HD 188753
Encyclopedia
HD 188753 is a triple star system approximately 149 light-year
s away in the constellation
of Cygnus
(the Swan
). In 2005, an extrasolar planet
was announced to be orbiting the primary star (designated HD 188753 A) in the system. Follow-up measurements by an independent group in 2007 did not confirm the planet's existence.
star with an unsure spectral type. It is calculated that the star has a mass
greater than the Sun
's, a larger radius
, and a brighter luminosity
. Because of its temperature, scientists believe that the star is approximately 5.6 billion years old.
Orbiting the primary at a distance of 12.3 AU
are two stars orbiting each other. The distance is approximately midway between the Sun
-Saturn
and Sun
-Uranus
distance. The pair have a total mass of 1.63 solar masses, and orbit the primary with an eccentricity of 0.50 (an earlier estimate put the eccentricity at 0.26±0.07).
The secondary star HD 188753 B has a spectral class of K0 (orange dwarf
), and its companion, HD 188753 C, is an M2-type (red dwarf
). They orbit each other in 156 days, and the primary in 25.7 years.
astronomer working in the United States
, Dr. Maciej Konacki
. This planet was not the first known planet in a triple star system - for example, the planet 16 Cygni Bb
had been discovered earlier, orbiting one of the components of a wide triple system also in the constellation of Cygnus.
Since HD 188753 Ab was orbiting in a multi-star system, Konacki referred to planets of this type as "Tatooine planets" after Luke Skywalker
's home world
.
The detection of this planet has been challenged by Eggenberger et al.
The planet, a hot Jupiter
gas giant slightly more massive than Jupiter, was thought to orbit the star HD 188753 A once every 80 hours or so (3.3 days), at a distance of about 8 million kilometers, a twentieth of the distance between Earth and the Sun. The existence of HD 188753 Ab in a relatively close triple star system challenged the current models of planet formation. The current idea is that giant planets form in the outer reaches of their system (in orbits similar to those of Jupiter
and Saturn
). Once formed, some of these planets may migrate close to their stars, becoming hot Jupiters. The theoretical difficulty in understanding HD 188753 Ab is that any protoplanetary disk
would have ended around 1 astronomical unit
from the primary star (due to the presence of the secondary stars). A Jovian planet should not have been able to form so close to the primary, and with no disk material beyond 1 AU, a planet should not have been able to form beyond that distance to migrate inward. One of the possibilities suggested that the planet formed before the secondary stars had reached their current configuration. This suggests that the two secondary stars were once more distant than they are now.
An attempt to confirm the discovery failed. In 2007, a team at the Geneva Observatory stated that they had the precision and sampling rate sufficient to have detected the would-be planet, and that they did not detect it. Konacki responded to this, stating that the precision of the follow-up measurements was not sufficient to confirm or deny the planet's existence and that he planned to release an update in 2007. , no update appears to have been published.
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away 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....
of Cygnus
Cygnus (constellation)
Cygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...
(the Swan
Swan
Swans, genus Cygnus, are birds of the family Anatidae, which also includes geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini. Sometimes, they are considered a distinct subfamily, Cygninae...
). In 2005, an extrasolar planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
was announced to be orbiting the primary star (designated HD 188753 A) in the system. Follow-up measurements by an independent group in 2007 did not confirm the planet's existence.
Stellar components
The primary star, HD 188753 A, is a Solar twin, yellow dwarfYellow dwarf
A G-type main-sequence star , often called a yellow dwarf, is a main-sequence star of spectral type G and luminosity class V. Such a star has about 0.8 to 1.2 solar masses and surface temperature of between 5,300 and 6,000 K., Tables VII, VIII...
star with an unsure spectral type. It is calculated that the star has a mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
greater 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...
's, a larger radius
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
, and a brighter luminosity
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...
. Because of its temperature, scientists believe that the star is approximately 5.6 billion years old.
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
are two stars orbiting each other. The distance is approximately midway between 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...
-Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
and 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...
-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...
distance. The pair have a total mass of 1.63 solar masses, and orbit the primary with an eccentricity of 0.50 (an earlier estimate put the eccentricity at 0.26±0.07).
The secondary star HD 188753 B has a spectral class of K0 (orange dwarf
Orange dwarf
A K-type main-sequence star , also referred to orange dwarf, are main-sequence stars of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars and yellow G-type main-sequence stars...
), and its companion, HD 188753 C, is an M2-type (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....
). They orbit each other in 156 days, and the primary in 25.7 years.
Possible planet
In 2005 the discovery of a planet orbiting the primary star of the triple star system was announced. The planet, which received the designation HD 188753 Ab, was announced by a PolishPoland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
astronomer working in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, Dr. Maciej Konacki
Maciej Konacki
Dr. Maciej Konacki is a Polish astronomer, notable for his tentative discovery of HD 188753 Ab, a possible planet discovered in a three star system. The planet would be similar to Jupiter.- Education :...
. This planet was not the first known planet in a triple star system - for example, the planet 16 Cygni Bb
16 Cygni Bb
16 Cygni Bb or 16 Cyg Bb is an extrasolar planet approximately 70 light-years away in the constellation of Cygnus. The planet was discovered orbiting the sun-like star 16 Cygni B, one of two solar-mass components of the triple star system 16 Cygni...
had been discovered earlier, orbiting one of the components of a wide triple system also in the constellation of Cygnus.
Since HD 188753 Ab was orbiting in a multi-star system, Konacki referred to planets of this type as "Tatooine planets" after Luke Skywalker
Luke Skywalker
Luke Skywalker is a fictional character and the main protagonist of the original film trilogy of the Star Wars franchise, where he is portrayed by Mark Hamill. He is introduced in Star Wars Episode IV: A New Hope, in which he is forced to leave home, and finds himself apprenticed to the Jedi master...
's home world
Tatooine
Tatooine is a fictional planet and setting for many key scenes in the Star Wars saga, appearing in every Star Wars film except The Empire Strikes Back, although it is mentioned at the end of the movie...
.
The detection of this planet has been challenged by Eggenberger et al.
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
gas giant slightly more massive than Jupiter, was thought to orbit the star HD 188753 A once every 80 hours or so (3.3 days), at a distance of about 8 million kilometers, a twentieth of the distance between Earth and the Sun. The existence of HD 188753 Ab in a relatively close triple star system challenged the current models of planet formation. The current idea is that giant planets form in the outer reaches of their system (in orbits similar to those of 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,...
and Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
). Once formed, some of these planets may migrate close to their stars, becoming hot Jupiters. The theoretical difficulty in understanding HD 188753 Ab is that any protoplanetary disk
Protoplanetary disk
A protoplanetary disk is a rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star...
would have ended around 1 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
from the primary star (due to the presence of the secondary stars). A Jovian planet should not have been able to form so close to the primary, and with no disk material beyond 1 AU, a planet should not have been able to form beyond that distance to migrate inward. One of the possibilities suggested that the planet formed before the secondary stars had reached their current configuration. This suggests that the two secondary stars were once more distant than they are now.
An attempt to confirm the discovery failed. In 2007, a team at the Geneva Observatory stated that they had the precision and sampling rate sufficient to have detected the would-be planet, and that they did not detect it. Konacki responded to this, stating that the precision of the follow-up measurements was not sufficient to confirm or deny the planet's existence and that he planned to release an update in 2007. , no update appears to have been published.
External links
- HD 188753 A, B, and C. Extrasolar Visions. Retrieved on 2008-06-23.