Measuring Accretion in Young Substellar Objects: Approaching the Planetary Mass Regime

• Published in: The Astrophysical journal 2005-06, Vol.625 (2), p.906-912
• Main Authors: Muzerolle, James, Luhman, Kevin L, Briceño, César, Hartmann, Lee, Calvet, Nuria
• Format: Article
• Language: English
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/429483

We present observations of Ha emission-line profiles taken at Magellan Observatory for a sample of 39 young low-mass stars and brown dwarfs in the Taurus and Chamaeleon I star-forming regions. We have identified 11 new substellar accretors, more than tripling the number of known brown dwarfs with measurable accretion activity. These include the lowest-mass objects yet seen with accretion, with masses down to 60.015 M sub( ). Using models of Ha emission produced in magnetospheric accretion flows, the most widely applicable primary calibrator now available, we determine the first estimates of mass accretion rates for objects at such extremely low masses. For the six objects with masses 0.03 M sub( ), we find accretion rates of 65 x 10 super(-12) M sub( )yr super(-1), among the smallest yet measured. These new results continue the trend of decreasing mass accretion rate with decreasing (sub)stellar mass that we have noted previously for samples of more massive objects; the overall correlation is M 8 M super(2.1), and it now extends over a mass range of over 2 orders of magnitude. Finally, the absence of a discontinuity in the distribution of accretion rates with mass tends to suggest that stars and brown dwarfs share similar formation histories.