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Session 60 - Multiple Stars.
Display session, Wednesday, June 12
Great Hall,

[60.04] Hubble Space Telescope FGS Transfer Function Observations of L726-8

P. J. Shelus (McD Obs.), O. G. Franz, L. H. Wasserman (Lowell Obs.), G. F. Benedict, R. L. Duncombe, P. D. Hemenway, W. H. Jefferys, B. McArthur, E. Nelan, D. Story, A. L. Whipple (UTx), W. F. van Altena (Yale), L. W. Fredrick (UVa)

The M dwarf visual binary L726-8 is an interesting astrophysical object and one of the nearest stellar systems to the Sun. Almost 50 years of ground-based photographic and visual observations of position angle and separation now exist. The system is a difficult one to observe and its components are now rapidly nearing closest approach. At the present time the separation of the components is less than 1.5 seconds of arc. Periastron passage is predicted to occur in early 1998. It is also an important candidate to search for orbital perturbations that might be caused by extra-Solar System planets. As such, L726-8 is an excellent object for HST FGS attention. Because of the binary nature of the system and the extreme scarcity of suitable background reference objects, we are choosing to observe this object with HST Fine Guidance Sensor #3 in transfer function mode. Beginning in the summer 1995 a number of observational sets have been obtained, using Astrometry Science Team Guaranteed Time Observations. It is expected that HST observations of L726-8 will continue in this mode until at least July 1997. In this poster we are presenting the available HST observations and some analytical results, alone and co- mingled with ground-based observations, that furnish dynamical information of the system. Eventually, and only when a sufficiently accurate and precise orbit is obtained, we will examine the residuals for indications of a perturbation in the system, possible evidence of one or more unseen companions.

Program listing for Wednesday