RS Persei is the red star closest to the centre of NGC 884, the right hand cluster (north is down).
Epoch J2000 Equinox J2000
|Right ascension||2h 22m 24.288s|
|Declination||+57° 06′ 34.08″|
|Apparent magnitude (V)||7.82-10.0|
|Radial velocity (Rv)||−38.0±2 km/s|
|Proper motion (μ)|| RA: −0.371±0.137 mas/yr |
Dec.: −0.931±0.165 mas/yr
|Parallax (π)||0.6437 ± 0.0822 mas|
|Distance||approx. 5,100 ly |
(approx. 1,600 pc)
|Absolute magnitude (MV)||−6.18|
|Radius||491 - 547 R☉|
|Luminosity||33,000 - 34,000 L☉|
|Surface gravity (log g)||−0.2±0.05 cgs|
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 4,200±1,500 days.
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 145,000 L☉ and a radius around 1,000 R☉. More recently, 2014 calculations across all wavelengths gives the star a lower luminosity of 77,600+9,500
−8,400 L☉ based on an assumed distance, and a radius of 770±30 R☉ based on the measured angular diameter and luminosity.
Even more recent measurements based on its Gaia Data Release 2 parallax gives a luminosity below 40,000 L☉ with a corresponding radius of 491 R☉. 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.