SDSS J102915+172927
Population II star in the constellation Leo
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SDSS J102915+172927 or Caffau's Star is a population II star in the galactic halo, seen in the constellation Leo. It is about 13 billion years old, making it one of the oldest stars in the Galaxy.[4] At the time of its discovery, it had the lowest metallicity of any known star.[5] It is small (less than 0.8 solar masses),[6] deficient in carbon, nitrogen, oxygen, and completely devoid of lithium. Because carbon and oxygen provide a fine structure cooling mechanism that is critical in the formation of low-mass stars, the origins of Caffau's Star are somewhat mysterious. It has been suggested, both for theoretical and observational reasons, that the formation of low-mass stars in the interstellar medium requires a critical metallicity somewhere between 1.5×10−8 and 1.5×10−6.[7]
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Leo[1] |
| Right ascension | 10h 29m 15.1490s[2] |
| Declination | +17° 29′ 27.925″[2] |
| Apparent magnitude (V) | +16.92 |
| Characteristics | |
| B−V color index | 0.03[3] |
| Astrometry | |
| Proper motion (μ) | RA: −10.720(63) mas/yr[2] Dec.: −3.921(54) mas/yr[2] |
| Parallax (π) | 0.6482±0.0598 mas[2] |
| Distance | 5,000 ± 500 ly (1,500 ± 100 pc) |
| Details | |
| Mass | ≤ 0.8 M☉ |
| Temperature | 5811[3] K |
| Metallicity | ≤ 6.9×10−7[3] |
| Other designations | |
| 2MASS J10291514+1729278 | |
| Database references | |
| SIMBAD | data |
The metallicity of Caffau's Star is less than 6.9×10−7.[7] According to Schneider et al., cooling by dust rather than the fine structure lines of CII and OI may have enabled the creation of such low-mass, metal-poor stars in the early universe.[6][8] The absence of lithium implies past temperatures of at least two million Kelvin.[7]
Data from Gaia's DR2 released in 2018 confirmed that SDSS J102915+172927 is a dwarf star.[3]
The star was described by Elisabetta Caffau et al. in an article published by the journal Nature in September 2011. Caffau had been searching for extremely metal-poor stars for the past ten years.[9] It was identified by automated software which analyzed data from the Sloan Digital Sky Survey. This was followed up by observations with the X-shooter and UVES instruments on the Very Large Telescope in Chile.[5] As of 2011[update] Caffau and her team expect to find between five and fifty similar stars with the telescope in the future.[8][needs update]
See also
- Ultra low metallicity / ultra metal poor stars