Upsilon
1 Hydrae (υ
1 Hydrae, abbreviated Ups
1 Hya, υ
1 Hya), also named Zhang,
is a yellow-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 ...
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 ...
of
Hydra. It is visible to the naked eye, having an
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 4.12.
[ Based upon an annual ]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 ...
shift of 12.36 mas as seen from Earth,[ it is located about 264 ]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
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
. The star is moving closer to the Sun with a 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 temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...
of −14.34 km/s.[ In 2005 it was announced that it had a substellar companion.]
Nomenclature
''υ1 Hydrae'' ( Latinised to ''Upsilon1 Hydrae'') is the star's Bayer designation
A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...
.
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 ...
, (), meaning '' Extended Net'', refers to an asterism consisting of Upsilon1 Hydrae, Lambda Hydrae
λ Hydrae, Latinised as Lambda Hydrae, is a spectroscopic binary star in the constellation Hydra. Its apparent magnitude is 3.61 Located around distant. The spiral galaxy NGC 3145 is only away to the southwest.
The primary is an ...
, Mu Hydrae
μ Hydrae, Latinised as Mu Hydrae, is a solitary, orange-hued star in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 3.83. Positioned just 1.8° to the south-southwest is the pl ...
, HD 87344, Kappa Hydrae and Phi1 Hydrae. Consequently, Upsilon1 Hydrae itself is known as (), "the First Star of Extended Net".[香港太空館 - 研究資源 - 亮星中英對照表]
, Hong Kong Space Museum. Accessed on line November 23, 2010. In 2016, the International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
(IAU) organized a Working Group on Star Names
The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...
(WGSN) to catalog and standardize proper names for stars. The WGSN approved the name ''Zhang'' for this star on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.
Properties
With a 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 G6/8 III, Upsilon1 Hydrae is an evolved
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation t ...
G-type 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 ...
. It has an estimated 3.3 times the mass of the Sun
The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
and has expanded to 14.7 times the Sun's radius. The star is about 270 million years old with a projected rotational velocity
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface.
The rotation of a star produces an equatorial bulge ...
of just 2.11 km/s. It is radiating 162 times the Sun's luminosity
The solar luminosity (), is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun.
One nominal ...
from its photosphere
The photosphere is a star's outer shell from which light is radiated.
The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...
at an effective temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...
of .[
]
Substellar companion
The Okayama Planet Search team published a paper in 2005 reporting investigations on 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 temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...
variations observed for a set of class G giants and announcing the detection of a brown dwarf
Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...
companion in 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 ...
around Upsilon1 Hydrae. The 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 ...
for this companion is roughly 4.1 years, and it has a high eccentricity
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-Centre (geometry), center, in geometry
* Eccentricity (g ...
of 0.57. Since the inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...
of the orbit to the line-of-sight is unknown, only a lower bound on the mass can be determined. It has at least 49 times the mass of Jupiter
Jupiter mass, also called Jovian mass, is the unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jupiter. Jupiter is b ...
.
References
{{DEFAULTSORT:Upsilon1 Hydrae
G-type giants
Planetary systems with one confirmed planet
Hydra (constellation)
Hydrae, Upsilon1
BD-14 2963
Hydrae, 39
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