Kinematic detection of a planet carving a gap in a protoplanetary disk

Abstract

We still do not understand how planets form, or why extra-solar planetary systems are so different from our own solar system. But the last few years have dramatically changed our view of the discs of gas and dust around young stars. Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) and extreme adaptive-optics systems have revealed 1 arXiv:1907.02538v1 [astro-ph.SR] 4 Jul 2019 that most -if not all -discs contain substructure, includind rings and gaps 1-3 , spirals 4-6 azimuthal dust concentrations 7 , and shadows cast by misaligned inner discs 5, 8 . These features have been interpreted as signatures of newborn protoplanets, but the exact origin is unknown. Here we report the kinematic detection of a few Jupiter-mass planet located in a gas and dust gap at 130 au in the disc surrounding the young star HD 97048. An embedded planet can explain both the disturbed Keplerian flow of the gas, detected in CO lines, and the gap detected in the dust disc at the same radius. While gaps appear to be a common feature in protoplanetary discs 2, 3 , we present a direct correspondence between a planet and a dust gap, indicating that at least some gaps are the result of planet-disc interactions.A variety of mechanisms have been proposed to explain the formation of rings and gaps in discs, e.g. snow-lines, non-ideal MHD effects, zonal flows, and self-induced dust-traps 9-13 . The most straightforward explanation is that the gaps are the results of forming planets interacting with the disc 14 . Recent ALMA surveys suggest that planets could indeed be responsible for carving out several of the observed gaps 2, 3, 15 , but until now definite evidence has remained elusive. Despite much effort, direct imaging of planets in young discs remains difficult. Many of the claimed detections have been refuted, or require confirmation [16][17][18] . The most promising detection to date is a companion imaged in the cleared inner disc around PDS 70 [19][20][21][22] . However, the mass estimate from photometry remains uncertain, and it is not yet clear if PDS 70 b falls within the planetary regime.Our approach is to search for the dynamical effect of a planet on the surrounding gas disc.

Nine Localized Deviations from Keplerian Rotation in the DSHARP Circumstellar Disks: Kinematic Evidence for Protoplanets Carving the Gaps

“…With the exception of HD 143006, such masses are larger by a factor 4 to 10 than the masses derived from the continuum gaps by Zhang et al (2018) or Lodato et al (2019). We found a similar discrepancy for HD 97048 (Pinte et al 2019), where to get a coherent match to both the continuum and line data, our models required the dust grains dominating the emission to have a Stokes number of a few 10 −2 , suggesting very porous and/or fluffy aggregates.…”

“…Because the velocity deviations created by an embedded planet are small (around 10% of the Keplerian velocity for a Jupiter mass planet at a few tens of au), a planet kink can often only be detected in a single channel at the DSHARP spectral resolution (≈ 640 m.s −1 ), making it difficult to assess whether the detection is robust or whether it is affected by imaging artefacts. For HD 163296 and HD 97048 (Pinte et al 2018a(Pinte et al , 2019, the high velocity resolution (≈ 100 to 200 m.s −1 ) enabled detection of the kinks in several subsequent channels, providing for robust detections.…”

A hot Jupiter around the very active weak-line T Tauri star TAP 26

“…The alternative explanation, and the one that is of interest to us, is that these gaps are induced by embedded young planets due to its dynamical interaction with the disk (Rosotti et al 2016;Dipierro et al 2016;Dong & Fung 2017). Although disk-planet interaction has long been predicted, (Goldreich & Tremaine 1980;Lin & Papaloizou 1993), direct observational evidence has only come recently (Pinte et al 2019(Pinte et al , 2020, which relies on careful kinematic measurements. On the other hand, annular dust gaps are readily observed global features and thus offer a promising indirect method to detect planets.…”

Channels for streaming instability in dusty discs

“…Whether these structures are created by planets or not is still a matter of ardent discussions. Recent direct imaging of massive planets inside the disc around PDS 70 (Keppler et al 2018;Christiaens et al 2019;Keppler et al 2019), or analysis of gas kinematics (Pinte et al 2018;Teague et al 2018;Pinte et al 2019) suggest that at least some of these structures are indeed created by young planets. This raises the question of forming these objects in less than a typical million years.…”