Iota Horologii

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**Iota Horologii**
Observation data Epoch J2000.0
Iota Horologii
Constellation (pronunciation)	Horologium
Right ascension	02^h 42^m 31.65^s
Declination	-50° 48' 12.29"
Apparent magnitude (V)	+5.40
Characteristics
Spectral type	G0Vp
U-B color index	?
B-V color index	0.57
Variable type	none
Astrometry
Radial velocity (R_v)	15.5 km/s
Proper motion (μ)	RA: 333.73 mas/yr Dec.: 219.21 mas/yr
Parallax (π)	58.00 ± 0.55 mas
Distance	50.6 ly (16.8 pc)
Absolute magnitude (M_V)	4.27
Details
Mass	1.25^[1] M_☉
Radius	1.5^[1] R_☉
Luminosity	1.8^[1] L_☉
Temperature	6125 ± 30 K
Metallicity	[Fe/H] = +0.11 ± 0.04
Rotation	8.6 days
Age	30 – 2000 million years
Other designations
HR 810, HD 17051, Gliese 108
Database references
SIMBAD	data

Iota Horologii (ι Hor / ι Horologii) is a solar twin star approximately 56 light-years away in the constellation Horologium. The star is classified as a G0Vp^[1] yellow dwarf (it has previously been classified as G3 and a subgiant [IV]). It has a mass and radius larger than the Sun, and is about 50% more luminous.

As of 1998, a single extrasolar planet is known orbiting Iota Horologii. Because the planet orbits in a near Earth orbit, Iota Horologii was ranked 69th in the list of candidates for NASA's planned Terrestrial Planet Finder mission. In 2000, a dust disc was announced around the star, yet this was later determined to be an instrumental artifact.

1 Distance and visibility
2 Planetary system
3 See also
4 References
5 External links

[edit] Distance and visibility

Since Iota Horologii is in the minor constellation of Horologium and that it is quite dim in the sky, the star has not been given a traditional name. Inside the constellation, Iota Horologii is placed near the stars Mu Horologii and R Horologii (despite not being close to them in distance).

The star exhibits higher chromospheric activity than the Sun and so is probably younger than the Sun's 4.6 billion years of age. Spectrographic analysis indicates the star must have formed together with the stars of the Hyades cluster^[2] but must have slowly drifted away, being presently more than 130 light-years away from its original birthplace. This also means that the amount of metals present in the star is due to the original cloud from which it formed and not because it engulfed planetary material.

In its current position, Iota Horologii is closest to the star Chi Eridani (a yellow subgiant), approximately 7 light-years away. The closest planetary systems to Iota Horologii is HD 10647 (a yellow dwarf), approximately 9 light-years away; and Epsilon Reticuli (an orange subgiant), approximately 16 light-years away. Other star systems close to Iota Horologii include Nu Phoenicis and Zeta Reticuli.

[edit] Planetary system

As of 1998, Iota Horologii is known to have an extrasolar planet. The planet designated Iota Horologii b was the result of a long-term survey of forty solar-type stars that was begun in November 1992.

Observations of Iota Horologii in October 2000 appeared to show a dust disc around the star at a distance of 65 AU, similar to the Kuiper belt in our solar system. However further analysis revealed the dust disc to be an instrumental artifact and the discovery claim was retracted.

Based on residuals in the radial velocity curve, a planet in an eccentric orbit with a period of approximately 600 days was proposed, however this was not confirmed and it seems likely that the effect was due to activity on Iota Horologii itself.