LMC,SMC not in bound binary orbit

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Session 78 -- Galactic Structure and Star Counts
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[78.01] LMC,SMC not in bound binary orbit

Serge Demers (U. Montreal), Mike Irwin (RGO, Cambridge, UK)

We report on radial velocities of over 200 newly identified carbon stars in the region between the Magellanic Clouds and on the periphery of both LMC and SMC. Our findings, combined with velocities of early-type stars measured by our group and reported a few years ago, are interpreted in terms of disrup- tive tidal encounter scenarios first explored by the Toomres in the early 1970's. The models are constrained by the current separation between the Clouds, the relative radial velocities of their centers of mass, and the spread of velocities seen both in the inter-Cloud carbon stars, as well as the inter-Cloud early-type stars. This spread, of 100km/sec for the carbon stars, and 60km/s for the early types, in the annular regions from five to ten degrees from the SMC's center, is excessive for any bound elliptical orbit of the SMC about the LMC. These velocites, taken together with the inter-Cloud neutral hydrogen data of McGee and Newton of 1986, and the recent report by Hatzidimi- trious, Cannon, and Hawkins (1993) of the elongation of the SMC along the line of sight, form a highly consistent picture with a disruptive tidal impulse, timed by our color-magnitude arrays of inter-Cloud early type stars to have occurred between 0.05 and 0.2 Gyrs ago. The velocity range can be simulated for closed orbits only with much smaller inter-Cloud separation. Attempts to construct models that maintain the current Cloud separation, debris velocities, and SMC deformation with closed elliptical orbits were not successful, while open orbits, with eccentricities greater than 1.2, produce far better matches.

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