Advanced International Journal for Research

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Long-Term Photometric Behaviour of the RS CVn Binary IM Pegasi

Author(s) Mr. Yogesh Gopinath Chavan, Dr. Pramod Karbhari Pawar, Dr. Anil Nagorao Ardad
Country India
Abstract Abstract
IM Pegasi (HR 8703) is a long-period RS CVn binary whose brightness changes as large starspots rotate in and out of view. We study Johnson V-band photoelectric photometer (PEP) measurements of the star from the American Association of Variable Star Observers (AAVSO) International Database for the seasons 2001–2008. Seven observing windows, one in each of 2001–2006 and 2008, are examined season by season, and a Lomb–Scargle period search is run on the whole series and on each window. In 2001–2004 the star stays near a mean of V ≈ 5.79 and moves up and down by about 0.12–0.24 mag, with successive faint or bright phases 22–28 d apart. The Lomb–Scargle periodogram of the 406 measurements peaks at about 24.9 d (false-alarm probability ~10⁻²⁵), within one resolution element (0.24 d) of the 24.649 d orbital period. Six of the seven single-season periods lie between 23.3 and 26.1 d and average 24.66 ± 1.02 d; the seventh, from 2005, is a 0.5 d sampling artefact. Single seasons cannot separate the orbital period from the slightly shorter photometric period reported in the literature. The mean level then slips to V ≈ 5.87 in 2006 and V ≈ 5.89 in 2008, which echoes the changing spot coverage found in earlier light-curve modelling, but sparse sampling and possible zero-point drift mean that a real fading is not yet established.
Keywords Variable Stars; IM Pegasi; Photometry; Photoelectric Photometer (PEP); RS CVn; Starspots; Period Analysis
Field Physics > Astronomy
Published In Volume 7, Issue 5, September-October 2026
Published On 2026-10-31
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