Upsilon Andromedae
Encyclopedia
Upsilon Andromedae (υ Andromedae, υ And) is a binary star
located approximately 44 light-year
s away from Earth in the constellation
Andromeda
. The primary star
(Upsilon Andromedae A) is a yellow-white dwarf
star that is somewhat younger than the Sun
. The second star in the system (Upsilon Andromedae B) is a red dwarf
located in a wide orbit.
As of 2010, four confirmed extrasolar planets are known in orbit
around the primary star. All four are likely to be jovian planets that are comparable to Jupiter
. Upsilon Andromedae was both the first multiple-planet planetary system
to be discovered around a main sequence
star, and the first multiple-planet system known in a multiple star
system. Upsilon Andromedae A was ranked 21st in the list of top 100 target stars for the NASA
Terrestrial Planet Finder
mission, which has, however, been reported to have been cancelled as of 2011.
: the parallax
of Upsilon Andromedae A was measured by the Hipparcos
astrometry
satellite
as 74.12 milliarcseconds, corresponding to a distance of 13.49 parsec
s (44 light years). Upsilon Andromedae A has an apparent magnitude
of +4.09, making it visible to the naked eye
even under moderately light-polluted skies, about 10 degree
s east of the Andromeda Galaxy
. The dimmer star Upsilon Andromedae B is only visible with a telescope
.
F8V, similar to the Sun, but younger, more massive, and more luminous
. According to its entry in the Geneva-Copenhagen survey, the star is around 3.1 billion years old, and has a similar proportion of iron
relative to hydrogen
to the Sun. At around 1.3 solar mass
es, it will have a shorter lifetime than the Sun. The amount of ultraviolet
radiation received by any planets in the star's habitable zone
would be similar to the ultraviolet flux
the Earth receives from the Sun.
Upsilon Andromedae B is a red dwarf of spectral type M4.5V located at a distance (in the plane of the sky) of 750 AU
from the primary star. The true separation between the two stars is unknown because the displacement along the line of sight
between us and the Upsilon Andromedae stars is unknown, so this value is a minimum separation. It was discovered in 2002 in data collected as part of the Two Micron All Sky Survey
. The star is less massive and far less luminous than the Sun.
The Washington Double Star Catalog
lists two optical
components; however, these do not share the system's proper motion
and only appear close to Upsilon Andromedae because they happen to lie near the same line of sight.
and the innermost planet of 55 Cancri
. The discovery was made by Geoffrey Marcy
and R. Paul Butler
, both astronomer
s at San Francisco State University
. The planet, designated Upsilon Andromedae b
, was discovered by measuring changes in the star's radial velocity
induced by the planet's gravity. Because of its closeness to the parent star, it induced a large wobble which was detected relatively easily. The planet appears to be responsible for enhanced activity in the chromosphere
of its star.
Even when this planet was taken into account, there still remained significant residuals in the radial velocity measurements, and it was suggested there might be a second planet in orbit. In 1999, astronomers at both San Francisco State University
and the Harvard-Smithsonian Center for Astrophysics
independently concluded that a three-planet model best fit the data. The two outer planets were designated Upsilon Andromedae c
and Upsilon Andromedae d
in order of increasing distance from the star. Both of the two outer planets are in more eccentric
orbits than any of the planets in the Solar System (including Pluto
). The outermost planet resides in the system's habitable zone
.
The system is not coplanar. The mutual inclination between c and d is 35 degrees. In 2001, preliminary astrometric measurements suggested the orbit of the outermost planet is inclined
at 155.5° to the plane of the sky. However, subsequent investigation of the data reduction techniques used suggests that the Hipparcos measurements are not precise enough to adequately characterize the orbits of substellar companions. Astrometry of the innermost planet, meanwhile, constrained its inclination to 30-90 degrees. Full publication is expected in 2008. The orbit of Upsilon Andromedae c gradually oscillates between circular and eccentric states every 6,700 years. The existence of further planets too small or distant to detect has not been ruled out, though the presence of Jupiter-mass planets as close as 5 AU from Upsilon Andromedae A would make the system unstable.
Some simulations show that the eccentricity of the system's planets may have arisen from a close encounter between the outer planet and a fourth planet, with the result that the fourth planet was ejected from the system or destroyed. If so, the rogue planet would have had to eject immediately; it is unclear how likely this situation might be. Other models are possible. However, a fourth planet (Upsilon Andromedae e
) was discovered in 2010. This planet is in a 3:1 resonance with Upsilon Andromedae d.
Upsilon Andromedae does not appear to have a circumstellar dust disk similar to the Kuiper belt
in the Solar System. This may be the result of perturbations from the companion star removing material from the outer regions of the Upsilon Andromedae A system.
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...
located approximately 44 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away from 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....
Andromeda
Andromeda (constellation)
Andromeda is a constellation in the northern sky. It is named after Andromeda, the princess in the Greek legend of Perseus who was chained to a rock to be eaten by the sea monster Cetus...
. The primary 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...
(Upsilon Andromedae A) is a yellow-white dwarf
Yellow-white dwarf
An F-type main-sequence star is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K., Tables VII and VIII. This temperature range gives the F-type stars a...
star that is somewhat younger 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...
. The second star in the system (Upsilon Andromedae B) 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....
located in a wide orbit.
As of 2010, four confirmed extrasolar planets are known in orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
around the primary star. All four are likely to be jovian planets that are comparable to 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,...
. Upsilon Andromedae was both the first multiple-planet planetary system
Planetary system
A planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...
to be discovered around a 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, and the first multiple-planet system known in a multiple star
Multiple star
A multiple star consists of three or more stars which appear from the Earth to be close to one another in the sky. This may result from the stars being physically close and gravitationally bound to each other, in which case it is physical, or this closeness may be merely apparent, in which case...
system. Upsilon Andromedae A was ranked 21st in the list of top 100 target stars for 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...
Terrestrial Planet Finder
Terrestrial Planet Finder
The Terrestrial Planet Finder was a proposed project by NASA to construct a system of telescopes for detecting extrasolar terrestrial planets. TPF was postponed several times and finally cancelled...
mission, which has, however, been reported to have been cancelled as of 2011.
Distance and visibility
Upsilon Andromedae is located fairly close to the Solar SystemSolar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
: the 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"...
of Upsilon Andromedae A was measured by the Hipparcos
Hipparcos
Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
astrometry
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...
satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
as 74.12 milliarcseconds, corresponding to a distance of 13.49 parsec
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
s (44 light years). Upsilon Andromedae A 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 +4.09, making it visible to 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"...
even under moderately light-polluted skies, about 10 degree
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
s east of the Andromeda Galaxy
Andromeda Galaxy
The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years from Earth in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the...
. The dimmer star Upsilon Andromedae B is only visible with a 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...
.
System components
Upsilon Andromedae A is a yellow-white dwarf of spectral typeStellar 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...
F8V, similar to the Sun, but younger, more massive, and more luminous
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
. According to its entry in the Geneva-Copenhagen survey, the star is around 3.1 billion years old, and has a similar proportion of 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...
relative to 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...
to the Sun. At around 1.3 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, it will have a shorter lifetime than the Sun. The amount of 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...
radiation received by any planets in the star's habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...
would be similar to the ultraviolet flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...
the Earth receives from the Sun.
Upsilon Andromedae B is a red dwarf of spectral type M4.5V located at a distance (in the plane of the sky) of 750 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
from the primary star. The true separation between the two stars is unknown because the displacement along the line of sight
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
between us and the Upsilon Andromedae stars is unknown, so this value is a minimum separation. It was discovered in 2002 in data collected as part of the Two Micron All Sky Survey
2MASS
Observations for the Two Micron All-Sky Survey began in 1997 and were completed in 2001 at two telescopes located one each in the northern and southern hemispheres to ensure coverage of the entire sky...
. The star is less massive and far less luminous than the Sun.
The Washington Double Star Catalog
Washington Double Star Catalog
The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for 102,387 pairs of double stars. The catalog also includes multiple stars...
lists two optical
Double star
In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...
components; however, these do not share the system's 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...
and only appear close to Upsilon Andromedae because they happen to lie near the same line of sight.
Planetary system
The innermost planet of the Upsilon Andromedae system was discovered in 1996 and announced in January 1997, together with the planet of Tau BoötisTau Boötis
Tau Boötis is a yellow-white dwarf approximately 51 light-years away in the constellation of Boötes. The system is also a binary star system, with the secondary star being a red dwarf...
and the innermost planet of 55 Cancri
55 Cancri
55 Cancri , also cataloged Rho1 Cancri or abbreviated 55 Cnc, is a binary star approximately 41 light-years away from Earth in the constellation of Cancer...
. The discovery was made by Geoffrey Marcy
Geoffrey Marcy
Geoffrey W. Marcy is an American astronomer, who is currently Professor of Astronomy at the University of California, Berkeley, famous for discovering more extrasolar planets than anyone else, 70 out of the first 100 to be discovered, along with R...
and R. Paul Butler
R. Paul Butler
R. Paul Butler is an astronomer who searches for extrasolar planets.He received a BA and an MS from San Francisco State University, completing a Master's thesis with Geoffrey Marcy, and then completed his doctoral studies at the University of Maryland, College Park in 1993...
, both 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...
s at San Francisco State University
San Francisco State University
San Francisco State University is a public university located in San Francisco, California. As part of the 23-campus California State University system, the university offers over 100 areas of study from nine academic colleges...
. The planet, designated Upsilon Andromedae b
Upsilon Andromedae b
Upsilon Andromedae b, occasionally referred to as Upsilon Andromedae Ab , is an extrasolar planet approximately 44 light-years away from Earth in the constellation of Andromeda . The planet was discovered orbiting the Solar twin star, Upsilon Andromedae, approximately every five days...
, was discovered by measuring changes in the star's 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...
induced by the planet's gravity. Because of its closeness to the parent star, it induced a large wobble which was detected relatively easily. The planet appears to be responsible for enhanced activity in the chromosphere
Chromosphere
The chromosphere is a thin layer of the Sun's atmosphere just above the photosphere, roughly 2,000 kilometers deep....
of its star.
San Francisco State University
San Francisco State University is a public university located in San Francisco, California. As part of the 23-campus California State University system, the university offers over 100 areas of study from nine academic colleges...
and the Harvard-Smithsonian Center for Astrophysics
Harvard-Smithsonian Center for Astrophysics
The Harvard–Smithsonian Center for Astrophysics is one of the largest and most diverse astrophysical institutions in the world, where scientists carry out a broad program of research in astronomy, astrophysics, earth and space sciences, and science education...
independently concluded that a three-planet model best fit the data. The two outer planets were designated Upsilon Andromedae c
Upsilon Andromedae c
Upsilon Andromedae c is an extrasolar planet or star orbiting the Sun-like star Upsilon Andromedae A every 241.2 days. Its discovery in April 1999 by Geoffrey Marcy and R. Paul Butler made Upsilon Andromedae the first known star to host a multiple-planet planetary system...
and Upsilon Andromedae d
Upsilon Andromedae d
Upsilon Andromedae d is an extrasolar planet orbiting the Sun-like star Upsilon Andromedae A. Its discovery in April 1999 by Geoffrey Marcy and R. Paul Butler made Upsilon Andromedae the first star to be known to host a multiple-planet planetary system...
in order of increasing distance from the star. Both of the two outer planets are in more eccentric
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...
orbits than any of the planets in the Solar System (including Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
). The outermost planet resides in the system's habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...
.
The system is not coplanar. The mutual inclination between c and d is 35 degrees. In 2001, preliminary astrometric measurements suggested the orbit of the outermost planet is inclined
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
at 155.5° to the plane of the sky. However, subsequent investigation of the data reduction techniques used suggests that the Hipparcos measurements are not precise enough to adequately characterize the orbits of substellar companions. Astrometry of the innermost planet, meanwhile, constrained its inclination to 30-90 degrees. Full publication is expected in 2008. The orbit of Upsilon Andromedae c gradually oscillates between circular and eccentric states every 6,700 years. The existence of further planets too small or distant to detect has not been ruled out, though the presence of Jupiter-mass planets as close as 5 AU from Upsilon Andromedae A would make the system unstable.
Some simulations show that the eccentricity of the system's planets may have arisen from a close encounter between the outer planet and a fourth planet, with the result that the fourth planet was ejected from the system or destroyed. If so, the rogue planet would have had to eject immediately; it is unclear how likely this situation might be. Other models are possible. However, a fourth planet (Upsilon Andromedae e
Upsilon Andromedae e
Upsilon Andromedae e is the outermost extrasolar planet orbiting the star Upsilon Andromedae in the constellation of Andromeda. This planet is more Jupiter-like than any other known exoplanet.-Discovery:...
) was discovered in 2010. This planet is in a 3:1 resonance with Upsilon Andromedae d.
Upsilon Andromedae does not appear to have a circumstellar dust disk similar to the Kuiper belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
in the Solar System. This may be the result of perturbations from the companion star removing material from the outer regions of the Upsilon Andromedae A system.
See also
- 51 Pegasi51 Pegasi51 Pegasi is a Sun-like star located 15.6 parsecs from Earth in the constellation Pegasus...
- Binary starBinary starA 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...
- List of extrasolar planets
- PSR 1257+12
- Solar analogSolar analogSolar-type, solar analog, and solar twin stars are those stars that are particularly similar to the Sun. The classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type...
External links
- HR 0458
- CCDM 01367+4125
- Hypothetic object ups And e
- Extrasolar Planet Interactions by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona
- Sky map