TIPSY: Trajectory of Infalling Particles in Streamers around Young stars

Dynamical analysis of the streamers around S CrA and HL Tau^★

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
e-mail: Aashish.Gupta@eso.org
² Institute for Astronomy, University of Hawaii, Honolulu, HI 96822, USA
³ University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, 81679 Munich, Germany
⁴ Exzellenzcluster ORIGINS, Boltzmannstr. 2, 85748 Garching, Germany
⁵ Niels Bohr Institute, University of Copenhagen, Øster Voldgade 5, 1350 Copenhagen, Denmark
⁶ Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
⁷ Max-Planck Institute for Extraterrestrial Physics, Gießenbachstraße 1, 85748 Garching bei München, Germany
⁸ Academia Sinica Institute of Astronomy and Astrophysics, 1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan

Received: 18 September 2023
Accepted: 6 January 2024

Abstract

Context. Elongated trails of infalling gas, often referred to as “streamers,” have recently been observed around young stellar objects (YSOs) at different evolutionary stages. This asymmetric infall of material can significantly alter star and planet formation processes, especially in the more evolved YSOs.

Aims. In order to ascertain the infalling nature of observed streamer-like structures and then systematically characterize their dynamics, we developed the code TIPSY (Trajectory of Infalling Particles in Streamers around Young stars).

Methods. Using TIPSY, the streamer molecular line emission is first isolated from the disk emission. Then the streamer emission, which is effectively a point cloud in three-dimensional (3D) position–position–velocity space, is simplified to a curve-like representation. The observed streamer curve is then compared to the theoretical trajectories of infalling material. The best-fit trajectories are used to constrain streamer features, such as the specific energy, the specific angular momenta, the infall timescale, and the 3D morphology.

Results. We used TIPSY to fit molecular-line ALMA observations of streamers around a Class II binary system, S CrA, and a Class I/II protostar, HL Tau. Our results indicate that both of the streamers are consistent with infalling motion. For the S CrA streamer, we could constrain the dynamical parameters well and find it to be on a bound elliptical trajectory. On the other hand, the fitting uncertainties are substantially higher for the HL Tau streamer, likely due to the smaller spatial scales of the observations. TIPSY results and mass estimates suggest that S CrA and HL Tau are accreting material at a rate of ≳27 M_jupiter Myr^–1 and ≳5 M_jupiter Myr^–1, respectively, which can significantly increase the mass budget available to form planets.

Conclusions. TIPSY can be used to assess whether the morphology and kinematics of observed streamers are consistent with infalling motion and to characterize their dynamics, which is crucial for quantifying their impact on the protostellar systems.