Astronomy:Mu Cassiopeiae

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μ Cassiopeiae
Cassiopeia constellation map.svg
Red circle.svg
Location of μ Cassiopeiae (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Cassiopeia
Right ascension  01h 08m 16.39470s[1]
Declination +54° 55′ 13.2264″[1]
Apparent magnitude (V) 5.159[2](5.14/11.45[3])
Spectral type G5Vb[4]
U−B color index +0.10[5]
B−V color index +0.70[5]
Variable type Suspected[6]
Radial velocity (Rv)−98.3[2] km/s
Proper motion (μ) RA: 3,422.23[1] mas/yr
Dec.: −1,598.93[1] mas/yr
Parallax (π)132.38 ± 0.82[1] mas
Distance24.6 ± 0.2 ly
(7.55 ± 0.05 pc)
Absolute magnitude (MV)5.78/11.6[7]
Companionμ Cas B
Period (P)21.75 yr
Semi-major axis (a)1.01″
Eccentricity (e)0.56
Inclination (i)110°
Longitude of the node (Ω)47.3°
Periastron epoch (T)1975.74
Argument of periastron (ω)
Mass0.74[8] M
Radius0.791 ± 0.008[9] R
Luminosity0.442 ± 0.014[9] L
Surface gravity (log g)4.51[10] cgs
Temperature5,341[11] K
Metallicity [Fe/H]−0.81[11] dex
Rotational velocity (v sin i)8[12] km/s
Age3.1[2]–5.9[13] Gyr
Mass0.17[8] M
Radius0.29[3] R
Luminosity0.0062[3] L
Temperature3,025[3] K
Other designations
30 Cassiopeiae, Gl 53, HR 321, BD+54°223, HD 6582, LHS 8, LTT 10460, GCTP 219.00, SAO 22024, FK5 1030, LFT 107, HIP 5336, GC 1360, CCDM J01080+5455
Database references

Mu Cassiopeiae (μ Cassiopeiae, abbreviated μ Cas) is a binary star system in the constellation Cassiopeia. This system shares the name Marfak /ˈmɑːrfæk/ with Theta Cassiopeiae, and the name was from Al Marfik or Al Mirfaq (المرفق), meaning "the elbow".[14]

Mu Cassiopeiae is given as a standard star for the spectral class G5Vb,[4] although it is frequently described as a subdwarf, meaning it has a luminosity below that expected for a G5 main sequence star.[9]

There are five visible companions to Mu Cassiopeiae listed in the Washington Double Star Catalog. All are distant background objects fainter than 11th magnitude. The brightest of these is catalogued as component B, but the very high proper motion of Mu Cassiopeiae has caused it to almost double its distance from B. There are now two other stars brighter than magnitude 10 that are closer to Mu Cassiopeiae, although they are also background objects.[15] The companions C and D are separated from each-other by four arc seconds and form a binary system about 4,000 ly away.[16][17] Mu Cassiopeiae itself is known as an astrometric binary, a star that is observed to oscillate due to the gravitational influence of an unseen companion, and that companion has now been resolved.[3]

In 1961 the close binary nature of this system was discovered by Nicholas E. Wagman at the Allegheny Observatory.[18] Since then the orbital elements of the two stars have been fairly well established. The two stars are separated by a semimajor axis of 7.61 AUs with distance range of 3.3-11.9 AUs.[19] In 1966, the individual components were first resolved by the American astronomer Peter A. Wehinger using the 84-inch reflector at the Kitt Peak National Observatory, allowing an initial estimate of separate masses.[20] The companion is over six magnitudes (330 times) fainter than the primary star, and it is presumed to be a red dwarf, a class M main sequence or subdwarf star.[3]

Compared to other nearby stars, this pair are moving at a relatively high velocity of 167 km/s through the Milky Way galaxy. They are low metal, Population II stars that are thought to have formed before the galactic disk first appeared.

This star will move into the constellation Perseus around 5200 AD.[21]


  1. 1.0 1.1 1.2 1.3 1.4 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode2007A&A...474..653V 
  2. 2.0 2.1 2.2 Nordström, B. et al. (May 2004), "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs", Astronomy and Astrophysics 418 (3): 989–1019, doi:10.1051/0004-6361:20035959, Bibcode2004A&A...418..989N 
  3. 3.0 3.1 3.2 3.3 3.4 3.5 Drummond, Jack D; Christou, Julian C; Fugate, Robert Q (1995). "Full Adaptive Optics Images of ADS 9731 and MU Cassiopeiae: Orbits and Masses". Astrophysical Journal 450: 380. doi:10.1086/176148. Bibcode1995ApJ...450..380D. 
  4. 4.0 4.1 Keenan, Philip C; McNeil, Raymond C (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series 71: 245. doi:10.1086/191373. Bibcode1989ApJS...71..245K. 
  5. 5.0 5.1 Carney, B. W. (October 1979), "Subdwarf ultraviolet excesses and metal abundances", Astrophysical Journal, Part 1 233: 211–225, doi:10.1086/157383, Bibcode1979ApJ...233..211C 
  6. Samus, N. N. et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published in: 2009yCat....102025S 1. Bibcode2009yCat....102025S. 
  7. Jao, Wei-Chun; Nelan, Edmund P.; Henry, Todd J.; Franz, Otto G.; Wasserman, Lawrence H. (2016), "Cool Subdwarf Investigations. III. Dynamical Masses of Low-metallicity Subdwarfs", The Astronomical Journal 152 (6): 153, doi:10.3847/0004-6256/152/6/153, Bibcode2016AJ....152..153J 
  8. 8.0 8.1 8.2 Gontcharov, G. A.; Kiyaeva, O. V. (August 2002), "Photocentric orbits from a direct combination of ground-based astrometry with Hipparcos. I. Comparison with known orbits", Astronomy and Astrophysics 391 (2): 647–657, doi:10.1051/0004-6361:20020896, Bibcode2002A&A...391..647G 
  9. 9.0 9.1 9.2 Boyajian, Tabetha S. et al. (August 2008), "Angular Diameters of the G Subdwarf μ Cassiopeiae A and the K Dwarfs σ Draconis and HR 511 from Interferometric Measurements with the CHARA Array", The Astrophysical Journal 683 (1): 424–432, doi:10.1086/589554, Bibcode2008ApJ...683..424B 
  10. Soubiran, C. et al. (March 2008), "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants", Astronomy and Astrophysics 480 (1): 91–101, doi:10.1051/0004-6361:20078788, Bibcode2008A&A...480...91S 
  11. 11.0 11.1 Heiter, U.; Jofré, P.; Gustafsson, B.; Korn, A. J.; Soubiran, C.; Thévenin, F. (2015), "Gaia FGK benchmark stars: Effective temperatures and surface gravities", Astronomy and Astrophysics 582: A49, doi:10.1051/0004-6361/201526319, Bibcode2015A&A...582A..49H 
  12. Takeda, Yoichi et al. (February 2005), "High-Dispersion Spectra Collection of Nearby F--K Stars at Okayama Astrophysical Observatory: A Basis for Spectroscopic Abundance Standards", Publications of the Astronomical Society of Japan 57 (1): 13–25, doi:10.1093/pasj/57.1.13, Bibcode2005PASJ...57...13T 
  13. Mamajek, Eric E. et al. (November 2008), "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics", The Astrophysical Journal 687 (2): 1264–1293, doi:10.1086/591785, Bibcode2008ApJ...687.1264M 
  14. Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 148, ISBN 978-0-486-21079-7,, retrieved 2010-12-12 
  15. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal 122 (6): 3466. doi:10.1086/323920. Bibcode2001AJ....122.3466M. 
  16. Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  17. Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  18. Lippincott, S. L.; Wyckoff, S. (September 1964), "Parallax and orbital motion of the astrometric binary mu Cassiopeiae from photographs taken with the 24-inch Sproul refractor", Astronomical Journal 69: 471–474, doi:10.1086/109301, Bibcode1964AJ.....69..471L 
  19. Professor Jim Kaler, Mu Cassiopeiae,, retrieved 2019-02-13 
  20. Wehinger, Peter A.; Wyckoff, Susan (February 1966), "Preliminary Mass Determination of μ Cas", Astronomical Journal 71: 185, doi:10.1086/110028, Bibcode1966AJ.....71Q.185W, 
  21. Patrick Moore; Robin Rees (2011), Patrick Moore's Data Book of Astronomy, Cambridge University Press, 

External links