MY Cephei (IRC +60375) is a

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) 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. Betelg ...

located in the

open cluster An open cluster is a type of star cluster made of tens 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, and ...

NGC 7419 in the constellation of

Cepheus Cepheus (Ancient Greek: Κηφεύς ''Kepheús'') may refer to: In Greek mythology * Cepheus (father of Andromeda), and King of Aethiopia * Cepheus (son of Aleus), a king of Tegea, Arcadia In astronomy * Cepheus (constellation), one of the 88 m ...

. It is 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. It shows considerable periodicity in its light changes, accompanied or sometimes interrupted by various i ...

with a maximum brightness of magnitude 14.4 and a minimum of magnitude 15.5.

Observations and variability

Observations of the open cluster NGC 7419 in 1954 showed that four of its members were luminous red stars, most likely red supergiants. In addition, an unusually red star was found to be variable and probably an even more luminous supergiant. This star was given the

variable star designation In astronomy, a variable-star designation is a unique identifier given to variable stars. It extends the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constellation in whic ...

MY Cephei in 1973 in the 59th name-list of variable stars. MY Cephei is classified as

semiregular variable In astronomy, a semiregular variable star, a type of variable star, is a Red giant, giant or supergiant of intermediate and late (cooler) spectral type. It shows considerable periodicity in its light changes, accompanied or sometimes interrupted b ...

star of sub-type SRc, indicating it is a cool supergiant, although its pulsational period is not known. It has been observed as bright as magnitude 14.4 and as faint as magnitude 15.5. The star, along with another late red supergiant star,

S Persei 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 ph ...

, are sometimes considered prototypes for the class of M6–7 supergiants.

Distance

The distance of MY Cephei is assumed to be around or based on it being a member of the NGC 7419

Gaia Early Data Release 3 The ''Gaia'' catalogues are star catalogues created using the results obtained by ''Gaia (spacecraft), Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also mis ...

gives a parallax of for MY Cep, implying a similar distance of .

Stellar properties

The spectral type of MY Cephei is given in the

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars in the Milky Way Galaxy. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR, edited by and Pavel Parenago. Second a ...

as M6–7 Iab, indicating the star is an intermediate-size luminous supergiant star, although most authors gives M7–M7.5 I. Classification is difficult because of the lack of comparable standard stars, but its

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

appears to be later than M5, earlier than

VX Sagittarii VX Sagittarii is an asymptotic giant branch star located more than 1.5 kiloparsec away from the Sun in the constellation of Sagittarius. It is a pulsating variable star with an unusually large magnitude range. It is one of the lar ...

when at M9, and more luminous than M7

giant star A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsp ...

s. A 2021 study gives a spectral class of M3 based on

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

observations, and a correspondingly higher temperature. MY Cephei is a very luminous, cool and large extreme supergiant star, with a luminosity more than 100,000 times that of the Sun () and a radius in excess of a thousand times the Sun's radius (). It is likely the most luminous, coolest, and the largest

supergiant star Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute magnitude, absolute visual magnitudes between about −3 and −8. The temperatures of supe ...

in its open cluster, and occupies the upper-right hand corner of the

Hertzsprung–Russell diagram The Hertzsprung–Russell diagram (abbreviated as H–R diagram, HR diagram or HRD) is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities and their stellar classifications or effective temp ...

. A 2018 paper gives the star a temperature of , corresponding a radius of based on a luminosity of . The mass of MY Cephei is uncertain, but expected to be around 14.5 times the Sun's mass (). Mass is being lost at per year, one of highest mass loss rates known for a supergiant star. A study from 2020 based on SED integration gives an unexpectedly higher

bolometric luminosity Luminosity is an absolute measure of radiated electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electromagnetic energy emitted per ...

of , close to the empirical upper luminosity limit of red supergiants (i.e. Humphreys–Davidson limit). This implies a higher radius of based on an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of derived using the DUSTY model, considerably larger than the upper radius limit of red supergiants at roughly respectively. Older studies frequently calculated even more lower temperatures and an estimated radius of .

Notes

References

{{DEFAULTSORT:My Cephei Cepheus (constellation) Cephei, MY M-type supergiants Semiregular variable stars J22543171+6049388 IRAS catalogue objects TIC objects

Observations and variability

Distance

Stellar properties

See also

Notes

References