S Persei
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Perseus |
| Right ascension | 2h 22m 51.70928s |
| Declination | 58° 31′ 11.4476″ |
| Apparent magnitude (V) | 9.23 (7.9 - 12.0) |
| Characteristics | |
| Spectral type | M4.5I (M3Iae - M7) |
| B−V color index | 2.65 |
| Variable type | SRc |
| Astrometry | |
| Radial velocity (Rv) | -39.71 km/s |
| Proper motion (μ) |
RA: −0.49 ± 0.23 mas/yr Dec.: −1.19 ± 0.20 mas/yr |
| Parallax (π) | 0.413 ± 0.017mas |
| Distance | 7,900 ± 300 ly (2,420 ± 100 pc) |
| Absolute magnitude (MV) | −6.36 (at mV 9.23) |
| Details | |
| Mass | 20 M☉ |
| Radius | 780 - 1,230 R☉ |
| Luminosity | 86,000 - 186,000 L☉ |
| Surface gravity (log g) | 0.0 cgs |
| Temperature | 3,000–3,600 K |
| Other designations | |
| Database references | |
| SIMBAD | data |
S Persei is a red supergiant located near the Double Cluster in Perseus, north of the cluster NGC 869. It is a member of the Perseus OB1 association and one of the largest known stars. It is also a semiregular variable, a star whose variations are subject to more irregularities than those of Mira variables.
S Persei was named by German astronomer Adalbert Krueger in 1874 after observing that it varied in brightness. It was subsequently listed in major stellar catalogues of that era as HD 14528, BD+57 552.
S Persei varies slowly by several magnitudes, a factor of over 40 in brightness. It has a main period of somewhat over two years, but shows significant unpredictability. There is a strong variation in the amplitude from around one magnitude to about four magnitudes, and these have been interpreted as beats due to a second period of about 940 days. Other analyses find only the primary period of 813 ± 60 days.
S Persei is classified as a semiregular variable star of type SRc, indicating that it is a supergiant, and it has one of the largest visual amplitudes of any variable of this type. While the General Catalogue of Variable Stars lists it as varying between magnitudes 7.9 and 12.0, it has since been seen fainter.
The spectral type of S Persei also varies. Typically it is a red supergiant of spectral class M3 or M4, but particularly at deep visual minima it may show a much cooler spectral type of M7 or M8, highly unusual for a supergiant.
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