W Orionis
W Orionis is a carbon star in the constellation Orion, approximately away. It varies regularly in brightness between extremes of magnitude 4.4 and 6.9 roughly every 7 months. When it is near its maximum brightness, it is faintly visible to the naked eye of an observer with good observing conditions.
Variability
Evelyn Leland discovered that the star is a variable star based on observations done in the last decades of the 19th century, when it was known as BD +00°939. The discovery was announced in 1895. It was listed with its variable star designation, W Orionis, in Annie Jump Cannon's 1907 work Second Catalog of Variable Stars.W Orionis is a semiregular variable with an approximately 212‑day cycle. A long secondary period of 2,450 days has also been reported.
Properties
The angular diameter of W Orionis has been measured using interferometry and a value of 9.7 mas is found. Although it is known to be a pulsating variable star, no changes in the diameter were seen.Technetium has not been detected in W Orionis, an unexpected result since this s-process element should be dredged up in all thermally-pulsating AGB stars and especially in carbon stars.