Van Maanen's star
Encyclopedia
Van Maanen's star (van Maanen 2) is a white dwarf
star
. Out of the white dwarfs known, it is the third closest to the Sun, after Sirius B and Procyon B, in that order, and the closest known solitary white dwarf. Discovered in 1917 by Adriaan van Maanen
, Van Maanen's star was the third white dwarf identified, after 40 Eridani B and Sirius B, and the first that was not a member of a multi-star system.
star Lalande 1299, in 1917 Adriaan van Maanen discovered a star with an even larger proper motion located a few arcminutes to the northeast. He estimated the annual proper motion of the latter as 3 arcseconds. This star had been previously recorded on a plate taken November 11, 1896 for the Carte du Ciel
Catalog of Toulouse, and it showed an apparent magnitude of 12.3. The initial spectral classification was type F0.
In 1918, Frederick Seares
obtained a refined visual magnitude of 12.34, but the distance to the star remained unknown. Two years later, van Maanen published a parallax estimate of 0.246″, giving it an absolute magnitude of +14.8. This made it the faintest F-type star known at that time. In 1923, Willem Luyten published a study of stars with large proper motions in which he identified what he called "van Maanen's star" as one of only three known white dwarf
s, a term he coined. These are stars that have an unusually low absolute magnitude for their spectral class, lying well below the main sequence
.
The high mass density of white dwarfs was demonstrated in 1925 by Walter Adams when he measured the gravitational redshift
of Sirius B
as 21 km/s. In 1926, Ralph Fowler used the new theory of quantum mechanics
to show that these stars are supported by electron gas in a degenerate state
. Leon Mestel
demonstrated in 1952 that the energy emitted by a white dwarf is the surviving heat from a prior period of nuclear fusion
. He showed that nuclear burning no longer occurs within a white dwarf, and calculated the internal temperature of van Maanen's star as . He also gave a preliminary age estimate of 1011/A years, where A is the mean atomic weight
of the nuclei in the star.
, about 2° to the south of the star Delta Piscium
, and has a relatively high proper motion
of 2.98" annually. It is too faint to be seen with the naked eye
. Like other white dwarfs, it is a very dense star: its mass has been estimated to be about 70% of the Sun's
, and its radius is roughly 1% of the Sun's. It has a relatively cool temperature of approximately 6,220 K
. As white dwarfs cool with time, the star's temperature can be used to estimate its age, thought to be around 3 billion years.
The progenitor of this white dwarf had an estimated 2.6 solar mass
es and remained on the main sequence
for about . This gives the star a combined total age of about 4.1 billion years. When this star left the main sequence, it became a red giant
that had a maximum radius of 1,000 times the current radius of the Sun, or 50 astronomical unit
s. Any planets that were orbiting within this radius would have interacted directly with the star's extended envelope.
The stellar classification
of this white dwarf is DZ8,
where the DZ indicates the presence of elements heavier than helium in the spectrum. Indeed, this star is the prototype for white dwarfs of this class. Based upon physical models of white dwarfs, elements with mass greater than helium should sink below the photosphere
of the star, leaving only hydrogen and helium to be visible in the spectrum. Hence, for heavier elements to appear, there must have been an external source. It is unlikely that the heavy elements were obtained from the interstellar medium
. Instead, the surface of the star was likely polluted by circumstellar material, such as by the remains of a rocky, terrestrial planet
.
White dwarfs with a spectrum that indicates high levels of metal contamination often possess a circumstellar disk
. However, in the case of van Maanen's star, observations of the star at a wavelength of 24 μm
do not show the infrared
excess that might be generated by a dusty disk. Instead there is a noticeable deficit. The predicted flux at 24 μm is 0.23 mJy, whereas the measured value is . This deficit may be explained by collision-induced absorption in the atmosphere of the star. However, this is normally only known to happen with white dwarfs with temperatures below 4,000 K, due to collisions between hydrogen molecules or between hydrogen molecules and helium.
In the galactic coordinate system
, this star is moving with space velocity components of = , for a net velocity of relative to the Sun. The star made its closest approach to the Sun about 34,300 years ago at a distance of 10.85 ly.
companion remains uncertain. As recently as 2004, there was one paper confirming and one denying its detection. As of 2008, observations with the Spitzer Space Telescope
appear to rule out any companions within 1,200 AU
of the star that have four jupiter mass
es or greater.
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...
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...
. Out of the white dwarfs known, it is the third closest to the Sun, after Sirius B and Procyon B, in that order, and the closest known solitary white dwarf. Discovered in 1917 by Adriaan van Maanen
Adriaan Van Maanen
Adriaan van Maanen was a Dutch–American astronomer.Van Maanen, born into a well-to-do family in Friesland, studied astronomy at the University of Utrecht and worked briefly at the University of Groningen...
, Van Maanen's star was the third white dwarf identified, after 40 Eridani B and Sirius B, and the first that was not a member of a multi-star system.
Observation history
While searching for a companion to the large proper motionProper 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...
star Lalande 1299, in 1917 Adriaan van Maanen discovered a star with an even larger proper motion located a few arcminutes to the northeast. He estimated the annual proper motion of the latter as 3 arcseconds. This star had been previously recorded on a plate taken November 11, 1896 for the Carte du Ciel
Carte du Ciel
The Carte du Ciel and the Astrographic Catalogue were two distinct but connected components of a massive international astronomical project, initiated in the late 19th century, to catalogue and map the positions of millions of stars as faint as 11th or 12th magnitude...
Catalog of Toulouse, and it showed an apparent magnitude of 12.3. The initial spectral classification was type F0.
In 1918, Frederick Seares
Frederick Hanley Seares
Frederick Hanley Seares, May 17, 1873–July 20, 1964 , was an American astronomer. He worked at Mount Wilson Observatory and won the Bruce Medal in 1940....
obtained a refined visual magnitude of 12.34, but the distance to the star remained unknown. Two years later, van Maanen published a parallax estimate of 0.246″, giving it an absolute magnitude of +14.8. This made it the faintest F-type star known at that time. In 1923, Willem Luyten published a study of stars with large proper motions in which he identified what he called "van Maanen's star" as one of only three known 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...
s, a term he coined. These are stars that have an unusually low absolute magnitude for their spectral class, lying well below 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...
.
The high mass density of white dwarfs was demonstrated in 1925 by Walter Adams when he measured the gravitational redshift
Gravitational redshift
In astrophysics, gravitational redshift or Einstein shift describes light or other forms of electromagnetic radiation of certain wavelengths that originate from a source that is in a region of a stronger gravitational field that appear to be of longer wavelength, or redshifted, when seen or...
of Sirius B
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 21 km/s. In 1926, Ralph Fowler used the new theory of quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
to show that these stars are supported by electron gas in a degenerate state
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...
. Leon Mestel
Leon Mestel
Leon Mestel is a British astronomer and astrophysicist and Emeritus Professor at the University of Sussex. His research interests are in the areas of star formation and structure, especially stellar magnetism and astrophysical magnetohydrodynamics. He has won both the Eddington Medal and the Gold...
demonstrated in 1952 that the energy emitted by a white dwarf is the surviving heat from a prior period of nuclear fusion
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...
. He showed that nuclear burning no longer occurs within a white dwarf, and calculated the internal temperature of van Maanen's star as . He also gave a preliminary age estimate of 1011/A years, where A is the mean atomic weight
Atomic weight
Atomic weight is a dimensionless physical quantity, the ratio of the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12...
of the nuclei in the star.
Characteristics
Van Maanen's star is located 14.1 light years from the Sun in the constellation PiscesPisces (constellation)
Pisces is a constellation of the zodiac. Its name is the Latin plural for fish, and its symbol is . It lies between Aquarius to the west and Aries to the east...
, about 2° to the south of the star Delta Piscium
Delta Piscium
Delta Piscium is a binary star in the constellation Pisces.-In fiction:Linteum is the most notable star the moon will be closest to on the solstice of December 21, 2012. Some works of fiction mention Linteum combining myths about the Maya calendar and Revelation 13:5...
, and has a relatively 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...
of 2.98" annually. It is too faint to be seen with the naked eye
Naked eye
The naked eye is a figure of speech referring to human visual perception unaided by a magnifying or light-collecting optical device, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is considered "naked"...
. Like other white dwarfs, it is a very dense star: its mass has been estimated to be about 70% of the Sun's
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
, and its radius is roughly 1% of the Sun's. It has a relatively cool temperature of approximately 6,220 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...
. As white dwarfs cool with time, the star's temperature can be used to estimate its age, thought to be around 3 billion years.
The progenitor of this white dwarf had an estimated 2.6 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 and remained 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...
for about . This gives the star a combined total age of about 4.1 billion years. When this star left the main sequence, it became a red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
that had a maximum radius of 1,000 times the current radius of the Sun, or 50 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s. Any planets that were orbiting within this radius would have interacted directly with the star's extended envelope.
The 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 this white dwarf is DZ8,
where the DZ indicates the presence of elements heavier than helium in the spectrum. Indeed, this star is the prototype for white dwarfs of this class. Based upon physical models of white dwarfs, elements with mass greater than helium should sink below 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...
of the star, leaving only hydrogen and helium to be visible in the spectrum. Hence, for heavier elements to appear, there must have been an external source. It is unlikely that the heavy elements were obtained from the interstellar medium
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
. Instead, the surface of the star was likely polluted by circumstellar material, such as by the remains of a rocky, terrestrial planet
Terrestrial planet
A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun...
.
White dwarfs with a spectrum that indicates high levels of metal contamination often possess a circumstellar disk
Circumstellar disk
A circumstellar disk is a torus, pancake or ring-shaped accumulation of matter composed of gas, dust, planetesimals, asteroids or collision fragments in orbit around a star. Around the youngest stars, they are the reservoirs of material out of which planets may form...
. However, in the case of van Maanen's star, observations of the star at a wavelength of 24 μm
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
do not show 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...
excess that might be generated by a dusty disk. Instead there is a noticeable deficit. The predicted flux at 24 μm is 0.23 mJy, whereas the measured value is . This deficit may be explained by collision-induced absorption in the atmosphere of the star. However, this is normally only known to happen with white dwarfs with temperatures below 4,000 K, due to collisions between hydrogen molecules or between hydrogen molecules and helium.
In 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 star is moving with space velocity components of = , for a net velocity of relative to the Sun. The star made its closest approach to the Sun about 34,300 years ago at a distance of 10.85 ly.
Possible companion
The possible existence of a substellarBrown 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...
companion remains uncertain. As recently as 2004, there was one paper confirming and one denying its detection. As of 2008, observations with the Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
appear to rule out any companions within 1,200 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
of the star that have four jupiter mass
Jupiter mass
Jupiter mass , is the unit of mass equal to the total mass of the planet Jupiter . Jupiter mass is used to describe masses of the gas giants, such as the outer planets and extrasolar planets. It is also used in describing brown dwarfs....
es or greater.
See also
- List of nearest stars
- List of stars named after people
- Van Maanen's star in fiction