Eta Andromedae (Eta And, η Andromedae, η And) is a
spectroscopic binary star
A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...
in the
constellation of
Andromeda
Andromeda most commonly refers to:
* Andromeda (mythology), a princess from Greek mythology
* Andromeda (constellation), a region of the Earth's night sky
* The Andromeda Galaxy, an astronomical object within the constellation
Andromeda may also ...
. It consists of two
G-type
Gaea
Gaea is one of the Elder Gods of Earth.
Gaia
Gaia, also known as the Guardian of the Universal Amalgamator, is a fictional superhero, depicted as possibly being a mutant or extraterrestrial. Created by Larry Hama, she first appeared in ...
subgiant
A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...
or
giant star
A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...
s orbiting each other with a period of 115.7 days and has an overall
apparent visual 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 lig ...
of approximately 4.403.
[The spectroscopic binary eta Andromedae: Determination of the orbit by optical interferometry, C. A. Hummel et al., ''Astronomical Journal'' 106, #6 (December 1993), pp. 2486–2492, , .]
History
Eta Andromedae was discovered to be a double-lined
spectroscopic binary in a series of spectra taken in 1899 and 1900. Its orbit was computed in 1946 from spectroscopic observations. Because spectroscopy only reveals the
radial velocity
The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...
of a star towards or away from the viewer, such a computation does not determine all
orbital elements
Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same ...
. In observations made from 1990 to 1992, Eta Andromedae was resolved
interferometrically
Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opti ...
by the
Mark III Stellar Interferometer The Mark III Stellar Interferometer was a long-baseline optical astronomical interferometer, located at the Mount Wilson Observatory, California, United States.The Mark III stellar interferometer, M. Shao et al., ''Astronomy and Astrophysics'' 193 ...
at
Mount Wilson Observatory
The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles.
The observ ...
,
California
California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...
,
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...
. This allowed a more complete orbit to be computed and, in 1993, published.
Naming
In
Chinese
Chinese can refer to:
* Something related to China
* Chinese people, people of Chinese nationality, citizenship, and/or ethnicity
**''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation
** List of ethnic groups in China, people of v ...
, (), meaning ''
Legs
A leg is a weight-bearing and animal locomotion, locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single ...
(asterism)'', refers to an asterism consisting of η Andromedae, 65 Piscium,
ζ Andromedae
Zeta Andromedae (Zeta And, ζ Andromedae, ζ And) is a star system in the constellation Andromeda. It is approximately 189 light-years from Earth.
Zeta Andromedae is the star's Bayer designation. It also has the F ...
,
ε Andromedae
Epsilon Andromedae, Latinized from ε Andromedae, is a star in the constellation of Andromeda. It can be seen with the naked eye, having an apparent visual magnitude of 4.4. Based upon an annual parallax shift of 21.04 ...
,
δ Andromedae
Delta Andromedae, Latinized from δ Andromedae, is a triple star system in the northern constellation of Andromeda. The system is visible to the naked eye as a point of light with a combined apparent visual magnitude of 3.28. Based up ...
,
π Andromedae
Pi Andromedae (Pi And, π Andromedae, π And) is the Bayer designation for a binary star system in the northern constellation of Andromeda. With an apparent visual magnitude of 4.4, it is visible to the naked eye. It i ...
,
ν Andromedae,
μ Andromedae
Mu Andromedae (Mu And, μ Andromedae, μ And) is the Bayer designation for a star in the northern constellation of Andromeda. It has an apparent visual magnitude of 3.87, making it readily visible to the naked eye. Based ...
,
β Andromedae
Beta Andromedae, Latinized from β Andromedae, and officially named Mirach , is a prominent star in the northern constellation of Andromeda. It is northeast of the Great Square of Pegasus and is potentially visible to all observers ...
,
σ Piscium,
τ Piscium
Tau Piscium (τ Piscium) is an orange-hued star in the zodiac constellation of Pisces. With an apparent visual magnitude of +4.52, it is a dim star but visible to the naked eye. Based upon an annual parallax shift of 19.32  ...
, 91 Piscium,
υ Piscium
Upsilon Piscium is a solitary, white-hued star in the zodiac constellation of Pisces. It is faintly visible to the naked eye, having an apparent visual magnitude of +4.75. Based upon an annual parallax shift of as seen from Earth, it i ...
,
φ Piscium,
χ Piscium
Chi Piscium (χ Piscium) is a solitary, orange-hued star in the zodiac constellation of Pisces. It can be seen with the naked eye, having an apparent visual magnitude of +4.64. Based upon an annual parallax shift of 8.50 mas as ...
and
ψ¹ Piscium. Consequently, the
Chinese name
Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are oft ...
for η Andromedae itself is (, en, the First Star of Legs.)
[AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 19 日]
/ref>
Visual companion
Eta Andromedae has a visual companion 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 ...
of apparent visual 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 lig ...
11.5, BD+22°153B, visible 129.2 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 away.[Entry 00572+2325, discoverer code FOX 116, components AB,]
The Washington Double Star Catalog
,
United States Naval Observatory
United States Naval Observatory (USNO) is a scientific and military facility that produces geopositioning, navigation and timekeeping data for the United States Navy and the United States Department of Defense. Established in 1830 as the Depo ...
. Accessed on line August 23, 2008.
References
External links
Image η Andromedae
{{DEFAULTSORT:Eta Andromedae
Andromeda (constellation)
G-type giants
005516
Andromedae, 38
Andromedae, Eta
004463
Spectroscopic binaries
Triple stars
BD+22 0153
0271