Detectability of giant planets in protoplanetary disks by CO emission lines

Abstract

In this paper we intend to provide an indirect method to detect Jovian planets by studying near infrared emission spectra originating in the protoplanetary disks around T Tauri stars. Our idea is to investigate whether a massive planet could induce any observable effect on the spectral lines emerging in the disks atmosphere. As a tracer molecule we propose CO, which is excited in the ro-vibrational fundamental band in the disk atmosphere to a distance of ~2-3 AU (depending on the stellar mass) where terrestrial planets are thought to form. The synthetic molecular spectral line profiles were calculated by an own developed semi-analytical double layer disk model. 2D gas dynamics were incorporated in the calculation of synthetic spectral lines. We demonstrate that a massive planet embedded in a protoplanetary disk strongly influences the originally circular Keplerian gas dynamics. The perturbed motion of the gas can be detected by comparing the CO line profiles in emission, which is emerge from planet-bearing to those of planet-free disk models. The planet signal has two major characteristics: a permanent line profile asymmetry, and short timescale variability correlated with the orbital phase of the giant planet. We have found that the strength of the asymmetry depends on the physical parameters of the star-planet-disk system, such as the disk inclination angle, the planetary and stellar masses, the orbital distance, and the size of the disk inner cavity. The permanent line profile asymmetry is caused by a disk in an eccentric state in the gap opened by the giant planet. However, the variable component is a consequence of the local dynamical perturbation by the orbiting giant planet. We show that a forming giant planet, still embedded in the protoplanetary disk, can be detected using contemporary or future high-resolution near-IR spectrographs like VLT/CRIRES and ELT/METIS.

19 pages, 10 figures

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• Radiation thermo-chemical models of protoplanetary discs. IV Modelling CO ro-vibrational emission from Herbig Ae discs
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• Tracing large-scale structures in circumstellar disks with ALMA
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• Accretion of Gas Giants Constrained by the Tidal Barrier
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• The Evolution of Inner Disk Gas in Transition Disks
• Vortex Formation and Evolution in Planet Harboring Disks under Thermal Relaxation
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• Observational signatures of eccentric Jupiters inside gas cavities in protoplanetary discs
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• Near Infrared High Resolution Spectroscopy and Spectro-astrometry of Gas in Disks around Herbig Ae/Be Stars
• A Simplified Model for the Secular Dynamics of Eccentric Discs and Applications to Planet-Disc Interactions
• Asymmetric fundamental band CO lines as a sign of an embedded giant planet
• On the asymmetry of the OH ro-vibrational lines in HD 100546
• An alternative model for the origin of gaps in circumstellar disks
• Planet Formation Imager (PFI): science vision and key requirements