Brown Dwarf Binaries Multiplicity in Star Formation John

Brown Dwarf Binaries Multiplicity in Star Formation John Gizis May 17, 2007

Outline The Field brown dwarf sample Observed characteristics of brown dwarf binaries The young TW Hya Association The halo

Field Dwarfs • Bright • Resolution advantages • Sample “average” environment • Ages unknown • Masses unknown

Brown Dwarf Evolution Burrows et al. 1993, 1997

Brown Dwarf Evolution Burrows et al. 1993, 1997

The field sample • Selected by magnitude and color • 2 MASS, DENIS, SDSS • Not parallax • Lack of wide systems?

HST Imaging • 0. 1 arcsec resolution • Mass ratio q>0. 6 • Gizis et al. : 102 M/L dwarfs • Also AO imaging

HST Imaging • 20% of L dwarfs are resolved in nearequal luminosity doubles • Separations 2 -16 AU • Wide binaries rare (<1. 7%)

H-R Diagram • Narrowness of “main sequence” limits the fraction of binaries. • ~5% binary fraction for <1. 6 AU • +15% in range 1. 616 AU • ~20% +- 7% total binary fraction (Gizis et al. ) Dahn et al.

Wide Binaries • For sufficiently wide systems, we can discover the secondary independent of the primary. • A few percent of BDs are wide (>~1000 AU) companions to main sequence stars

Orbital Separations Gizis et al.

Mass ratios Burgasser et al.

Mass & Separation Close et al: v_esc = 3. 8 km/s Burgasser et al.

Mass & Binding Energy Burgasser et al.

TW Hya: 2 M 1207 • 8 Myr young association at d~50 pc DSS R 2 MASS K

2 M 1207 Spectral Energy Distribution: Disk Riaz & Gizis

2 M 1207 in Ultraviolet: Accretion and circumstellar gas • CIV accretion • No Si. IV • H 2 pumped by Ly Gizis et al.

2 M 1207 B

TW Hya Association • 2 M 1139: ~25 MJ, (Single) • TWA 5 B, ~25 MJ, (110 AU) • 2 M 1207 A, ~25 MJ (Primary) • SSS 1102, ~20 MJ (40, 000 AU) • 2 M 1207 B, ~5 MJ (40 AU) • Note that TWA 5 A is a triple star. TW Hya may be related to Sco-Cen. Certainly low-density. Is this close to primordial?

The halo • We do not have a sample of halo brown dwarf • The cool LHS stars are at distances of ~100 pc. • In a sample of 25 M subdwarfs, we do not resolve any binaries. • Bad luck? Perhaps different conditions of star formation? Jao later today…