WR 124 is a

Wolf–Rayet star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface ...

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 ...

Sagitta Sagitta is a dim but distinctive constellation in the northern sky. Its name is Latin for 'arrow', not to be confused with the significantly larger constellation Sagittarius 'the archer'. It was included among the 48 constellations listed by t ...

surrounded by a ring

nebula A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...

of expelled material known as M1-67. It is one of the fastest runaway

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s in the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

with a radial velocity around . It was discovered by

Paul W. Merrill Paul Willard Merrill (August 15, 1887 – July 19, 1961) was an American astronomer whose specialty was spectroscopy. He was the first to define S-type stars in 1922. Career He received his Ph.D. at the University of California (now UC Berkeley) ...

in 1938, identified as a high-velocity Wolf–Rayet star. It is listed in the

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and thi ...

as QR Sagittae with a range of 0.08 magnitudes.

Distance

A 2010 study of WR 124 directly measured the expansion rate of the M1-67

expelled from the star using

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

camera images taken 11 years apart, and compared that to the expansion velocity measured by the

Doppler shift The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

of the nebular emission lines. This yielded a distance of , which is less than previous studies, and the resulting

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 ...

of 150,000 times 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 ...

() is much lower than previously calculated. The luminosity is also lower than predicted by models for a star of this spectral class. Previous studies had found distances of to , with corresponding luminosities of , as expected for a typical WN8h which is a very young star just moving away from the

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

. The distance to WR 124 calculated from the

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 objects ...

published in

Gaia Data Release 2 The ''Gaia'' catalogues are star catalogues created using the results obtained by ''Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, especia ...

is .

Gaia Early Data Release 3 The ''Gaia'' catalogues are star catalogues created using the results obtained by '' Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, espec ...

gives a similar parallax, which would suggest a distance .

Physical characteristics

With an assumed visual

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...

of −7.22 and 3.1 magnitudes of

extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

, WR 124 would be away. The temperature of around means that most of its energy is emitted at

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 ...

wavelengths, the

bolometric 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 s ...

is and the radius is . The mass is calculated from evolutionary models to be . WR 124 is measured to still be about 15% hydrogen with most of the remaining mass being helium. A young highly massive and luminous WN8h star would still be burning hydrogen in its core, but a less luminous and older star would be burning helium in its core. The result of modelling the star purely from its observed characteristics is a luminosity of and a mass of , corresponding to a relatively young hydrogen-burning star at around . In either case, it has only a few hundred thousand years before it explodes as a type Ib or Ic

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

. The mass loss rate is – per year, depending on the distance and properties determined for the star.

Nebula

WR 124 is surrounded by an intensely hot nebula formed from the star's extreme stellar wind. The nebula M1-67 is expanding at a rate of over and is nearly 6

light-year 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 ...

s across, leading to the dynamical age of 20,000 years. M1-67 has little internal structure, though large clumps of material have been detected, some of which have 30 times the mass of

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

and stretch out up to . If placed in 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 ...

, one of these clumps would span the distance from the Sun to

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

External links

*http://apod.nasa.gov/apod/ap981109.html *http://hubblesite.org/newscenter/archive/releases/1998/38/image/a

References

{{DEFAULTSORT:WR 124 Wolf–Rayet stars Runaway stars Sagitta Sagittae, QR Merrill's star 094289