Abstract
In the pre-main-sequence stage, star-disc interactions have been shown to remove stellar angular momentum and regulate the rotation periods of stars with M2 and earlier spectral types. Whether disc regulation also extends to stars with later spectral types still remains a matter of debate. Here we present a star-disc interaction study in a sample of over 180 stars with spectral types M3 and later (corresponding to stellar masses $\leq 0.3 M_\odot$) in young stellar cluster NGC 2264. Combining rotation periods from the literature, new and literature spectral types, and newly presented deep Spitzer observations, we show that stars with masses below 0.3 $M_\odot$ with discs also rotate slower than stars without a disc in the same mass regime. Our results demonstrate that disc-regulation still operates in these low-mass stars, although the efficiency of this process might be lower than in higher-mass objects. We confirm that stars with spectral types earlier and later than M2 have distinct period distributions and that stars with spectral types M5 and later rotate even faster M3 and M4-type stars.
Highlights
The angular momentum of a recently born star is one of the fundamental parameters such as the initial mass and chemical composition
The optical spectra of M dwarfs are dominated by molecular absorption bands mainly from titanium oxide (TiO) and vanadium oxide (VO)
We confirm that stars with spectral types earlier and later than M2 have distinct period distributions
Summary
The angular momentum of a recently born star is one of the fundamental parameters such as the initial mass and chemical composition. Stars are supposed to inherit their own rotation from the natal molecular core, but this angular momentum is larger than the star could bear without breaking out itself (Bodenheimer 1995). Observations show that this does not happen, but speeds typically only reach up to a 10 % of the break-up speed Several processes have been proposed to slow down the stellar rotation, e.g. magnetic braking, discs, mass-loss, expanding envelopes, etc. In the case of low–mass (0.3-2.0 M ) stars, it is believed that the major mechanism regulating the stellar rotation is the star-disc interaction
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