We present spectroscopy that confirms periodic Doppler-shifts along with photometry that reinforces a lack of eclipsing in the double-lined spectroscopic binary 57 Cygni. Our spectroscopy concentrates on a range encompassing H-alpha and the helium 667.8 nm line, where we find Doppler-shifts of both stars resolved in the helium line but less so in the broader H-alpha profile. Although we find the radial velocities derived from both lines reasonably consistent, we retained only the helium-line derived velocities for sinusoidal curve-fits to the orbital dependence. The fit-amplitudes specify the ratio of the stellar masses as 1.03 ± 0.05, in agreement with previous assessments. We find an eccentricity of 0.028 ± 0.024 and a longitude of periastron of 163.5 ± 2.5°. The former is significantly lower than that previously reported, while the latter is in agreement but calls into question the apsidal motion predicted four decades ago. Our modeling suggests the presence of an external third body implicit in this previous apsidal motion, as well as the dominant mechanism for our reported change in eccentricity. Based upon the spectral type assignment, the near-circular orbit, and the well-established mass ratio, we can place restrictions on the orbital inclination from 51.5-to-53.0°, in reasonable agreement with previous estimates.
Perturbations Observed in The Orbital Elements of the Spectroscopic Binary 57 Cygni
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Kenneth W. McLaughlin, Janak Panthi; Perturbations Observed in The Orbital Elements of the Spectroscopic Binary 57 Cygni. The Journal of the Iowa Academy of Science 1 January 2018; 125 (1-4): 1–11. doi: https://doi.org/10.17833/0896-8381-125.1.1
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