Theta Circini (θ Cir), is a

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

located in the southern

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Circinus Circinus is a small, faint constellation in the southern sky, first defined in 1756 by the French astronomer Nicolas-Louis de Lacaille. Its name is Latin for compass (drawing tool), compass, referring to the Technical drawing, drafting tool used ...

, to the northwest of

Alpha Circini Alpha Circini (α Cir, α Circini) is a variable star in the faint, southern, circumpolar constellation of Circinus. At an apparent visual magnitude of 3.19, it is the brightest star in the constellation and can be readily seen with the n ...

. It is faintly visible to the naked eye with an apparent visual magnitude of 5.110. Based upon an annual parallax shift of 11.82

mas Mas, Más or MAS may refer to: Film and TV * Más y Menos, fictional superhero characters, from the Teen Titans animated television series * Más (Breaking Bad), "Más" (''Breaking Bad''), a season three episode of ''Breaking Bad'' Songs * Más ( ...

, it is located at a distance of about 276

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s from the Sun. This is an

astrometric binary A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

star system with an orbital period of about 39.6 years, an eccentricity of 0.3, and a semimajor axis of 85.64 mas. The pair show a combined

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

of B3 Ve, which matches a B-type main sequence star. The 'e' suffix on the class indicates this is a Be star. Alternate classifications include B4 Vnp and B4npe, with the 'n' indicating broad ("nebulous")

absorption line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

s due to rotation and the 'p' meaning a chemically peculiar star. The two components appear to have similar visual magnitude, mass, and classification. The system behaves as a Gamma Cassiopeiae variable showing occasional outbursts of up to 0.27 in magnitude.

References

External links

*http://server3.wikisky.org/starview?object_type=1&object_id=2046 *http://varsao.com.ar/Curva_theta_Cir.htm (light curve) {{DEFAULTSORT:Theta Circini Circini, Theta Gamma Cassiopeiae variable stars Circinus Circini, Theta 131492 073129 5551 Astrometric binaries Durchmusterung objects