Rotational evolution of solar-type protostars during the star-disk interaction phase

TL;DR

This paper investigates how star-disk interactions influence the rotational evolution of solar-type protostars during the pre-main sequence phase, challenging the traditional disk-locking hypothesis with new torque models.

Contribution

It introduces a novel torque model based on simulations to study the impact of magnetospheric ejections and stellar winds on star spin evolution.

Findings

Magnetospheric ejections significantly affect stellar spin-down.

Stellar winds and magnetic field strength influence rotation rates.

The traditional disk-locking assumption is not fully supported by the model.

Abstract

The early pre-main sequence phase during which they are still likely surrounded by an accretion disk represents a puzzling stage of the rotational evolution of solar-mass stars. While they are still accreting and contracting they do not seem to spin-up substantially. It is usually assumed that the magnetospheric star-disk interaction tends to maintain the stellar rotation period constant (disklocking), but this hypothesis has never been thoroughly verified. Our aim is to investigate the impact of the star-disk interaction mechanism on the stellar spin evolution during the accreting pre-main sequence phases. We devise a model for the torques acting onto the stellar envelope based on studies of stellar winds and develop a new prescription for the star-disk coupling grounded on numerical simulations of star-disk interaction and magnetospheric ejections. We then use this torque model to follow the long-term evolution of the stellar rotation. Magnetospheric ejections and accretion powered stellar winds play an important role in the spin evolution of solar-type stars. However, kG dipolar magnetic fields are not uncommon but not ubiquitous. Besides, it is unclear how massive stellar winds can be powered, while numerical models of the propeller regime display a strong variability that has no observational confirmation. Better observational statistics and more realistic models could contribute to soften our calculations' requirements.