A Connection Between Disk Mass and Binary Separation

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Session 62 -- Very Young Stars
Display presentation, Thursday, 9:20-4:00, Pauley Room

[62.21] A Connection Between Disk Mass and Binary Separation

E.L. Jensen, R.D. Mathieu (U. of Wisconsin-Madison), G.A. Fuller (NRAO)

Beckwith et al. (1990, AJ 99, 924; BSCG) noted that massive disks are rarely found in binary systems with separations $<$ 100 AU but are common in systems with wider separations. However, many of their upper limits on the disk masses of the closer binaries were comparable to the detected disk masses among the wider binaries. Also, numerous ``single'' stars in their sample have since been found to be binaries.

We have made sensitive 800 $\mu$m continuum observations at the James Clerk Maxwell Telescope for most pre-main sequence binary stars in the Taurus region with separations between 1 AU and 20 AU, with no detections. Using the disk models of BSCG, we set 3$\sigma$ upper limits on disk masses of typically less than $4 \times 10^{-3} M_{\sun}$. These mass limits are smaller than almost all of the masses found by BSCG for wider binaries. Combining our results with those of BSCG and only considering upper limits comparable to the smallest detected disk mass, we find that 6 out of 10 binaries with projected separations $\ge$ 100 AU have massive disks, comparable to the rate of disk detection around single stars. In contrast, only 3 out of the 13 systems with separations $ < 100$ AU are detected, and those three have separations greater than 40 AU.

Thus, as suggested by Beckwith et al., massive disks seem to be inhibited in the environments of binaries with separations of tens of AU. At the same time, we have detected submillimeter emission from the binary GW Ori with a separation of only 1 AU (Mathieu et al., this volume). These results suggest tidal truncation of circumstellar and circumbinary disks. For $R_{disk} \approx 100$ AU, binaries with separations of tens of AU will dynamically clear a large range of radii in disks, whereas in closer or wider systems much of the disk mass will be undisturbed. In addition, density waves excited in circumstellar disks by close companions may deplete those disks by increasing the accretion rate (Ostriker et al. 1992, ApJ 399, 192). Alternatively, the consumption of disk material during binary formation may depend on separation.

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