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Session 60 - Stellar Astrophysics I.
Oral session, Tuesday, January 16
Salon del Rey North, Hilton
EE Peg is among the binary systems with accurately known masses and radii (Andersen 1991, Astron. Astrophys. Rev., 3, 91). With component masses of 2.15 M_\sun, 1.33 M_\sun and an orbital period of 2.63^d, this low distortion system is an excellent first test case for application of a new spectrum synthesis program for binary stars (Linnell amp; Hubeny 1994, ApJ, 434, 738). The existing standard light curve solution is by Lacy amp; Popper (1984, ApJ, 281, 268), analyzing an excellent B light curve by Ebbighausen. That paper also includes component mass determinations to 1%, based on spectra by Lacy.
Our synthetic spectrum fits determine an iron abundance of log Fe=3.0x solar, and a calcium abundance of Ca=0.5x solar, consistent with the Am spectral type of the primary component.
Calculation of a synthetic spectrum depends on prior knowledge of component dimensions and T_eff values. Consequently there is an interdependence with the light curve solution. Our light curve solution applied the light synthesis program by Linnell (1984, ApJS, 54, 17). We found that use of the Planck Law to represent component radiative properties, a common procedure, produced a B-V component difference in strong disagreement with Popper's calibration of flux and T_eff for main sequence stars. A program modification permitted direct use of our synthetic spectrum results to represent the component radiative properties, with improved results.
Since our program is applicable to systems of any distortion, successful analysis of EE Peg invites future discussion of distorted systems for which single values of T_eff and log g are inadequate.
Program listing for Tuesday