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SX Herculis

SX Herculis is a fine, bright semiregular variable with a period around 100 days.  Its light curve isn't too irregular, but it's clear that it undergoes changes in amplitude over time.  It is one of the prototypical SRd variables, classified by the GCVS as yellow supergiants that exhibit reasonably stable pulsations but with a wide range of periods -- from as little as 30 days to over 1000.  SX Her is a rather middle-of-the-road member of the class.  This 1000-day stretch of data shows SX Her during one of its more regular periods; when AAVSO visual data are averaged into bins (14 days in this light curve) the light variations become very clear.  Given their spectral types and their semiregularity, they're sometimes mentioned alongside a similar class of pulsator -- the RV Tauri star.  They exhibit similar pulsational characteristics, but they're distinctly different classes.

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484