Mu Cassiopeiae

Mu Cassiopeiae, Latinized from μ Cassiopeiae, 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".[10] It is dimly visible to the naked eye as a point of light with an apparent visual magnitude of 5.16.[2] The system is located at a distance of 24.6 light years from the Sun based on parallax,[1] and is moving closer with a high radial velocity of −98 km/s.[2] This star will move into the constellation Perseus around 5200 AD.[11]

μ Cassiopeiae
Location of μ Cassiopeiae (circled)
Observation data
Epoch J2000      Equinox J2000
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])
Characteristics
Spectral type G5Vb[4]
U−B color index +0.10[5]
B−V color index 0.695±0.006[6]
Variable type Suspected[7]
Astrometry
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[8]
Orbit[6]
Companionμ Cas B
Period (P)21.568±0.015 yr
Semi-major axis (a)0.9985±0.0013″
Eccentricity (e)0.5885±0.0011
Inclination (i)110.671±0.064°
Longitude of the node (Ω)223.868±0.064°
Periastron epoch (T)1,997.2235±0.0067
Argument of periastron (ω)
(secondary)		330.37±0.18°
Details[6]
Aa
Mass0.7440±0.0122 M☉
Radius0.789±0.008 R☉
Luminosity0.445±0.005 L☉
Surface gravity (log g)4.515±0.011 cgs
Temperature5,306±31 K
Metallicity [Fe/H]−0.81±0.03 dex
Rotational velocity (v sin i)2.4 km/s
Age12.7±2.7[6]
3.1[2]
5.9[9] Gyr
Ab
Mass0.1728±0.0035[6] M☉
Radius0.29[3] R☉
Luminosity0.0062[3] L☉
Temperature3,025[3] K
Other designations
μ Cas, 30 Cassiopeiae, BD+54°223, FK5 1030, GC 1360, GJ 53, HD 6582, HIP 5336, HR 321, SAO 22024, CCDM J01080+5455, LFT 107, LHS 8, LTT 10460
Database references
SIMBADdata

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.[12] The metallicity, or abundance of heavy elements, is about one-sixth that in the Sun.[6] It is slightly smaller than the Sun with less mass and a lower luminosity.[6]

This is one of the first high-velocity stars to be identified.[6] Compared to other nearby stars including the Sun, this pair are moving at a relatively high velocity of 167 km/s through the Milky Way galaxy.[6] They are low metal, Population II stars that are thought to have formed before the galactic disk first appeared.

Companions

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.[13] The companions C and D are separated from each-other by four arc seconds and form a binary system about 4,000 ly away.[14][15] 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.[16] 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.[17] 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.[18] 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]

References
  1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600
  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, arXiv:astro-ph/0405198, Bibcode:2004A&A...418..989N, doi:10.1051/0004-6361:20035959, S2CID 11027621
  3. 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. Bibcode:1995ApJ...450..380D. doi:10.1086/176148.
  4. Keenan, Philip C; McNeil, Raymond C (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
  5. Carney, B. W. (October 1979), "Subdwarf ultraviolet excesses and metal abundances", Astrophysical Journal, Part 1, 233: 211–225, Bibcode:1979ApJ...233..211C, doi:10.1086/157383
  6. Bond, Howard E.; et al. (December 2020), "Hubble Space Telescope Astrometry of the Metal-poor Visual Binary μ Cassiopeiae: Dynamical Masses, Helium Content, and Age", The Astrophysical Journal, 904 (2): 19, arXiv:2010.06609, Bibcode:2020ApJ...904..112B, doi:10.3847/1538-4357/abc172, 112.
  7. Samus, N. N.; Durlevich, O. V.; 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. Bibcode:2009yCat....102025S.
  8. 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, arXiv:1607.01304, Bibcode:2016AJ....152..153J, doi:10.3847/0004-6256/152/6/153, S2CID 15983830
  9. 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, arXiv:0807.1686, Bibcode:2008ApJ...687.1264M, doi:10.1086/591785, S2CID 27151456
  10. 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
  11. Patrick Moore; Robin Rees (2011), Patrick Moore's Data Book of Astronomy, Cambridge University Press, p. 296, ISBN 9781139495226
  12. 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, arXiv:0804.2719, Bibcode:2008ApJ...683..424B, doi:10.1086/589554, S2CID 8886682
  13. 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. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  14. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  15. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  16. 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, Bibcode:1964AJ.....69..471L, doi:10.1086/109301
  17. Professor Jim Kaler, Mu Cassiopeiae, archived from the original on 2006-08-24, retrieved 2019-02-13
  18. Wehinger, Peter A.; Wyckoff, Susan (February 1966), "Preliminary Mass Determination of μ Cas", Astronomical Journal, 71: 185, Bibcode:1966AJ.....71Q.185W, doi:10.1086/110028
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