WR 147 is a

multiple 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 speaki ...

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 Cygnus. The system is extremely reddened by

interstellar extinction In astronomy, extinction is the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer. Interstellar extinction was first documented as such in 1930 by Robert Julius Trumple ...

– that is, dust in front of the star scatters much of the blue light coming from WR 147, leaving the star appearing reddish.

Distance

The distance of WR 147 has been calculated to be based on

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

photometry, which would place it in front of the

OB association In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as t ...

known as

Cygnus OB2 Cygnus OB2 is an OB association that is home to some of the most massive and most luminous stars known, including suspected Luminous blue variable Cyg OB2 #12. It also includes one of the largest known stars, NML Cygni. The region is em ...

. The extinction in the visual range was calculated to be 11.5 magnitudes and the absolute visual magnitude assumed to be −6.7. This would make WR 147 one of the closest known Wolf-Rayet stars, despite its faint

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 ...

. A later calculation using optical and

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 ...

photometry derived a slightly lower value for the extinction. Combined with an assumption of a brighter absolute magnitude, this gave a

distance modulus The distance modulus is a way of expressing distances that is often used in astronomy. It describes distances on a logarithmic scale based on the astronomical magnitude system. Definition The distance modulus \mu=m-M is the difference between the ...

of 10.6 corresponding to a distance of about 1,200 pc. This is still one of the nearest Wolf–Rayet systems to the sun. A

Gaia 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, especia ...

parallax of corresponds to a distance of around although there is considerable uncertainly on that value.

System

WR 147 consists of at least two very massive stars. The primary 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 ...

, designated WR 147S or just WR 147. A companion, designated WR 147N, is a B-type

main-sequence star 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 Hert ...

or O-type

giant In folklore, giants (from Ancient Greek: '' gigas'', cognate giga-) are beings of human-like appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''giant'' is first attested in 1297 fr ...

) away to the north. A much closer companion is also suspected on the basis of a "radio pinwheel" which would be produced as the companion orbits through the wind of the primary star with a period of 1.7 years. WR 147 was resolved into two components in the 1990s, separated first at radio wavelengths. Based on an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of about , this translates to an projected (i.e. minimum) separation of about , which is about thirteen times the distance between

Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...

and 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 ...

. The location of the companion resolved in the near-infrared is slightly further from the primary than the radio source originally called WR 147N, and it has been referred to as WR 147NIR. The Wolf–Rayet star in the system (WR 147S) has a luminosity of , making it one of the most luminous stars known. The B-type companion is much less luminous, at . The

orbital element Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same ...

s of WR 147's

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

are poorly known, as the two components are separated far enough that no

orbital motion In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

has been detected, but it is estimated that one orbit would take 1,300 years. The inclination of WR 147's orbit to our line of sight is also unknown: numerous studies have given values ranging from 30° to 60°. Constraining the value of the inclination is important because the true separation of the stars depends on the value.

Colliding wind

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 ...

from these two stars collide and emit

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

s and

radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (short ...

s. The Wolf–Rayet star is losing mass at a rate of /yr and the companion is losing mass at a rate of /yr. The

plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...

generated from the wind collision may reach temperatures as high as 2.7

keV Kev can refer to: Given name * Kev Adams, French comedian, actor, screenwriter and film producer born Kevin Smadja in 1991 * Kevin Kev Carmody (born 1946), Indigenous Australian singer-songwriter * Kev Coghlan (born 1988), Scottish Grand Prix motor ...

, or 31 million

kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...

s. Despite the name, the colliding wind shock is actually considered to be collisionless, that is the ions in the wind do not for the most part directly collide.

X-rays

In 2010, X-ray emission from WR 147 was resolved into two sources: one where the wind collision is thought to be occurring, and another directly from the Wolf–Rayet star, the cause of which is not clear. It was hypothesized to be another massive star orbiting the Wolf–Rayet star; if so, it would have an

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 15 to 20

day A day is the time period of a full rotation of the Earth with respect to the Sun. On average, this is 24 hours, 1440 minutes, or 86,400 seconds. In everyday life, the word "day" often refers to a solar day, which is the length between two so ...

s, with the total mass of the system being , leading to a separation of about 0.33 AU.

References

{{Stars of Cygnus Wolf–Rayet stars Cygnus (constellation) Astronomical X-ray sources B-type main-sequence stars J20364364+4021075 IRAS catalogue objects

Distance

System

Colliding wind

X-rays

See also

References