Alpha Persei Cluster
Open cluster in the constellation Perseus
title: "Alpha Persei Cluster" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["alpha-persei-cluster", "open-clusters", "perseus-(constellation)"] description: "Open cluster in the constellation Perseus" topic_path: "general/alpha-persei-cluster" source: "https://en.wikipedia.org/wiki/Alpha_Persei_Cluster" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0
::summary Open cluster in the constellation Perseus ::
::data[format=table title="Infobox open cluster"]
| Field | Value |
|---|---|
| name | Alpha Persei Cluster |
| image | Melotte 20.jpg |
| epoch | 2000.0 |
| constellation | Perseus |
| ra | |
| dec | |
| appmag_v | 1.2 |
| size_v | |
| dist_ly | 175 pc |
| dist_pc | |
| age | |
| names | Per OB3, Cr 39, Mel 20, OCl 392.0 |
| :: |
| name = Alpha Persei Cluster | image = Melotte 20.jpg | epoch = 2000.0 | constellation = Perseus | ra = | dec = | appmag_v = 1.2 | size_v = | dist_ly = 175 pc | dist_pc = | mass_msol = | radius_ly = | age = | notes = | names = Per OB3, Cr 39, Mel 20, OCl 392.0
The Alpha Persei Cluster, also known as Melotte 20 or Collinder 39, is an open cluster of stars in the northern constellation of Perseus. To the naked eye, the cluster consists of several blue-hued spectral type B stars. The most luminous member is the ~2nd magnitude yellow supergiant Mirfak, also known as Alpha Persei. Bright members also include Delta, Sigma, Psi, 29, 30, 34, and 48 Persei. The Hipparcos satellite and infrared color-magnitude diagram fitting have been used to establish a distance to the cluster of ~172 pc. The distance established via the independent analyses agree, thereby making the cluster an important rung on the cosmic distance ladder. As seen from the Earth, the extinction of the cluster due to interstellar dust is around 0.30.
The cluster is centered to the northeast of Alpha Persei. It has a core radius of 3.49 ±, a half-mass radius of 5.6 pc, and a tidal radius of 21.65 ±, with 517 members being identified within the latter. The cluster shows solid evidence of having undergone mass segregation, with the mean stellar mass decreasing toward the edge. The age of this cluster is about 50–70 million years. Cluster member stars show a near-solar metallicity, meaning the abundance of elements with atomic numbers higher than 2 are similar to those in the Sun. The cluster shows evidence of tidal tails, which are most likely of galactic origin.
The cluster field displays evidence of a much larger, background star stream. This feature is quite a bit older than the cluster, with an estimated age of 5 ± 1 Gyr. The center of the stream lies 90 pc from the cluster and it has an overall thickness of 180 pc along the line of sight. This is most likely the remains of an old, massive cluster that now has a combined mass of .
Members
The following prominent stars are considered members of the cluster with high likelihood:
::data[format=table] | Designation | Spectral type | Visual magnitude | |---|---|---| | α Per (33 Per) | F5Ib | 1.81 | | δ Per (39 Per) | B5III | 3.01 | | ε Per (45 Per) | B1V | 2.88 | | ψ Per | B5Ve | 4.31 | | HD 21278 | B5V | 4.99 | | 31 Per | B5V | 5.05 | | 29 Per | B3V | 5.16 | | 30 Per | B8V | 5.49 | | 34 Per | B3V | 4.67 | | 48 Per | B3Ve | 4.03 | | HD 21699 | B8 III | 5.49 | | HD 21071 | B7V | 6.09 | ::
A fainter, Sun-like star, TOI-6109, is known to host two Neptune-sized exoplanets.
References
| title=Stellar Membership and Dusty Debris Disks in the α Persei Cluster | display-authors=1 | last1=Zuckerman | first1=B. | last2=Melis | first2=Carl | last3=Rhee | first3=Joseph H. | last4=Schneider | first4=Adam | last5=Song | first5=Inseok | journal=The Astrophysical Journal | volume=752 | issue=1 | id=58 | pages=12 | date=June 2012 | arxiv=1204.3950 | bibcode=2012ApJ...752...58Z | doi=10.1088/0004-637X/752/1/58 | s2cid=119207634 }}
| title=The binary fraction and mass segregation in Alpha Persei open cluster | last1=Sheikhi | first1=Najmeh | last2=Hasheminia | first2=Maryam | last3=Khalaj | first3=Pouria | last4=Haghi | first4=Hosein | last5=Zonoozi | first5=Akram Hasani | last6=Baumgardt | first6=Holger | display-authors=1 | journal=Monthly Notices of the Royal Astronomical Society | volume=457 | issue=1 | pages=1028–1036 | date=March 2016 | arxiv=1601.02186 | bibcode=2016MNRAS.457.1028S | doi=10.1093/mnras/stw059 | doi-access=free }}
| title=A 5D view of the α Per, Pleiades, and Praesepe clusters | last1=Lodieu | first1=N. | last2=Pérez-Garrido | first2=A. | last3=Smart | first3=R. L. | last4=Silvotti | first4=R. | display-authors=1 | journal=Astronomy & Astrophysics | volume=628 | id=A66 | pages=26 | date=August 2019 | arxiv=1906.03924 | bibcode=2019A&A...628A..66L | doi=10.1051/0004-6361/201935533 | s2cid=182952614 }}
| title=The Relation of the Alpha Persei Star Cluster with the Nearby Stellar Stream | last1=Nikiforova | first1=Victoria V. | last2=Kulesh | first2=Maxim V. | last3=Seleznev | first3=Anton F. | last4=Carraro | first4=Giovanni | display-authors=1 | journal=The Astronomical Journal | volume=160 | issue=3 | id=142 | pages=11 | date=September 2020 | arxiv=2007.11211 | bibcode=2020AJ....160..142N | doi=10.3847/1538-3881/aba753 | s2cid=220686998 | doi-access=free }}
| last=van Leeuwen | first=F. | title=Parallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue | journal=Astronomy & Astrophysics | volume=497 | issue=1 | date=2009 | pages=209–242 | bibcode=2009A&A...497..209V | arxiv=0902.1039 | doi=10.1051/0004-6361/200811382 | s2cid=16420237
| last1=Majaess | first1=D. | last2=Turner | first2=D. | last3=Lane | first3=D. | last4=Krajci | first4=T. | title=Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting delta Scuti Stars | journal=Journal of the American Association of Variable Star Observers | date=2011 | volume=39 | issue=2 | page=219 | bibcode=2011JAVSO..39..219M | arxiv=1102.1705 }}
| last1=Paunzen | first1=E. | last2=Mermilliod | first2=J.-C. | url=http://www.univie.ac.at/webda/cgi-bin/ocl_page.cgi?cluster=Alpha+Persei | website=Universität Wien | access-date=2020-10-17 | title=WEBDA: Alpha Persei }}
| display-authors=1 | last1=Prosser | first1=Charles F. | last2=Randich | first2=Sofia | last3=Stauffer | first3=Joh R. | last4=Schmitt | first4=J. H. M. M. | last5=Simon | first5=Theodore | title=ROSAT Pointed Observations of the Alpha Persei Cluster | journal=Astronomical Journal | volume=112 | page=1570 | date=October 1996 | doi=10.1086/118124 | bibcode=1996AJ....112.1570P | doi-access=free }}
| title=Global survey of star clusters in the Milky Way. II. The catalogue of basic parameters | last1=Kharchenko | first1=N. V. | last2=Piskunov | first2=A. E. | last3=Schilbach | first3=E. | last4=Röser | first4=S. | last5=Scholz | first5=R.-D. | display-authors=1 | journal=Astronomy and Astrophysics | postscript=. | volume=558 | id=A53 | pages=8 | date=2013 | bibcode=2013A&A...558A..53K | arxiv=1308.5822 | doi=10.1051/0004-6361/201322302 | s2cid=118548517 }}
| title=Cl Melotte 20 | access-date=2020-10-17}}
| title=Wavelength dependence of polarization. XXXIII - The Alpha Persei star cluster | display-authors=1 | last1=Coyne | first1=G. V. | last2=Tapia | first2=S. | last3=Vrba | first3=F. J. | journal=Astronomical Journal | volume=84 | date=March 1979 | pages=356–369 | doi=10.1086/112431 | bibcode=1979AJ.....84..356C | doi-access=free }}
| last1=Morrell | first1=Nidia | last2=Abt | first2=Helmut A. | title=Spectroscopic binaries in the Alpha Persei cluster | journal=Astrophysical Journal, Part 1 | postscript=. | volume=393 | issue=2 | date=July 10, 1992 | pages=666–673 | doi=10.1086/171534 | bibcode=1992ApJ...393..666M }}
| title=OB association members in the ACT and TRC catalogues | last1=Hoogerwerf | first1=Ronnie | journal=Monthly Notices of the Royal Astronomical Society | volume=313 | issue=1 | pages=43–65 | date=March 2000 | doi=10.1046/j.1365-8711.2000.03192.x | bibcode=2000MNRAS.313...43H | doi-access=free }}
References
- Danner, Christopher A.. (2025-06-09). "Precise Age For The Binary HD 21278 In The Young Alpha Persei Cluster". [[The Astrophysical Journal]].
- (September 2025). "THYME XIII: Two young Neptunes orbiting a 75-Myr star in the Alpha Persei Cluster". [[The Astronomical Journal]].
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