Self-consistent evolution of accreting low-mass stars and brown dwarfs

TL;DR

This paper introduces self-consistent models combining hydrodynamics and stellar evolution to study how accretion affects the evolution and lithium depletion in young low-mass stars and brown dwarfs, explaining observed lithium anomalies.

Contribution

It provides the first self-consistent accretion models that reveal complex effects on lithium depletion and stellar evolution, matching recent observations.

Findings

Accretion history influences luminosity spread in HR diagrams.

Early accretion can cause abnormal lithium depletion.

Models explain lithium excess in fast rotators in NGC 2264.

Abstract

We present self-consistent calculations coupling numerical hydrodynamics simulations of collapsing pre-stellar cores and stellar evolution models of accreting objects. We analyse the main impact of consistent accretion history on the evolution and lithium depletion of young low-mass stars and brown dwarfs. These consistent models confirm the generation of a luminosity spread in Herzsprung-Russell diagrams at ages $\sim$ 1-10 Myr. They also confirm that early accretion can produce objects with abnormal Li depletion, as found in a previous study that was based on arbitrary accretion rates. The results strengthen that objects with anomalously high level of Li depletion in young clusters should be extremely rare. We also find that early phases of burst accretion can produce coeval models of similar mass with a range of different Li surface abundances, and in particular with Li-excess compared to the predictions of non-accreting counterparts. This result is due to a subtle competition between the effect of burst accretion and its impact on the central stellar temperature, the growth of the stellar radiative core and the accretion of fresh Li from the accretion disk. Only consistent models could reveal such a subtle combination of effects. This new result could explain the recent, puzzling observations of Li-excess of fast rotators in the young cluster NGC 2264. Present self-consistent accreting models are available in electronic form.