Accretion in brown dwarfs down to nearly planetary masses

Details Accretion in brown dwarfs down to nearly planetary masses Accretion in brown dwarfs down to nearly planetary masses

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005an....326..891m&link_type=abstract

Astronomische Nachrichten, Vol.326, Issue 10, p.891-894

Astronomy and Astrophysics

Astronomy

6

Stars: Low-Mass, Brown Dwarfs, Stars: Formation

Scientific paper

We show that in accreting ultra low-mass stars and brown dwarfs, the CaII λ8662 emission line flux correlates remarkably well with the mass accretion rate (\dot{M}), just as it does in higher mass classical T Tauri stars (CTTs). A straightforward measurement of the CaII flux thus provides an easier \dot{M} determination technique than detailed modeling of the Hα emission line profile (except at the very lowest accretion rates, where CaII does not appear to be in emission for ultra low-mass objects, and Hα modeling is required). Using optical high-resolution spectra, we infer \dot{M} from CaII emission for young ultra low-mass objects down to nearly the deuterium-burning (planetary-mass) limit. Our results, in combination with previous determinations of \dot{M} in CTTs, illustrate that the accretion rate declines steeply with mass, roughly as \dot{M}∝ {M*}2 (albeit with considerable scatter). A similar relationship has been suggested by previous studies; we extend it down to nearly the planetary regime. The physical reason for this phenomenon is not yet clear; we discuss various possible mechanisms.

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