HD 154672 is a yellow

subgiant A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of ...

(

spectral type In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

G3 IV). It is about 65

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s away from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

that is larger than, but of a similar mass to, the Sun. However, HD 154672 is much older. The star is very metal-rich, which is one of the reasons why it was targeted for a planet search by the

N2K Consortium The N2K Consortium is a collaborative multinational effort by United States, American, Chilean and Japanese astronomers to find additional extrasolar planets around stars that are not already being surveyed. The N2K is shorthand for the set of rough ...

, which discovered the gas giant planet HD 154672 b using

Doppler Spectroscopy Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in t ...

; the discovery was reported in October 2008. The N2K collaboration chose HD 154672 primarily because it aimed to discover the correlation between a star's

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

and the mass of orbiting planets. HD 154672 was targeted by the

Magellan Telescopes The Magellan Telescopes are a pair of optical telescopes located at Las Campanas Observatory in Chile. The two telescopes are named after the astronomer Walter Baade and the philanthropist Landon T. Clay. First light for the telescopes was on Se ...

. It is the host of the first planet discovered from the telescopes by N2K.

Observational history

HD 154672 was first targeted for a planet search in 2004 by the

, a collaboration of astronomers hoping to take

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

measurements of previously untargeted stars using

Doppler spectroscopy Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in t ...

; however, HD 154672 had been previously targeted by a series of surveys, and was previously included in the Henry Draper catalog and the catalog of the

European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

satellite. Magellan Campanas

N2K deliberately biased its search towards closely orbiting Jupiter-size planets (

Hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere temp ...

s) in the orbit of metal-rich stars, as the consortium hoped to discover how the mass of a planet relates to its host star's metal content. Initially, HD 154672 was noted as a host to a short-orbit Hot Jupiter, although additional observations revealed that the prospective planetary body had a longer orbit than previously expected, as revealed by the

at Chile's

Las Campanas Observatory Las Campanas Observatory (LCO) is an astronomical observatory owned and operated by the Carnegie Institution for Science (CIS). It is in the southern Atacama Desert of Chile in the Atacama Region approximately northeast of the city of La Serena. ...

. Use of the Magellan Clay telescope's Magellan Inamori Kyocera Echelle spectrograph (MIKE) helped collect sixteen radial velocity measurements for HD 154672; a team of American astronomers and one from the Vatican City used these measurements to confirm the existence of planet HD 154672 b and to determine its mass. The discovery of HD 154672's planet was reported in the ''

Astronomical Journal ''The Astronomical Journal'' (often abbreviated ''AJ'' in scientific papers and references) is a peer-reviewed monthly scientific journal owned by the American Astronomical Society (AAS) and currently published by IOP Publishing. It is one of the p ...

'' on October 7, 2008 along with a planet in the orbit of

HD 205739 HD 205739 is a yellow-white hued star in the southern constellation of Piscis Austrinus, positioned near the western constellation boundary with Microscopium. It has the proper name Sāmaya, which was selected in the NameExoWorlds campa ...

Host star

HD 154672 is a sunlike G-type star that has a

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...

of 1.06 times that of the Sun and a

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

that is 1.27 times that of the Sun. Thus, it is slightly larger than the Sun, although it has a similar mass. The star has an

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. Effective temperature is often used as an estimate of a body's surface temperature ...

of 5714 K, slightly cooler than the Sun; however, it is far richer in iron, with a measured

of e/H= 0.26. This means that the star has 1.82 times more iron than the Sun does. HD 154672 is far older than the Sun, as its estimated gyrochronological age is estimated at 9.28 billion years. HD 154672's spectrum suggests that the star's

chromosphere A chromosphere ("sphere of color") is the second layer of a star's atmosphere, located above the photosphere and below the solar transition region and corona. The term usually refers to the Sun's chromosphere, but not exclusively. In the Su ...

(its outer layer) is not active. HD 154672 is located 65.8

s (214.6

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s) away from Earth. It has an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

(V) of 8.22, making the star too dim to see from Earth with the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...

. The star is slightly dimmer than planet

Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...

as perceived with the naked eye, which has an apparent magnitude of 7.78 at its brightest. The star's actual brightness is measured with an

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...

of 4.12, similar to that of the Sun.

Planetary system

HD 154672 b is a

, as it is a closely orbiting planet with a high mass. Specifically, HD 154672 has a

that is 5.02 times greater than Jupiter's mass. It also orbits at a distance of 0.6 AU, or about 60% of the mean distance between the Earth and Sun. This orbit is completed every 163.91 days. HD 154672 b has an

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betwee ...

of 0.61, denoting a very elliptical orbit. The planet's discoverers noted that if water existed in the planet's atmosphere, it might change from a liquid state to a gaseous state as the planet swings closer to its host star, increasing its temperature.

References

* {{DEFAULTSORT:HD 154672 Durchmusterung objects 154672 083983 Planetary systems with one confirmed planet G-type subgiants Ara (constellation)

Observational history

Host star

Planetary system

See also

References