HIP 13044 is a red

horizontal-branch The horizontal branch (HB) is a stage of stellar evolution that immediately follows the red-giant branch in stars whose masses are similar to the Sun's. Horizontal-branch stars are powered by helium fusion in the core (via the triple-alpha process) ...

star about 2,300

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s (700 pc) from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

in the constellation Fornax. The star is part of the

Helmi stream The Helmi Stream is a stellar stream of the Milky Way galaxy. It started as a dwarf galaxy, now absorbed by the Milky Way as a stream. It was discovered in 1999, is formed of old stars deficient in heavy elements, and has a mass of 10 to 100 millio ...

, 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. The relatively fast rotation of the star may be due to having engulfed one or more planets during the red-giant phase.

Observational history

A science team from the

Max Planck Institute for Astronomy The Max-Planck-Institut für Astronomie (Max Planck Institute for Astronomy, MPIA) is a research institute of the Max Planck Society (MPG). It is located in Heidelberg, Baden-Württemberg, Germany near the top of the Königstuhl, adjacent to the ...

first observed HIP 13044 using Fiber-fed Extended Range Optical Spectrograph (FEROS) at the

European Southern Observatory The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental organization, intergovernmental research organisation made up of 16 mem ...

's La Silla Observatory in Chile. The first follow-up led to the collection of 36

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

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 the supposed discovery of the planet ''HIP 13044 b'', although this claim was later refuted.

Characteristics

HIP 13044 is an F-type star located approximately 701 parsecs (2,286

s) from Earth in the

—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 the 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 that 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 star fusing helium in its core, and has therefore already passed the red-giant phase of its evolution. It lies near the blue end of the red horizontal branch bordering the

instability strip The unqualified term instability strip usually refers to a region of the Hertzsprung–Russell diagram largely occupied by several related classes of pulsating variable stars: Delta Scuti variables, SX Phoenicis variables, and rapidly oscillati ...

. Its surface temperature is about 6025 K and its radius is approximately 6.7 solar radii. HIP 13044's mass is estimated to be 0.8

solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

es. Having a rotation period of 5–6 days, HIP 13044 is a fast-rotating star for its type. It is possible that this is because it has swallowed planets during its red-giant phase. HIP 13044 has an apparent magnitude of 9.94 and cannot be seen with the unaided eye.

Claims of a planetary system

In 2010, it was announced that a giant planet in a 16.2-day orbit had been discovered by the radial velocity measurements. This would have had implications for planet formation in metal-poor systems and survival of planets being engulfed by expanded giant stars. Subsequent analysis of the data revealed problems with the detection: for example an erroneous barycentric correction had been applied (the same error had also led to claims of planets around

HIP 11952 HIP 11952 is a star in the Milky Way galaxy, located 375 light-years away from the Sun. While the spectral lines strongly indicate that the star is of spectral type F2V-IV, previous analyses have stated that the star is a G8III giant star ...

that were subsequently refuted). After applying the corrections, there is no evidence for a planet orbiting the star.

References

{{DEFAULTSORT:HIP 13044 F-type giants Horizontal-branch stars Hypothetical planetary systems Fornax CD-36 01052 013044