Characterization of the long-period companions of the exoplanet host stars: HD196885, HD1237 and HD27442

TL;DR

This study characterizes long-period companions of exoplanet host stars HD196885, HD1237, and HD27442 using near-infrared imaging and spectroscopy, confirming their nature and spectral types, and highlighting systems suitable for further planetary system evolution studies.

Contribution

It provides the first spectral characterization of these companions, confirming their nature as low-mass stars or white dwarfs, and details their potential impact on exoplanet systems.

Findings

HD196885 B is a low-mass M1V star and comoving with its primary.

HD1237 B is a low-mass M4V star and comoving with its primary.

HD27442 B is a white dwarf with a hydrogen-dominated atmosphere.

Abstract

We present the results of near-infrared, follow-up imaging and spectroscopic observations at VLT, aimed at characterizing the long-period companions of the exoplanet host stars HD196885, HD1237 and HD27442. The three companions were previously discovered in the course of our CFHT and VLT coronographic imaging survey dedicated to the search for faint companions of exoplanet host stars. We used the NACO near-infrared adaptive optics instrument to obtain astrometric follow-up observations of HD196885 A and B. The long-slit spectroscopic mode of NACO and the integral field spectrograph SINFONI were used to carry out a low-resolution spectral characterization of the three companions HD196885 B, HD1237 B and HD27442 B between 1.4 and 2.5 microns. We can now confirm that the companion HD196885 B is comoving with its primary exoplanet host star, as previously shown for HD1237 B and HD27442 B. We find that both companions HD196885 B and HD1237 B are low-mass stars of spectral type M1V and M4V respectively. HD196885 AB is one of the closer (~23 AU) resolved binaries known to host an exoplanet. This system is then ideal for carrying out a combined radial velocity and astrometric investigation of the possible impact of the binary companion on the planetary system formation and evolution. Finally, we confirm via spectroscopy that HD27442 B is a white dwarf companion, the third one to be discovered orbiting an exoplanet host star, following HD147513 and Gliese 86. The detection of the broad Bracket gamma line of hydrogen indicates a white dwarf atmosphere dominated by hydrogen.