Solar analog

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"Solar twins" redirects here. For the musical group, see Solar Twins (band). For a star that likely came from the same stellar nursery as the Sun, see Solar sibling.

Solar-type star, solar analogs (also analogues), and solar twins are stars that are particularly similar to the Sun. The stellar classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type.[1] Observations of these stars are important for understanding better the properties of the Sun in relation to other stars and the habitability of planets.[2]

By similarity to the Sun[edit]

Defining the three categories by their similarity to the Sun reflects the evolution of astronomical observational techniques. Originally, solar-type was the closest that similarity to the Sun could be defined. Later, more precise measurement techniques and improved observatories allowed for greater precision of key details like temperature, enabling the creation of a solar analog category for stars that were particularly similar to the Sun. Later still, continued improvements in precision allowed for the creation of a solar-twin category for near-perfect matches.

Similarity to the Sun allows for checking derived quantities—such as temperature, which is derived from the color index—against the Sun, the only star whose temperature is confidently known. For stars that are not similar to the Sun, this cross-checking cannot be done.[1]

Solar-type[edit]

The Sun (left) compared to the similar but slightly smaller and less active Tau Ceti (right).

These stars are broadly similar to the Sun. They are main-sequence stars with a B−V color between 0.48 and 0.80, the Sun having a B−V color of 0.65. Alternatively, a definition based on spectral type can be used, such as F8V through K2V, which would correspond to B−V color of 0.50 to 1.00.[1] This definition fits approximately 10% of stars,[3] so a list of solar-type stars would be quite extensive.[4]

Solar-type stars show highly correlated behavior between their rotation rates and their chromospheric activity (e.g. Calcium H & K line emission) and coronal activity (e.g. X-ray emission)[5] Because solar-type stars spin down during their main-sequence lifetimes due to magnetic braking, these correlations allow rough ages to be derived. Mamajek & Hillenbrand (2008)[6] have estimated the ages for the 108 solar-type (F8V–K2V) main-sequence stars within 52 light-years (16 parsecs) of the Sun based on their chromospheric activity (as measured via Ca, H, and K emission lines).

The following table shows a sample of solar-type stars within 50 light years that nearly satisfy the criteria for solar analogs (B−V color between 0.48 and 0.80), based on current measurements: (The Sun is listed for comparison.)

Sample of solar-type stars
Identifier J2000 Coordinates[7] Distance[7]
(ly)
Stellar
Class
[7]
Temperature
(K)
Metallicity
(dex)
Age
(Gyr)
Notes
Right ascension Declination
Sun 0.00 G2V 5,778 +0.00 4.6 [8]
Tau Ceti [9] 01h 44m 04.1s −15° 56′ 15″ 11.9 G8V 5,344 –0.52 5.8 [10]
82 Eridani [11] 03h 19m 55.7s −43° 04′ 11.2″ 19.8 G8V 5,338 –0.54 6.1 [12]
Delta Pavonis [13] 20h 08m 43.6s −66° 10′ 55″ 19.9 G8IV 5,604 +0.33 ~7 [14]
V538 Aurigae [15] 05h 41m 20.3s +53° 28′ 51.8″ 39.9 K1V 5,257 −0.20 3.7 [12]
HD 14412 [16] 02h 18m 58.5s −25° 56′ 45″ 41.3 G5V 5,432 −0.46 9.6 [12]
HR 4587 [17] 12h 00m 44.3s −10° 26′ 45.7″ 42.1 G8IV 5,538 0.18 8.5 [12]
HD 172051 [18] 18h 38m 53.4s −21° 03′ 07″ 42.7 G5V 5,610 −0.32 4.3 [12]
72 Herculis [19] 17h 20m 39.6s +32° 28′ 04″ 46.9 G0V 5,662 −0.37 5 [12]
HD 196761 [20] 20h 40m 11.8s −23° 46′ 26″ 46.9 G8V 5,415 −0.31 6.6 [14]
Nu² Lupi [21] 15h 21m 48.1s −48° 19′ 03″ 47.5 G4V 5,664 −0.34 10.3 [14]

Solar analog[edit]

These stars are photometrically similar to the Sun, having the following qualities:[1]

  • Temperature within 500 K from that of the Sun (5278 to 6278 K)
  • Metallicity of 50–200% (± 0.3 dex) of that of the Sun, meaning the star's protoplanetary disk would have had similar amounts of dust from which planets could form
  • No close companion (orbital period of ten days or less), because such a companion stimulates stellar activity

Solar analogs not meeting the stricter solar twin criteria include, within 50 light years and in order of increasing distance (The Sun is listed for comparison.):

Identifier J2000 Coordinates[7] Distance[7]
(ly)
Stellar
Class
[7]
Temperature
(K)
Metallicity
(dex)
Age
(Gyr)
Notes
Right ascension Declination
Sun 0.00 G2V 5,778 +0.00 4.6 [8]
Sigma Draconis [22] 19h 32m 21.6s +69° 39′ 40″ 18.8 K0V 5,297 −0.20 4.7 [23]
Beta Canum Venaticorum [24] 12h 33m 44.5s +41° 21′ 27″ 27.4 G0V 5,930 −0.30 6.0 [12]
61 Virginis [25] 13h 18m 24.3s −18° 18′ 40″ 27.8 G5V 5,558 −0.02 6.3 [14]
Zeta Tucanae [26] 00h 20m 04.3s –64° 52′ 29″ 28.0 F9.5V 5,956 −0.14 2.5 [10]
Beta Comae Berenices [27] 13h 11m 52.4s +27° 52′ 41″ 29.8 G0V 5,970 −0.06 2.0 [12]
61 Ursae Majoris [28] 11h 41m 03.0s +34° 12′ 06″ 31.1 G8V 5,483 −0.12 1.0 [12]
HR 511 [29] 01h 47m 44.8s +63° 51′ 09″ 32.8 K0V 5,333 +0.05 3.0 [12]
Alpha Mensae [30] 06h 10m 14.5s –74° 45′ 11″ 33.1 G5V 5,594 +0.10 5.4 [10]
HD 69830 [31] 08h 18m 23.9s −12° 37′ 56″ 40.6 K0V 5,410 −0.03 10.6 [10]
HD 10307 [32] 01h 41m 47.1s +42° 36′ 48″ 41.2 G1.5V 5,848 −0.05 7.0 [12]
HD 147513 [33] 16h 24m 01.3s −39° 11′ 35″ 42.0 G1V 5,858 +0.03 0.4 [14]
58 Eridani [34] 04h 47m 36.3s −16° 56′ 04″ 43.3 G3V 5,868 +0.02 0.6 [10]
47 Ursae Majoris [35] 10h 59m 28.0s +40° 25′ 49″ 45.9 G1V 5,954 +0.06 6.0 [10]
HD 84117 [36] 09h 42m 14.4s –23° 54′ 56″ 48.5 F8V 6,167 −0.03 3.1 [10]
HD 4391 [37] 00h 45m 45.6s –47° 33′ 07″ 48.6 G3V 5,878 −0.03 1.2 [10]
20 Leonis Minoris [38] 10h 01m 00.7s +31° 55′ 25″ 49.1 G3V 5,741 +0.20 6.5 [12]
Nu Phoenicis [39] 01h 15m 11.1s –45° 31′ 54″ 49.3 F8V 6,140 +0.18 5.7 [10]
51 Pegasi [40] 22h 57m 28.0s +20° 46′ 08″ 50.9 G2.5IVa 5,804 +0.20 7.0 [10]

Solar twin[edit]

To date no solar twin with an exact match as that of the Sun has been found, however, there are some stars that come very close to being identical to that of the Sun, and are such considered solar twins by the majority of the public. 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.[41] 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.[42][43][44]

Morgan-Keenan spectral classification of stars. Most common star type in the universe are M-dwarfs, 76%. The sun is a 4.6 billion year-old G-class (G2V) star and is more massive than 95% of all stars. Only 7.6% are G-class stars

The stars below are more similar to the Sun and having the following qualities:[1]

  • Temperature within 50 K from that of the Sun (5728 to 5828 K)[a]
  • Metallicity of 89–112% (± 0.05 dex) of that of the Sun, meaning the star's proplyd would have had almost exactly the same amount of dust for planetary formation
  • No stellar companion, because the Sun itself is a solitary star
  • An age within 1 billion years from that of the Sun (3.6 to 5.6 Ga)

The following are the known stars that come closest to satisfying the criteria for a solar twin. The Sun is listed for comparison. Highlighted boxes are out of range for a solar twin, but the star may have been noted as solar twin in the past.

Identifier J2000 Coordinates[7] Distance[7]
(ly)
Stellar
Class
[7]
Temperature
(K)
Metallicity
(dex)
Age
(Gyr)
Notes
Right ascension Declination
Sun 0.00 G2V 5,778 +0.00 4.6 [8]
18 Scorpii [45] 16h 15m 37.3s –08° 22′ 06″ 45.1 G2Va 5,790 −0.03 2.9 [46][47]
HD 150248 [48] 16h 41m 49.8s –45° 22′ 07″ 88 G2 5,750 −0.04 6.2 [47]
HD 164595 [49] 18h 00m 38.9s +29° 34′ 19″ 91 G2 5,810 −0.06 4.5 [47]
HD 195034 [50] 20h 28m 11.8s +22° 07′ 44″ 92 G5 5,760 −0.04 2.9 [51]
HD 117939 [52] 13h 34m 32.6s –38° 54′ 26″ 98 G3 5,730 −0.10 6.1 [47]
HD 138573 [53] 15h 32m 43.7s +10° 58′ 06″ 101 G5IV-V 5689 +0.10 5.6 [47][54]
HD 71334 [55] 08h 25m 49.5s −29° 55′ 50″ 124 G2 5,701 −0.075 8.1 [56]
HD 98649 [57] 11h 20m 51.769s –23° 13′ 02″ 135 G4V 5759 −0.02 2.3 [47]
HD 143436 [58] 16h 00m 18.8s +00° 08′ 13″ 141 G0 5,768 +0.00 3.8 [54]
HD 129357 [59] 14h 41m 22.4s +29° 03′ 32″ 154 G2V 5,749 −0.02 8.2 [54]
HD 133600 [60] 15h 05m 13.2s +06° 17′ 24″ 171 G0 5,808 +0.02 6.3 [46]
HIP 11915 [61] 02h 33m 49.02s −19° 36′ 42.5″ 190 G5V 5,760 –0.059 4.1 [62]
HD 101364 [63] 11h 40m 28.5s +69° 00′ 31″ 208 G5V 5,795 +0.02 3.5 [46][64]
HD 197027 [65] 20h 41m 54.6s –27° 12′ 57″ 250 G3V 5,723 −0.013 8.2 [66]
Kepler-452 [67] 19h 44m 00.89s +44° 16′ 39.2″ 1400 G2V 5,757 +0.21 6.0 [68]
YBP 1194 [69] 08h 51m 00.8s +11° 48′ 53″ 2934 G5V 5,780 +0.023 ~ 4.2 [70]

Some other stars are sometimes mentioned as solar-twin candidates such as: Beta Canum Venaticorum; however it has too low metallicities (–0.21) for solar twin. 16 Cygni B is sometimes noted as twin, but is part of a triple star system and is very old for a solar twin at over 9 Gyr.

By potential habitability[edit]

Another way of defining solar twin is as a "habstar" — a star with qualities believed to be particularly hospitable to an Earth-like planet. Qualities considered include variability, mass, age, metallicity, and close companions.[71][b]

  • At least 3 billion years old
  • On the main sequence
  • Non-variable
  • Capable of harboring terrestrial planets
  • Support a dynamically stable habitable zone
  • No stellar companion star.

The requirement that the star remain on the main sequence for at least 3 Ga sets an upper limit of approximately 1.5 solar masses, corresponding to a hottest spectral type of F5 V. Such stars can reach an absolute magnitude of 2.5, or 8.55 times as bright as the Sun, at the end of the main sequence.[71][74]

Non-variability is ideally defined as variability of less than 1%, but 3% is the practical limit due to limits in available data. Variation in irradiance in a star's habitable zone due to a companion star with an eccentric orbit is also a concern.[42][43][71][75]

Terrestrial planets in multiple star systems, those containing three or more stars, are not likely to have stable orbits in the long term. Stable orbits in binary systems take one of two forms: S-Type (satellite or circumstellar) orbits around one of the stars, and P-Type (planetary or circumbinary) orbits around the entire binary pair. Eccentric Jupiters may also disrupt the orbits of planets in habitable zones.[71]

Metallicity of at least 40% solar ([Fe/H] = −0.4) is required for the formation of an Earth-like terrestrial planet. High metallicity strongly correlates to the formation of hot Jupiters, but these are not absolute bars to life, as some gas giants end up orbiting within the habitable zone themselves, and could potentially host Earth-like moons.[71]

One example of such a star is HD 70642 [76], a G5V, at temperature of 5533K and is younger than the sun, at 3.8 billion years old.[77]

Another such example would be HIP 11915, which has a planetary system containing a Jupiter-like planet orbiting at a similar distance that the planet Jupiter does in the Solar System.[78] To strengthen the similarities, the star is class G5V, very similar temperature of 5750 K, its sun-like mass and radius, and is only 500 million years younger than the Sun. As such, the habitable zone would extend in the same area as the zone in the Solar System, around 1 AU. This would allow an Earth-like planet to exist around 1 AU.

See also[edit]

Footnotes[edit]

  1. ^ A true solar twins as noted by the Lowell Observatory should have a temperature within ~10 K of the Sun. Space Telescope Science Institute, Lowell Observatory, noted in 1996 that temperature precision of ~10 K can be measured. A temperature of ~10 K reduces the solar twin list to near zero, so ±50 K is used for the chart.[2]
  2. ^ habstar or habitability, is currently defined as an area, such as a planet or a moon, where liquid water can exist for at least a short duration of time.[72][73]

References[edit]

  1. ^ a b c d e Soderblom, David R.; King, Jeremy R. (1998). "Solar-Type Stars: Basic Information on Their Classification and Characterization". In Jeffrey C. Hall. Solar Analogs: Characteristics and Optimum Candidates. The Second Annual Lowell Observatory Fall Workshop – October 5–7, 1997. Lowell Observatory. pp. 41–60. Bibcode:1998saco.conf...41S. Retrieved 2 March 2013. 
  2. ^ a b David R. Soderblom & Jeremy R. King. "Solar-Type Stars: Basic Information on Their Classification and Characterization". Space Telescope Science Institute. Lowell Observatory,. Retrieved 2016-09-30. 
  3. ^ Owlcation STEM, Astronomy, Different Types of Stars in the Universe, June 13, 2016
  4. ^ Atlas of the Universe, The Classification of Stars
  5. ^ NASA, Chromospheric variations in main-sequence stars, Jan. 01, 1995
  6. ^ E. E. Mamajek; L. A. Hillenbrand (2008). "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics". Astrophysical Journal. 687 (2): 1264. arXiv:0807.1686Freely accessible. Bibcode:2008ApJ...687.1264M. doi:10.1086/591785. 
  7. ^ a b c d e f g h i "SIMBAD Astronomical Database". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2009-01-14. 
  8. ^ a b c Williams, D.R. (2004). "Sun Fact Sheet". NASA. Retrieved 2009-06-23. 
  9. ^ Tau Ceti at SIMBAD - Ids - Bibliography - Image.
  10. ^ a b c d e f g h i j Santos, N. C.; Israelian, G.; Randich, S.; García López, R. J.; Rebolo, R. (October 2004). "Beryllium anomalies in solar-type field stars". Astronomy and Astrophysics. 425 (3): 1013–1027. arXiv:astro-ph/0408109Freely accessible. Bibcode:2004A&A...425.1013S. doi:10.1051/0004-6361:20040510. 
  11. ^ 82 Eridani at SIMBAD - Ids - Bibliography - Image.
  12. ^ a b c d e f g h i j k l Holmberg J., Nordstrom B., Andersen J.; Nordström; Andersen (July 2009). "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics". Astronomy and Astrophysics. 501 (3): 941–947. arXiv:0811.3982Freely accessible. Bibcode:2009A&A...501..941H. doi:10.1051/0004-6361/200811191.  See Vizier catalogue V/130.
  13. ^ Delta Pavonis at SIMBAD - Ids - Bibliography - Image.
  14. ^ a b c d e Sousa, S. G.; et al. (August 2008). "Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes". Astronomy and Astrophysics. 487 (1): 373–381. arXiv:0805.4826Freely accessible. Bibcode:2008A&A...487..373S. doi:10.1051/0004-6361:200809698.  See VizieR catalogue J/A+A/487/373.
  15. ^ V538 Aurigae at SIMBAD - Ids - Bibliography - Image.
  16. ^ HD 14412 at SIMBAD - Ids - Bibliography - Image.
  17. ^ HR 4587 at SIMBAD - Ids - Bibliography - Image.
  18. ^ HD 172051 at SIMBAD - Ids - Bibliography - Image.
  19. ^ 72 Herculis at SIMBAD - Ids - Bibliography - Image.
  20. ^ HD 196761 at SIMBAD - Ids - Bibliography - Image.
  21. ^ nu2 lupi at SIMBAD - Ids - Bibliography - Image.
  22. ^ Sigma Draconis at SIMBAD - Ids - Bibliography - Image.
  23. ^ Boyajian, Tabetha S.; et al. (August 2008). "Angular Diameters of the G Subdwarf µ Cassiopeiae A and the K Dwarfs s Draconis and HR 511 from Interferometric Measurements with the CHARA Array". The Astrophysical Journal. 683 (1): 424–432. arXiv:0804.2719Freely accessible. Bibcode:2008ApJ...683..424B. doi:10.1086/589554. 
  24. ^ Beta Canum Venaticorum at SIMBAD - Ids - Bibliography - Image.
  25. ^ 61 Virginis at SIMBAD - Ids - Bibliography - Image.
  26. ^ Zeta Tucanae at SIMBAD - Ids - Bibliography - Image.
  27. ^ Beta Comae Berenices at SIMBAD - Ids - Bibliography - Image.
  28. ^ 61 Ursae Majoris at SIMBAD - Ids - Bibliography - Image.
  29. ^ HR 511 at SIMBAD - Ids - Bibliography - Image.
  30. ^ Alpha Mensae at SIMBAD - Ids - Bibliography - Image.
  31. ^ HD 69830 at SIMBAD - Ids - Bibliography - Image.
  32. ^ HD 10307 at SIMBAD - Ids - Bibliography - Image.
  33. ^ HD 147513 at SIMBAD - Ids - Bibliography - Image.
  34. ^ 58 Eridani at SIMBAD - Ids - Bibliography - Image.
  35. ^ 47 Ursae Majoris at SIMBAD - Ids - Bibliography - Image.
  36. ^ HD 84117 at SIMBAD - Ids - Bibliography - Image.
  37. ^ HD 4391 at SIMBAD - Ids - Bibliography - Image.
  38. ^ 20 Leonis Minoris at SIMBAD - Ids - Bibliography - Image.
  39. ^ Nu Phoenicis at SIMBAD - Ids - Bibliography - Image.
  40. ^ 51 Pegasi at SIMBAD - Ids - Bibliography - Image.
  41. ^ NASA, Science News, Solar Variability and Terrestrial Climate, Jan. 8, 2013
  42. ^ a b University of Nebraska-Lincoln astronomy education group, Stellar Luminosity Calculator
  43. ^ a b National Center for Atmospheric Research, The Effects of Solar Variability on Earth's Climate, 2012 Report
  44. ^ Most of Earth’s twins aren’t identical, or even close!, by Ethan on June 5, 2013
  45. ^ 18 Scorpii at SIMBAD - Ids - Bibliography - Image.
  46. ^ a b c Meléndez, Jorge; Ramírez, Iván (November 2007). "HIP 56948: A Solar Twin with a Low Lithium Abundance". The Astrophysical Journal. 669 (2): L89–L92. arXiv:0709.4290Freely accessible. Bibcode:2007ApJ...669L..89M. doi:10.1086/523942. 
  47. ^ a b c d e f Porto de Mello, G. F.; da Silva, R.; da Silva, L.; de Nader, R. V. (March 2014). "A photometric and spectroscopic survey of solar twin stars within 50 parsecs of the Sun; I. Atmospheric parameters and color similarity to the Sun". Astronomy and Astrophysics. 563: A52. arXiv:1312.7571Freely accessible. Bibcode:2014A&A...563A..52P. doi:10.1051/0004-6361/201322277. 
  48. ^ HD 150248 at SIMBAD - Ids - Bibliography - Image.
  49. ^ HD 164595 at SIMBAD - Ids - Bibliography - Image.
  50. ^ HD 195034 at SIMBAD - Ids - Bibliography - Image.
  51. ^ Takeda, Yoichi; Tajitsu, Akito (2009). "High-Dispersion Spectroscopic Study of Solar Twins: HIP 56948, HIP 79672, and HIP 100963". Publications of the Astronomical Society of Japan. 61 (3): 471–478. arXiv:0901.2509Freely accessible. Bibcode:2009PASJ...61..471T. doi:10.1093/pasj/61.3.471. 
  52. ^ HD 117939 at SIMBAD - Ids - Bibliography - Image.
  53. ^ HD 138573 at SIMBAD - Ids - Bibliography - Image.
  54. ^ a b c King, Jeremy R.; Boesgaard, Ann M.; Schuler, Simon C. (November 2005). "Keck HIRES Spectroscopy of Four Candidate Solar Twins". The Astronomical Journal. 130 (5): 2318–2325. arXiv:astro-ph/0508004Freely accessible. Bibcode:2005AJ....130.2318K. doi:10.1086/452640. 
  55. ^ HD 71334 at SIMBAD - Ids - Bibliography - Image.
  56. ^ Marília Carlos1, Poul E. Nissen2 and Jorge Meléndez1 (December 18, 2015). "Correlation between lithium abundances and ages of solar twin stars, page 4" (PDF). arxiv.org. Retrieved 2016-09-26. 
  57. ^ HD 98649 at SIMBAD - Ids - Bibliography - Image.
  58. ^ HD 143436 at SIMBAD - Ids - Bibliography - Image.
  59. ^ HD 129357 at SIMBAD - Ids - Bibliography - Image.
  60. ^ HD 133600 at SIMBAD - Ids - Bibliography - Image.
  61. ^ HIP 11915 at SIMBAD - Ids - Bibliography - Image.
  62. ^ M. Bedell; J. Meléndez; J. L. Bean; I. Ramírez; M. Asplund; A. Alves-Brito; L. Casagrande; S. Dreizler; T. Monroe; L. Spina; M. Tucci Maia (June 26, 2015). "The Solar Twin Planet Search II. A Jupiter twin around a solar twin" (PDF). The European SouthernObservatory(ESO): 8. Retrieved 17 July 2015. 
  63. ^ HIP 56948 at SIMBAD - Ids - Bibliography - Image.
  64. ^ 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.
  65. ^ HIP 102152 at SIMBAD - Ids - Bibliography - Image.
  66. ^ Monroe, T. R.;; et al. (2013). "High Precision Abundances of the Old Solar Twin HIP 102152: Insights on Li Depletion from the Oldest Sun". The Astrophysical Journal Letters. 774 (2): 22. arXiv:1308.5744Freely accessible. Bibcode:2013ApJ...774L..32M. doi:10.1088/2041-8205/774/2/L32. 
  67. ^ Kepler-452 at SIMBAD - Ids - Bibliography - Image.
  68. ^ "Planet Kepler-452 b". Retrieved 6 July 2016. 
  69. ^ Cl* NGC 2682 YBP 1194 at SIMBAD - Ids - Bibliography - Image.
  70. ^ A. Önehag; A. Korn; B. Gustafsson; E. Stempels; D. A. VandenBerg (2011). "M67-1194, an unusually Sun-like solar twin in M67". Astronomy and Astrophysics. 528: A85. arXiv:1009.4579Freely accessible. Bibcode:2011A&A...528A..85O. doi:10.1051/0004-6361/201015138. 
  71. ^ a b c d e Turnbull, M. C.; Tarter, J. C. (2002). "Target Selection for SETI. I. A Catalog of Nearby Habitable Stellar Systems". The Astrophysical Journal Supplement Series. 145: 181. arXiv:astro-ph/0210675Freely accessible. Bibcode:2003ApJS..145..181T. doi:10.1086/345779. 
  72. ^ Sol Company, solstation.com, Stars and Habitable Planets, 2012
  73. ^ Britannica, Habitable zone, By Jack J. Lissauer, 8-24-2016
  74. ^ Space.com, Double-Star Systems Can Be Dangerous for Exoplanets, By Mike Wall, January 6, 2013
  75. ^ Most of Earth’s twins aren’t identical, by Ethan on June 5, 2013
  76. ^ HD 70642 at SIMBAD - Ids - Bibliography - Image.
  77. ^ "Solar System 'twin' found". BBC News. 2003-07-03. 
  78. ^ "Jupiter Twin Discovered Around Solar Twin". eso.org/. Retrieved 16 July 2015. 

Further reading[edit]

  • G. W. Lockwood & B. A. Skiff; Skiff; Radick (1997). "The Photometric Variability of Sun-like Stars: Observations and Results, 1984—1995". The Astrophysical Journal. 485 (2): 789–811. Bibcode:1997ApJ...485..789L. doi:10.1086/304453. 
  • G. Porto de Mello, R. da Silva, & L. da Silva; Da Silva; Da Silva (2000). "A Survey of Solar Twin Stars within 50 Parsecs of the Sun". Bioastronomy 99: A New Era in the Search for Life. 213: 73. Bibcode:2000ASPC..213...73P. 
  • M. C. Turnbull & J. C. Tarter; Tarter (2003). "Target Selection for SETI. II. Tycho-2 Dwarfs, Old Open Clusters, and the Nearest 100 Stars". The Astrophysical Journal Supplement Series. 149 (2): 423–436. Bibcode:2003ApJS..149..423T. doi:10.1086/379320. 
  • J. C. Hall & G. W. Lockwood; Lockwood (2004). "The Chromospheric Activity and Variability of Cycling and Flat Activity Solar-Analog Stars". The Astrophysical Journal. 614 (2): 942–946. Bibcode:2004ApJ...614..942H. doi:10.1086/423926. 
  • J. D. Jr do Nascimento, M. Castro, J. Meléndez, M. Bazot, S. Théado, G. F. Porto de Mello; Castro; Meléndez; Bazot; Théado; Porto De Mello; De Medeiros (2009). "Age and mass of solar twins constrained by lithium abundance". Astronomy and Astrophysics. 501 (1): 687–694. arXiv:0904.3580Freely accessible. Bibcode:2009A&A...501..687D. doi:10.1051/0004-6361/200911935.