Epoch J2000 Equinox J2000
|Right ascension||11h 14m 06.50142s|
|Declination||20° 31′ 25.3853″|
|Apparent magnitude (V)||2.56|
|Spectral type||A4 V|
|U−B color index||+0.12|
|B−V color index||+0.12|
|Variable type||Delta Scuti|
|Radial velocity (Rv)||-20.2 km/s|
|Proper motion (μ)|| RA: +143.42 mas/yr |
Dec.: -129.88 mas/yr
|Parallax (π)||55.82 ± 0.25 mas|
|Distance||58.4 ± 0.3 ly |
(17.91 ± 0.08 pc)
|Absolute magnitude (MV)||+1.29|
|Radius||2.14 ± 0.040 R☉|
|Luminosity||15.5 ± 1.8 L☉|
|Surface gravity (log g)||3.91 cgs|
|Rotational velocity (v sin i)||180 km/s|
Delta Leonis (δ Leonis, abbreviated Delta Leo, δ Leo), formally named Zosma //, is a star in the zodiac constellation of Leo. Based upon parallax measurements, it lies at a distance of about 58.4 light-years (17.9 parsecs) from the Sun.
δ Leonis is a main sequence star with a stellar classification of A4 V, meaning it is larger and hotter than the Sun. It is a fairly well-studied star, allowing relatively accurate measurements of its age and size. The radius of the star, as measured directly using an interferometer, is about 214% of the Sun's radius and it is emitting more than 15 times as much luminosity as the Sun. The energy is being emitted from the outer envelope with an effective temperature 8,296 K, giving it the white hue characteristic of an A-type star. Having a larger mass than the Sun it will have a shorter lifespan, and in another 600 million years or so will swell into an orange or red giant star before decaying quietly into a white dwarf.
This star is rotating rapidly, with a projected rotational velocity of 180 km s−1. The inclination of the axis of rotation to the line of sight from the Earth is estimated at 38.1°, which would mean the azimuthal velocity along the equator is about 280 km s−1. This rotation is producing an equatorial bulge, giving the star a pronounced oblate spheroidal shape. The polar radius is about 84% of the radius along the equator.
Based upon the location and trajectory of this star through space, it may be a member of the Ursa Major Moving Group, a type of stellar kinematics group that share a common origin and motion through space. The age of this group is about 500 million years.
It bore the traditional names Zosma or Zozma and Duhr (rare spellings included Zozca, Zosca, Al-Zubra الزبرة, traditional Arabic for both shoulder, and a lion's mane and Dhur ظهر, the latter meaning 'back' in Arabic). Zosma means 'girdle' in ancient Greek, referring to the star's location in its constellation, on the hip of the lion. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Zosma for this star.
In Chinese, 太微右垣 (Tài Wēi Yòu Yuán), meaning Right Wall of Supreme Palace Enclosure, refers to an asterism consisting of δ Leonis, β Virginis, σ Leonis, ι Leonis and θ Leonis. Consequently, the Chinese name for δ Leonis itself is 太微右垣五 (Tài Wēi Zuǒ Yuán wu, English: the Fifth Star of Right Wall of Supreme Palace Enclosure.), representing 西上相 (Xīshǎngxiāng), meaning The First Western Minister. 西上相 (Xīshǎngxiāng), spelled Shang Seang by R.H. Allen, means "the Higher Minister of State" 
- 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
- Wielen, R.; et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions, Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W
- Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819
- Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J
- Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
- Kaler, James B., ZOSMA (Delta Leonis), University of Illinois, retrieved 2010-05-12[permanent dead link]
- Akeson, R. L.; et al. (February 2009), "Dust in the inner regions of debris disks around a stars", The Astrophysical Journal, 691 (2): 1896–1908, arXiv:0810.3701, Bibcode:2009ApJ...691.1896A, doi:10.1088/0004-637X/691/2/1896
- Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series, 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M
- Royer, F.; et al. (2002), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i in the northern hemisphere", Astronomy and Astrophysics, 393 (3): 897–911, arXiv:astro-ph/0205255, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943
- Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 260
- "del Leo -- Variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2010-05-12
- Davis, George A. (1944). "The pronunciations, derivations, and meanings of a selected list of star names". Popular Astronomy. 52: 8–30.
- "IAU Catalog of Star Names". Retrieved 28 July 2016.
- Nakajima, Tadashi; Morino, Jun-Ichi; Fukagawa, Misato (September 2010), "Potential Members of Stellar Kinematical Groups within 20 pc of the Sun", The Astronomical Journal, 140 (3): 713–722, Bibcode:2010AJ....140..713N, doi:10.1088/0004-6256/140/3/713
- King, Jeremy R.; et al. (April 2003), "Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group", The Astronomical Journal, 125 (4): 1980–2017, Bibcode:2003AJ....125.1980K, doi:10.1086/368241
- "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
- "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
- (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.
- (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived August 19, 2010, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
- (in Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name Archived August 10, 2010, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.