SDSS J102915+172927
 SDSS J102915 172927 as seen by ESO - VLT |
|
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Leo |
| Right ascension | 10h 29m 15.15s |
| Declination | 17° 29′ 28″ |
| Apparent magnitude (V) | +16.92 |
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.[1] At the time of its discovery, it had the lowest metallicity of any known star.[2] It is small (less than 0.8 solar masses),[3] 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.[4] The metallicity of Caffau's star is less than 6.9×10−7.[4] 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.[3][5] The absence of lithium implies past temperatures of at least two million Kelvins.[4]
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.[6] 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.[2] Caffau and her team expect to find between five and fifty similar stars with the telescope in the future.[5]
See also
- Ultra low metallicity / ultra metal poor stars
References
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