Dramatic Period Decrease in T Ursae Minoris

Volume 23 number 2 (1995)

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Mattei Janet A.

AAVSO, Cambridge, MA

Grant Foster

AAVSO, Cambridge, MA

Abstract

The Mira-type long period variable T Ursae Minoris has exhibited a remarkable decrease in its period recently. Analyzing AAVSO visual observations from 1905 to 1994, we identify six distinct episodes during which T UMi has shown a different period. We discuss the various methods used to determine the changes in the period. From 1905 to 1979, its period shows small variations. However, beginning in 1979, its period has sharply decreased from 315 to 274 days. We propose that this star, with its unprecedented period decrease, may be immediately after the helium flash stage of its evolution.