1982-1988 Photometry of the Totally Eclipsing Chromospherically Active Binary V792 Herculis=HD 155638

Details 1982-1988 Photometry of the Totally Eclipsing Chromospherically Active Binary V792 Herculis=HD 155638 1982-1988 Photometry of the Totally Eclipsing Chromospherically Active Binary V792 Herculis=HD 155638

Mar 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aj....111.1322k&link_type=abstract

Astronomical Journal v.111, p.1322

Astronomy and Astrophysics

Astronomy

6

Stars: Individual: Hd 155638, Binaries: Eclipsing

Scientific paper

We present 1985-1988 UBV and VRI photometry obtained at three different observatories and analyze it along with previously published 1982-1984 UBV photometry. New times of midprimary eclipse along with previously published times yield the improved orbital ephemeris T(pri.min.)=JD 2446674.185 (±0.007) +27d53707(±0d.00026)n. Periodogram analysis of previously published radial velocities, for both the K giant and the F subgiant, yields orbital ephemeris constants consistent with the one above, but of lesser precision. Fitting the seven years of photometry with a cos(2θ) curve, after removing the eclipse points, yields 0m.021±0m.006 for the full amplitude of the ellipticity effect in V. Residuals from that cos(2θ) fit give light curves which reveal continuing starspot variability, which had been seen in the 1982-1984 photometry. These residuals, in ten data groups, are analyzed with a two-spot light-curve fitting procedure. Six long-lived spots are identified, the largest producing a light loss of 0m.166 in V. Lifetimes were >2.85, 0.81, 1.88, 1.84, >0.58, and >0.45 yr. Rotation periods for these six spots have a mean of 27d.36±0d.06, thus confirming synchronous rotation, and a range which indicates a differential rotation coefficient of k=0.031. With respect to the value of 0.65 below which strong dynamo action is expected in a convective star, the Rossby number for the K giant, believed to be the spotted star, is 0.17, well below the threshold and so large starspots are expected.

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