WR 46 (DI Crucis) is a Wolf-Rayet star 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 the

Southern Cross Crux () is a constellation of the southern sky that is centred on four bright stars in a cross-shaped asterism commonly known as the Southern Cross. It lies on the southern end of the Milky Way's visible band. The name ''Crux'' is Latin for c ...

apparent 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 li ...

+10.8. It is located at 55

arcmin A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

north of Theta² Crucis. The star is a member of the distant

stellar association A stellar association is a very loose star cluster, looser than both open clusters and globular clusters. Stellar associations will normally contain from 10 to 100 or more stars. The stars share a common origin, but have become gravitationally u ...

Cru OB4, and is around 2,900

parsecs The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...

or 9,300

light years 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 ...

from the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...

Features

WR 46 has

spectral type 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 ...

WN3, with peculiarities in the spectrum including unusually broad

emission lines A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

. Its

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 colors i ...

is characterized by the presence of strong lines of N_V and He_II and the absence of

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

lines. It is known as a weak-lined WNE star because of the high temperature but relatively weak emission strength. The physical parameters of WR 46 are all estimates from assumptions about the distance and models for stars of its type, complicated by the suspicion that there is a companion star. The

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 ...

is over 110,000K, the luminosity greater than 200,000 times the

solar 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 s ...

(), the mass around 14 times that of 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 ...

() and a radius of 1.36 times the

solar radius Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.957\tim ...

(). The

terminal velocity Terminal velocity is the maximum velocity (speed) attainable by an object as it falls through a fluid (air is the most common example). It occurs when the sum of the drag force (''Fd'') and the buoyancy is equal to the downward force of gravit ...

of the

stellar wind A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. D ...

reaches 2450 km/s with a total mass loss rate of 4 × 10⁻⁶ per

year A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hou ...

. WR 46 is a known source of X-rays, an aspect that was discovered by the Einstein Observatory. The X-ray

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

between 0.2 and 10.0 keV is 7.7 × 10³² erg/s. Its X-ray spectrum is dominated by a soft component but there is also a hard component above 3 keV (a hard tail).

Variability

WR 46 exhibits complex variability on relatively short time scales of a few hours. In the past there have been regular but intermittent changes in the

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 ...

, multiple periods and photometric variation at some wavelengths, particularly

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

. It has been proposed that this short-term behavior is due to non-radial pulsations, fast rotational modulation, or the presence of a lower-mass companion. Theories that are now discounted include WR 46 being a

Super soft X-ray source A luminous supersoft X-ray source (SSXS, or SSS) is an astronomical source that emits only low energy (i.e., soft) X-rays. Soft X-rays have energies in the 0.09 to 2.5 keV range, whereas hard X-rays are in the 1–20 keV range. SSSs emit few or no p ...

or a V Sagittae star, The radial velocity changes of the spectral lines originating most deeply within the

show clear radial velocity variations with a period of 7.9 hours. However the lines do not change their shape or intensity, which would be expected from a pulsating star Non-radial pulsations have been proposed, with multiple pulsation periods of varying amplitude accounting for the apparently irregular brightness changes.

Binary star

WR 46 has been suspected to be a

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 thi ...

with an OB companion. 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 ...

of the system has been reported at 0.311 days and 0.329 days. Most recent research refutes the idea of a companion, instead favoring the single WN star theory.

References

{{DEFAULTSORT:WR 46 Crux

WR 46 WR 46 (DI Crucis) is a Wolf-Rayet star in the constellation of the Crux, Southern Cross of apparent magnitude +10.8. It is located at 55 Minute of arc, arcmin north of Theta2 Crucis. The star is a member of the distant stellar associati ...

104994 Crucis, DI J12051871-6203101 058954 CD-61 3331 Irregular variables