Theta Cassiopeiae

Theta Cassiopeiae or θ Cassiopeiae is a solitary^[3] star in the northern constellation of Cassiopeia. It shares the traditional name Marfak /ˈmɑːrfæk/ with μ Cassiopeiae, positioned less than half a degree to the WSW,^[11] which is derived from the Arabic term Al Marfik or Al Mirfaq (المرفق), meaning "the elbow".^[12] At an apparent visual magnitude of 4.3,^[2] Theta Cassiopeiae 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,^[13] and is slowly drifting further away from the Sun with a radial velocity of 2.5 km/s.^[5]

Theta Cassiopeiae

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]
Characteristics
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]
Astrometry
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 mas[1]
Distance	134 ± 1 ly (41.0 ± 0.4 pc)
Absolute magnitude (MV)	+1.28[6]
Details[7]
Mass	1.83 M☉
Radius	2.6[8] R☉
Surface gravity (log g)	4.03±0.14 cgs
Temperature	8,202±279 K
Rotational velocity (v sin i)	103[9] km/s
Age	650 Myr
Other designations
Marfak, θ Cas, 33 Cassiopeiae, BD+54°236, HD 6961, HIP 5542, HR 343, SAO 22070[10]
Database references
SIMBAD	data

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.^[14] Consequently, θ Cassiopeiae itself is known as 閣道四 (Gé Dào sì, English: the Fourth Star of Flying Corridor.)^[15]

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,^[16] 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.^[17] It is a suspected Delta Scuti variable.^[4]

The star appears to be a member of a leading tidal tail of the Hyades cluster.^[18]

References

1. 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, S2CID 18759600.
2. 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. 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, S2CID 14878976.
4. 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, S2CID 59451347, 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. 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, S2CID 33401607.
8. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R_*) is given by:

   ${\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(41.0\cdot 0.58\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 5.1\cdot R_{\bigodot }\end{aligned}}}$

9. 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, S2CID 18475298.
10. "* tet Cas". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-02-16.
11. Sinnott, Roger W.; Perryman, Michael A. C. (1997), Millennium Star Atlas, vol. 1, Sky Publishing Corporation and the European Space Agency, p. 64, ISBN 0-933346-84-0.
12. 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
13. 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, S2CID 2603568.
14. (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.
15. (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.
16. 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.
17. 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, S2CID 18154947.
18. Röser, Siegfried; et al. (January 2019), "Hyades tidal tails revealed by Gaia DR2", Astronomy & Astrophysics, 621: 5, arXiv:1811.03845, Bibcode:2019A&A...621L...2R, doi:10.1051/0004-6361/201834608, S2CID 118909033, L2.

External links

• Kaler, James B., "Theta Cassiopeiae", Stars, University of Illinois.</ref>