Procyon

Procyon

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Procyon is the brightest 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...

 in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Canis Minor
Canis Minor
Canis Minor is a small constellation. It was included in the 2nd century astronomer Ptolemy's 48 constellations, and is still included among the 88 modern constellations...

. To the naked eye, it appears to be a single star, the seventh brightest in the night sky with a visual 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 0.34. It is actually a binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...

 system, consisting of a white 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...

 star of spectral type F5 IV-V, named Procyon A, and a faint white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...

 companion of spectral type DA, named Procyon B. The reason for its brightness is not its intrinsic luminosity but its closeness to 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...

; at a distance of 3.51 pc
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....

 or 11.46 light years, Procyon is one of our near neighbours. Its closest neighbour is Luyten's Star
Luyten's Star
Luyten's Star is a red dwarf star in the constellation Canis Minor. It is located at a distance of around 12.36 light-years and has a visual magnitude of 9.9, making it too faint to be viewed with the unaided eye. It is named after Willem Jacob Luyten, who first determined its proper motion.This...

, 0.34 pc or 1.11 ly away.

Procyon forms one of the three vertices
Vertex (geometry)
In geometry, a vertex is a special kind of point that describes the corners or intersections of geometric shapes.-Of an angle:...

 of the Winter Triangle, along with Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...

 and Betelgeuse
Betelgeuse
Betelgeuse, also known by its Bayer designation Alpha Orionis , is the eighth brightest star in the night sky and second brightest star in the constellation of Orion, outshining its neighbour Rigel only rarely...

.

System


Procyon A 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 F5IV-V. The effective surface temperature
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...

 of the star is an estimated 6,530 K, giving it a white hue. It is 1.4 times the mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...

, twice the radius, and 6.9 times more luminous than 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...

. Procyon A is bright for its spectral class, suggesting that it is a subgiant that has nearly fused
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

 its core 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...

 into helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

, after which it will expand as "burning" moves outside the core. As it continues to expand, the star will eventually swell to about 80 to 150 times its current diameter and become a red or orange color. This will probably happen within 10 to 100 million years.

Like Sirius B, Procyon's companion is a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...

 that was inferred from astrometric
Astrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...

 data long before it was observed. Its existence had been postulated by Friedrich Bessel
Friedrich Bessel
-References:* John Frederick William Herschel, A brief notice of the life, researches, and discoveries of Friedrich Wilhelm Bessel, London: Barclay, 1847 -External links:...

 as early as 1844, and although its orbital elements had been calculated by Arthur Auwers
Arthur Auwers
Georg Friedrich Julius Arthur von Auwers was a German astronomer.Auwers was born in Göttingen, attended the University of Göttingen and worked at the University of Königsberg. He specialized in astrometry, making very precise measurements of stellar positions and motions...

 in 1862 as part of his thesis, Procyon B was not visually confirmed until 1896 when John Martin Schaeberle
John Martin Schaeberle
John Martin Schaeberle was a German-American astronomer.-Biography:...

 observed it at the predicted position using the 36-inch refractor at Lick Observatory
Lick Observatory
The Lick Observatory is an astronomical observatory, owned and operated by the University of California. It is situated on the summit of Mount Hamilton, in the Diablo Range just east of San Jose, California, USA...

. It is more difficult to observe from Earth than Sirius B, due to a greater 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...

 difference and smaller angular separation from its primary. The average separation of the two components is 15.0 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

s, a little less than the distance between Uranus
Uranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...

 and the Sun, though the eccentric orbit carries them as close as 8.9 AUs and as far as 21.0 AU.

At 0.6 solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...

es, Procyon B is considerably less massive than Sirius B; however, the peculiarities of degenerate matter
Degenerate matter
Degenerate matter is matter that has such extraordinarily high density that the dominant contribution to its pressure is attributable to the Pauli exclusion principle. The pressure maintained by a body of degenerate matter is called the degeneracy pressure, and arises because the Pauli principle...

 ensure that it is larger than its more famous neighbor, with an estimated radius of 8,600 km, versus 5,800 km for Sirius B. With a surface temperature of 7,740 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...

, it is also much cooler than Sirius B; this is a testament to its lesser mass and greater age. The mass of the progenitor star for Procyon B was about 2.5 solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...

es and it came to the end of its life some ago, after a main sequence lifetime of 400–600 Myr. For this reason, the age of Procyon A is expected to be at least 2 Gyr.

Oscillations controversy


In late June 2004, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

's orbital MOST satellite telescope carried out a 32-day survey of Procyon A. The continuous optical monitoring was intended to confirm solar-like oscillations
Solar-like oscillations
The term solar-like oscillations refers to oscillations in other stars that are excited in the same way as those in the Sun, namely by convection in its outer layers.-See also:* asteroseismology* helioseismology* variable stars* Procyon...

 in its brightness observed from Earth and to permit asteroseismology
Asteroseismology
Asteroseismology also known as stellar seismology is the science that studies the internal structure of pulsating stars by the interpretation of their frequency spectra. Different oscillation modes penetrate to different depths inside the star...

. No oscillations were detected and the authors concluded that the theory of stellar oscillations may need to be reconsidered. However, others argued that the non-detection was consistent with published ground-based radial velocity
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...

 observations of solar-like oscillations
Solar-like oscillations
The term solar-like oscillations refers to oscillations in other stars that are excited in the same way as those in the Sun, namely by convection in its outer layers.-See also:* asteroseismology* helioseismology* variable stars* Procyon...

.

Photometric
Photometry (astronomy)
Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical object's electromagnetic radiation...

 measurements from the NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 Wide Field Infrared Explorer
Wide Field Infrared Explorer
The Wide Field Infrared Explorer was a satellite launched on 5 March 1999 on the Pegasus XL rocket into a polar orbit between 409 km and 426 km above the Earth's surface...

 (WIRE) satellite from 1999 and 2000 showed evidence of granulation (convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

 near the surface of the 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...

) and solar-like oscillations
Solar-like oscillations
The term solar-like oscillations refers to oscillations in other stars that are excited in the same way as those in the Sun, namely by convection in its outer layers.-See also:* asteroseismology* helioseismology* variable stars* Procyon...

. Unlike the MOST result, the variation seen in the WIRE photometry was in agreement with radial velocity
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...

 measurements from the ground.

Life


Life is unlikely around Procyon, because the habitable zone around 2.7 AU from the primary may not contain stable orbits, due to the white dwarf companion with a periastron of 8.9 AU. Also the white dwarf companion to Procyon would have stressed life severely during its red-giant phase. Procyon emits more of its light in the ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 spectrum, which may be damaging to life. Still, life cannot be ruled out for other stars of the spectral type of Procyon but such life would have a relatively short time to evolve and would face heavy bombardment from comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

s and meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

s as happened in the first few million years of the Earth’s
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...

 existence. Shortly after the phase of heavy bombardment has ended for a planet orbiting a star like Procyon the star is likely to leave 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...

 preventing further development of life.

X-ray source


Attempts to detect X-ray emission from Procyon with nonimaging, soft X-ray sensitive detectors prior to 1975 failed. Extensive observations of Procyon were carried out with the Copernicus and TD-1A
TD-1A
TD-1A, or Thor-Delta 1A, was a European astrophysical research satellite which was launched in 1972. Operated by the European Space Research Organisation, TD-1A made astronomical surveys primarily in the ultraviolet, but also using x-ray and gamma ray detectors.-Spacecraft:TD-1A was named after the...

 satellites in the late 1970s. The X-ray source associated with Procyon A/B was observed on April 1, 1979, with the Einstein Observatory
Einstein Observatory
Einstein Observatory was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories...

 high-resolution imager (HRI). The HRI X-ray pointlike source location is ~4" south of Procyon A, on the edge of the 90% confidence error circle, indicating identification with Procyon A rather than Procyon B which was located about 5" north of Procyon A (about 9" from the X-ray source location).

Etymology and cultural significance


Its name comes from the Greek προκύον (prokyon), meaning "before the dog", since it precedes the "Dog Star" Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...

 as it travels across the sky due to 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...

's rotation. (Although Procyon has a greater right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...

, it also has a more northerly declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...

, which means it will rise above the horizon
Horizon
The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...

 earlier than Sirius from most northerly latitudes.) In Greek mythology, Procyon is associated with Maera
Maera (hound)
In Greek mythology, Maera was the hound of Erigone, daughter of Icarius of Athens. Icarius was a follower of the wine god Dionysus and had been taught how to make wine. While travelling, Icarius met some shepherds, who killed him. Erigone was worried about her father, and set off with Maera to find...

, a hound belonging to Erigone
Erigone (daughter of Icarius)
In Greek mythology, Erigone was the daughter of Icarius of Athens. Icarius was from Athens. He was cordial towards Dionysus, who gave his shepherds wine. They became intoxicated and killed Icarius, thinking he had poisoned them. His daughter, Erigone, and her dog, Maera, found his body. Erigone...

, daughter of Icarius of Athens. These two dog stars are referred to in the most ancient literature and were venerated by the Babylon
Babylon
Babylon was an Akkadian city-state of ancient Mesopotamia, the remains of which are found in present-day Al Hillah, Babil Province, Iraq, about 85 kilometers south of Baghdad...

ians and the Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

ians.

Rarer names are the Latin translation of Procyon, Antecanis, and the Arabic-derived names Al Shira and Elgomaisa. The first derives from الشعرى الشامية aš-ši‘ra aš-šamiyah "the Syrian sign" (the other sign being Sirius; "Syria" is supposedly a reference to its northern location relative to Sirius); the second from الغميصاء al-ghumaisa’ "the bleary-eyed (woman)", in contrast to العبور "the teary-eyed (woman)", which is Sirius. (See Gomeisa.) The modern Arabic name for Procyon is غموص ghumūṣ. It is known as 南河三 (Mandarin nánhésān, the Third Star in the Southern River) in Chinese.

Procyon appears on the flag of Brazil
Flag of Brazil
The national flag of Brazil is a blue disc depicting a starry sky spanned by a curved band inscribed with the national motto, within a yellow rhombus, on a green field. Brazil officially adopted this design for its national flag on November 19, 1889, replacing the flag of the second Empire of Brazil...

, symbolising the state of Amazonas.

See also