Spot activity on HD 89546 (FG UMa) from long-term photometry

Details Spot activity on HD 89546 (FG UMa) from long-term photometry Spot activity on HD 89546 (FG UMa) from long-term photometry

Feb 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012an....333..138o&link_type=abstract

Astronomische Nachrichten, Vol.333, Issue 2, p.138

Astronomy and Astrophysics

Astronomy

Binaries: Spectroscopic, Stars: Activity, Stars: Individual (Hd 89546), Stars: Rotation, Starspots, Techniques: Photometric

Scientific paper

We present the analysis of 20 years of time-series BV photometry of the SB1 RS CVn binary HD 89546. The system's yearly mean V brightness, the B-V color index, the photometric period, and the light curve amplitude all show clear cyclic variability with an ≈9-year time scale. We also find some evidence for brightness variability on a time scale longer than the 20-year time span of our observations, perhaps indicating a longer cycle analogous to the solar Gleissberg cycle. We estimate the unspotted V magnitude of HD 89546 to be 7.154m, which is ≈0.2m brighter than the observed maximum brightness. Spot modelling of the system shows that spot temperature variations affect the observed B-V color as well as the V brightness. Two active longitudes are observed, centered around 180° and 360° longitude on the G9 III primary, each covering a longitude range of 120°. Furthermore, two inactive longitude zones are seen spanning only 60° between the two active longitudes. The longitudinal distribution of the spots exhibits no strong cyclic variability but does show rapid jumps of 120° that look like the flip-flop phenomenon. We estimate the differential rotation coefficient of the star as k=0.086 by considering the range of observed photometric period variations and assumed latitudinal spot variations over 45°.
Based on data obtained with the Tennessee State University T3 0.4 m APT at Fairborn Observatory, operated by Tennessee State University, and T30 0.3 m telescope of the Ege University Observatory in Izmir.

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