| Discovery | |
|---|---|
| Discovered by | Lopez-Moraleset al. |
| Discovery site | Las Campanas Observatory |
| Discovery date | September 5, 2008 |
| Doppler spectroscopy | |
| Orbital characteristics | |
| Apastron | 0.961 AU (143,800,000 km) |
| Periastron | 0.233 AU (34,900,000 km) |
| 0.597+0.2 −0.17[1]AU | |
| Eccentricity | 0.61 ± 0.03 |
| 163.94 ± 0.01d 0.44884y | |
Averageorbital speed | 39.8 |
| 3045.3 ± 0.1[1] | |
| 265 ± 2[1] | |
| Star | HD 154672 |
| Physical characteristics | |
| Mass | 4.96+0.4 −0.35[1]MJ |
| Temperature | 300–600 K (27–327 °C; 80–620 °F) |
HD 154672 b is anextrasolar planet located approximately 210light-years away[2] in theconstellation ofAra, orbiting the metal-rich and agedstarHD 154672. This planet has aminimum mass five times that ofJupiter and orbits at about 60% the distance between theEarth to theSun. Its orbit is very elliptical, which causes temperatures on the planet to vary significantly as it proceeds along its orbit. This planet was discovered inLas Campanas Observatory on September 5, 2008 using theradial velocity method (Doppler spectroscopy). Along withHD 205739 b, the planets were the first to be discovered by theN2K Consortium using theMagellan Telescopes.
Astronomers hoped to implement a survey called theN2K Consortium, a collaboration which usesDoppler spectroscopy to findradial velocity measurements of stars that hadn't been previously surveyed. The project searched particularly for gas giants with shortorbits around metal-rich stars to find how themetallicity of the star and the mass of the planet are related.[3]
Radial velocity observations had been taken by the N2K program using theMagellan Telescopes'Magellan Inamori Kyocera Echelle spectrograph (MIKE) atLas Campanas Observatory in Chile since 2004. Based on these observations, the stars HD 154672 andHD 205739 were among those flagged as potential planetary host stars. The two stars were identified originally as having short-orbithot 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 theAstronomical Journal by theAmerican Astronomical Society, appearing in the journal on October 7, 2008 alongside the planetHD 205739 b. The two planets were the first to be discovered by the N2K program that worked out of the Magellan telescopes.[3]
HD 154672 b was later observed by a different team of astronomers investigating the role ofmetallicity, or the amount of metal present in a star, in the formation of planets. Six radial velocity measurements of the host star, collected using theHARPS instrument at Chile'sLa 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.[4]
HD 154672 is aG-type star like the Sun. The star has amass that is 1.06 times that of the Sun, and a radius 1.27 times thesolar radius. Theeffective temperature, or the temperature it would emit if it were ablack body, is 5714K, 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.[1] Based on its spectrum, HD 154672 is not a very active star.[3]
Theapparent magnitude (v) of HD 154672 is 8.22, which means that it is not visible to thenaked eye.[1] It is slightly dimmer thanNeptune, which has an apparent magnitude of 7.78 at its brightest.[5]
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 0.6AU every 163.91 days.[1] Earth, in comparison, orbits the Sun at a distance of 1 AU every 365.25 days.[6] However, HD 154672 b has anorbital eccentricity of 0.61, which indicates a very elliptical orbit.[1] Because HD 154672 b has such an eccentric orbit, theequilibrium temperature of the planet varies between 300 K and 600 K, which is significantly higher than that of Jupiter (124 K[6]). 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.[3]
The high eccentricity of the planet's orbit suggests that either theKozai mechanism (there is an exchange between theinclination 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.[3]
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.[3]
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