RS Persei

RS Persei is a red supergiant variable star located in the Double Cluster in Perseus. The star's apparent magnitude varies from 7.82 to 10.0, meaning it is never visible to the naked eye.

Location
RS Persei is a member of the cluster NGC 884, χ Persei, one half of the famous Double Cluster.

Variability
RS Persei is classified as a semiregular variable star, with its brightness varying from magnitude 7.82 to 10.0 over 245 days, Detailed studies show that it also pulsates with a long secondary period of $-38$ days.

Properties
RS Persei is a large cool star with a temperature of 3,500 K. This makes it luminous, although much of its radiation is emitted in the infrared. In 2005, RS Per was calculated to have a bolometric luminosity of and a radius around. More recently, 2014 calculations across all wavelengths gives the star a lower luminosity of $4,880$ based on an assumed distance, and a radius of $1,497$ based on the measured angular diameter and luminosity. A 2023 paper gives an even smaller luminosity of.

The angular diameter of RS Persei was measured at $547$. At a distance of 1497parsecs, this corresponds to a radius of. Another paper from the same author gives $775$ and a radius of, altought the distance used isn't is mentioned. It is surrounded by dust that has condensed from material lost by the star.

RS Persei has sometimes been considered to be a highly evolved low mass Asymptotic Giant Branch (AGB) star, but calculations of its current mass suggest that it is a low mass supergiant. NGC 244 is also too young to host AGB stars.