Beta Hydri (β Hyi, β Hydri) is a star 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 p ...

Hydrus Hydrus is a small constellation in the deep Southern Celestial Hemisphere, 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 ap ...

. (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, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of 2.8, this is the brightest star in the constellation. Based upon

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measurements the distance to this star is about . This star has about 113% of the mass of the Sun and 184% of the Sun's radius, with more than three times the Sun's luminosity. The

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

of this star matches 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 gratin ...

of G2 IV, with the

luminosity class 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 gratin ...

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 the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

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. 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. At a distance of 13°, it is the closest easily visible star to the south

celestial pole The north and south celestial poles are the two points in the sky where Earth's axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to observers at ...

, and around 150 BC it was within two degrees of it, which made it the southern pole star.

Search for planets

In 2002, Endl et al. inferred the possible presence of an unseen companion orbiting Beta Hydri as hinted by a

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative 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 List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

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 The High Accuracy Radial Velocity Planet Searcher (HARPS) is a high-precision Echelle grating, echelle planet-finding spectrograph installed in 2002 on the ESO 3.6 m Telescope, ESO's 3.6m telescope at La Silla Observatory in Chile. The First l ...

measurements published in 2012. Instead, the long-term radial velocity variations may be caused by the star's magnetic cycle. Similarly, a 2023 study detected long-period radial velocity variations that were attributed to stellar activity.

References

External links

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Stellar Activity - Beta Hydri
{{Stars of Hydrus Hydri, Beta Hydrus G-type subgiants Hydri, Beta Hypothetical planetary systems Zeta Herculis Moving Group 002021 002151 0098 0019 CD-77 00015 Southern pole stars

Search for planets

See also

References

External links