High resolution imaging in the near infrared H band, performed by the PIONIER (Precision Integrated-Optics Near-infrared Imaging ExpeRiment) instrument at the Very Large Telescope Interferometer (VLTI), detected an object fainter than the Ap star (difference of magnitudes ≈ 1.8) and having an angular separation (18.72 mas) compatible with the orbital parameters of the system (Schöller et al 2020). Further, the TESS (Transiting Exoplanet Survey Satellite) 2 light curve showed clear photometric variability, compatible with a period of ≈ 2.1 days, and two flare-like features (Schöller et al 2020). On the other hand, the highly sensitive visible spectra of KQ Vel show spectral features related to the Ap star only (Bailey et al 2015;Schöller et al 2020).…”

“…Finally, Oskinova et al (2020) favored a scenario involving the presence of a hot shell surrounding a massive degenerate unseen companion (a propelling magnetic neutron star) as responsible for the observed Xray emission. However, the detection of a faint infrared source close to the bright Ap star, with short-period (2.1 d) photometric variability, and of flares (Schöller et al 2020) re-opened the possibility that the companion of the Ap star is a binary system composed of a pair of non-degenerate stars, with masses close to the mass of the Sun and characterized by solar-like magnetic activity able to explain the measured X-ray emission level.…”

“…But, this hypothesis was discarded due to the lack of evidence of the typical spectral signatures of chromospheric magnetic activity (Bailey et al 2015). On the other hand, the evidence of photometric variability and flares (Schöller et al 2020) motivates reconsideration of the existence of a late type companion.…”