Young Binary Stars and Associated Disks

Figure 1. The relative velocity of the binary stars' components as a function of their mean separation. The observed velocities are consistent with orbital motion since they (1) decrease with separation and (2) are generally greater for systems with higher mass primary stars (M₁ > 1 M and M₁ < 1 M are plotted as squares and circles respectively). The measurements are compared to that expected from a set of randomly oriented binary stars with total masses of 0.2, 1, 3, and 7 M. Although any individual total mass estimate is unreliable due to projection effects, the sample has an average total dynamical mass of ~ 1.7 M. (Taken from Ghez et al. 1995.)

Figure 2. Location of TY CrA primary and secondary stars in the theoretical H-R diagram. The hatched regions designate high-confidence domains for the primary and secondary based on light-curve analyses. Dotted lines are drawn at constant radii. Solid and dashed lines correspond to pre-main-sequence tracks of Swenson et al. (1994), calculated for the masses of the TY CrA components at solar (solid curve) and Hyades (dashed curve) compositions. Open boxes and triangles mark isochrone points at ages of 3 x 10⁶ yr and 10 x 10⁷ yr, respectively. (Taken from Casey et al. 1998.)

Figure 3. The stars of the GG Tau quadruple system compared with the theoretical evolutionary tracks of Baraffe et al. (1998; =1.9). The range of plausible temperatures for each component are determined using a dwarf temperature scale (solid squares; Leggett et al. 1996) and a giant temperature scale (open diamonds; Perrin et al. 1998). Since the dwarf and giant temperature scales are nearly identical for the two hottest components, these two stars define an isochrone (dashed line) that can be used to test evolutionary models and the T Tauri temperature scale at lower masses. Of the models tested, the Baraffe et al. models yield the most consistent ages using a temperature scale intermediate between that of dwarfs and giants. These tracks and the implied coeval temperature scale (asterisks) yield a substellar mass of 0.044 0.04 M for the lowest mass component of GG Tau. (Taken from White et al. 1999)

Figure 4. Owens Valley Radio Observatory = 1.3 mm continuum map (top) of UZ Tau, a young quadruple system, along with a schematic model for the system (bottom). UZ Tau W is a 50 AU binary, separated by 500 AU from the sub-AU binary UZ Tau E\null. UZ Tau E has a massive circumbinary disk, seemingly undisturbed by either the central close binary or by UZ Tau W located several disk radii away in projection. In contrast UZ Tau W, a binary with a separation similar to typical disk radii, shows substantially less disk emission, though it retains some mass in one or two unresolved circumstellar disks. (Adapted from Jensen et al. 1996b.)

Figure 5. Left---The stellar components of the GG Tau binary are shown as stars. The circumbinary ring is evident in the light shaded region, displaying 1.3 mm continuum emission. The contours display three velocity channels of ¹³CO 2-1 emission: 5.55 km/sec, 6.30 km/sec and 7.05 km/sec, increasing from left to right in the figure. The spatial gradient in the line emission is consistent with Keplerian motion about a binary of 1.3 (D/140 pc) M. The synthesized beam is 0.88'' x 0.56''. Right---The J-band adaptive optics image. The white ellipse is the same in both figures and represents the ring average radius. Evidently the light in the near infrared coincides with the circumbinary ring seen in millimeter light, and is interpreted as scattered light off the inner edge of the ring. (Taken from Guilloteau et al. 1999; the J-band image is from Roddier et al. 1996.)

Figure 6. VLA image of the L1551 IRS5 region at 7 mm. The two compact sources are interpreted as protoplanetary disks in a gravitationally bound protobinary system. The masses of the individual disks are of order 0.05 M, adequate to form planetary systems like our own. However the spatially resolved projected semimajor axes are only 10 AU, perhaps due to dynamical truncation by the stars. The half-power contour of the VLA beam was 0.05", opening a new forefront in high-resolution observations of young binary systems. (Taken from Rodriguez et al. 1998.)