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Brightest star in the constellation Caelum From Wikipedia, the free encyclopedia
Alpha Caeli (α Cae, α Caeli) is the brightest star in the constellation Caelum. It is in fact a binary star, made up of a F-type star of magnitude 4.46 and a red dwarf of magnitude 12.5. They are separated by 6.6" in the sky. Parallax measurements by the Gaia spacecraft imply a distance of 20.4 pc (67 ly) to Alpha Caeli. A debris disk has been detected around the primary component of the system.
The primary component (α Caeli A) has a spectral classification of F2V,[6] meaning that it is a main sequence star, currently fusing hydrogen into helium at its core. It is estimated to be 1.5 billion years old, has 50% more mass[13] and has 1.55 times the Sun's radius.[14] Its photoshpere, which is emitting 5 times the solar luminosity, has an effective temperature of 7000 K,[14] so it is hotter than the Sun and has a white hue, typical of early F-type stars.[19] α Caeli A is a rapid rotator, spinning at its own axis at a projected rotational velocity of 47 km/s.[16]
The star is suspected of being a Delta Scuti variable star.[8] The variation in the brightness is of 0.03 magnitudes.[3] It was first suspected to be a variable star by M. Petit in 1979.[20]
It presents a significant infrared excess at the 100 μm wavelength, which indicates that it is surrounded by a debris disk. The disk extends up to a radius of 46 AU from the star and has a temperature of 60 Kelvin (-213 °C). Its mass is estimated to be about 1/11000 times Earth's mass (ME), and was equivalent to about 1/7100 ME when α Caeli was only 1 million years old.[13]
The companion (α Caeli B) is a red dwarf star, with spectral class of M0.5V[6] and absolute magnitude 9.80.[12] It is a flare star that undergoes random increases in luminosity.[9] This star was separated from the primary by an angle of 6.6 arcseconds in 2008,[18] but this separation changes over time.[15] They are physically separated by 133 astronomical units and take 1,300 years to fully orbit each other.[5]
Because of the small angular separation and faintness (12.5m) of the companion, Alpha Caeli B is hard to be seen by a small telescope.[15]
Alpha Caeli is approximately 66.5 light years from Earth[10] and is an estimated 1.5 billion years old.[13] The space velocity components of this system are U = 10, V = 6 and W = -10 km/s. It is orbiting the Milky Way galaxy at an average distance of 8.006 kpc from the Galactic Center and with an orbital eccentricity of 0.07. This orbit lies close to the galactic plane, and the system travels no more than 0.05 kpc above or below this plane.[11] Alpha Caeli is probably a member of the Ursa Major moving group of stars that have similar kinematic properties and probably originated from the same star cluster.[21]
The nearest star to Alpha Caeli is LHS 1678, a stellar system formed by a red dwarf star, which is orbited by three exoplanets smaller than Earth, and a possible brown dwarf star.[22][23]
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