Alpha Caeli

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title: "Alpha Caeli" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["f-type-main-sequence-stars", "m-type-main-sequence-stars", "binary-stars", "caelum", "bayer-objects", "bright-star-catalogue-objects", "durchmusterung-objects", "henry-draper-catalogue-objects", "hipparcos-objects", "gliese-and-gj-objects", "wise-objects", "lucidae"] description: "Brightest star in the constellation Caelum" topic_path: "science/astronomy" source: "https://en.wikipedia.org/wiki/Alpha_Caeli" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Brightest star in the constellation Caelum ::

| name = α Caeli | image = {{Location mark |image=Caelum constellation map.png|alt=|float=center|width=260 |label=|position=right |mark=Red circle.svg|mark_width=10 |x=550|y=587 | caption = Location of α Caeli in Caelum (circled) | epoch = J2000.0 | equinox = J2000.0 | constell = Caelum | component1 = A | ra1 = | dec1 = | appmag_v1 = 4.444.47 | component2 = B | ra2 = | dec2 = | appmag_v2 = 12.5 | component = A | type = main sequence | class = F2V | u-b = 0.01 | b-v = +0.34 | variable = suspected Delta Scuti | component2 = B | type2 = Red dwarf | class2 = M0.5V | variable2 = Flare star | component1 = A | radial_v = | prop_mo_ra = −139.843 | prop_mo_dec = −75.677 | pm_footnote = | parallax = 49.062 | p_error = 0.00937 | parallax_footnote = | dist_footnote = | absmag_v = | component2 = B | radial_v2 = | prop_mo_ra2 = | prop_mo_dec2 = | absmag_v2 = 9.8 | reference = | primary = A | name = B | axis_unitless = | period_unitless = 406,000 days (406000 day years) | component1 = A | mass = 1.54 | radius = 1.546 | luminosity = 5.156 | temperature = 7,002 | gravity = 4.12 | metal_fe = | age_gyr = 1.5 | rotation = 1.4 days | rotational_velocity = | component2 = B | radius2 = 0.45 | temperature2 = 3,355 | reference = | primary = A | component = B | epoch = 2008 | angdistsec = 6.6 | names = | Simbad=alf+cae|sn=A | Simbad2=alf+cae+b|sn2=B

Alpha Caeli is a binary star system in the southern constellation Caelum. Its name is a Bayer designation that is Latinized from α Caeli, and abbreviated Alpha Cae or α Cae. With a combined apparent visual magnitude of 4.45, it is only visible to the naked eye in places far from light pollution, but still is the brightest star in the constellation. Parallax measurements by the Gaia spacecraft indicate a distance of 66.48 ly to Alpha Caeli. It has a relatively low radial velocity, estimated at 0.7 km/s relative to the Sun.

This system consists of an F-type star of magnitude 4.46 and a small red dwarf of magnitude 12.5. As of 2008, they are separated by 6.6" in the sky. A debris disk has been detected around the primary component of the system.

Physical properties

Primary

The primary component (α Caeli A) has a spectral classification of F2V, meaning that it is an ordinary F-type 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 and has 1.55 times the Sun's radius. Its photosphere, which is emitting 5 times the solar luminosity, has an effective temperature of , so it is hotter than the Sun and has a white hue, typical of early F-type stars. is a rapid rotator, spinning at its own axis at a projected rotational velocity of .

The star is suspected of being a Delta Scuti variable star. The variation in the brightness is of 0.03 magnitudes. It was first suspected to be a variable star by M. Petit in 1979.

It presents a significant infrared excess at the 100μm wavelength, which indicates that it is surrounded by an orbiting debris disk. The disk extends up to a radius of 46AU from the star and has a temperature of 60 K. Its mass is estimated to be about 1/11,000 times Earth's mass (), and was equivalent to about when α Caeli was only old.

Companion + Orbit

The companion (α Caeli B) is a small red dwarf star with spectral class of M0.5V and absolute magnitude 9.80. It is a flare star that undergoes random increases in luminosity. This star was separated from the primary by an angle of 6.6 arcseconds in 2008, but this separation changes over time. They are physically separated by 133astronomical units and take 406000 dayyears to fully orbit each other.

Because of the small angular separation and faintness (12.5m) of the companion, Alpha Caeli B is hard to see with a small telescope.

Motion

Alpha Caeli is approximately 66.5 light years from Earth and is an estimated 1.5 billion years old. 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 8.006kpc 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 0.05kpc above or below this plane. 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.

The nearest star to Alpha Caeli is LHS 1678, which is 3.4 light-years from it. This is closer than Proxima Centauri is to the Earth at 4.25 ly. ::data[format=table title="Nearest stars to Alpha Caeli"] | Name | Distance (light-years) | |---|---| | LHS 1678 | 3.4 | | L 447-6 | 5.9 | | HD 29220 | 6.1 | | SCR J0509-4325 | 6.5 | | UPM J0448-3539 | 7.4 | ::

References

References

1. "Alpha Caeli".
2. "alf Cae B".
3. {{Cite Gaia DR3. 4815660547961306112
4. {{Cite Gaia DR3. 4815660547960117760
5. (November 1983). "Predicted infrared brightness of stars within 25 parsecs of the sun.". The Astrophysical Journal Supplement Series.
6. "★ Alpha Caeli".

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