|Right ascension||11h 40m 28.48381s|
|Declination||+69° 00′ 30.5995″|
|Apparent magnitude (V)||8.70|
|B−V color index||0.60|
|Radial velocity (Rv)||5.4 km/s|
|Proper motion (μ)||RA: –126.96 mas/yr
Dec.: –2.13 mas/yr
|Parallax (π)||15.68 ± 0.67 mas|
|Distance||208 ± 9 ly
(64 ± 3 pc)
|Absolute magnitude (MV)||4.81|
|Mass||1.02 ± 0.02 M☉|
|Surface gravity (log g)||4.409 cgs|
|Metallicity [Fe/H]||0.02 dex|
HIP 56948 (also known as HD 101364) is a solar twin star of type G5V. It is the most sun-like star yet known in terms of size, mass, temperature, chemical makeup and, arguably, age. Our sun is about 4.6 billion years old, and HIP 56948 is believed to be about a billion years older—so both stars are between a third and a halfway through their life on the main sequence.
It is 208 light years away in the constellation of Draco, lying about halfway between Polaris and Dubhe on the celestial sphere. Astronomers have looked for planets in the system, so far without finding any. These observations suggest that the star does not have any hot Jupiters.
Other solar analogs such as 18 Scorpii are unlike the sun in that they have several times the lithium abundance. HIP 56948 is the best candidate for a solar twin because of the known possible contenders, its lithium abundance most resembles that of our own star. A 2009 high-dispersion spectroscopic study from the Astronomical Society of Japan confirms this.
In the abstract to their paper, the star's discoverers say:
For more than a decade, 18 Sco (HD 146233) has been considered the star that most closely resembles the Sun, even though significant differences such as its Li content, which is about 3 times solar, exist. Using high-resolution, high-S/N spectra obtained at McDonald Observatory, we show that the stars HIP 56948 and HIP 73815 are very similar to the Sun in both stellar parameters and chemical composition, including a low Li abundance, which was previously thought to be peculiar in the Sun. HIP 56948, in particular, has stellar parameters identical to solar within the observational uncertainties, being thus the best solar twin known to date. HIP 56948 is also similar to the Sun in its lack of hot Jupiters. Considering the age of this star (~1 ± 1 Gyr older than the Sun)[Notes 1] and its location and orbit around the Galaxy, if terrestrial planets exist around it, they may have had enough time to develop complex life, making it a prime target for SETI.— Jorge Meléndez and Iván Ramírez
- van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
- Vázquez, M.; Pallé, E.; Rodríguez, P. Montañés (2010). "Is Our Environment Special?". The Earth as a Distant Planet: A Rosetta Stone for the Search of Earth-Like Worlds. Astronomy and Astrophysics Library. Springer New York. pp. 391–418. doi:10.1007/978-1-4419-1684-6. ISBN 978-1-4419-1683-9. See table 9.1.
- Nordström, B.; et al. (May 2004). "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs". Astronomy and Astrophysics 418 (3): 989–1019. arXiv:astro-ph/0405198. Bibcode:2004A&A...418..989N. doi:10.1051/0004-6361:20035959.
- Do Nascimento, J. D., Jr.; Castro, M.; Meléndez, J.; Bazot, M.; Théado, S.; Porto de Mello, G. F.; de Medeiros, J. R. (July 2009). "Age and mass of solar twins constrained by lithium abundance". Astronomy and Astrophysics 501 (2): 687–694. arXiv:0904.3580. Bibcode:2009A&A...501..687D. doi:10.1051/0004-6361/200911935.
- Takeda, Yoichi; Tajitsu, Akito (June 2009). "High-Dispersion Spectroscopic Study of Solar Twins: HIP 56948, HIP 79672, and HIP 100963". Publications of the Astronomical Society of Japan 61 (3): 471–480. arXiv:0901.2509. Bibcode:2009PASJ...61..471T. doi:10.1093/pasj/61.3.471.
- Cowing, Keith: The remarkable solar twin HIP 56948 is a prime target in the quest for other earths. Spaceref.com, published 13 April 2012, retrieved 16 April 2012.
- Meléndez, Jorge; Iván Ramírez (2007). "HIP 56948: A Solar Twin with a Low Lithium Abundance (abstract)". Astrophysical Journal Letters 669 (2): L89. arXiv:0709.4290. Bibcode:2007ApJ...669L..89M. doi:10.1086/523942.
- Shiga, David (2007-10-03). "Sun's 'twin' an ideal hunting ground for alien life". New Scientist. Retrieved 2009-05-28.
- The Telegraph, retrieved 5 November 2010.
- New Scientist, retrieved 5 October 2009.
- "Light of the Dragon: Astronomers Discover Sun's Twin at McDonald Observatory". Astrobiology Magazine. 2007-11-13. Retrieved 2009-05-28.
- Mosher, Dave (2007-11-09). "Astronomers find the sun's long-lost twin: Happy reunion unlikely, as the star is about 200 light-years away". MSNBC. Retrieved 2009-05-28.