The spectral type isfixed starTemperature classification system based on stellar spectrumtypeThe stars are divided into O, B, A, F, G, K and M types.amongG starThere are also two variants, R and N, and K has one variant, S.
eachspectrumThey can be further divided into digital subtypes, ranging from 0 to 9. Higher numbers represent lower energy spectra and redder colors.Add after the numberRoman numeralsorletterexpressStellar evolutionStage (for example, the solar spectral type is G2V).[1]
Oh Be A Fine Girl(or Guy),Kiss me!(Oh, be a good girl/guy, kiss me!) This sentence just happens to be the order of spectrum type, is it easy to remember?
Morgan KenThe spectral classification method is the most common star classification method at present. It is sorted from high to low according to the temperature of stars (mass, radius and brightness are all compared with the sun), but its spectral labeling is still usedHarvard spectrumThe spectrum of stars is divided into seven categories, and each category is subdivided into ten sub categories.But at present, the hottest star is O5, and the coldest star is M5, that is, there are only five subcategories of O type and six subcategories of M type, totaling 61 subcategories.
The characteristics of each type are as follows:
O: Blue.Ionized helium with temperature higher than 25000 Kspectrum, spectral line of hydrogen（Absorption line）Not obvious, the continuous spectrum in the ultraviolet region is strong.Most atoms are highionizationFor example, nitrogen loses two electrons, silicon loses three, and helium loses one.
B: Blue to bluish white.When the temperature is between 11000 and 25000 K, the spectral line of helium atom is neutral, silicon loses one or two electrons, and oxygen and magnesium lose one electron.For example, B0 has no free spectral line of helium, hydrogenSpectral lineIt is already obvious.
A: Blue white to white.The temperature is between 7500 and 11000K, and the spectral line of hydrogen atom is the strongest. Silicon, magnesium, iron, calcium, titanium, etc. are all free spectral lines, but the spectral line of metal is very weak.For example, A0 has no spectral line of helium, weak spectral line of magnesium and silicon, and spectral line of calcium.
F: White to yellowish white.The temperature is between 6000 and 7500K, and there are ionized metal spectral lines. The spectral lines of hydrogen become weak but still obvious, and the spectral lines of iron, chromium and other natural metals begin to appear.For example, the calcium ion line of F0 is strong, and the spectrum line of hydrogen has weakened, but the spectrum line of neutral hydrogen atom and the first order metal ion line are both obvious.
G: Yellow white to yellow.The temperature is between 5000 and 6000K. There are free metal, calcium and some metal spectral lines. The spectral line of hydrogen atom is weak, and molecular spectral line (CH) has appeared.For example, the G0 spectral line is dominated by neutral metal lines, with strong neutral calcium, magnesium and iron absorption lines. The calcium ion line is the strongest, and the hydroxyl (G-band) absorption line is very strong.
K: Yellow to orange.The temperature is between 3500 and 5000K, mainly metal spectral lines.For example, the intensity of K0 is weak in the blue continuous region, the hydrogen line is weak, and there are neutral metal spectral lines, molecular spectral lines（CH、CN）It still exists.
Spectral type
M: Orange to red.When the temperature is lower than 3500K, there are spectral lines of metals, molecules and oxides,Titanium oxideThe spectral line of (TiO) becomes the most important, and the hydrogen line disappears.For example, M0 has strong molecular bands, especially the strong spectral lines of titanium oxide and calcium atoms, and the red area presents continuous spectrum;The spectral line of M5 calcium atom is very strong, and the strength of titanium oxide exceeds that of calcium.(Type M and K are also calledRed dwarf）
In addition, because there are other elements involved in nuclear reaction in the region of giant stars, there are three classifications of R, S and N that are only used in the giant star branch;Some stars are not easy to classify because of some special spectral lines, and they will also be distinguished by the letters used for annotations.At the beginning of the development of Harvard Spectral ClassificationSolar spectrumThe naming method of "A" is based on the atomic spectrum of hydrogen, and is marked in the order of letters A, B, C, D according to the strength. Type A is the strongest hydrogen spectral line, type B is weaker than type A, type C is weaker, and so on.But we know that the spectral lines of hydrogen are only obvious within a specific temperature range, and the spectral lines will be weakened if the temperature is too high or too low. So when Morgan and Kenna use temperature to arrange, the letters can no longer be arranged in order;At the same time, referring to the spectral lines of other atoms, some duplicate types were merged and deleted, and the original 16 classifications of the Harvard classification were changed to the types we see today.
The classification system has been extended to failed stars (too small to sustain hydrogenfusion, but the quality is much higher than normalGiant planet）[2], i.eBrown dwarfUp, divided into L-shaped stars andT-star。
Spectrum ranking
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Morgan Kener spectrumastronomyIt is widely used on. In order to facilitate students' memory, many memory formulas have been developed, among which the most familiar one is this sentence: Oh!Be A Fine Girl Kiss Me, ironically, almost all astronomers are male, but it is a group of female astronomers who formulated the Harvard Spectral Classification.
These are also traditional memory formulas. You can also find formulas in different occasions (including politics) on the Internet.
O. Type B, and A are sometimes called early form spectra, and K and M are called late form spectra. This is independent of observation, and is based on the theory of the early 20th century. At that time, it was believed that the star was born in the early stage of high temperature, and then the temperature gradually decreased to the late stage of low temperature.The study found that this statement is completely wrong.
There are some rare spectral classifications that are only applicable to a few stars:
Rare spectral types
W: 25000~50000K - huge Wolf Rayet stars.
L：1,500-2,700 K –fixed starThe mass of is not enough to allow the nuclear fusion of hydrogen to continueBrown dwarf。L stands for lithium, which will rapidly degenerate in a star.
T: 300-1500K – T brown dwarf with lower temperature than L brown dwarf and methane in the spectrumSpectral line。asMethane Dwarf 。
Three types of brown dwarfs
Y: <300K - The lowest temperature brown dwarf star, almost does not emit light.
D stands forWhite dwarf, the end point of low-quality stars at the end of their lives.The spectrum of white dwarfs can be subdivided into DA, DB, DC, DO, DX, DZ, and DQ.It should be noted that the additional letters are not used for the star itself, but only to describe the condition of the atmosphere outside the white dwarf.
The classification of white dwarfs is as follows:
DA: There is abundant hydrogen in the periphery or atmosphere, and there are spectral lines of Balman series in the spectrum.
DB: There is abundant helium in the periphery or atmosphere, and there are spectral lines of neutral helium atoms in the spectrum.
DO: The spectrum is dominated by helium ion spectral lines, and there may also be weak hydrogen and helium atomic spectral lines.
DQ: There is abundant carbon in the periphery or atmosphere, and there are carbon source or molecular spectral lines in the spectrum.
DZ: There are abundant metals in the periphery or atmosphere, and there are spectral lines of calcium ions in the spectrum.
DC: There are no spectral lines with the above characteristics in the spectrum, that is, the spectrum is almost continuous.
DX: The characteristics of spectral lines are not clear and cannot be classified accurately.
A. If the characteristics of B, O, Q isospectral lines appear in the spectrum of the same white dwarf star, they can also be listed at the same time.
Physical properties (additional letters)
In order to more clearly describe the physical state of the white dwarf, the second letter will be used to describe:
P: Spectrum is polarized
H: The spectral line splits under the magnetic field due to the Zeeman effect
Temperature indication: the spectrum of white dwarfs also has a range of surface temperature defined by a number series from 1 to 9. The temperature of 1 is about 37500K, and the temperature of 9 is about 5500K.Is based on 50400K, divided by theEffective temperatureThe quotient obtained.
