S Persei is a

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) of spectral type 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 Ant ...

hypergiant 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 ...

located near the

Double Cluster The Double Cluster (also known as Caldwell 14) consists of the open clusters NGC 869 and NGC 884 (often designated h Persei and χ (chi) Persei, respectively), which are close together in the constellation Perseus. Both visible with the ...

in Perseus, north of the cluster NGC 869. It is a member of the Perseus OB1

association Association may refer to: *Club (organization), an association of two or more people united by a common interest or goal *Trade association, an organization founded and funded by businesses that operate in a specific industry *Voluntary associatio ...

and one of the largest known stars. If placed in the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

, its photosphere would engulf the

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...

. It is also a

semiregular variable In astronomy, a semiregular variable star, a type of variable star, is a giant or supergiant of intermediate and late (cooler) spectral type showing considerable periodicity in its light changes, accompanied or sometimes interrupted by various irre ...

, a star whose variations are less regular than those of

Mira variable Mira variables (named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wavele ...

Discovery

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 and BD+57°552.

Variability

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 In astronomy, a semiregular variable star, a type of variable star, is a giant or supergiant of intermediate and late (cooler) spectral type showing considerable periodicity in its light changes, accompanied or sometimes interrupted by various irre ...

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 The General Catalogue of Variable Stars (GCVS) is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and thi ...

lists it as varying between magnitudes 7.9 and 12.0, it has since been seen fainter. The

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

of S Persei also varies. Typically it is a

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.

Properties

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

and has a radius over 700 times the sun's radius (). Its angular diameter has been measured directly and found to be somewhat elliptical. Modelled as a uniform disk, the radius corresponds to . The temperature has been calculated from the spectrum using a DUSTY model, giving an effective photospheric temperature of 3,500 K and a temperature of 1,000 K for the surrounding dust torus. This is consistent with previous studies, but the derived luminosity from different authors varies from to . Older studies frequently calculated higher luminosities, lower temperatures, and consequently larger values for the radius. The mass of S Persei is also uncertain, but expected to be around . Mass is being lost at 2.4 to per year, leading to an extensive and complex circumstellar environment of gas and dust.

Location

S Persei is surrounded by clouds containing water molecules which produce

maser A maser (, an acronym for microwave amplification by stimulated emission of radiation) is a device that produces coherent electromagnetic waves through amplification by stimulated emission. The first maser was built by Charles H. Townes, Ja ...

emission. This allows the distance to be measured very accurately using

very long baseline interferometry Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. In VLBI a signal from an astronomical radio source, such as a quasar, is collected at multiple radio telescopes on Earth or in space. T ...

, giving an annual parallax of 0.413 ± 0.017

milliarcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The n ...

s. For comparison the

Gaia Data Release 2 The ''Gaia'' catalogues are star catalogues created using the results obtained by '' Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, espec ...

parallax is . It lies somewhat further away than the centres of the Double Cluster

open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, an ...

s, but definitely within the Per OB1 association and the

Perseus Arm The Perseus Arm is one of two major spiral arms of the Milky Way galaxy. The second major arm is called the Scutum–Centaurus Arm. The Perseus Arm begins from the distal end of the long Milky Way central bar. Previously thought to be 13,000 lig ...

of the galaxy. S Persei is a double star. The red supergiant has an A0 11th magnitude companion at 69". There are also several other 8th to 10th magnitude stars within half a degree of S Persei.

References

{{DEFAULTSORT:S Persei M-type supergiants Perseus (constellation) Persei, S 014528 M-type hypergiants Semiregular variable stars 011093 BD+57 0552 Double stars Emission-line stars