A correlation between accretion and outflow rates for class II young stellar objects with full and transition disks

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
² INAF – Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
³ Instituto de Radioastronomía y Astrofísica (IRyA-UNAM), Morelia, Michoacán 58089, Mexico
⁴ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
⁵ Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
⁶ Dipartimento di Fisica e Astronomia Augusto Righi, Universitá di Bologna, Viale Berti Pichat 6/2, Bologna, Italy
⁷ Department of Physics and Astronomy, Rice University, 6100 Main Street, MS-108, Houston, TX 77005, USA
⁸ Dipartimento di Fisica, Universitá degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy

^★ Corresponding author: rota@strw.leidenuniv.nl

Received: 25 February 2025
Accepted: 21 May 2025

Abstract

Context. Magnetohydrodynamic (MHD) winds and jets are processes that influence the global evolution of the star and planet formation process. They originate in a wide range of regions of protoplanetary disks (∼ 1–30 au) and are thought to be the primary mechanisms driving accretion onto the central star. One indirect signature of these processes is the free-free emission from ionized gas close to the star.

Aims. We analyzed a sample of 31 class II young stellar objects (YSOs) with different types of disks: 18 full disks and 13 transition disks. All sources show evidence of excess free-free emission over the contribution of thermal dust. We investigated the origin of this emission and whether it is associated with other observables in disks with different types of substructures.

Methods. We first analyzed a sample of objects in Taurus, exploring possible correlations with the properties of the central star, the disk, and other disk-wind tracers. We then compared our findings with a sample of transition disks, for which free-free emission was already shown to be likely associated with an MHD wind and/or jet.

Results. We find no correlation between the detected free-free emission and either the X-ray or the [O I]6300 Å line properties. We find a strong correlation between the ionized mass-loss rate, as inferred from the free-free emission, and the accretion rate, suggesting that free-free emission in YSOs with full disks is associated with an MHD wind and/or jet.

Conclusions. The detected free-free emission in YSOs with both transition disks and full disks is likely associated with a similar mechanism, i.e., ionized gas close to the star from an MHD wind and/or jet. The free-free emission detected in transition disks shows hints of shallower correlations with accretion properties than in full disks. Whereas the efficiency in transforming accretion into outflow might differ in transition disks and full disks, considering the correlations between free-free emission and accretion properties, this difference could simply result from a bias toward strong accretors in the transition disk sample. Therefore, additional observations of a more complete and uniform sample are necessary to determine whether this change in correlation holds only for strong accretors or for transition disks in general.