Spectral class
The spectral class, also called spectral type, is in astronomy, a classification of the stars according to the appearance of their light spectrum.
The system is based on the discovery by Joseph von Fraunhofer in 1813, which was dark absorption lines in the solar spectrum. Robert Wilhelm Bunsen and Gustav Robert Kirchhoff discovered in 1859 that these lines to the position are identical to the emission lines, which are released by certain chemical elements.
This suggested that these elements had to be present in the sun. The spectral analysis was justified. In addition to the analysis of materials on Earth, the stellar spectra were then analyzed.
Principle of spectral classification
Spectral classes of the MK system ( by William Wilson Morgan and Philip C. Keenan) are determined by the visual comparison of the spectra of stars with spectra of standard stars. An instrumental effect on the classification, such as a higher spectral resolution ruled out, even a standard instrumentation was specified. However, since the development of astronomical instruments since the original MK system is well advanced, the classification resolution has since been increased several times. New standard stars were included in the system, and others that have been recognized to be very suitable, removed from the system. The spectral range to which applies the MK classification ranges from about 390 to about 500 nm, due to the photographic emulsions used in the original system.
The MK classification includes no explicit classification according to secondary certain physical quantities, but makes use of the ability of the human brain for pattern recognition advantage. Recently, however, neural networks were trained with some success to the MK- classification. This ensures that the classification remains consistent, even if change the findings on stellar physics.
Classification
It has become common to refer to the spectral classes O to A as an early spectral classes, the spectral classes F to G as the average spectral classes and the other spectral types as late spectral classes. The terms early, middle and late come from the now outdated assumption, the spectral say something about the development status of a star. Despite this erroneous classification of these terms are still in use today, and one star is regarded as sooner or later, if its spectral class is closer to the Class O or Class M of another in comparison to the.
There are the following seven basic classes and three classes for brown dwarfs and three subclasses for nucleosynthesis caused by the chemical features of red giant stars:
In order to classify the stars in more detail, the spectra continue to be graded in the individual classes 0-9. There are today several systems of spectral classification, the spectral type of this notation serve themselves and their classes to align this system. Harvard the original system and its extension, the MT system, which in addition defines the brightness classes, not all of these subtypes have been also used. On B3 star example was immediately followed by B5 stars, the Class B4 was skipped. With increasingly better tools could be distinguished finer over time so that intermediate classes have been defined, for example, there are between B0 and B1 now even three additional classes, B0.2, B0.5, B0.7 and shall be called.
The spectral classes with her seven basic types (O, B, A, F, G, K, M) account for around 99% of all the stars, so the other classes are often neglected. As a mnemonic for these spectral classes serve the sentences:
There are many other variants corresponding mnemonics.
Classes outside of the standard sequences
The following classes can not be categorized into the sequences described above:
Prefixes and suffixes
The division of the spectral can be refined further by suffixes and prefixes.
Suffixes
Some of these additives are an indication of the luminosity class, which were introduced in 1943 by William Wilson Morgan and Philip Keenan (hence: MK system) superfluous.
Prefixes
History
First attempts to bring order to the brightness and temperature of stars had, the Italian Father Angelo Secchi made in 1865 with a three -point scale and 1874 Hermann Carl Vogel with a system in which the previously known stellar evolution theories were incorporated, leading to constant changes resulted. In 1868, Angelo Secchi developed the following four basic types:
- Type I: white and blue stars with a strong hydrogen line ( A-Class )
- Type III: orange to red stars with complex bands ( M- class)
- Type IV: red stars with significant carbon bands and lines ( carbon stars )
In 1878 he added a further added:
- Type V: bright spectral lines (Be, Bf, etc.)
Based on extensive spectra of Henry Draper, a new classification was developed. Edward Charles Pickering started in 1890, together with Williamina Fleming, Antonia Maury and Annie Jump Cannon appropriate work. This Pickering went before alphabetically and arranged the classes with uppercase letters from A to Z to the Balmer series ( transitions of the electron orbits in the hydrogen spectrum ). This scheme was replaced by the so-called Harvard classification Through further research, which provided for a subdivision into types AQ.
However, Annie Jump Cannon introduced very soon realized that the order did not make sense: after graduation, the blue - white glowing, hot O-stars came to the red, relatively cool M and N stars. It was also revealed that some of the classes were based only on exposure errors, or had no meaning and were therefore omitted. The step was taken not from the spectrum, but by the temperature of the star -dependent. Based on these findings, the previous subdivision in 1912 was re-sorted, and it was followed by the subdivision used today in the seven above-mentioned spectral classes.