S Persei

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title: "S Persei" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["m-type-supergiants", "perseus-(constellation)", "objects-with-variable-star-designations", "henry-draper-catalogue-objects", "m-type-hypergiants", "semiregular-variable-stars", "hipparcos-objects", "durchmusterung-objects", "double-stars", "emission-line-stars"] description: "Star in the constellation Perseus" topic_path: "science/astronomy" source: "https://en.wikipedia.org/wiki/S_Persei" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Star in the constellation Perseus ::

| name = S Persei | image= |image=Double Cluster.jpg|alt=|float=center|width=300 |label=|position=right |mark=GoldF39400 circle.svg|mark_width=10|mark_link=S Per|x=16|y=422 |caption=Location of S Persei (circled) near the Double Cluster (north is left) | epoch=J2000 | ra= | dec= | appmag_v=+9.23 (7.9 - 12.0) | constell=Perseus | class=M3 Iae–M7 | b-v=+2.65 | u-b= | variable=SRc | radial_v=-39.71 | prop_mo_ra=–0.49 ± 0.23 | prop_mo_dec=−1.19 ± 0.20 | parallax=0.413 | p_error=0.017 | parallax_footnote= | absmag_v=–6.36 (at mV 9.23) | mass=20 | radius= | luminosity=123,000 – 186,000 | temperature=3,000 – 3,600 | metal= | rotation= | gravity=0.0 | age= | names= | Simbad = 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 is 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.

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

::figure[src="https://upload.wikimedia.org/wikipedia/commons/b/b0/SPerLightCurve.png" caption="visual band]] [[light curve]] for S Persei, plotted from AAVSO data"] ::

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.

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 hypergiant 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, 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 . 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 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 . 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.

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

References

1. Norris, Ryan. (2023). "Student Science at NMT: Learning Optical Interferometry Through Projects on Evolved Stars". [[CHARA array.
2. Norris, Ryan. (2019). "Seeing Stars Like Never Before: A Long-term Interferometric Imaging Survey of Red Supergiants". [[Georgia State University]].
3. (March 2020). "The 'red supergiant problem': the upper luminosity boundary of Type II supernova progenitors". [[MNRAS]].
4. (2018). "Searching for Cool Dust. II. Infrared Imaging of the OH/IR Supergiants, NML Cyg, VX SGR, S Per, and the Normal Red Supergiants RS per and T per". The Astronomical Journal.
5. (2018). "Searching for Cool Dust. II. Infrared Imaging of the OH/IR Supergiants, NML Cyg, VX SGR, S Per, and the Normal Red Supergiants RS per and T per". The Astronomical Journal.
6. (1988). "Mass loss rates in the Hertzsprung-Russell diagram". Astronomy and Astrophysics Supplement Series.
7. (1999). "User Manual for DUSTY".
8. (2003). "Interferometric observations of the supergiant S Persei: Evidence for axial symmetry and the warm molecular layer". American Astronomical Society Meeting 203.
9. (2009). "The Biggest Stars of All". The Biggest.
10. (1974). "S Persei a Semi-Regular Variable with Two Periods". Journal of the American Association of Variable Star Observers.
11. (2006). "Variability in red supergiant stars: Pulsations, long secondary periods and convection noise". Monthly Notices of the Royal Astronomical Society.
12. "Download Data". AAVSO.
13. (1874). "Anzeige eines neuen veränderlichen Sternes (S Persei)". Astronomische Nachrichten.
14. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics.
15. (2003). "An Electronic Version of the Second Volume of the General Catalogue of Variable Stars with Improved Coordinates". Astronomy Letters.
16. (August 2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought". The Astrophysical Journal.
17. (2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data". Astronomy and Astrophysics.
18. (2009). "The dust condensation sequence in red supergiant stars". Astronomy and Astrophysics.
19. (2010). "Distance and Proper Motion Measurement of the Red Supergiant, S Persei, with Vlbi H2O Maser Astrometry". The Astrophysical Journal.
20. (1994). "Circumstellar Envelope Structure of Late Type Stars as Revealed by MERLIN Observations of 22-GHZ Water Masers". Monthly Notices of the Royal Astronomical Society.
21. (2011). "The mass-loss rates of red supergiants and the de Jager prescription". Astronomy and Astrophysics.
22. (2012). "Maser Observations of Westerlund 1 and Comprehensive Considerations on Maser Properties of Red Supergiants Associated with Massive Clusters". The Astrophysical Journal.
23. (2007). "Lithium and zirconium abundances in massive Galactic O-rich AGB stars". Astronomy and Astrophysics.
24. (2000). "Elemental Abundances in Evolved Supergiants. II. The Young Clusters H and χ Persei". The Astronomical Journal.
25. (2012). "The distance and size of the red hypergiant NML Cygni from VLBA and VLA astrometry". Astronomy & Astrophysics.
26. (1994). "Catalogue des composantes d'etoiles doubles et multiples (CCDM) premiere edition - Catalogue of the components of double and multiple stars (CCDM) first edition". Communications de l'Observatoire Royal de Belgique.
27. (1994). "Photometry of Stars in the Field of S Persei". Information Bulletin on Variable Stars.
28. {{cite DR2

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