Epoch J2000.0  Equinox J2000.0 
|Right ascension||02h 47m 37.442s |
|Declination||−36° 06′ 27.05″ |
|Radial velocity (Rv)||300 km/s|
|Distance||701 ± 20 pc|
|Spectral type||F2III |
|Apparent magnitude (V)||9.982|
|Mass||0.8 ± 0.1 M☉|
|Radius||6.7 ± 0.3 R☉|
|Temperature||6025 ± 63 K|
|Metallicity||−2.09 ± 0.26 [Fe/H]|
|Rotation||5.53 ± 0.73 d|
HIP 13044 is a red horizontal-branch star about 2,300 light years (700 pc) away from the Earth in the constellation Fornax. The star is part of the Helmi stream, a former dwarf galaxy that merged with the Milky Way between six and nine billion years ago. As a result, HIP 13044 circles the galactic center at a highly irregular orbit with respect to the galactic plane. HIP 13044 is slightly less massive than the Sun, but is approximately seven times its size. The star, which is estimated to be at least nine billion years old, has passed the red giant phase. A planet, a hot Jupiter, was discovered in 2010. There is evidence that other planets may be present, but these planets are engulfed, a possible cause for HIP 13044's high rotational speed. At the time of its discovery, HIP 13044 was the most metal-poor exoplanetary host star discovered.
A science team from the Max Planck Institute for Astronomy first observed HIP 13044 using Fiber-fed Extended Range Optical Spectrograph (FEROS) at the European Southern Observatory's La Silla Observatory in Chile. The first follow-up led to the collection of 36 radial velocity measurements taken between September 2009 and July 2010.
The team also used photometric data that had been passively collected by and publicly released into the archive of the SuperWASP collaboration, which had been observing the region where the star was located. In this data, HIP 13044 was found to oscillate; the signal was blocked roughly every sixteen days. Analysis of the SuperWASP and FEROS data led to discovering HIP 13044 b.
HIP 13044 is an F-type star located approximately 701 parsecs (2,286 light years) away from Earth in the Helmi stream—a group of low metallicity stars moving with large velocities relative to the Sun. The star follows an eccentric galactic orbit, with a distance from the galactic center ranging from 7 to 16 kiloparsecs. The orbit does not lie in galactic plane, and can reach distances as high as 13 kpc above it. This indicates that it once was part of a satellite galaxy of the Milky Way, which was disrupted 6–9 billion years ago. The star itself is estimated to be at least nine billion years old.
HIP 13044 is fairly evolved core helium burning star, which has already passed the red giant stage of its evolution. It lies near the blue end of the red horizontal branch bordering the instability strip. It surface temperature is about 6025 K and the radius is about 6.7 solar radii. The star is also estimated to be 0.8 solar masses. Having the rotation period of 5–6 days, HIP 13044 is a fast rotating star for its type. It is possible that this is because it may have swallowed inner planets during its red giant phase.
Claims of a planetary system
In 2010, a a hot Jupiter that orbits its host star at a distance of 0.116 AU (11.6% the mean distance between the Earth and the Sun) was announced. The planet completes an orbit every 16.2 days. HIP 13044 b has a mass estimated at 1.25 times that of Jupiter. HIP 13044 b also has, with an orbital eccentricity of 0.25, an elliptical orbit. HIP 13044 b's proximity to its host star is not unusual, but a close planet with such a high eccentricity is rare. One model suggests that HIP 13044 b is the remnant of a multi-planetary system that collapsed as HIP 13044 entered the red giant phase, and that the engulfing of inner planets caused irregularities that shifted HIP 13044 b's orbit; another model suggests that an asymmetrical distribution of mass in the star caused the same effect. At the time of its discovery, HIP 13044 b was thought to have been the planet with the most metal-poor star discovered. In January of 2014, the existence of this planet came under question as no signal was discovered. 
(in order from star)
|b (unconfirmed)||1.25 MJ||0.116||16.2||0.25||—||—|
- "SIMBAD query result". Retrieved 2010-11-19.
- Setiawan, Johny et al. (2010). "A Giant Planet Around a Metal-poor Star of Extragalactic Origin". Science 330 (6011): 1642–1644. arXiv:1011.6376. Bibcode:2010Sci...330.1642S. doi:10.1126/science.1193342. PMID 21097905.
- Than, Ker (2010-11-18). "New Planet Discovered: First Spotted Outside Our Galaxy". NationalGeographic.com. National Geographic Society. Retrieved 2010-11-19.
- Klement, R.; Setiawan, J.; Thomas Henning; Hans-Walter Rix; Boyke Rochau; Jens Rodmann; Tim Schulze-Hartung; MPIA Heidelberg et al. (2010). "The visitor from an ancient galaxy: A planetary companion around an old, metal-poor red horizontal branch star". arXiv:1011.4938 [astro-ph.EP].
- "Notes for Planet HIP 13044 b". exoplanet.eu. Retrieved 2010-11-22.
- No evidence of the planet orbiting the extremely metal-poor extragalactic star HIP13044: M. I. Jones, J. S. Jenkins: January 3, 2014