Diagram of the possible structure of the Beta Hydri star system

Beta Hydri (β Hyi, β Hydri) is a

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 southern

circumpolar constellation A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles. Circumpolar stars are therefore visible from said location toward the nearest po ...

Hydrus Hydrus is a small constellation in the deep southern sky. It was one of twelve constellations created by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman and it first appeared on a 35-cm (14 in) ...

. (Note that Hydrus is not the same as Hydra.) With 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 2.8, this is the

brightest star ''Brightest Star'' is the debut mini-album from J-pop vocal group Bright. This was their first CD released under major label Rhythm Zone (RZN) is a record label in the Avex Group that releases urban contemporary Japanese music. History Th ...

in the constellation. Based upon

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 object ...

measurements the distance to this star is about . This star has about 104% of the mass of the Sun and 181% of the Sun's radius, with more than three times the Sun's luminosity. 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 color ...

of this star matches a

stellar classification In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting t ...

of G2 IV, with the

luminosity class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting th ...

of 'IV' indicating this is a

subgiant star 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 of ...

. As such, it is a slightly more

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 te ...

star than the Sun, with the supply of hydrogen at its core becoming exhausted. It is one of the oldest stars in the

solar neighborhood The Local Interstellar Cloud (LIC), also known as the Local Fluff, is an interstellar cloud roughly across, through which the Solar System is moving. This feature overlaps a region around the Sun referred to as the solar neighborhood. It is unk ...

. This star bears some resemblance to what the Sun might look like in the far distant future, making it an object of interest to astronomers.

Planetary system

In 2002 Endl et al. inferred the possible presence of an unseen companion orbiting Beta Hydri as hinted by radial velocity linear trend with a periodicity exceeding 20 years. A substellar object such as a planet with a minimum mass of 4

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandt ...

masses and orbital separation of roughly 8 AU could explain the observed trend. If confirmed, it would be a true

-analogue, though 4 times more massive. So far no planetary/substellar object has been certainly detected. These results were not confirmed in CES and HARPS measurements published on the arXiv in 2012. Instead the long-term radial velocity variations may be caused by the star's magnetic cycle.

References

External links

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Stellar Activity - Beta Hydri
{{DEFAULTSORT:Beta Hydri Hydri, Beta Hydrus (constellation) G-type subgiants Hydri, Beta Hypothetical planetary systems Zeta Herculis Moving Group 002021 002151 0098 0019 Durchmusterung objects

Planetary system

See also

References

External links