HD 40307 d
|Extrasolar planet||List of extrasolar planets|
HD 40307 d is in the foreground. Credit: ESO
|Right ascension||(α)||05h 54m 04.2409s|
|Declination||(δ)||−60° 01′ 24.498″|
|Distance||41.8 ± 0.3 ly
(12.83 ± 0.09 pc)
|Radius||(r)||0.716 ± 0.010 R☉|
|Temperature||(T)||4977 ± 59 K|
|Metallicity||[Fe/H]||−0.31 ± 0.03|
|Age||1.2 (≥ 0.2) Gyr|
|Semimajor axis||(a)||0.13210.12550.1387 AU|
|Orbital period||(P)||20.43220.40820.454 d|
|Minimum mass||(m sin i)||9.5811.2 M⊕|
|Discovery date||June 16, 2008|
|Discoverer(s)||Mayor et al.|
|Discovery method||radial velocity, using HARPS|
|Discovery site||La Silla Observatory, Chile|
HD 40307 d is an extrasolar planet orbiting the star HD 40307, located 42 light-years from Earth in the direction of the southern constellation Pictor. The planet was discovered by the radial velocity method, using the HARPS apparatus in June 2008. It is the most massive of the six proposed planets in the system. The planet is of interest as this star has relatively low metallicity, supporting a hypothesis that different metallicities in protostars determine what kind of planets they will form.
HD 40307 d was discovered through the Doppler spectroscopy method, which functions by measuring the variations in radial velocity in a star produced by the gravitational effect of orbiting exoplanets. The radial velocities were measured by the High Accuracy Radial Velocity Planet Searcher spectrography system (HARPS) at the La Silla Observatory in Chile's Atacama Desert. The other less massive planets orbiting HD 40307 were discovered in the same way: HD 40307 b and HD 40307 c first, and then HD 40307 e, HD 40307 f, and HD 40307 g. The discovery of HD 40307 d and the former two was announced at the astrophysics conference that took place on June 16–18, 2008 in Nantes, France.
Orbit and mass
HD 40307 d has a mass of at least 9.2 times Earth's; assuming that all planets in the system have coplanar orbits, it is the most massive planet known in the system. The planet orbits approximately 0.135 astronomical units from its primary star, as compared to Earth's orbit at approximately one astronomical unit away from the Sun. As a result, one year on HD 40307 d constitutes approximately 20.45 Earth days. The eccentricity of the planet's orbit was found to not differ significantly from zero, meaning that there is insufficient data to distinguish the orbit from an entirely circular one.
The star around which HD 40307 d orbits has an unusually low metallicity compared to that of other planet-bearing stars. This supports a hypothesis concerning the possibility that the metallicity of stars during their births may determine whether a protostar's accretion disk forms gas giants or terrestrial planets.
The planet has not been found to transit and, further, it is not likely to. It has also not been imaged. More specific physical characteristics such as radius, composition, and average surface temperature cannot be observed.
A dynamical study of planets b, c, and d showed tidal effects at least on b and c, to the extent that b had to be a sub-Neptune. All the planets from b to at least f must have migrated inward. That study implied that d was a sub-Neptune as well.
- "HD 40307". SIMBAD. Centre de Données astronomiques de Strasbourg. 2008. Retrieved 18 June 2008.
- HD 40307, database entry, Geneva-Copenhagen Survey of Solar neighbourhood, J. Holmberg et al., 2007, CDS database V/117A, accessed November 19, 2008; described in The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ~14 000 F and G dwarfs, B. Nordström, M. Mayor, J. Andersen, J. Holmberg, F. Pont, B. R. Jørgensen, E. H. Olsen, S. Udry, and N. Mowlavi, Astronomy and Astrophysics 418 (May 2004), pp. 989–1019, Bibcode: 2004A&A...418..989N, doi:10.1051/0004-6361:20035959.
- HD 40307, entry, CDS database J/A+A/450/735; described in Effective temperature scale and bolometric corrections from 2MASS photometry, E. Masana, C. Jordi, and I. Ribas, Astronomy and Astrophysics 450, #2 (May 2006), pp. 735–746. Bibcode: 2006A&A...450..735M. doi:10.1051/0004-6361:20054021.
- M. Mayor, S. Udry, C. Lovis, F. Pepe, D. Queloz, W. Benz, J.-L. Bertaux, F. Bouchy, C. Mordasini, D. Segransan (2009). "The HARPS search for southern extra-solar planets. XIII. A planetary system with 3 Super-Earths (4.2, 6.9, & 9.2 Earth masses)". Astronomy and Astrophysics 493 (2): 639–644. arXiv:0806.4587. Bibcode:2009A&A...493..639M. doi:10.1051/0004-6361:200810451.
- Tuomi, Anglada-Escude, Gerlach, Jones, Reiners, Rivera, Vogt, Butler, Mikko, Guillem, Enrico, Hugh R. R., Ansgar, Eugenio J., Steven S., R. Paul (2012). "Habitable-zone super-Earth candidate in a six-planet system around the K2.5V star HD 40307". arXiv:1211.1617v1 [astro-ph].
- Mayor et al. (2008-06-16). "Trio of 'super-Earths' discovered". BBC news. Retrieved 2008-06-16.
- Characterizing Extrasolar Planets, Timothy M. Brown, chapter 3, Extrasolar Planets: XVI Canary Islands Winter School of Astrophysics, edited by Hans Deeg, Juan Antonio Belmonte, and Antonio Aparicio, Cambridge, UK: Cambridge University Press, 2007, ISBN 0-521-86808-4.
- Barnes, R., Jackson, B., Raymond, S., West, A., Greenberg, R. (2009). "The HD 40307 Planetary System: Super-Earths or Mini-Neptunes?". The Astrophysical Journal 695 (2): 1006. arXiv:0901.1698. Bibcode:2009ApJ...695.1006B. doi:10.1088/0004-637X/695/2/1006.
- Barnes, J., O'Brien, D. (2002). "Stability of Satellites around Close-in Extrasolar Giant Planets". The Astrophysical Journal 575 (2): 1087–1093. arXiv:astro-ph/0205035. Bibcode:2002ApJ...575.1087B. doi:10.1086/341477.