SDSS J102915+172927

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.[2] At the time of its discovery, it had the lowest metallicity of any known star.[3] It is small (less than 0.8 solar masses),[4] 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.[5] The metallicity of Caffau's Star is less than 6.9×10−7.[5] 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.[4][6] The absence of lithium implies past temperatures of at least two million kelvins.[5]

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
Characteristics
B−V color index 0.03[1]
Astrometry
Parallax (π)0.734±0.073[1] mas
Distance1370+150
−120[1] pc
Details
Mass≤ 0.8 M☉
Temperature5811[1] K
Metallicity≤ 6.9×10−7[1]
Other designations
2MASS J10291514+1729278
Database references
SIMBADdata

Data from Gaia's DR2 released in 2018 confirms that SDSS J102915+172927 is a dwarf star.[1]

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.[7] 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.[3] Caffau and her team expect to find between five and fifty similar stars with the telescope in the future.[6]

See also
Ultra low metallicity / ultra metal poor stars

References
  1. Bonifacio, P.; Caffau, E.; Spite, M.; Spite, F.; François, P.; Zaggia, S.; Arenou, F.; Haigron, R.; Leclerc, N.; Marchal, O.; Panuzzo, P.; Plum, G.; Sartoretti, P. (2 May 2018). "Gaia Confirms that SDSS J102915+172927 is a Dwarf Star". Research Notes of the AAS. 2 (2): 19. arXiv:1804.10419. Bibcode:2018RNAAS...2b..19B. doi:10.3847/2515-5172/aac0f4.
  2. Lemonick, Michael D. (2011-09-06). "Cosmic Anomaly: The Star That Shouldn't Exist". TIME. Retrieved 2012-08-20.
  3. "The Star That Should Not Exist". ESO. 2011-08-31. Retrieved 2012-08-20.
  4. Schneider, Raffaella; et al. (2012-03-19). "The formation of the extremely primitive star SDSS J102915+172927 relies on dust". Monthly Notices of the Royal Astronomical Society: Letters. 423 (1): L60–L64. arXiv:1203.4234. Bibcode:2012MNRAS.423L..60S. doi:10.1111/j.1745-3933.2012.01257.x.
  5. Caffau, Elisabetta; Bonifacio, Piercarlo; François, Patrick; Sbordone, Luca; et al. (1 September 2011). "An extremely primitive star in the Galactic halo". Nature. 477 (7362): 67–69. arXiv:1203.2612. Bibcode:2011Natur.477...67C. doi:10.1038/nature10377. PMID 21886158.
  6. Doyle, Amanda (2011-09-01). "A forbidden star". Astronomynow.com. Archived from the original on 2012-10-19. Retrieved 2012-08-20.
  7. Redd, Nola Taylor (2011-08-31). "Impossible Star Defies Astronomers' Theories". Space.com. Retrieved 2012-08-20.
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