Am. Ghez et al., HIGH-SPATIAL-RESOLUTION IMAGING OF PRE-MAIN-SEQUENCE BINARY STARS - RESOLVING THE RELATIONSHIP BETWEEN DISKS AND CLOSE COMPANIONS, The Astrophysical journal, 490(1), 1997, pp. 353-367
In order to study the passive and active effects of young close compan
ion stars and to constrain possible multiple star formation mechanisms
, we have carried out a high-resolution imaging program of six multipl
e T Tauri star systems using the Hubble Space Telescope from 0.3 to 0.
9 mu m and ground-based speckle imaging from 1 to 2 mu m. Each system
(GG Tau, UZ Tau, DF Tau, RW Aur, V773 Tau, and V410 Tau) has at least
one binary pair with separation between 0.'' 07 and 0.'' 4 (10-50 AU).
In addition to the previously known companions, a third component is
discovered in the V410 Tau system. Many of the companion stars contrib
ute significantly to the unresolved spectral energy distribution and t
hereby bias the inferred stellar and circumstellar properties. Age is
the most systematically biased quantity; neglecting a companion causes
an overestimate in age by a factor of similar to 2 typically and more
than 10 in the extreme. Excess emission above the photospheric level
is detected at ultraviolet (UV) and near-infrared (NIR) wavelengths fo
r several of the components, which suggests that some close (10-50 AU)
T Tauri binaries support at least a minimal circumstellar disk at an
age of similar to 1 Myr. These inner disks not only provide a potentia
l reservoir of material for planetary formation but also may play a ke
y role in the evolution of the components' angular momenta. Possible m
ultiple star formation scenarios are explored in light of the componen
ts' relative stellar and circumstellar properties for systems studied
here as well as wider and closer systems whose properties are reported
in the literature. In summary, the components (1) are coeval, (2) hav
e secondary mass and mass ratio distributions that appear to be indepe
ndent of both the primary stars' mass and the binary separation, and (
3) have UV and NIR excess emission that is either similar or more domi
nant in the primary. These properties support a scenario in which bina
ry stars form via core fragmentation.