Sigma Puppis, Latinized from σ Puppis, 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 ...

system in the

southern Southern may refer to: Businesses * China Southern Airlines, airline based in Guangzhou, China * Southern Airways, defunct US airline * Southern Air, air cargo transportation company based in Norwalk, Connecticut, US * Southern Airways Express, M ...

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 ...

Puppis Puppis is a constellation in the southern sky. Puppis, the Latin translation of "poop deck", was originally part of an over-large constellation Argo Navis (the ship of Jason and the Argonauts), which centuries after its initial description, was ...

. It has an apparent visual magnitude of 3.25, which is bright enough to be visible to the naked eye at night from the Southern Hemisphere. Through a telescope, it appears as a bright, orange-hued

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

with a nearby white companion.

Parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

measurements indicate this star is located at a distance of about from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

This is a

spectroscopic binary A binary star is a system of two star, stars that are gravity, 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 separa ...

system, consisting of an

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

ing pair of stars that have not been individually resolved with a telescope. Their

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

is 257.8 days and the eccentricity is 0.17. The pair form an eclipsing binary of the Beta Lyrae type and a period of 130.5 days, or one half of their orbital period. The eclipse of the primary component causes a decline of 0.04 of a magnitude, while the secondary eclipse reduces the magnitude by 0.03. The 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 ...

is K5 III, which matches the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

of a giant star. The measured

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it is ...

of the primary star is . At the estimated distance of this system, this yields a physical size of about 107 times the

radius of the Sun Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.957\t ...

. The primary component shows the behavior of a slow irregular variable. In addition to its binary components, Sigma Puppis has a more distant companion that has a matching

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

, suggesting that it may be gravitationally bound to the binary. This magnitude 8.5 star is at an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of 22.4

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

s with a position angle of 74° from Sigma Puppis, which is equivalent to a

projected separation This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outsid ...

of . In 1970, American astronomer

Olin J. Eggen Olin Jeuck Eggen (July 9, 1919 – October 2, 1998) was an American astronomer. Biography Olin Jeuck Eggen was born to Olin Eggen and Bertha Clare Jeuck in the village of Orfordville in Rock County, Wisconsin. Both of his parents were of Norw ...

suggested that Sigma Puppis belonged to a

moving group In astronomy, stellar kinematics is the Observational astronomy, observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar Velocity, velocities in the Milky W ...

of stars that share a similar motion through space, and thereby a common origin. It served as the

eponym An eponym is a person, a place, or a thing after whom or which someone or something is, or is believed to be, named. The adjectives which are derived from the word eponym include ''eponymous'' and ''eponymic''. Usage of the word The term ''epon ...

for this, the σ Puppis group. The existence of this group was later brought into question.

References

{{DEFAULTSORT:Sigma Puppis K-type giants Beta Lyrae variables Slow irregular variables Spectroscopic binaries Puppis Puppis, Sigma Durchmusterung objects 059717 036377 2878