DY Persei
DY Persei is a variable star and carbon star in the Perseus constellation. At maximum it is 11th magnitude and at its faintest it drops to 16th magnitude. DY Persei is the prototype of the very rare DY Persei class of variables that pulsate like red variables but also fade from sight like R Coronae Borealis variables. Location. DY Persei is located on the outskirts of the Trumpler 2 open cluster, near the famous Double Cluster. At 1,500 pc, DY Persei is thought to be much further away than Trumpler 2 and not a member. Variability. DY Persei  was reported to be variable in 1947. It was initially classified as a semiregular variable star with a brightness range of magnitude 10.6 to 13.2 and an approximate period of 900 days. Further study revealed that it showed deep declines every few years as well as continuous variations with a rough period of 792 days. The deep declines were considered to be related to the declines seen in R CrB stars, but DY Persei was a unique example, being a cool carbon star and showing large amplitude semiregular variations when not in decline. DY Persei is now classed as a  member of the very rare class of DY Persei variables, with only four known in the Milky Way and 13 more in the Magellanic Clouds. It has shown declines as deep as visual magnitude 16.0. The deep declines of DY Persei occur much more regularly than those of most R CrB stars, and they are generally symmetrical with slower decline and recovery rates than other R CrB stars. It is unclear whether it is really a member of the class or a pulsating asymptotic giant branch star with unrelated veiling ejections, or just the cooler version of R CrB stars.<ref >