Star in the constellation Perseus
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! style="text-align: center; background-color: #FFFFC0;" colspan="2" | Observation dataEpoch J2000      Equinox J2000
! style="text-align:left" | Constellation
! style="text-align:left" | Right ascension
! style="text-align:left" | Declination
! style="text-align:left" | Apparent magnitude (V)
! style="background-color: #FFFFC0; text-align: center;" colspan="2"| Characteristics
! style="text-align:left" | Evolutionary stage
! style="text-align:left" | Spectral type
! style="text-align:left" | Variable type
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XX Persei (IRC +50052 / HIP 9582 / BD+54°444) is a semiregular variable red supergiant star in the constellation Perseus, between the Double Cluster and the border with Andromeda.
Variability.
In 1917 it was announced that Ida E. Woods had discovered that this star is a variable star, by examining 520 photographs taken from December 1, 1887 through February 4, 1913. It was given its variable star designation in 1921. XX Persei is a semiregular variable star of sub-type SRc, indicating a cool supergiant. The General Catalogue of Variable Stars gives the period as 415 days. It also shows a long secondary period which was originally given at 4,100 days. A more recent study shows only slow variations with a period of 3,150 ± 1,000 days. Another study failed to find any long period up to 10,000 days.
Distance.
The most likely distance of XX Per is , from assumed membership of the Perseus OB1 association. Gaia Data Release 3 includes a parallax of , corresponding to a distance of around .
Characteristics.
XX Per is a red supergiant of spectral type M4Ib with an effective temperature below 4,000 K. It has a large infrared excess, indicating surrounding dust at a temperature of 900 K, but no masers have been detected.
XX Persei has a mass of 16 solar masses, above the limit beyond which stars end their lives as supernovae. This makes XX Persei similar to the more well-known red supergiant Antares.
Companions.
XX Persei is listed in multiple star catalogues with a companion of magnitude 9.8 away. This star is BD+54°445 and it is an unrelated foreground object. In addition, the spectrum of XX Persei shows absorption lines of a hot companion too close to be resolved. The combined spectral type has been given as M4Ib + B7V, while the UV spectrum of the companion has been used to derive a spectral classification of A.
References.
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