Parenago 1540: A Pre-Main-Sequence Double-Lined Spectroscopic Binary Near the Orion Trapezium

Spectroscopic and photometric observations of the star Parenago 1540 (V = 11.3), located 10 arcmin west of the Trapezium in Orion, have shown the star to be a pre-main-sequence double-lined spectroscopic binary. Thirty-seven radial-velocity measurements were obtained from which the orbital elements of the binary were determined, in particular an orbital period P = 33.73 + 0.03 days and an eccentricity of e = 0.12 + 0.01. Highdispersion spectra reveal strong Li 6707 A absorption lines in each of the components of P1540. A spectrum at lower dispersion also shows strong Ca II H and K emission lines, not resolved into individual components. P1540 also has an x-ray emission of 4 x 10(30) ergs s(-1). UBVRI photometry, combined with relative luminosities at V determined from spectra, have been used to determine the locus of each component in the theoretical H-R diagram. Assuming membership in the Orion star-forming region, both stars lie substantially above the ZAMS in the pre-main-sequence domain of the diagram. All of these data support the conclusion that both components of P1540 are pre-main-sequence stars. The masses of the individual components, determined from theoretical evolutionary tracks and the regiment of satisfying the dynamical mass ratio, are approximately 2.25 M and 1.7 M. Interestingly, no pair of stars satisfying both the dynamical and photometric constraints is compatible with coeval formation of the stars. If coeval formation is demanded, then the premain-sequence evolutionary tracks of the components of P1540 are not consistent with theoretical single-star evolutionary tracks presented by Cohen and Kuhi. Alternatively, the noncoevality of the components of P1540 might be attributed to an exchange occurring during a close stellar encounter. The space velocity of P1540 indicated that the binary is escaping from the Orion Nebula region, perhaps as the result of such a close encounter in the Trapezium cluster. Required Publisher's Statement Original version available from the publisher at: http://iopscience.iop.org/1538-3881 This article is available at The Cupola: Scholarship at Gettysburg College: http://cupola.gettysburg.edu/physfac/89 1 9 8 8 A J . . . . . 9 6 . 1 9 5 6 M