摘要：Hαis a powerful tracer of accretion and chromospheric activity, which has been detected in the case of young brown dwarfs and even recently in planetary mass companions (e.g. PDS70 b and c). Hαdetections and characterisation of brown dwarf and planet companions can further our knowledge of their formation and evolution, and expanding such a sample is therefore our primary goal. We used the Zurich Imaging POLarimeter (ZIMPOL) of the SPHERE instrument at the Very Large Telescope (VLT) to observe the known 38−72 MJcompanion orbiting PZ Tel, obtaining simultaneous angular differential imaging observations in both continuum and narrow Hαband. We detect Hαemission from the companion, making this only the second Hαdetection of a companion using the SPHERE instrument. We used our newly added astrometric measurements to update the orbital analysis of PZ Tel B, and we used our photometric measurements to evaluate the Hαline flux. Given the estimated bolometric luminosity, we obtained an Hαactivity (log(LHα/Lbol)) between −4.16 and −4.31. The Hαactivity of PZ Tel B is consistent with known average activity levels for M dwarf of the same spectral type. Given the absence of a known gaseous disk and the relatively old age of the system (24 Myr), we conclude that the Hαemission around PZ Tel B is likely due to chromospheric activity.
关键词：eninstrumentation: high angular resolutionmethods: observationalstars: activitystars: individual: PZ Telstars: imaging
