Infrared spectroscopy of the merger candidate KIC 9832227

Abstract

Context. It has been predicted that the object KIC 9832227 – a contact binary star – will undergo a merger in 2022.2 ± 0.7. We describe the near-infrared (NIR) spectrum of this object as an impetus to obtain pre-merger data. Aims. We aim to characterise (i) the nature of the individual components of the binary and (ii) the likely circumbinary environment, so that the merger – if and when it occurs – can be interpreted in an informed manner. Methods. We use infrared (IR) spectroscopy in the wavelength range 0.7–2.5 μm, to which we fit model atmospheres to represent the individual stars. We use the binary ephemeris to determine the orbital phase at the time of observation. Results. We find that the IR spectrum is best fitted by a single component with effective temperature 5920 K, log[g] = 4.1, and solar metallicity, consistent with the fact that the system was observed at conjunction. Conclusions. The strength of the IR H lines is consistent with a high value of logg, and the strength of the Ca II triplet indicates the presence of a chromosphere, as might be expected from rapid stellar rotation. The He I absorption we observe likely arises in He excited by coronal activity in a circumstellar envelope, suggesting that the weakness of the Ca II triplet is also likely chromospheric in origin.