Theta Cassiopeiae

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Theta Cassiopeiae
Diagram showing star positions and boundaries of the Reticulum constellation and its surroundings
Cercle rouge 100%.svg
Location of θ Cassiopeiae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cassiopeia
Right ascension  01h 11m 06.16225s[1]
Declination +55° 08′ 59.6472″[1]
Apparent magnitude (V) 4.334[2]
Spectral type A7 V[3]
U−B color index +0.130[2]
B−V color index +0.170[2]
Variable type Suspected δ Sct[4]
Radial velocity (Rv)2.5±0.6[5] km/s
Proper motion (μ) RA: +226.77[1] mas/yr
Dec.: −18.75[1] mas/yr
Parallax (π)24.42 ± 0.24[1] mas
Distance134 ± 1 ly
(41.0 ± 0.4 pc)
Absolute magnitude (MV)+1.28[6]
Mass1.83 M
Radius2.6[8] R
Surface gravity (log g)4.03±0.14 cgs
Temperature8,202±279 K
Rotational velocity (v sin i)103[9] km/s
Age650 Myr
Other designations
Marfak, θ Ret, 33 Cassiopeiae, BD+54° 236, HD 6961, HIP 5542, HR 343, SAO 22070.[10]
Database references

Theta Cassiopeiae (θ Cas, θ Cassiopeiae) is a solitary[3] star in the northern constellation of Cassiopeia. It shares the traditional name Marfak /ˈmɑːrfæk/ with μ Cassiopeiae to the southeast, which is derived from the Arabic term Al Marfik or Al Mirfaq (المرفق), meaning "the elbow".[11] At an apparent visual magnitude of 4.3,[2] it is visible to the naked eye. Based upon an annual parallax shift of 24.42 mas,[1] it is located about 134 light years from the Sun. It has a total annual proper motion of 0.227 arcseconds per year.[12]

In Chinese, 閣道 (Gé Dào), meaning Flying Corridor, refers to an asterism consisting of θ Cassiopeiae, ι Cassiopeiae, ε Cassiopeiae, δ Cassiopeiae, ν Cassiopeiae and ο Cassiopeiae.[13] Consequently, θ Cassiopeiae itself is known as 閣道四 (Gé Dào sì, English: the Fourth Star of Flying Corridor.)[14]

This is an A-type main sequence star with a stellar classification of A7 V.[3] The measured angular diameter of this star is 0.58±0.02 mas,[15] which, at the estimated distance of this star, yields a physical size of about 2.6 times the radius of the Sun.[8] It is about 650[7] million years in age and is spinning with a projected rotational velocity of 103 km/s.[9] This is a candidate Vega-type system, which means it displays an infrared excess suggesting it has an orbiting debris disk.[16] It is a suspected Delta Scuti variable.[4]


  1. ^ a b c d e f van Leeuwen, F. (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.
  2. ^ a b c d Oja, T. (August 1991), "UBV photometry of stars whose positions are accurately known. VI", Astronomy and Astrophysics Supplement Series, 89 (2): 415–419, Bibcode:1991A&AS...89..415O.
  3. ^ a b c Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  4. ^ a b Frolov, M. S. (April 1970), "List of Probable Delta Scuti Stars", Information Bulletin on Variable Stars, 427: 1, Bibcode:1970IBVS..427....1F.
  5. ^ de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, A61.
  6. ^ Eggen, Olin J. (July 1998), "The Age Range of Hyades Stars", The Astronomical Journal, 116 (1): 284–292, Bibcode:1998AJ....116..284E, doi:10.1086/300413.
  7. ^ a b David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146.
  8. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
  9. ^ a b Royer, F.; et al. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224.
  10. ^ "* tet Cas". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-02-16.
  11. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc., p. 148, ISBN 0-486-21079-0, retrieved 2010-12-12
  12. ^ Lépine, Sébastien; Shara, Michael M. (March 2005), "A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)", The Astronomical Journal, 129 (3): 1483–1522, arXiv:astro-ph/0412070, Bibcode:2005AJ....129.1483L, doi:10.1086/427854.
  13. ^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  14. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2011-01-30 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  15. ^ Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.
  16. ^ Song, Inseok; et al. (January 2001), "Ages of A-Type Vega-like Stars from uvbyβ Photometry", The Astrophysical Journal, 546 (1): 352–357, arXiv:astro-ph/0010102, Bibcode:2001ApJ...546..352S, doi:10.1086/318269.

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