CS Cha B: A disc-obscured M-type star mimicking a polarised planetary companion

Abstract

Context. Direct imaging provides a steady flow of newly discovered giant planets and brown dwarf companions. These multi-object systems can provide information about the formation of low-mass companions in wide orbits and/or help us to speculate about possible migration scenarios. Accurate classification of companions is crucial for testing formation pathways. Aims. In this work we further characterise the recently discovered candidate for a planetary-mass companion CS Cha b and determine if it is still accreting. Methods. MUSE is a four-laser-adaptive-optics-assisted medium-resolution integral-field spectrograph in the optical part of the spectrum. We observed the CS Cha system to obtain the first spectrum of CS Cha b. The companion is characterised by modelling both the spectrum from 6300 $\unicode{x212B}$ to 9300 $\unicode{x212B}$ and the photometry using archival data from the visible to the near-infrared (NIR). Results. We find evidence of accretion and outflow signatures in H$\alpha$ and OI emission. The atmospheric models with the highest likelihood indicate an effective temperature of $3450\pm 50$ K with a $\log g$ of $3.6\pm 0.5$ dex. Based on evolutionary models, we find that the majority of the object is obscured. We determine the mass of the faint companion with several methods to be between 0.07 $M_{\odot }$ and 0.71 $M_{\odot }$ with an accretion rate of $\dot{M}=4\times 10^{-11\pm 0.4}$ Myr${}^{-1}$. Conclusions. Our results show that CS Cha B is most likely a mid-M-type star that is obscured by a highly inclined disc, which has led to its previous classification using broadband NIR photometry as a planetary-mass companion. This shows that it is important and necessary to observe over a broad spectral range to constrain the nature of faint companions

9 pages, 6 figures, accepted for publication by A&A

References in corpus (17)

• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• The Gemini Planet Imager: First Light
• Analytical theory for the initial mass function: CO clumps and prestellar cores
• Two accreting protoplanets around the young star PDS 70
• The MUSE Hubble Ultra Deep Field Survey: I. Survey description, data reduction and source detection
• On the diversity and statistical properties of protostellar discs
• Direct Imaging and Spectroscopy of a Planetary Mass Candidate Companion to a Young Solar Analog
• The Disk Population of the Chamaeleon I Star-Forming Region
• Comparative statistics and origin of triple and quadruple stars
• On the gas content of transitional disks: a VLT/X-Shooter study of accretion and winds
• Tracing Slow Winds from T Tauri Stars via Low Velocity Forbidden Line Emission
• Pre-main sequence spectroscopic binaries suitable for VLTI observations
• Misaligned Protoplanetary Disks in a Young Binary System
• The Young Suns Exoplanet Survey: Detection of a wide orbit planetary mass companion to a solar-type Sco-Cen member
• Discovery of an Optically Thick, Edge-on Disk around the Herbig Ae star PDS 144N
• The 2008 outburst in the Young Stellar System Z CMa. III - Multi-epoch high-angular resolution images and spectra of the components in near-infrared
• An ALMA Dynamical Mass Estimate of the Proposed Planetary-mass Companion FW Tau C

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