Solar analog
A sun-like star is a star that is similar in size, luminosity, spectral type, or depending on the context in other parameters of the sun. The vague term is used in the English technical language adopted more precise through the three attributes of solar -type solar- analog and solar twin, which describe in the above order is a growing consensus of the parameters of a star with those of the sun. The observation of such star for the understanding of the solar properties compared to other stars (and vice versa ) is important, especially for parameters that are available in the sun on measurement methods which are not applicable to other stars.
Solar -type stars
Here are main-sequence stars listed with a BV color index from 0.48 to 0.80 ( Sun: 0.65). ( A similar list based on spectral F8V to K2V correspond to a BV color index from 0.50 to 1.00. )
Such stars usually show a high correlation with respect to its rotational period, the activity of its chromosphere (eg, H and K emission lines of calcium ), and coronary activity (eg, in X-rays ). Since such stars are, while they remain on the main sequence of a deceleration of its rotation, can be estimated from the parameters mentioned her age. Mamajek and Hillenbrand (2008) have estimated in this way the age of 108 such main-sequence stars in Spektralklassenbereich F8V - K2V in a distance range of 16 pc due to their chromospheres activity ( H and K emission lines of calcium ).
In the table for the deviations from the following list (see the " solar analog stars" ) specified criteria are color coded.
Solar analog stars
The listed stars are photometrically similar to the sun and meet the following criteria:
- Surface temperature of the sun ± 500 K, i.e., about 5200 to 6300 K.
- Metallicity 50-200 % (± 0.3 index ) as compared to the sun, i.e., a proto disc can be assumed by a comparable amount of dust to form as in the planetary sun
- There are no close stellar companion ( orbital period 10 days or less) available. Such companions would require increased stellar activity.
The table lists those stars in the distance range 50 light-years, which are not listed in the table below sunlike star:
Solar twins
The listed stars correspond wholly or mainly enggefassten following criteria ( deviations in the table displayed in color ):
- Surface temperature of the sun ± 50 K, i.e., about 5720 to 5830 K.
- Metallicity 89-112 % (± 0.053 index ) as compared to the sun, i.e., a proto disk, a similar amount of dust in the formation of planets as assumed at the sun.
- The asterisk does not belong to a multi- star system.
- The star corresponds to the age of the Sun ± 1 billion years, ie about 3.5-5.6 × 109 years.
Sun similarity for life -friendly planets possible
The sun similarity of a star is sometimes also described about the opportunity to be orbited by a planet in the habitable zone, which in a similar way as the Earth is Earth-like and potentially life- friendly. The following parameters can be considered:
- The star is at least 3 billion years old main sequence star. This corresponds to an upper limit for the mass of about 1.5 solar masses, according to an earliest spectral type F5V. Such stars form an absolute brightness of up to 2.5M reach ( 8.55 -fold sun brightness ) at the end of their main sequence existence.
- The star is not a variable star. Ideally, a variability of less than 1% is assumed, practically is a limit of 3 % according to the accuracy of available data. In multiple star systems with a highly eccentric orbit of a companion star and the consequent variable radiation intensity in the habitable zone is observed.
- The habitable zone must be dynamically stable. For Earth-like planets in multiple star systems with three or more stars the probability is low that their orbits are stable over time ( while in double systems orbits around one of the partners (S- type ) or total (P- type) can be stable for a closest Instant star pair ). Eccentric Jupiter can change the orbits of planets in the habitable zone.
An example of such a star is HD 70,642th