FIRST DIRECT SIMULATION OF BROWN DWARF FORMATION IN A COMPACT CLOUD CORE

Journal Article · Fri Jul 10 04:00:00 EDT 2009 · Astrophysical Journal (Online)

DOI:https://doi.org/10.1088/0004-637X/699/2/L157; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21313034

Machida, Masahiro N; Inutsuka, Shu-ichiro ^[1]; Matsumoto, Tomoaki ^[2]

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1. Department of Physics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan)
2. Faculty of Humanity and Environment, Hosei University, Fujimi, Chiyoda ku, Tokyo 102-8160 (Japan)

Brown dwarf formation and star formation efficiency are studied using a nested grid simulation that covers 5 orders of magnitude in spatial scale (10{sup 4}-0.1 AU). Starting with a rotating magnetized compact cloud with a mass of 0.22 M {sub sun}(225 M {sub Jup}), we follow the cloud evolution until the end of the main accretion phase. An outflow of {approx}5 km s{sup -1} emerges {approx}100 yr before the protostar formation and does not disappear until the end of the calculation. The mass accretion rate declines from {approx}10{sup -6} M {sub sun} yr{sup -1} to {approx}10{sup -8}-10{sup -12} M {sub sun} yr{sup -1} in a short time ({approx}10{sup 4} yr) after the protostar formation. This is because (1) a large fraction of mass is ejected from the host cloud by the protostellar outflow and (2) the gas escapes from the host cloud by the thermal pressure. At the end of the calculation, 74% (167 M {sub Jup}) of the total mass (225 M {sub Jup}) is outflowing from the protostar, in which 34% (77 M {sub Jup}) of the total mass is ejected by the protostellar outflow with supersonic velocity and 40% (90 M {sub Jup}) escapes with subsonic velocity. On the other hand, 20% (45 M {sub Jup}) is converted into the protostar and 6% (13 M {sub Jup}) remains as the circumstellar disk. Thus, the star formation efficiency is {epsilon} = 0.2. The resultant protostellar mass is in the mass range of brown dwarfs. Our results indicate that brown dwarfs can be formed in compact cores in the same manner as hydrogen-burning stars, and the magnetic field and protostellar outflow are essential in determining the star formation efficiency and stellar mass.

• OSTI ID: 21313034
• Journal Information: Astrophysical Journal (Online), Journal Name: Astrophysical Journal (Online) Journal Issue: 2 Vol. 699; ISSN 1538-4357
• Country of Publication: United States
• Language: English

Related Subjects

99 GENERAL AND MISCELLANEOUS
DWARF STARS
HYDROGEN BURNING
MAGNETIC FIELDS
MASS
STAR EVOLUTION