Omicron Andromedae (ο And, ο Andromedae) is a

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speak ...

in the

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 ...

Andromeda. It is approximately 692

light years 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 ...

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 ...

. The system as a whole is classified as a blue-white B-type

giant In folklore, giants (from Ancient Greek: '' gigas'', cognate giga-) are beings of human-like appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''giant'' is first attested in 1297 fr ...

, with a mean combined

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of +3.62.

System

Omicron Andromedae is a multiple star containing at least three components. It may consist of two close pairs in a wider orbit, making a four-star system, although the binarity of the primary star is in doubt. This star system has a

peculiar velocity Peculiar motion or peculiar velocity refers to the velocity of an object relative to a ''rest frame'' — usually a frame in which the average velocity of some objects is zero. Galactic astronomy In galactic astronomy, peculiar motion refers to ...

of . The components A and B were first resolved in 1949, when they were reported to be separated by less than 0.1". In 1975 they were separated by 0.375" and by 2014 by only 0.21". An orbit has been derived with a period of 118 years. The companion is 2.3 magnitudes fainter than the primary star. In 1975, a companion was discovered by

speckle interferometry Speckle imaging describes a range of high-resolution astronomical imaging techniques based on the analysis of large numbers of short exposures that freeze the variation of atmospheric turbulence. They can be divided into the shift-and-add ("''i ...

only 0.05" from component A. Components Aa and Ab orbit every 5.6 years, although the existence of this companion is now doubted. 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 ...

in the system was suspected and in 1988 it was confirmed. Although a clear 33.01 day period was seen, it was unclear which component was the pair seen in the spectrum. Eventually, it was settled that component B was a close

Properties

Omicron Andromedae is a Gamma Cassiopeiae type

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...

and the system's brightness varies from magnitude +3.58 to +3.78. The variable component is the brightest and most massive star in the system, Aa. Omicron Andromedae also shows variations with a period of about a day, similar to a β Lyrae-type eclipsing variable, but these are thought to be intrinsic to one of the components and not due to eclipses. The spectrum is predominantly that of a B6

giant star A giant star is a star with substantially larger radius and luminosity than a main sequence, main-sequence (or ''dwarf'') star of the same effective temperature, surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moo ...

, from the brightest component in the system. It is a

shell star A shell star is a star having a spectrum that shows extremely broad absorption lines, plus some very narrow absorption lines. They typically also show some emission lines, usually from the Balmer series but occasionally of other lines. The broad ...

and the spectrum contains

emission 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 with variable profiles. Spectral lines similar to an A2 star are also detectable in the spectrum and these are thought to originate in the B component.

References

External links

Image ο Andromedae
{{DEFAULTSORT:Omicron Andromedae Andromeda (constellation) Andromedae, Omicron B-type giants Andromedae, 01 4 Spectroscopic binaries Gamma Cassiopeiae variable stars 113726 8762 Durchmusterung objects 217675 6