Kapteyn's Star

Star

Kapteyn's Star - a nearby red subdwarf 12.8 light-years away in Pictor, and one of the strangest stars in the neighbourhood: an ancient, metal-poor HALO star racing backwards through the Galaxy, probably torn from the disrupted globular cluster now seen as Omega Centauri. No planets are confirmed.

Open in 3D viewSee Kapteyn's Star in the live, interactive 3D map

Key facts

Mass

5.59 × 10²⁹ kg

0.281 M☉

Radius

202,449 km

29% of the Sun's radius

Surface temperature

3,570 K (3,297 °C)

Luminosity

4.59 × 10²⁴ W

Spectral type

sdM1 (metal-poor red subdwarf)

Science

Physical

Mass: 5.59 × 10²⁹ kg · 0.281 M☉
Radius: 202,449 km · 29% of the Sun's radius
Density: 16,080 kg/m³ · 16× water; Computed from mass and radius
Spectral type: sdM1 (metal-poor red subdwarf)

Motion through space

Proper motion: 8.64 arcseconds per year · its drift across our sky; SIMBAD — 2020yCat.1350....0G, 2018A&A...616A...7S
Radial velocity: +245.2 km/s · moving away from the Sun; SIMBAD — 2020yCat.1350....0G, 2018A&A...616A...7S
Speed across our line of sight: 161 km/s; Computed from proper motion and parallax
Speed through space, relative to the Sun: 293 km/s; Computed from proper motion, parallax and radial velocity

Composition

By mass: A red subdwarf about 28% of the Sun's mass. Very metal-poor and extremely old (~11 billion years), it belongs to the Galaxy's halo and moves retrograde — likely stripped from the progenitor of Omega Centauri.

Temperature

Surface: 3,570 K (3,297 °C)

Radiation & temperature

Luminosity: 4.59 × 10²⁴ W · 0.012 L☉
Surface temperature: 3,570 K (3,297 °C)
Peak wavelength: 812 nm · near-infrared (mostly invisible to the eye); Computed (Wien's law) from the surface temperature

Discovery & history

Discovered: 1898
By: Jacobus C. Kapteyn
Method: Telescope
Name: Named for the Dutch astronomer Jacobus Cornelius Kapteyn, who measured its record proper motion in 1898.

In 1898 Jacobus Kapteyn found this star's enormous proper motion - then the largest known - marking it as a very close, fast neighbour. Two planet claims in 2014 caused excitement but were shown by 2021 to be artefacts of the star's rotation, and are not shown here.

Images

Where to find it — in Pictor, the Painter's Easel (IAU constellation chart). To the eye it is a single point of light; no telescope has imaged its surface. — IAU / Sky & Telescope, R. Sinnott & R. Fienberg (CC BY 3.0) · Wikimedia Commons

Images from open archives · credit shown per image