Evolution of starspots in the long-period RS CVN binary V1817 Cygni = HR 7428

• Published in: The Astronomical journal 1990-12, Vol.100, p.2017-2020
• Main Authors: Hall, Douglas S., Gessner, Susan E., Lines, Helen C., Lines, Richard D.
• Format: Article
• Language: English
• Subjects: 640102 - Astrophysics & Cosmology- Stars & Quasi-Stellar, Radio & X-Ray Sources; Astrophysics; BINARY STARS; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; GIANT STARS; MOTION; ORBITS; PHOTOMETRY; ROTATION; STARS; STARSPOTS; STELLAR ACTIVITY; VARIABLE STARS; VARIATIONS
• ISSN: 0004-6256; 1538-3881
• DOI: 10.1086/115656

Photometry between 1982 and 1989, published and unpublished, is analyzed. The ellipticity effect produces variability with a full amplitude of 0.033 m in V. A recent time of light minimum (JD 2445988.0 + or - 0.3 d) combined with an old spectroscopic time of conjunction from the 1920's yields a much improved orbital period (108.854 + or - 0.003). Removal of the ellipticity effect reveals starspot variability. Four different spots were observed at various times, two of them present simultaneously in the light curve during 1985. Mean spot lifetimes were around 2 years and the largest amplitude attributed to starspots was 0.04 m in V during 1986. Derived rotation periods for two spots were 5.3 + or - 1.2 percent slower than synchronous and 3.0 + or - 0.4 percent faster. The differential rotation coefficient for the K2 giant is k = 0.25 + or - 0.04, compared to k = 0.186 for the sun. V1817 Cygni has the longest orbital period of any binary known to execute synchronous rotation.