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 ...

(

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

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 centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

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 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 roughly 2,000 of th ...

, 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 ...

; 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 the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

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 ...

. 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 of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

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 ...

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

Henry Draper catalog The ''Henry Draper Catalogue'' (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the ''Henry Draper Extension'' (HDE), published between 192 ...

and the catalog of the

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

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 and distances of ...

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 (i.e. Jupiter analogue, Jupiter analogues) but that have very short orbital periods (). The close proximity to t ...

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 astronomy, astronomical observatory managed by the Carnegie Institution for Science (CIS). Located in Chile's Atacama Region, it sits about northeast of the city of La Serena, Chile, La Serena. The LCO's telesc ...

. 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 ...

'' on October 7, 2008 along with a planet in the orbit of HD 205739.

Host star

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

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

of 1.06 times that of the Sun and a

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

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", from the Ancient Greek words χρῶμα (''khrôma'') 'color' and σφαῖρα (''sphaîra'') 'sphere') is the second layer of a Stellar atmosphere, star's atmosphere, located above the photosphere and below t ...

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

s (214.6

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s) away from Earth. It has an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

(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 magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

. The star is slightly dimmer than planet

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

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 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 be ...

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