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Session 113 - Observations of the Circumstellar Environment of YSOs.
Oral session, Thursday, January 18
Corte Real, Hilton
We have investigated the influence of young binaries on their associated disks using millimeter interferometry and submillimeter and infrared photometry. We find that binaries strongly influence their disks, reducing disk masses and radii, and in some cases clearing central holes.
Young binaries in Tau-Aur and Sco-Oph with projected separations between 1 and 50--100 AU have lower millimeter fluxes than wider binaries or single stars (Jensen, Mathieu, amp; Fuller 1996, ApJ, in press), consistent with close binaries clearing large gaps in their disks. Two-thirds of the binaries in our sample were detected by IRAS at 60 \mum, indicating that most binaries retain at least some circumstellar material.
Aperture-synthesis images of the young triple system UZ Tau at \lambda = 1.3 mm with 1^\prime\prime resolution show that UZ Tau W, a 50 AU binary, has 1.3 mm emission which is a factor of four lower than that from UZ Tau E, a ``single'' star 500 AU distant. UZ Tau E has a 150-AU radius circumstellar disk as traced by ^12CO (2\rightarrow1) emission. In contrast, UZ Tau W has unresolved continuum emission and no detectable CO emission, indicating that it has at least one circumstellar disk but no circumbinary disk. Since E and W have similar ages and stellar properties, differences in their disks must be attributed solely to the effects of multiplicity.
We have examined the spectral energy distributions (SEDs) of young binaries with separations less than 1 AU and infrared excesses to look for evidence of holes or gaps in their disks. Several show large dips in their SEDs which are consistent with inner holes on the size scale of the binary separation. However, others show near-power-law infrared SEDs and strong accretion diagnostics, suggesting that a close binary will not necessarily clear an evacuated central hole and that material may continue to flow from circumbinary to circumstellar disks.
This work is thesis research done under supervision of Robert Mathieu, and in collaboration with Gary Fuller, NRAO, and David Koerner, JPL.
