A faint companion around CrA-9: protoplanet or obscured binary?

Abstract

Understanding how giant planets form requires observational input from directly imaged protoplanets. We used VLT/NACO and VLT/SPHERE to search for companions in the transition disc of 2MASS J19005804-3645048 (hereafter CrA-9), an accreting M0.75 dwarf with an estimated age of 1-2 Myr. We found a faint point source at $\sim$0.7'' separation from CrA-9 ($\sim$108 au projected separation). Our 3-epoch astrometry rejects a fixed background star with a $5\sigma$ significance. The near-IR absolute magnitudes of the object point towards a planetary-mass companion. However, our analysis of the 1.0-3.8$\mu$m spectrum extracted for the companion suggests it is a young M5.5 dwarf, based on both the 1.13-$\mu$m Na index and comparison with templates of the Montreal Spectral Library. The observed spectrum is best reproduced with high effective temperature ($3057_{-36}^{+119}$K) BT-DUSTY and BT-SETTL models, but the corresponding photometric radius required to match the measured flux is only $0.60_{-0.04}^{+0.01}$ Jovian radius. We discuss possible explanations to reconcile our measurements, including an M-dwarf companion obscured by an edge-on circum-secondary disc or the shock-heated part of the photosphere of an accreting protoplanet. Follow-up observations covering a larger wavelength range and/or at finer spectral resolution are required to discriminate these two scenarios.

24 pages, 14 figures, 4 tables, to be published in MNRAS

References in corpus (45)

• The Gaia mission
• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• Two accreting protoplanets around the young star PDS 70
• The Catalina Surveys Periodic Variable Star Catalog
• An Optical Spectroscopic Study of T Tauri Stars. I. Photospheric Properties
• The Magnetic Fields of Classical T Tauri Stars
• Fundamental limitations of high contrast imaging set by small sample statistics
• On the diversity and statistical properties of protostellar discs
• Direct Imaging of Fine Structures in Giant Planet Forming Regions of the Protoplanetary Disk around AB Aurigae
• Characterizing Young Brown Dwarfs using Low Resolution Near-IR Spectra
• A radio pulsing white dwarf binary star
• VIP: Vortex Image Processing package for high-contrast direct imaging
• The Disk Population of the Chamaeleon I Star-Forming Region
• Discovery of a warm, dusty giant planet around HIP65426
• Submillimeter emission associated with candidate protoplanets
• Accreting Circumplanetary Disks: Observational Signatures
• Consistent simulations of substellar atmospheres and non-equilibrium dust-cloud formation
• First direct detection of an exoplanet by optical interferometry; Astrometry and K-band spectroscopy of HR8799 e
• Discovery of a wide planetary-mass companion to the young M3 star GU Psc
• Constraining the Nature of the PDS 70 Protoplanets with VLTI/GRAVITY
• Characterization of exoplanets from their formation III: The statistics of planetary luminosities
• No Clear, Direct Evidence for Multiple Protoplanets Orbiting LkCa 15: LkCa 15 bcd are Likely Inner Disk Signals
• Discovery of a low-mass companion inside the debris ring surrounding the F5V star HD206893
• ALMA survey of Class II protoplanetary disks in Corona Australis: a young region with low disk masses
• Very Low-Mass Objects in the Coronet Cluster: The Realm of the Transition Disks
• Keck/NIRC2 $L$'-Band Imaging of Jovian-Mass Accreting Protoplanets around PDS 70
• Evidence for a circumplanetary disk around protoplanet PDS 70 b
• VLT/SPHERE robust astrometry of the HR8799 planets at milliarcsecond-level accuracy Orbital architecture analysis with PyAstrOFit
• Flybys in protoplanetary discs: II. Observational signatures
• The Nature of Transition Circumstellar Disks II. Southern Molecular Clouds
• Effects of the Planetary Temperature on the Circumplanetary Disk and on the Gap
• Vortices and spirals in the HD135344B transition disk
• Gap, shadows, spirals, streamers: SPHERE observations of binary-disk interactions in GG Tau A
• Separating extended disc features from the protoplanet in PDS 70 using VLT/SINFONI
• The Planetary Accretion Shock: I. Framework for Radiation-hydrodynamical Simulations and First Results
• Dwarf nova-type cataclysmic variable stars are significant radio emitters
• Exploring the formation by core accretion and the luminosity evolution of directly imaged planets: The case of HIP 65426 b
• Strong H$\alpha$ emission and signs of accretion in a circumbinary planetary mass companion from MUSE
• Are the spiral arms in the MWC 758 protoplanetary disc driven by a companion inside the cavity?
• Gas inside the 97 au cavity around the transition disk Sz\,91
• CTCV J2056-3014: An X-ray-faint Intermediate Polar Harboring An Extremely Fast-spinning White Dwarf
• An ALMA Dynamical Mass Estimate of the Proposed Planetary-mass Companion FW Tau C
• A Flare of AE Aquarii Observed with XMM-Newton
• CS Cha B: A disc-obscured M-type star mimicking a polarised planetary companion

Cited by in corpus (12)

• Confirmation and Keplerian motion of the gap-carving protoplanet HD 169142 b
• Analysis of the arm-like structure in the outer disk of PDS 70. Spiral density wave or vortex?
• Dust Traffic Jams in Inclined Circumbinary Protoplanetary Discs I. Morphology and Formation Theory
• In-depth direct imaging and spectroscopic characterization of the young Solar System analog HD 95086
• External or internal companion exciting the spiral arms in CQ Tau?
• Kinematic and thermal signatures of the directly imaged protoplanet candidate around Elias 2-24
• Zodiacal Exoplanets in Time (ZEIT) XII: A Directly-Imaged Planetary-Mass Companion to a Young Taurus M Dwarf Star
• Keplerian motion of a compact source orbiting the inner disc of PDS 70: a third protoplanet in resonance with b and c?
• Polarimetric differential imaging with VLT/NACO. A comprehensive PDI pipeline for NACO data (PIPPIN)
• Exoplanet Imaging Data Challenge, phase II: Characterization of exoplanet signals in high-contrast images
• The SPHERE view of multiple star formation
• Investigating 2M1155-7919B: a Nearby, Young, Low-Mass Star Actively Accreting from a Nearly Edge-on, Dusty Disk