Kapteyn's Star
Kapteyn's Star is a class M1 red subdwarf about 12.83 light-years from Earth in the southern constellation Pictor; it is the closest halo star to the Solar System. With an apparent magnitude of nearly 9 it is visible through binoculars or a telescope.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Pictor |
| Right ascension | 05h 11m 40.58984s |
| Declination | −45° 01′ 06.3617″ |
| Apparent magnitude (V) | 8.853±0.008 |
| Characteristics | |
| Spectral type | sdM1 or M1.5V |
| U−B color index | +1.21 |
| B−V color index | 1.57±0.012 |
| Variable type | BY Dra |
| Astrometry | |
| Radial velocity (Rv) | 245.05±0.13 km/s |
| Proper motion (μ) | RA: +6,491.223 mas/yr Dec.: −5,708.614 mas/yr |
| Parallax (π) | 254.1986 ± 0.0168 mas |
| Distance | 12.8308 ± 0.0008 ly (3.9339 ± 0.0003 pc) |
| Absolute magnitude (MV) | 10.89 |
| Details | |
| Mass | 0.281±0.014 M☉ |
| Radius | 0.291±0.025 R☉ |
| Luminosity | 0.012 L☉ |
| Surface gravity (log g) | 4.96±0.13 cgs |
| Temperature | 3,570±80 K |
| Metallicity [Fe/H] | −0.86±0.05 dex |
| Rotation | 124.71±0.19 d |
| Rotational velocity (v sin i) | 9.15 km/s |
| Age | 11.5+0.5 −1.5 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | The star |
| planet b | |
| planet c | |
Its diameter is 30% of the Sun's, but its luminosity just 1.2% that of the Sun. It may have once been part of the globular cluster Omega Centauri, itself a likely dwarf galaxy swallowed up by the Milky Way in the distant past. The discovery of two planets—Kapteyn b and Kapteyn c—was announced in 2014, but had a mixed history of rejections and confirmations, until a 2021 study refuted both planets. The "planets" are in fact artifacts of the star's rotation and activity.
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