| Extrasolar planet | List of extrasolar planets | |
|---|---|---|
| Parent star | ||
| Star | HIP 13044 | |
| Constellation | Fornax | |
| Right ascension | (α) | 02h 47m 37.4423s[1] |
| Declination | (δ) | -36° 06′ 27.051″[1] |
| Apparent magnitude | (mV) | 9.94[2] |
| Distance | 2286 ± 65 ly (701 ± 20[2] pc) |
|
| Spectral type | F2[1] | |
| Mass | (m) | 0.8 ± 0.1[2] M☉ |
| Radius | (r) | 6.7 ± 0.3[2] R☉ |
| Temperature | (T) | 6025 ± 63[2] K |
| Metallicity | [Fe/H] | -2.09 ± 0.26[2] |
| Age | >9[2] Gyr | |
| Orbital elements | ||
| Semimajor axis | (a) | 0.116 ± 0.001[2] AU |
| Eccentricity | (e) | 0.25 ± 0.05[2] |
| Orbital period | (P) | 16.2 ± 0.3[2] d |
| Argument of periastron |
(ω) | 219.8 ± 1.8[2]° |
| Physical characteristics | ||
| Minimum mass | (m sin i) | 1.25 ± 0.05[2] MJ |
| Discovery information | ||
| Discovery date | November 2010 | |
| Discoverer(s) | Johny Setiawan et al.[3] | |
| Detection method | Radial velocity | |
| Discovery status | Published | |
| Database references | ||
| Extrasolar Planets Encyclopaedia |
data | |
| SIMBAD | data | |
HIP 13044 b is a Jupiter-like extrasolar planet orbiting the old and metal-poor red giant star HIP 13044, which is situated approximately 2,000 light years away from the Earth in the constellation Fornax. Its discovery was announced on November 18, 2010[4] after observations using the FEROS spectrograph at La Silla Observatory. According to evolutionary theories, HIP 13044 was formed in another galaxy, and became part of the Milky Way when the star's parent galaxy was absorbed by our own between six and nine billion years ago, the remnants of the galaxy forming the Helmi stream.[5] The planet has a very irregular orbit that is probably derived from the gravitational instabilities associated with HIP 13044's transition into the red giant phase of its lifetime. At the time of its discovery, HIP 13044 b orbited what was noted as the oldest and most metal-poor star yet discovered.[5]
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The study that led to the discovery of the planet was performed by a team from the Max Planck Institute for Astronomy.[3] HIP 13044 b, the discovered planet, is the first time that a planetary system has been discovered in a stellar stream of extragalactic origin.[6]
Using the FEROS spectrograph of the 2.2m MPG/ESO telescope at the La Silla Observatory in Chile, the science team that discovered the planet took thirty-six radial velocity measurements,[5] a process that involves detecting small wobbles in a star caused by a planet as it tugs on it.[6] The science team analyzed their observations in search of false positive alternatives that could also explain the signals detected by FEROS using photometric measurements that were taken and publicly released by SuperWASP, an organization that searches for transiting planets. The team compared the oscillations that HIP 13044 undergoes to the absence of the aforementioned oscillation at a sixteen day interval, and determined that the most likely reason for the blockage of the signal was the presence of a planetary companion. It was also determined that the planet was most likely not captured from another star in the Milky Way after Helmi stream became a part of the galaxy, implying that HIP 13044 b indeed originated outside the Milky Way.[5]
The discovery of the planet may also suggest the need for rethinking issues in planet formation and survival, since it is the first planet ever discovered to be circling a star that is both very old and extremely metal-poor.[7] The planet thus challenges the core-accretion model of planet formation, given that it may be unlikely a planetary core of sufficient mass was formed, and may signify it was formed via the competing disk instability model of planet formation. The planet's discovery was announced on November 18, 2010.[8][9][10]
HIP 13044 is an F-type giant located in the Fornax constellation's Helmi stream, a stellar stream consisting of stars that originated in a dwarf galaxy that collided and merged with the Milky Way between six and nine billion years ago.[5] The star is rotating somewhat quickly, possibly indicating that it may have swallowed its inner planets during its red giant phase.[4] It has an eccentric galactic orbit, with a distance from 7 to 16 kiloparsecs.[11] HIP 13044 has a mass of 0.8 times that of the Sun and a radius that is 6.7 times that of the Sun, making it a very diffuse star. The star is estimated to have an effective temperature of 6025 K, making it hotter than the Sun; however, with a metallicity of [Fe/H] = −2.09, the star is extremely iron-deficient, having approximately 0.008 times the amount of iron measured in the Sun's spectrum.[11] HIP 13044 is an old star, and is estimated to be at most nine billion years old, nearly twice the age of the Sun.[11] Stars of this age, metallicity, and evolved stage are not known nor expected to have planets according to current theories on planetary formation.[5]
The star is now in the final stages of its life as a horizontal branch star, fusing helium in its core. It is likely that the planet orbited farther away from the star before its red giant phase, and arrived at its current location due to frictional interactions with the star's outer gas envelope. As the star is expected to undergo another phase of expansion before becoming a white dwarf, the planet's ultimate fate is uncertain.[4][6]
HIP 13044 is situated at a distance of 701 parsecs (2,286 light years) from Earth. It has an apparent magnitude of 9.94, and thus is not visible from Earth with the unaided eye.[11]
HIP 13044 b is a Hot Jupiter with a mass of 1.25 times that of Jupiter. The planet orbits at a distance of 0.116 AU every 16.2 days. HIP 13044 b has a large orbital eccentricity of 0.25, and thus has a very elliptical orbit.[11] The planet's orbital eccentricity is of special note, for such an eccentric orbit is not typical or predicted for planets of its kind. It is believed that an unevenly distributed pattern of mass loss may have shifted the planet's orbit to its present pattern, or that a third body in the system is manipulating HIP 13044 b's orbit.[5]
To compare, Mercury orbits the Sun at a distance of 0.387 AU every 87.97 days with an orbital eccentricity of 0.2056.[12]
HIP 13044 b may have been part of a multiplanetary system before its host star entered its red giant phase. The system's planets were most likely consumed by the expanding stellar envelope of the star. The gravitational disturbances caused by the expanding stellar envelope could have caused HIP 13044 b's orbit to deteriorate until it spiraled into its present, extremely close orbit.[5]
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