AAS 196th Meeting, June 2000
Session 46. Binary and Variable Stars
Display, Wednesday, June 7, 2000, 10:00am-7:00pm, Empire Hall South

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[46.03] Eclipsing Binaries in 47 Tuc: Bonus of an HST Planetary Search

E.F. Milone, C.R. Stagg, M.D. Williams (U. Calgary), T. M. Brown (NCAR), D. Charbonneau (NCAR,CfA), R.L. Gilliland, M.D. Albrow (STScI), A.S. Burrows (UA), W.D. Cochran, N. Baliber (U Texas), P.D. Edmonds (SAO), S. Frandsen, H. Bruntt (U. Aarhus), P. Guhathakurta, P. Choi, D.N.C. Lin, S.S. Vogt, J.H. Howell (UCSC), G.W. Marcy (UCB), M. Mayor, D. Naef (Obs. Geneve), A. Sarajedini (Wesleyan U.), S. Sigurdsson (PSU), D.A. VandenBerg (U. Victoria)

A direct benefit of the 8.3 d HST experiment described by R. L. Gilliland, et al. (see their poster), is the opportunity to obtain fundamental stellar data from an earlier generation of stars than are found in the local field and in (relatively young) open clusters, the sources of almost all our current knowledge of stellar parameters.

Of 32 variables examined thus far from time-series detections (see the Brown, et al., poster), 9 were previously known; of the 23 remaining, one remains a possible (though unlikely) planetary transit candidate. At present writing, 17 confirmed or potential eclipsing binary systems have been closely examined: five contact/over-contact; two short-period \beta Lyrae-type, four Algol-type; one asymmetric (O'Connell effect) light curve-, but likely eclipsing, variable; one possible ellipsoidal variable; and four others with asymmetric low-amplitude variation, still under investigation. Preliminary modeling is nearly complete for six binaries in this still incomplete sample, and is underway for the others.

Unadjusted and starting parameters are from VandenBerg's recent isochrone models and from an eclipsing binary simulation database of more than 8000 models created by Calgary students M. McClure, and B. Desnoyers-Winmill. Kurucz limb-darkening and atmospheric models straddling the metallicity range of the cluster are used in conjunction with Calgary versions of the Wilson-Devinney code, WD98 & wd98k93; the time-based mode is used to improve the periods and epochs. J Kallrath (BASF) developed and D. Terrell (SwRI) and W. Van Hamme (FIU) contributed to the value of these tools.

The eclipsing binary modeling is funded by NSERC of Canada and by the Univ. of Calgary Research Grants Committee through grants to EFM.

The author(s) of this abstract have provided an email address for comments about the abstract: milone@ucalgary.ca

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