HD 122563
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Boötes |
| Right ascension | 14h 02m 31.84551s |
| Declination | +09° 41′ 09.9444″ |
| Apparent magnitude (V) | 6.20 |
| Characteristics | |
| Spectral type | G8:III: Fe-5 |
| U−B color index | +0.38 |
| B−V color index | +0.90 |
| V−R color index | 0.50 |
| R−I color index | 0.58 |
| Variable type | Suspected |
| Astrometry | |
| Radial velocity (Rv) | −26.39 km/s |
| Proper motion (μ) | RA: −189.539 mas/yr Dec.: −70.415 mas/yr |
| Parallax (π) | 3.0991±0.0332 mas |
| Distance | 1,050 ± 10 ly (323 ± 3 pc) |
| Absolute magnitude (MV) | −0.69 |
| Details | |
| Mass | 0.77±0.05 M☉ |
| Radius | 28.86±0.63 R☉ |
| Luminosity | 339±13 L☉ |
| Surface gravity (log g) | 1.404±0.035 cgs |
| Temperature | 4,635±34 K |
| Metallicity [Fe/H] | −2.75±0.12 dex |
| Rotational velocity (v sin i) | 5.0 km/s |
| Age | 12.6 Gyr |
| Other designations | |
| BD+10°2617, HIP 68594, HD 122563, HR 5270, SAO 120251 | |
| Database references | |
| SIMBAD | data |
HD 122563 is an extremely metal-poor red giant star, and the brightest known metal-poor star in the sky. Its low heavy element content was first recognized by spectroscopic analysis in 1963. For more than twenty years it was the most metal-poor star known, being more metal-poor than any known globular cluster, and it is the most accessible example of an extreme population II or Halo star.
As the most extreme metal-poor star known, HD 122563's composition was crucial in constraining theories for galactic chemical evolution; in particular, its composition peculiarities provided signposts for understanding the accumulation of heavy elements by stellar nucleosynthesis in the Galaxy. For example, it has an excess of oxygen, [O/Fe] = +0.6, while the proportions of strontium, yttrium, zirconium, barium and the lanthanide elements suggest that the s-process has made no contribution to the material present in the star: in HD 122563, all these elements are products of the r-process instead. The implication is that the star formed at a time and place where there had not been enough time for any previous generation of stars to have produced s-process elements, though there was r-process material present.