27 Hydrae is a member of a

triple 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 speaking, ...

system in the

equatorial Equatorial may refer to something related to: *Earth's equator **the tropics, the Earth's equatorial region **tropical climate *the Celestial equator ** equatorial orbit **equatorial coordinate system ** equatorial mount, of telescopes * equatorial ...

constellation of Hydra, located 222 light years away from the Sun. It is visible to the naked eye as a faint, orange-hued star with a combined

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 4.82. The system is moving further from the Earth with a heliocentric radial velocity of +25.6 km/s. The magnitude 4.91 primary, component A, is an aging

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 ...

with a stellar classification of K0 III. It is a

red clump Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondary ...

giant, which indicates it is on the horizontal branch and is generating energy through

helium fusion The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon. Triple-alpha process in stars Helium accumulates in the cores of stars as a result of the proton–pro ...

at its

core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...

. The star is 1.9 billion years old with 2.17 times the mass of the Sun. It has swelled to 11 times the Sun's radius and is radiating 57.5 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 enlarged photosphere at an effective temperature of 4,965 K. The star is suspected to host a low-mass companion. The stellar companions to this star, designated components B and C, lie at an angular separation of from the primary, and form a binary pair with a separation of 9.20″ as of 2015. The brighter member of the pair, component B, is a seventh magnitude

F-type main-sequence star An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K.Tables VII ...

with a class of F4 V, while its companion is an eleventh magnitude

K-type main-sequence star A K-type main-sequence star, also referred to as a K-type dwarf or an orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence star ...

with a class of K2 V.

Substellar companion

The Okayama Planet Search team published a paper in late 2008 reporting investigations into radial velocity variations observed for a set of evolved stars, showing hints of a

substellar A substellar object, sometimes called a substar, is an astronomical object the mass of which is smaller than the smallest mass at which hydrogen fusion can be sustained (approximately 0.08 solar masses). This definition includes brown dwarfs and ...

companion orbiting the primary member of the wide

binary system A binary system is a system of two astronomical bodies which are close enough that their gravitational attraction causes them to orbit each other around a barycenter ''(also see animated examples)''. More restrictive definitions require that th ...

27 Hydrae. Its

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 ...

is estimated at 9.3 years, but no planet has been confirmed yet.

References

{{DEFAULTSORT:27 Hydrae K-type giants F-type main-sequence stars K-type main-sequence stars Horizontal-branch stars Triple star systems Hypothetical planetary systems Hydra (constellation) Hydrae, P Durchmusterung objects Hydrae, 27 080586 045811 3709