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Published April 20, 2009 | Published
Journal Article Open

HR 8257: a three-dimensional orbit and basic properties

Abstract

We have used interferometric and spectroscopic observations of HR 8257 to determine a three-dimensional orbit of the system. The orbit has a period of 12.21345 days and an eccentricity of 0.2895. The masses of the F0 and F2 dwarf components are 1.56 and 1.38 M☉ , respectively, with fractional errors of 1.4%. Our orbital parallax of 13.632 ± 0.095 mas, corresponding to a distance of 73.4 ± 0.6 pc, differs from the Hipparcos result by just 2% and has a significantly smaller uncertainty. From our spectroscopic observations and spectral energy distribution modeling we determine the component effective temperatures and luminosities to be T_eff(A) = 7030 ± 200 K and T_(eff)(B) = 6560 ± 200 K and L_A = 9.4 ± 0.3 L☉ and L_B = 4.7 ± 0.2 L☉ . The primary rotates pseudosynchronously, while the secondary is not far from its pseudosynchronous rotational velocity. Although both early-F stars are slowly rotating, neither component of this close binary is an Am star. A comparison with evolutionary tracks indicates that the stars are slightly metal poor, and although the components have evolved away from the zero-age main sequence, they are both still dwarfs.

Additional Information

© 2009 American Astronomical Society. Print publication: Issue 2 (2009 April 20); received 2008 December 8; accepted for publication 2009 January 28; published 2009 April 7. We thank D. Queloz for contributing the Coravel radial velocities. We are also grateful to P. Berlind, J. Caruso, G. Esquerdo, and R. P. Stefanik for their help with the CFA observations, and to R. J. Davis for maintaining the CFA echelle database. PTI science operations are conducted through the efforts of the PTI Collaboration; we acknowledge the invaluable contributions of our PTI colleagues, and particularly thank K. Rykoski for his professional operation of PTI. This research at Tennessee State University has been supported in part by NASA grant NCC5-511 and NSF grant HRD-9706268. G. Torres acknowledges partial support from NSF grant AST-0708229 and NASA's MASSIF SIM Key Project (BLF57-04).

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