HD 154672 b
Encyclopedia
HD 154672 b is an extrasolar planet
located approximately 215 light-year
s away in the constellation
of Ara
, orbiting the metal-rich and aged star
HD 154672
. This planet has a minimum mass
five times that of Jupiter
and orbits at about 60% the distance between the Earth
to the Sun
. Its orbit is very elliptical, which causes temperatures on the planet to vary significantly as it proceeds along its orbit. This planet was discovered in Las Campanas Observatory
on September 5, 2008 using the radial velocity
method (Doppler spectroscopy
). Along with HD 205739 b
, the planets were the first to be discovered by the N2K Consortium
using the Magellan Telescopes
.
Astronomers hoped to implement a survey called the N2K Consortium
, a collaboration which uses Doppler spectroscopy
to find radial velocity
measurements of stars that hadn't been previously surveyed. The project searched particularly for gas giants with short orbits
around metal-rich stars to find how the metallicity
of the star and the mass of the planet are related.
Radial velocity observations had been taken by the N2K program using the Magellan Telescopes
' Magellan Inamori Kyocera Echelle spectrograph (MIKE) at Las Campanas Observatory
in Chile since 2004. Based on these observations, the stars HD 154672 and HD 205739
were among those flagged as potential planetary host stars. The two stars were identified originally as having short-orbit hot Jupiter
planets, but 3.5 years of additional observations revealed that the planetary candidates' orbits were far longer than initially anticipated. HD 154672 b's discovery was reported in the Astronomical Journal
by the American Astronomical Society
, appearing in the journal on October 7, 2008 alongside the planet HD 205739 b
. The two planets were the first to be discovered by the N2K program that worked out of the Magellan telescopes.
HD 154672 b was later observed by a different team of astronomers investigating the role of metallicity
, or the amount of metal present in a star, in the formation of planets. Six radial velocity measurements of the host star, collected using the HARPS
instrument at Chile's La Silla Observatory
. The team used the radial velocity data to refine the parameters of HD 154672 b from what was published in its discovery paper a year earlier.
that is 1.06 times that of the Sun, and a radius 1.27 times the solar radius. The effective temperature
, or the temperature it would emit if it were a black body
, is 5714 K, slightly cooler than that of the Sun. However, with an [Fe/H] = 0.26 and an age of 9.28 billion years, HD 154672 has 182% more iron than the Sun, and is over two times older than the Sun. Based on its spectrum, HD 154672 is not a very active star.
The apparent magnitude
(v) of HD 154672 is 8.22, which means that it is not visible to the naked eye
. It is slightly dimmer than Neptune
, which has an apparent magnitude of 7.78 at its brightest.
every 163.91 days. Earth, in comparison, orbits the Sun at a distance of 1 AU every 365.25 days. However, HD 154672 b has an orbital eccentricity
of 0.61, which indicates a very elliptical orbit. Because HD 154672 b has such an eccentric orbit, the equilibrium temperature of the planet varies between 300 K and 600 K, which is significantly higher than that of Jupiter (124 K). If liquid water is present in the atmosphere of HD 154672 b, it could possibly convert between gaseous and liquid phases as the planet moves along its orbit.
The high eccentricity of the planet's orbit suggests that either the Kozai mechanism
(there is an exchange between the inclination of a planet and its eccentricity) is at work, or that the planet's orbit was distorted by the unstable orbit of other planets that used to be part of the HD 154672 system.
HD 154672 b had, at the time of its 2008 discovery, an orbital period larger than 90% of all discovered planets. It was the seventh planet known to have an eccentricity over 0.6 and an orbit shorter than 300 days.
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...
located approximately 215 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 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 Ara
Ara (constellation)
Ara is a southern constellation situated between Scorpius and Triangulum Australe. Its name is Latin for "altar". Ara was one of the 48 Greek constellations described by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations defined by the International Astronomical...
, orbiting the metal-rich and aged 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...
HD 154672
HD 154672
HD 154672 is a yellow subgiant . It is about 65 parsecs away from the Sun that is larger than, but of a similar mass to, the Sun. However, HD 154672 is much older...
. This planet has a minimum mass
Minimum mass
In astronomy, minimum mass is the lower-bound calculated mass of observed objects such as planets, stars and binary systems, nebulae, and black holes. Minimum mass is a widely cited statistic for extrasolar planets...
five times that 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 orbits at about 60% the distance between 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...
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...
. Its orbit is very elliptical, which causes temperatures on the planet to vary significantly as it proceeds along its orbit. This planet was discovered in Las Campanas Observatory
Las Campanas Observatory
Las Campanas Observatory is an astronomical observatory owned and operated by the Carnegie Institution for Science It was established in 1969 and remains the primary observing site of that institution. The headquarters is located in La Serena, Chile and the observatory is in the southern Atacama...
on September 5, 2008 using the 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...
method (Doppler spectroscopy
Doppler spectroscopy
Doppler spectroscopy, also known as radial velocity measurement, is a spectroscopic method for finding extrasolar planets. It involves the observation of Doppler shifts in the spectrum of the star around which the planet orbits....
). Along with HD 205739 b
HD 205739 b
HD 205739 b is an extrasolar planet located approximately 295 light-years away in the constellation of Piscis Austrinus, orbiting the star HD 205739. This planet has a minimum mass 37% more than Jupiter and orbits 90% of the distance between the Earth and the Sun...
, the planets were the first to be discovered by the N2K Consortium
N2K Consortium
The N2K Consortium is a collaborative multinational effort by American, Chilean and Japanese astronomers to find additional extrasolar planets around stars that are...
using the Magellan Telescopes
Magellan telescopes
The Magellan Telescopes are a pair of 6.5 m diameter optical telescopes located at Las Campanas Observatory in Chile. The two telescopes are named after the astronomer Walter Baade and the philanthropist Landon T...
.
Discovery
N2K Consortium
The N2K Consortium is a collaborative multinational effort by American, Chilean and Japanese astronomers to find additional extrasolar planets around stars that are...
, a collaboration which uses Doppler spectroscopy
Doppler spectroscopy
Doppler spectroscopy, also known as radial velocity measurement, is a spectroscopic method for finding extrasolar planets. It involves the observation of Doppler shifts in the spectrum of the star around which the planet orbits....
to find 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 of stars that hadn't been previously surveyed. The project searched particularly for gas giants with short orbits
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
around metal-rich stars to find how the metallicity
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...
of the star and the mass of the planet are related.
Radial velocity observations had been taken by the N2K program using the Magellan Telescopes
Magellan telescopes
The Magellan Telescopes are a pair of 6.5 m diameter optical telescopes located at Las Campanas Observatory in Chile. The two telescopes are named after the astronomer Walter Baade and the philanthropist Landon T...
' Magellan Inamori Kyocera Echelle spectrograph (MIKE) at Las Campanas Observatory
Las Campanas Observatory
Las Campanas Observatory is an astronomical observatory owned and operated by the Carnegie Institution for Science It was established in 1969 and remains the primary observing site of that institution. The headquarters is located in La Serena, Chile and the observatory is in the southern Atacama...
in Chile since 2004. Based on these observations, the stars HD 154672 and HD 205739
HD 205739
HD 205739 is a yellow-white dwarf . It is about 90 parsecs away from the Sun.A Jupiter-like planet has recently been detected in a Mercury-like eccentric orbit around this star....
were among those flagged as potential planetary host stars. The two stars were identified originally as having short-orbit hot Jupiter
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
planets, but 3.5 years of additional observations revealed that the planetary candidates' orbits were far longer than initially anticipated. HD 154672 b's discovery was reported in the Astronomical Journal
Astronomical Journal
The Astronomical Journal is a peer-reviewed monthly scientific journal owned by the American Astronomical Society and currently published by Institute of Physics Publishing. It is one of the premier journals for astronomy in the world...
by the American Astronomical Society
American Astronomical Society
The American Astronomical Society is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC...
, appearing in the journal on October 7, 2008 alongside the planet HD 205739 b
HD 205739 b
HD 205739 b is an extrasolar planet located approximately 295 light-years away in the constellation of Piscis Austrinus, orbiting the star HD 205739. This planet has a minimum mass 37% more than Jupiter and orbits 90% of the distance between the Earth and the Sun...
. The two planets were the first to be discovered by the N2K program that worked out of the Magellan telescopes.
HD 154672 b was later observed by a different team of astronomers investigating the role of metallicity
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...
, or the amount of metal present in a star, in the formation of planets. Six radial velocity measurements of the host star, collected using the HARPS
High Accuracy Radial Velocity Planet Searcher
The High Accuracy Radial velocity Planet Searcher is a high-precision echelle spectrograph installed in 2002 on ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003...
instrument at Chile's La Silla Observatory
La Silla Observatory
La Silla Observatory is an astronomical observatory in Chile with three telescopes built and operated by the European Southern Observatory organisation, and several others are partly maintained by ESO...
. The team used the radial velocity data to refine the parameters of HD 154672 b from what was published in its discovery paper a year earlier.
Host star
HD 154672 is a G-type star like the Sun. The star has a massSolar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
that is 1.06 times that of the Sun, and a radius 1.27 times the solar radius. The effective 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...
, or the temperature it would emit if it were a black body
Black body
A black body is an idealized physical body that absorbs all incident electromagnetic radiation. Because of this perfect absorptivity at all wavelengths, a black body is also the best possible emitter of thermal radiation, which it radiates incandescently in a characteristic, continuous spectrum...
, is 5714 K, slightly cooler than that of the Sun. However, with an [Fe/H] = 0.26 and an age of 9.28 billion years, HD 154672 has 182% more iron than the Sun, and is over two times older than the Sun. Based on its spectrum, HD 154672 is not a very active star.
The 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...
(v) of HD 154672 is 8.22, which means that it is not 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"...
. It is slightly dimmer than Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
, which has an apparent magnitude of 7.78 at its brightest.
Characteristics
HD 154672 b is a closely orbiting planet that is larger than Jupiter. Its mass was estimated as 5.02 that of Jupiter. HD 154672 b also orbits its host star at a distance of 0.6 AUAstronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
every 163.91 days. Earth, in comparison, orbits the Sun at a distance of 1 AU every 365.25 days. However, HD 154672 b has an orbital eccentricity
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 0.61, which indicates a very elliptical orbit. Because HD 154672 b has such an eccentric orbit, the equilibrium temperature of the planet varies between 300 K and 600 K, which is significantly higher than that of Jupiter (124 K). If liquid water is present in the atmosphere of HD 154672 b, it could possibly convert between gaseous and liquid phases as the planet moves along its orbit.
The high eccentricity of the planet's orbit suggests that either the Kozai mechanism
Kozai mechanism
In celestial mechanics, the Kozai mechanism, or the Lidov-Kozai mechanism, causes a periodic exchange between the inclination and eccentricity of an orbit...
(there is an exchange between the inclination of a planet and its eccentricity) is at work, or that the planet's orbit was distorted by the unstable orbit of other planets that used to be part of the HD 154672 system.
HD 154672 b had, at the time of its 2008 discovery, an orbital period larger than 90% of all discovered planets. It was the seventh planet known to have an eccentricity over 0.6 and an orbit shorter than 300 days.