Theta Leonis
A white-hot, chemically peculiar Am star in Leo.
Theta Leonis, also known by its Bayer designation θ Leonis and the official proper name Chertan, is a star located in the equatorial-northern constellation Leo. It shines with an apparent visual magnitude of +3.324, making it one of the brighter stars in that constellation and easily visible without a telescope. Parallax measurements place it roughly 165 light-years from the Sun.
This star is considerably larger than the Sun, with about 2.8 times its mass and four times its radius. Its spectrum places it in the stellar class A2 V, which typically describes an A-type main sequence star. However, the spectrum also reveals enhanced absorption lines of metals, classifying it as a chemically peculiar Am star. The star's metallicity—the abundance of elements heavier than hydrogen and helium—is roughly 12% higher than that of the Sun. From its outer atmosphere, Theta Leonis radiates 118 times the Sun's luminosity, with an effective temperature of 9,480 K, giving it a white-hot appearance.
Theta Leonis is much younger than the Sun, with an estimated age of about 550 million years. It rotates at a moderately high speed, with a projected rotational velocity that is measured; interferometric observations suggest it is actually a rapidly rotating star viewed nearly pole-on. Infrared measurements show an excess of emission from the star and its surroundings, indicating the presence of a circumstellar dust disk. The temperature of this emission suggests the disk orbits at a radius of about 36 AU.
The star's Bayer designation is θ Leonis, Latinized as Theta Leonis. It has traditional names including Chertan, Chort, and Coxa. Chertan comes from the Arabic for 'two small ribs', originally applied to both Delta Leonis and Theta Leonis; Chort derives from an Arabic term for 'small rib', while Coxa is Latin for 'hip'. In 2016, the International Astronomical Union's Working Group on Star Names (WGSN) approved Chertan as the official proper name for this star.
In Chinese astronomy, Theta Leonis is part of an asterism called the Right Wall of Supreme Palace Enclosure, which also includes Beta Virginis, Sigma Leonis, Iota Leonis, and Delta Leonis. The star itself is known as the Second Western Minister, or in Chinese, 西次相 (Xīcìxiāng), which R.H. Allen rendered as Tsze Seang, meaning "the Second Minister of State."
Quick Facts
- Apparent visual magnitude
- +3.324
- Distance from sun
- about 165 ly
- Mass
- 2.8 times the Sun's mass
- Radius
- four times the Sun's radius
- Spectral type
- A2 V (chemically peculiar Am star)
- Luminosity
- 118 times the Sun's luminosity
- Effective temperature
- 9,480 K
Facts from the source article.
Lore & Background
Theta Leonis is a large star with 2.8 times the mass of the Sun and four times its radius. Its spectrum matches a stellar classification of A2 V, making it a seemingly typical A-type main sequence star, but the spectrum shows enhanced absorption lines of metals, marking it as a chemically peculiar Am star. The abundance of elements other than hydrogen and helium—its metallicity—appears around 12% higher than in the Sun. It radiates 118 times the luminosity of the Sun from its outer atmosphere at an effective temperature of 9,480 K, giving it a white-hot glow.
The star is much younger than the Sun, with an estimated age of around 550 million years. It has a moderately high rate of rotation, with a projected rotational velocity noted but not specified in the reference. Interferometric observations suggest it is a rapidly rotating star being viewed nearly pole-on. Measurements in the infrared band show an excess of emission from the star and its surroundings, suggesting the presence of a circumstellar disk of dust; the temperature of this emission indicates the disk has an orbital radius of 36 AU.
It bore the traditional names Chertan, Chort, and Coxa. Chertan is derived from the Arabic 'two small ribs', originally referring to Delta Leonis and Theta Leonis; Chort from Arabic 'small rib', and Coxa is Latin for 'hip'. 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 Chertan for this star. In Chinese, the star is part of an asterism called 'Right Wall of Supreme Palace Enclosure', and its own Chinese name is 'The Second Western Minister'.
Reader's Guide
Theta Leonis, known formally as Chertan, holds significance as one of the brighter stars in the constellation Leo, visible to the naked eye at magnitude +3.324. Its legacy is rooted in multiple naming traditions: the Arabic-derived Chertan and Chort, and the Latin Coxa, reflecting its historical identification as part of the Lion's anatomy. The star's classification as a chemically peculiar Am star—with enhanced metal lines despite being an A-type main sequence star—makes it an object of interest for studies of stellar chemistry and evolution. Its youth, at roughly 550 million years, and its rapid rotation viewed nearly pole-on, add to its astrophysical relevance. The detection of an infrared excess and a circumstellar dust disk at 36 AU suggests ongoing planetary system formation or debris, offering a window into the processes around intermediate-mass stars. The star's inclusion in the Chinese asterism 'Right Wall of Supreme Palace Enclosure' and its designation as 'The Second Western Minister' underscore its cultural role in traditional Chinese astronomy. The formal approval of the name Chertan by the IAU's Working Group on Star Names in 2016 cemented its place in modern astronomical nomenclature, bridging ancient Arabic star lore with contemporary scientific cataloging.
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