Magnetic Models of the Brown Dwarfs HD 130948b and HD 130948c

Details Magnetic Models of the Brown Dwarfs HD 130948b and HD 130948c Magnetic Models of the Brown Dwarfs HD 130948b and HD 130948c

Apr 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010apj...713.1249m&link_type=abstract

The Astrophysical Journal, Volume 713, Issue 2, pp. 1249-1255 (2010).

Astronomy and Astrophysics

Astronomy

5

Brown Dwarfs, Stars: Evolution, Stars: Low-Mass, Stars: Magnetic Field

Scientific paper

Dynamical masses have been obtained by Dupuy et al. for the brown dwarf binary HD 130948BC. The components have luminosities log (L/L sun) of -3.82 and -3.90, and masses of 0.0555 and 0.0530 M sun. In a luminosity-age diagram, Dupuy et al. found that L bol for both B and C are brighter than theoretical tracks by factors of 2-3, if the age of the system is as old as their estimate of 0.79 Gyr (based on gyrochronology). Here, we apply our model of magnetic convection, in which the onset of convection is impeded in the presence of a vertical magnetic field: our goal is to replicate the observed properties not only in the luminosity-age diagram, but simultaneously in the T eff -age diagram and in the H-R diagram. Expressing the internal magnetic pressure as a fraction δ of the gas pressure, we obtain evolutionary tracks which fit both stars in an H-R diagram provided that δ lies in the range 0.007-0.038. With such values of δ, our models replicate the observed luminosities of both B and C, provided that the age is no larger than ~0.39 Gyr. This is significantly younger than the mean age estimated by Dupuy et al. for the primary star in the system, HD 130948A. However, there is sufficient uncertainty in the empirical parameters that an age as young as the one suggested by our magnetic models (~0.39 Gyr) is marginally within the permitted range.

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