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HIP 56948

Coordinates: Sky map 11h 40m 28.5s, +69° 00′ 30.6″
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HIP 56948
Observation data
Epoch       Equinox
Constellation Draco
Right ascension 11h 40m 28.48381s[1]
Declination +69° 00′ 30.5995″[1]
Apparent magnitude (V) 8.70
Characteristics
Spectral type G5V[2]
U−B color index 0.155
B−V color index 0.647 ± 0.014[1]
Variable type none
Astrometry
Radial velocity (Rv)5.4[3] km/s
Proper motion (μ) RA: –126.96[1] mas/yr
Dec.: –2.13[1] mas/yr
Parallax (π)15.68 ± 0.67 mas[1]
Distance208 ± 9 ly
(64 ± 3 pc)
Absolute magnitude (MV)4.81
Details
Mass1.02 ± 0.02[4] M☉
Radius0.99 R☉
Luminosity0.99[5] L☉
Surface gravity (log g)4.409[5] cgs
Temperature5795[5] K
Metallicity [Fe/H]0.02[5] dex
Age~3.5[4][6] Gyr
Other designations
HD 101364, BD+69 620, SAO 15590.
Database references
SIMBADdata
Exoplanet Archivedata

HIP 56948 (also known as HD 101364) is a solar twin star of type G5V.[2] It is one of the most sun-like stars yet known in terms of size, mass, temperature, and chemical makeup. Our sun is about 4.6 billion years old, and HIP 56948 is believed to be about a billion years younger, placing HIP 56948 just at the edge of a solar twin. Both stars are between a third and a halfway through their life on the main sequence.[6][7]

It is 208 light years away in the constellation of Draco,[8] lying about halfway between Polaris and Dubhe on the celestial sphere.[9] 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.[10]

Discovery

Jorge Meléndez of the Australian National University and Iván Ramírez of the University of Texas analysed the star in 2007 using the 2.7 metre Harlan J. Smith telescope at McDonald Observatory.[11]

Lithium abundance

Most other solar analogs such as 18 Scorpii are unlike the sun in that they have several times the lithium abundance. HIP 56948 is among the best candidates for a solar twin because of the known possible contenders, its lithium abundance most resembles that of our own star.[5][12] A 2009 high-dispersion spectroscopic study from the Astronomical Society of Japan confirms this.[5]

Significance

Cross-section of a solar-type star (NASA)

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 (HD 101364) 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, 8 October 2007

[7]

  • In 2009 with a better measurement, the age of HIP 56948 was revised to ~3.5. Billion years old, Gyr. [4]

Sun comparison

This chart compares the sun to HIP 56948.

Identifier J2000 Coordinates Distance
(ly) 		Stellar
Class 		Temperature
(K) 		Metallicity
(dex) 		Age
(Gyr) 		Notes
Right ascension Declination
Sun — — 0.00 G2V 5,778 +0.00 4.6 [13]
HD 101364 [14] 11h 40m 28.5s +69° 00′ 31″ 208 G5V 5,795 +0.02 3.5 [2]


An exact solar twin would be a G2V star with a 5,778K temperature, be 4.6 billion years old, with the correct metallicity and a 0.1% solar luminosity variation.[15] Stars with an age of 4.6 billion years are at the most stable state. Proper metallicity and size are also very important to low luminosity variation. [16][17]

See also

References

Footnotes
  1. ^ This age estimate is revised in Takeda and Tajitsu 2009.[5] and again in Meléndez et al. 2012.[6]
Citations
  1. ^ a b c d e f 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.Vizier catalog entry
  2. ^ a b c 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.
  3. ^ 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.
  4. ^ a b c 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ a b c d e f g 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.
  6. ^ a b c 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.
  7. ^ a b 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.
  8. ^ Shiga, David (2007-10-03). "Sun's 'twin' an ideal hunting ground for alien life". New Scientist. Retrieved 2009-05-28.
  9. ^ The Telegraph, retrieved 5 November 2010.
  10. ^ New Scientist, retrieved 5 October 2009.
  11. ^ "Light of the Dragon: Astronomers Discover Sun's Twin at McDonald Observatory". Astrobiology Magazine. 2007-11-13. Retrieved 2009-05-28.
  12. ^ 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.
  13. ^ Williams, D.R. (2004). "Sun Fact Sheet". NASA. Retrieved 2009-06-23.
  14. ^ HIP 56948 at SIMBAD - Ids - Bibliography - Image.
  15. ^ NASA, Science News, Solar Variability and Terrestrial Climate, Jan. 8, 2013
  16. ^ University of Nebraska-Lincoln astronomy education group, Stellar Luminosity Calculator
  17. ^ National Center for Atmospheric Research, The Effects of Solar Variability on Earth's Climate, 2012 Report



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