Wolf 359
Encyclopedia
Wolf 359 is a red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....

 star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

 that is located in the constellation Leo
Leo (constellation)
Leo is one of the constellations of the zodiac. Its name is Latin for lion. Its symbol is . Leo lies between dim Cancer to the west and Virgo to the east.-Stars:...

, near the ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...

. At a distance of approximately 7.8 light years from the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

, it has an apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 of 13.5 and can only be seen with a large telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

. Wolf 359 is one of the nearest stars to the solar system; only the Alpha Centauri
Alpha Centauri
Alpha Centauri is the brightest star in the southern constellation of Centaurus...

 system, Proxima Centauri
Proxima Centauri
Proxima Centauri is a red dwarf star about 4.2 light-years distant in the constellation of Centaurus. It was discovered in 1915 by Robert Innes, the Director of the Union Observatory in South Africa, and is the nearest known star to the Sun, although it is too faint to be seen with the naked eye...

, and Barnard's star
Barnard's star
Barnard's Star, also known occasionally as Barnard's "Runaway" Star, is a very low-mass red dwarf star approximately six light-years away from Earth in the constellation of Ophiuchus . In 1916, the American astronomer E.E...

 are known to be closer. Its proximity to Earth has led to its mention in several works of fiction.

Wolf 359 is one of the faintest and lowest-mass stars known. Its photosphere
Photosphere
The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to the fact that it is a spheric surface perceived...

 has a temperature of about 2,800 K
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

, which is low enough for chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

s to form and survive. The absorption lines of compounds such as water and titanium(II) oxide
Titanium(II) oxide
Titanium oxide is an inorganic chemical compound of titanium and oxygen. It can be prepared from titanium dioxide and titanium metal at 1500°C. It is non-stoichiometric in a range TiO0.7 to TiO1.3 and this is caused by vacancies of either Ti or O in the defect rock salt structure . In pure TiO...

 have been observed. The surface has a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

 that is stronger than the average magnetic field on the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

. As a result of magnetic activity, Wolf 359 is a flare star
Flare star
A flare star is a variable star that can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to solar flares in that they are due to magnetic reconnection in the atmospheres of the stars. The brightness increase is...

 that can undergo sudden increases in luminosity for several minutes. These flares emit strong bursts of X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 and gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...

 radiation that have been observed by space telescopes. Wolf 359 is a relatively young star with an age of less than a billion years. No companions or debris have been detected in orbit around it.

Observation history

Wolf 359 first came to the attention of astronomers because of the relatively high rate of transverse motion against the background, known as the proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...

. A high rate of proper motion may indicate that a star is located nearby, as more distant stars must move at higher velocities in order to achieve the same rate of angular travel across the celestial sphere
Celestial sphere
In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...

. The motion of Wolf 359 was first measured in 1917 by German astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

 Max Wolf
Max Wolf
Maximilian Franz Joseph Cornelius Wolf was a German astronomer and a pioneer in the field of astrophotography...

, with the aid of astrophotography
Astrophotography
Astrophotography is a specialized type of photography that entails recording images of astronomical objects and large areas of the night sky. The first photographs of an astronomical object were taken in the 1840s, but it was not until the late 19th century that advances in technology allowed for...

. In 1919 he published a catalog of over one thousand high proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...

 stars, including this one, that are still identified by his name. He listed this star as 359, and the star has since been referred to as Wolf 359 in reference to the position in Max Wolf's catalogue.

The first parallax
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. The term is derived from the Greek παράλλαξις , meaning "alteration"...

 measurement of Wolf 359 was reported in 1928 from the Mount Wilson Observatory
Mount Wilson Observatory
The Mount Wilson Observatory is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 5,715 foot peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles...

, yielding an annual shift in the star's position of . From this shift, and the known size of the Earth's orbit, the distance to the star could be estimated. It was the lowest-mass and faintest star known until the discovery of VB 10
VB 10
VB 10, also referred to as Van Biesbroeck's star, is a very small and very dim M-type red dwarf star located in the constellation Aquila...

 in 1944. The infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 magnitude of the star was measured in 1957. In 1969, a brief flare in luminosity was observed on it, linking it to the class of variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...

s known as flare star
Flare star
A flare star is a variable star that can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to solar flares in that they are due to magnetic reconnection in the atmospheres of the stars. The brightness increase is...

s.

Properties

Wolf 359 has a stellar classification
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 of M6.5, although various sources list a spectral class of M5.5, M6 or M8. This M-type star is known as a red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....

: it is called red, because the energy emission of the star reaches a peak in the red and infrared parts of the spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...

. Wolf 359 has a very low luminosity, emitting about 0.1% of the Sun's energy. If it were moved to the location of the Sun, it would appear ten times as bright as the full Moon
Full Moon
Full moon is a lunar phase.Full Moon may also refer to:- Literature :* Full Moon , a novel by P. G. Wodehouse* Full Moon o Sagashite or Full Moon, a manga* Full Moon Press, an American small-press publisher...

.

At an estimated 9% of the Sun's mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...

, Wolf 359 is just above the lowest limit at which a star can perform hydrogen fusion through the proton–proton chain reaction: 8% of the Sun's mass. (Substellar object
Substellar object
A substellar object, sometimes called a lump, is an astronomical object whose mass is smaller than the smallest mass, approximately 0.08 solar masses, at which a star can sustain hydrogen fusion...

s below this limit are known as brown dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...

s.) The radius of Wolf 359 is an estimated 16% of the Sun's radius, or about 110,000 km. For comparison, the equatorial radius of the planet Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

 is 71,492 km, which is 65% as large as Wolf 359's.

The entire star is undergoing convection
Convection zone
The convection zone of a star is the range of radii in which energy is transported primarily by convection. In the radiation zone, energy is transported by radiation...

, whereby the energy generated at the core is being transferred toward the surface by the convective motion of plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

, rather than by transmission through radiation
Radiation zone
The radiation zone is the middle zone in the Sun's interior. Energy travels out of the core into the radiation zone. Energy that travels through the radiation zone is in the form of electromagnetic radiation. The radiation zone is so dense that the waves bounce around...

. This circulation redistributes any accumulation of helium that is generated through stellar nucleosynthesis
Stellar nucleosynthesis
Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the elements heavier than hydrogen. Some small quantity of these reactions also occur on the stellar surface under various circumstances...

 at the core throughout the star. This will allow the star to remain on the main sequence
Main sequence
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 Hertzsprung and Henry Norris Russell...

 as a hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 fusing star proportionately longer than a star such as the Sun where the helium steadily accumulates at the core. In combination with a lower rate of hydrogen consumption due to the low mass, the convection will allow Wolf 359 to remain a main-sequence star for eight trillion years.

A search of this star by the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

 revealed no stellar companions, although this does not preclude the presence of smaller companions that are below the telescope's detection limit, such as a planet orbiting within one astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

 of the star. No excess infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 emission has been detected, which may indicate the lack of a debris disk
Debris disk
A debris disk is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris disks have been found around both evolved and young stars, as well as at least one debris disk in orbit around a...

 in orbit around it.

Outer atmosphere

The outer light-emitting layer of a star is known as the photosphere
Photosphere
The photosphere of an astronomical object is the region from which externally received light originates. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to the fact that it is a spheric surface perceived...

. Temperature estimates of the photosphere of Wolf 359 range from 2,500 K to 2,900 K, which is sufficiently cool for equilibrium chemistry
Equilibrium chemistry
Equilibrium chemistry is a concerned with systems in chemical equilibrium. The unifying principle is that the free energy of a system at equilibrium is the minimum possible, so that the slope of the free energy with respect to the reaction coordinate is zero. This principle, applied to mixtures at...

 to occur. The resulting chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

s survive long enough to be observed through their spectral lines. Numerous molecular
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

 lines appear in the spectrum of Wolf 359, including those of carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 (CO), iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 hydride
Hydride
In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...

 (FeH), chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

 hydride (CrH), water (H2O), magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

 hydride (MgH), vanadium(II) oxide
Vanadium(II) oxide
Vanadium oxide, VO, is one of the many oxides of vanadium. VO is a long-lived, electronically neutral reagent chemical. It adopts a distorted NaCl structure and contains weak V-V metal to metal bonds. As shown by band theory, VO is a conductor of electricity due to its partially filled conduction...

 (VO), titanium(II) oxide
Titanium(II) oxide
Titanium oxide is an inorganic chemical compound of titanium and oxygen. It can be prepared from titanium dioxide and titanium metal at 1500°C. It is non-stoichiometric in a range TiO0.7 to TiO1.3 and this is caused by vacancies of either Ti or O in the defect rock salt structure . In pure TiO...

 (TiO) and possibly the molecule CaOH. Since there are no lines of lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...

 in the spectrum, this element must have already been consumed by fusion at the core. This indicates the star must be at least 100 million years old.

Beyond the photosphere lies a nebulous, high temperature region known as the corona
Corona
A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...

. In 2001, Wolf 359 became the first star other than the Sun to have the spectrum of its corona observed from a ground-based telescope. The spectrum showed emission lines of Fe XIII, which is heavily ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

ized iron that has been stripped of twelve of its electrons. The strength of this line can vary over a time period of several hours, which may be evidence of microflare heating.

Wolf 359 is classified as a UV Ceti
Luyten 726-8
Luyten 726-8 is a binary star system that is one of Earth's nearest neighbors, at about 8.7 light years from Earth in the constellation Cetus...

-type flare star
Flare star
A flare star is a variable star that can undergo unpredictable dramatic increases in brightness for a few minutes. It is believed that the flares on flare stars are analogous to solar flares in that they are due to magnetic reconnection in the atmospheres of the stars. The brightness increase is...

, which is a star that undergoes brief, energetic increases in luminosity because of magnetic activity in the photosphere. Its variable star designation
Variable star designation
Variable stars are named using a variation on the Bayer designation format of an identifying label combined with the Latin genitive of the name of the constellation in which the star lies...

 is CN Leonis. Wolf 359 has a relatively high flare rate. Observations with the Hubble Space Telescope detected 32 flare events within a two hour period, with energies of 1027 erg
Erg
An erg is the unit of energy and mechanical work in the centimetre-gram-second system of units, symbol "erg". Its name is derived from the Greek ergon, meaning "work"....

s (1020 joule
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...

s) and higher. The mean magnetic field at the surface of Wolf 359 has a strength of about 2.2 kG
Gauss (unit)
The gauss, abbreviated as G, is the cgs unit of measurement of a magnetic field B , named after the German mathematician and physicist Carl Friedrich Gauss. One gauss is defined as one maxwell per square centimeter; it equals 1 tesla...

 (0.22 teslas
Tesla (unit)
The tesla is the SI derived unit of magnetic field B . One tesla is equal to one weber per square meter, and it was defined in 1960 in honour of the inventor, physicist, and electrical engineer Nikola Tesla...

), but this varies significantly on time scales as short as six hours. By comparison, the magnetic field of the Sun averages 1 gauss (100 µT), although it can rise as high as 3 kG (0.3 T) in active sunspot
Sunspot
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....

 regions. During flare activity, Wolf 359 has been observed emitting X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

s and gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...

s.

Motion

The rotation of a star causes a doppler shift to the spectrum. On average, this results in a broadening of the absorption lines in its spectrum, with the lines increasing in width with higher rates of rotation. However, only the rotational motion in the direction of the observer can be measured by this means, so the resulting data provides a lower limit on the star's rotation. This projected rotational velocity
Stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface....

 of Wolf 359's equator is less than 3 km/s, which is below the threshold of detection through spectral line broadening. This low rate of rotation may have been caused by loss of angular momentum
Angular momentum
In physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...

 through a stellar wind
Stellar wind
A stellar wind is a flow of neutral or charged 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.Different types of stars have...

. Typically, the time scale for the spin down of a star at spectral class M6 is roughly 10 billion years, because fully convective stars like this lose their rotation more slowly than other stars. However, evolutionary models suggest that Wolf 359 is a relatively young star with an age of less than a billion years.

The proper motion of this star against the background is 4.696 arcseconds per year, and it is moving away from the Sun at a velocity of 19 km/s. When translated into the galactic coordinate system
Galactic coordinate system
The galactic coordinate system is a celestial coordinate system which is centered on the Sun and is aligned with the apparent center of the Milky Way galaxy. The "equator" is aligned to the galactic plane...

, this motion corresponds to a space velocity of
= . The space velocity of Wolf 359 implies that it belongs to the population of old disk stars
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...

. It is following an orbit through the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

 galaxy that will carry it as close as 20.5 kly and as distant as 28 kly from the galactic core. The galactic orbit has an eccentrity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...

 of 0.156, and the star can travel as far as 444 ly away from the galactic plane
Galactic plane
The galactic plane is the plane in which the majority of a disk-shaped galaxy's mass lies. The directions perpendicular to the galactic plane point to the galactic poles...

. The closest stellar neighbor to Wolf 359 is the red dwarf star Ross 128
Ross 128
Ross 128 is a red dwarf star that is the eleventh closest star system to the Solar System, at a distance of 10.89 light years. It was first cataloged in 1926 by Frank Elmore Ross....

, 3.79 ly away. Approximately 13,850 years ago, Wolf 359 was at its minimal distance of about 7.35 ly from the Sun.

See also


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK