R Trianguli (abbreviated as R Tri) is a short-period oxygen-rich Mira variable in Triangulum with a period of 266.9 days, discovered by T. H. E. C. Espin in 1890. It is losing about , close to average for a short-period Mira variable. While most short-period Mira variables reside in the Galactic halo, R Trianguli is a member of the thick disk, and its proper motion is fairly high for its distance. Its angular diameter in the K band was measured in 2002 to be, on average, , with a shape suggesting that there is an optically thin disk structure surrounding the star.
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R Trianguli
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