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HD 205739 b
Extrasolar planet List of extrasolar planets
Parent star

<tr> <td colspan="2">Star</td> <td>HD 205739</td></tr><tr> <td colspan="2">Constellation</td> <td>Piscis Austrinus</td></tr><tr> <td>Right ascension</td> <td style="text-align: center">(α)</td> <td>21h 38m 08.404s[1]</td></tr><tr> <td>Declination</td> <td style="text-align: center">(δ)</td> <td>–31° 44′ 14.96″[1]</td></tr><tr> <td>Apparent magnitude</td> <td style="text-align: center">(mV)</td> <td>8.56</td></tr><tr><td colspan="2">Distance</td><td>350 ± 30[1] ly
(108 ± 10[1] pc)</td></tr><tr><td colspan="2">Spectral type</td> <td>F7V</td></tr>

Orbital elements

<tr><td>Semimajor axis</td><td style="text-align: center">(a)</td> <td>0.896+0.019
(134 Gm)</td></tr><tr><td> </td> <td style="text-align: center"> </td> <td>9.92 mas</td></tr><tr> <td>Periastron</td> <td style="text-align: center">(q)</td> <td>0.654 AU
(98 Gm)</td></tr><tr> <td>Apastron</td> <td style="text-align: center">(Q)</td> <td>1.138 AU
(170 Gm)</td></tr><tr> <td>Eccentricity</td> <td style="text-align: center">(e)</td> <td>0.27 ± 0.07</td></tr><tr><td>Orbital period</td><td style="text-align: center">(P)</td> <td>279.8 ± 0.1 d
(0.7660 y)</td></tr><tr> <td>Orbital speed</td> <td style="text-align: center">(υ)</td> <td>35.0 km/s</td></tr><tr> <td>Argument of
</td> <td style="text-align: center">(ω)</td> <td>301 ± 8°</td></tr><tr> <td>Time of periastron</td> <td style="text-align: center">(T0)</td> <td>3390.7 ± 0.7 JD</td></tr>

Physical characteristics

<tr><td>Minimum mass</td><td style="text-align: center">(m sin i)</td><td>1.37+0.07

Discovery information

<tr> <td colspan="2">Discovery date</td> <td>September 5, 2008</td></tr><tr> <td colspan="2">Discoverer(s)</td> <td>Lopez-Morales et al.</td></tr><tr> <td colspan="2">Discovery method</td> <td>Doppler spectroscopy</td></tr><tr> <td colspan="2">Discovery site</td> <td>Las Campanas Observatory</td></tr><tr> <td colspan="2">Discovery status</td> <td>Published</td></tr>

Other designations
HIP 106824 b

<tr style="background-color: #A0B0FF;"><td align=center colspan=3>Database references</td></tr><tr valign=baseline><td colspan=2>Extrasolar Planets
</td><td>data</td></tr><tr><td colspan=2>SIMBAD</td><td>data</td></tr>

HD 205739 b is an extrasolar planet located approximately 350 light-years away[1] 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 planet has a very elliptical orbit, which has led its discoverers to postulate that the planet's surface temperature varies by about 100 K along the entire orbit.[2] This planet was reported on September 5, 2008 after its discovery at Las Campanas Observatory, where the planet was observed for years by the N2K Consortium while using the Magellan Telescopes. Follow-up observations collected the radial velocity measurements necessary to confirm the candidate as a planet.[2]


HD 205739's designation is from the Henry Draper catalogue. The star was also observed by Hipparcos, which released its catalogue in 1997. The observations that led to the discovery of the planet HD 205739 b started when the N2K Consortium started an extended search for planets around 300 stars not usually targeted by Doppler spectroscopy surveys. In the case of HD 205739, the star was observed using the Magellan Telescopes at Las Campanas Observatory in Chile. HD 205739 was selected primarily because it was a metal-rich star; the N2K collaboration biased their search towards metal-rich stars with closely orbiting Jupiter-size planets, hoping to find a connection between a star's metallicity and its planets' masses.[2]

HD 205739 was flagged originally as a candidate hosting a Hot Jupiter, which is a large gas giant that orbits closely to its star, although later observations suggested that the planetary candidate orbited further out over the next 3.5 years of observation.[2]

The star was studied through the Magellan Inamori Kyocera Echelle spectrograph's (MIKE) ability to use Doppler spectroscopy to measure radial velocity. Twenty-four measurements were recorded for HD 205739. The measurements were analyzed for accuracy. They were then used to derive the planet's characteristics, which led to the planet's confirmation.[2]

The team of astronomers, which were from the United States, Chile, and the Vatican City, sent the paper to the Astronomical Journal on April 7, 2008. The paper was accepted, and was later published on October 7, 2008.[2]

Host starEdit

Main article: HD 205739

HD 205739 is an F-type star with a mass that is 1.22 times the mass of the Sun and a size that is 1.33 times the radius of the Sun. In other words, it is slightly more massive and slightly larger than the Sun is. With an effective temperature of 6176 K, HD 205739 is also hotter than the Sun, although it is younger, at an estimated age of 2.84 billion years.[3] The star is rich in iron; its measured metallicity is [Fe/H] = 0.19, or 1.55 times the iron detected in the Sun.[3] After analysis of HD 205739's spectrum, it can be concluded that HD 205739's chromosphere (its outermost layer) is not active.[2] HD 205739 cannot be seen from Earth with the naked eye because the star has an apparent magnitude (V) of 8.56.[3]


HD 205739 b is a Jupiter-size planet. The estimated minimum mass is 1.37 times the mass of Jupiter. The planet has been found to orbit its host star every 279.8 days at a distance of 0.896 AU, which is approximately 89.6% of the mean distance between the Sun and the Earth. HD 205739 b has a mildly elliptical orbit, given its orbital eccentricity of 0.27.[3] The planet's elliptical orbit is typical with respect to discovered planets whose orbits are longer than twenty days and have not grown circular because of tidal forces.[2] According to its discoverers, HD 205739 b's elongated orbit causes its surface temperature to fluctuate by up to 100 K.[2]

See alsoEdit


  1. 1.0 1.1 1.2 1.3 1.4 (2007). Validation of the new Hipparcos reduction. Astronomy and Astrophysics 474 (2): 653–664. Vizier catalog entry
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 (2008). Two Jupiter-Mass Planets Orbiting HD 154672 and HD 205739. The Astronomical Journal 136 (5): 1901–1905.
  3. 3.0 3.1 3.2 3.3 Jean Schneider (2008). Notes for star HD 205739. Extrasolar Planets Encyclopaedia. Retrieved 27 May 2011.

External linksEdit

Coordinates: Sky map 21h 38m 08.4055s, −31° 44′ 14.945″

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