HD 125823, also known as V761 Centauri or a Centauri, is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

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 first constellati ...

Centaurus Centaurus () is a bright constellation in the southern sky. One of the 88 modern constellations by area, largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one ...

. It is a blue-white star that is visible to the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

with a mean

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 +4.41. The distance to this star is approximately 460

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s based on

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. It is a member of the Upper Centaurus–Lupus subgroup of the

Scorpius–Centaurus association The Scorpius–Centaurus association (sometimes called Sco–Cen or Sco OB2) is the nearest OB association to the Sun. This stellar association is composed of three subgroups (Upper Scorpius, Upper Centaurus–Lupus, and Lower Centaurus–Crux) ...

. In 1965, W. P. Bidelman discovered that the intensities of the star's neutral helium lines had varied on photographic plates taken over the period 1908 to 1911. This variation was confirmed by A. D. Thackeray in 1966. The star ranges from a helium-strong B2 class to a helium-weak B8 with a period of 8.82 days. Radial velocity measurements during the 1970s showed differing velocity variations for helium and other elements. The magnetic field strength peaks at a negative maximum in phase with the maximum helium line strength. Weak emission has been detected in the singly-ionized lines of silicon, magnesium, and iron, but not in the neutral lines of hydrogen and helium. This is a magnetic peculiar Bp star that shows periodic variation in the strength of its neutral helium lines. It is classified as an SX Arietis type

and its brightness varies from magnitude +4.38 to +4.43 with a period of 8.82 days. The star displays very different helium abundances between the two hemispheres, and, unusually, helium-3 has been detected in the weaker southern hemisphere. Latitudinal abundance concentrations have been found for iron, nitrogen, and oxygen. The variation in helium concentration effects the density

scale height In atmospheric, earth, and planetary sciences, a scale height, usually denoted by the capital letter ''H'', is a distance ( vertical or radial) over which a physical quantity decreases by a factor of e (the base of natural logarithms, approx ...

of the atmosphere, causing helium rich regions to have a lower luminosity in the visual band but emitting stronger levels of far ultraviolet.

References

{{DEFAULTSORT:HD 125823 Ap stars SX Arietis variables Centaurus Centauri, a Durchmusterung objects 125823 070300 5378 Centauri, V761 B-type main-sequence stars