Alpha Persei Cluster

The Alpha Persei Cluster, also known as Melotte 20 or Collinder 39, is an open cluster in the constellation of Perseus. To the naked eye, the cluster consists of several blue spectral type B type stars. The most luminous member is the ~2nd magnitude white-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.[2][3] The distance established via the independent analyses agree, thereby making the cluster an important rung on the cosmic distance ladder. The age of this cluster is about 50-70 million years.[1][5]

Alpha Persei Cluster
Observation data (2000.0 epoch)
ConstellationPerseus
Right ascension 03h 26.9m
Declination+49° 07′
Distance557-650 ly[1][2][3] (171-200 pc)
Apparent magnitude (V)1.2
Apparent dimensions (V)185'
Physical characteristics
Other designationsPer OB3,[4] Cr 39, Mel 20

Members
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[6] 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 21071 B7V 6.09

References
  1. Prosser, Charles F.; Randich, Sofia; Stauffer, Joh R.; Schmitt, J. H. M. M.; Simon, Theodore (October 1996). "ROSAT Pointed Observations of the Alpha Persei Cluster". Astronomical Journal. 112: 1570. Bibcode:1996AJ....112.1570P. doi:10.1086/118124.
  2. van Leeuwen, F. "Parallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue", A&A, 2009
  3. Majaess, D.; Turner, D.; Lane, D.; Krajci, T. "Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting delta Scuti Stars", Journal of the American Association of Variable Star Observers, 2011
  4. Coyne, G. V.; et al. (March 1979), "Wavelength dependence of polarization. XXXIII - The Alpha Persei star cluster", Astronomical Journal, 84: 356–369, Bibcode:1979AJ.....84..356C, doi:10.1086/112431
  5. Paunzen, E., Mermilliod, J.-C. "WEBDA: Alpha Persei"
  6. Morrell, Nidia; Abt, Helmut A. (July 10, 1992), "Spectroscopic binaries in the Alpha Persei cluster", Astrophysical Journal, Part 1, 393 (2): 666–673, Bibcode:1992ApJ...393..666M, doi:10.1086/171534.


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