Location of S Persei (circled) near the Double Cluster (north is left) | |
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Perseus |
Right ascension | 2h 22m 51.70928s [1] |
Declination | 58° 31′ 11.4476″ [1] |
Apparent magnitude (V) | +9.23 [2] (7.9 - 12.0 [3] ) |
Characteristics | |
Spectral type | M3 Iae–M7 [3] |
B−V color index | +2.65 [2] |
Variable type | SRc [3] |
Astrometry | |
Radial velocity (Rv) | -39.71 [4] km/s |
Proper motion (μ) | RA: –0.49 ± 0.23 [5] mas/yr Dec.: −1.19 ± 0.20 [5] mas/yr |
Parallax (π) | 0.413 ± 0.017 mas [5] |
Distance | 7,900 ± 300 ly (2,420 ± 100 pc) |
Absolute magnitude (MV) | –6.36 (at mV 9.23) [2] |
Details | |
Mass | 20 [6] M☉ |
Radius | 1,298+64 −57 [7] –1,364±6 [8] R☉ |
Luminosity | 123,000 [9] – 186,000 [10] L☉ |
Surface gravity (log g) | 0.0 [11] cgs |
Temperature | 3,000 [12] – 3,600 [10] K |
Other designations | |
Database references | |
SIMBAD | data |
S Persei is a red supergiant or hypergiant 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. If placed in the Solar System, its photosphere would engulf the orbit of Jupiter. It is also a semiregular variable, a star whose variations are less regular than those of Mira variables.
S Persei was named by German astronomer Adalbert Krueger in 1874 after observing that it varied in brightness. [13] It was subsequently listed in major stellar catalogues of that era as HD 14528 and 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. [15] Other analyses find only the primary period of 813 ± 60 days. [16]
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. [3] While the General Catalogue of Variable Stars lists it as varying between magnitudes 7.9 and 12.0, it has since been seen fainter. [16]
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. [17]
Many of the visually bright variable stars belong to this class of semiregulars, as these stars are extremely large and luminous, and hence visible across long distances. S Persei has been described as a hypergiant [18] and has a radius over 700 times the sun's radius (R☉). [2] Its angular diameter has been measured directly and found to be somewhat elliptical. Modelled as a uniform disk, the radius corresponds to 1,212 ± 124 R☉. [19]
The temperature has been calculated from the spectrum using a DUSTY model, [20] giving an effective photospheric temperature of 3,500 K and a temperature of 1,000 K for the surrounding dust torus. [21] This is consistent with previous studies, but the derived luminosity from different authors varies from 86,000 L☉ to 186,000 L☉. [10] [22] [23] Older studies frequently calculated higher luminosities, lower temperatures, and consequently larger values for the radius. [24]
The mass of S Persei is also uncertain, but expected to be around 20 M☉. [6] Mass is being lost at 2.4 to 2.6×10−5 M☉ per year, [21] leading to an extensive and complex circumstellar environment of gas and dust. [10]
S Persei is surrounded by clouds containing water molecules which produce maser emission. This allows the distance to be measured very accurately using very long baseline interferometry, giving an annual parallax of 0.413 ± 0.017 milliarcseconds. For comparison the Gaia Data Release 2 parallax is 0.2217±0.1214 mas . [25] It lies somewhat further away than the centres of the Double Cluster open clusters, but definitely within the Per OB1 association and the Perseus Arm of the galaxy. [5]
S Persei is a double star. The red supergiant has an A0 11th magnitude companion at 69". [26] There are also several other 8th to 10th magnitude stars within half a degree of S Persei. [27]
Red supergiants (RSGs) are stars with a supergiant luminosity class and a stellar classification K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Antares A are the brightest and best known red supergiants (RSGs), indeed the only first magnitude red supergiant stars.
A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They are usually considered to be those with luminosity class I and spectral class B9 or earlier, although sometimes A-class supergiants are also deemed blue supergiants.
Phi Cassiopeiae is a multiple star in the constellation Cassiopeia with a combined apparent magnitude of +4.95. The two brightest components are A and C, sometimes called φ1 and φ2 Cas. φ Cas A is an F0 bright supergiant of magnitude 4.95 and φ Cas C is a 7.08 magnitude B6 supergiant at 134".
A yellow hypergiant (YHG) is a massive star with an extended atmosphere, a spectral class from A to K, and, starting with an initial mass of about 20–60 solar masses, has lost as much as half that mass. They are amongst the most visually luminous stars, with absolute magnitude (MV) around −9, but also one of the rarest, with just 20 known in the Milky Way and six of those in just a single cluster. They are sometimes referred to as cool hypergiants in comparison with O- and B-type stars, and sometimes as warm hypergiants in comparison with red supergiants.
V354 Cephei is a red supergiant star located within the Milky Way. It is an irregular variable located over 13,000 light-years away from the Sun. It has an estimated radius of 1,139 solar radii. If it were placed in the center of the Solar System, it would extend to between the orbits of Mars and Jupiter.
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MY Cephei is a red supergiant located in open cluster NGC 7419 in the constellation of Cepheus. It is a semiregular variable star with a maximum brightness of magnitude 14.4 and a minimum of magnitude 15.5.
A hypergiant (luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term hypergiant is defined as luminosity class 0 (zero) in the MKK system. However, this is rarely seen in literature or in published spectral classifications, except for specific well-defined groups such as the yellow hypergiants, RSG (red supergiants), or blue B(e) supergiants with emission spectra. More commonly, hypergiants are classed as Ia-0 or Ia+, but red supergiants are rarely assigned these spectral classifications. Astronomers are interested in these stars because they relate to understanding stellar evolution, especially star formation, stability, and their expected demise as supernovae. Notable examples of hypergiants include the Pistol Star, a blue hypergiant located close to the Galactic Center and one of the most luminous stars known; Rho Cassiopeiae, a yellow hypergiant that is one of the brightest to the naked eye; and Mu Cephei (Herschel's "Garnet Star"), one of the largest and brightest stars known.
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HD 168607 is a blue hypergiant and luminous blue variable (LBV) star located in the constellation of Sagittarius, easy to see with amateur telescopes. It forms a pair with HD 168625, also a blue hypergiant and possible luminous blue variable, that can be seen at the south-east of M17, the Omega Nebula.
PZ Cassiopeiae is a red supergiant star located in the constellation of Cassiopeia, and a semi-regular variable star.
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AH Scorpii is a red supergiant variable star located in the constellation Scorpius. It is one of the largest stars known by radius and is also one of the most luminous red supergiant stars in the Milky Way.
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