In 1917 it was announced thatIda E. Woods had discovered that this star is avariable star, by examining 520 photographs taken from December 1, 1887 through February 4, 1913.[10] It was given itsvariable star designation in 1921.[11] XX Persei is a semiregular variable star of sub-type SRc, indicating a cool supergiant. TheGeneral Catalogue of Variable Stars gives the period as 415 days.[4] It also shows a long secondary period which was originally given at 4,100 days.[6] A more recent study shows only slow variations with a period of 3,150 ± 1,000 days.[2] Another study failed to find any long period up to 10,000 days.[12]
The most likely distance of XX Per is2,290 pc, from assumed membership of thePerseus OB1 association.[13]Gaia Data Release 3 includes a parallax of0.3980±0.0316 mas, corresponding to a distance of around2,500 pc.[1]
XX Per is a red supergiant of spectral type M4Ib with an effective temperature below 4,000K. It has a large infrared excess, indicating surrounding dust at a temperature of 900 K, but no masers have been detected.[14][15]
XX Persei has a mass of 16solar masses, above the limit beyond which stars end their lives as supernovae.[6] This makes XX Persei similar to the more well-known red supergiantAntares.[16]
XX Persei is listed in multiple star catalogues with a companion of magnitude 9.8223″ away.[17] This star is BD+54°445 and it is an unrelated foreground object. In addition, thespectrum of XX Persei showsabsorption lines of a hot companion too close to be resolved. The combined spectral type has been given as M4Ib + B7V,[3] while the UV spectrum of the companion has been used to derive a spectral classification of A.[18]
^abProust, D.; Ochsenbein, F.; Pettersen, B. R. (1981). "A catalogue of variable-visual binary stars".Astronomy and Astrophysics Supplement Series.44: 179.Bibcode:1981A&AS...44..179P.
^abSamus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)".VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S.1.Bibcode:2009yCat....102025S.
^abcdStothers, R.; Leung, K. C. (1971). "Luminosities, masses and periodicities of massive red supergiants".Astronomy and Astrophysics.10: 290.Bibcode:1971A&A....10..290S.
^Percy, John R.; Sato, Hiromitsu (2009). "Long Secondary Periods in Pulsating Red Supergiant Stars".Journal of the Royal Astronomical Society of Canada.103 (1): 11.Bibcode:2009JRASC.103...11P.
^Fok, Thomas K. T.; Nakashima, Jun-Ichi; Yung, Bosco H. K.; Hsia, Chih-Hao; Deguchi, Shuji (2012). "Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated with Massive Clusters".The Astrophysical Journal.760 (1): 65.arXiv:1209.6427.Bibcode:2012ApJ...760...65F.doi:10.1088/0004-637X/760/1/65.S2CID53393926.
