Herotu

Terminology of stellar astronomy

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Hertzsprung – Russell diagram (English: Hertzsprung – Russell diagram, abbreviated as H – R diagram, HR diagram or HRD) is based on stars Absolute magnitude Or luminosity relative to spectral type or Effective temperature Drawn Scatter plot 。 More simply, it plots each star on a chart and can measure its temperature (color) and luminosity, which is independent of the position of each star. dependent Color magnitude diagram (CMD, colour – magnetic diagram) Apparent magnitude And colors are usually drawn for clusters of stars at the same distance.

This chart is that of Eina Herzpoon and Henry Norris Russell Created in the 1910s Stellar evolution A very important step.

The Herot chart can show the evolution process of stars. About 90% of stars are located from the upper left corner to the right of the Herot chart Lower corner On the ribbon, this Line be called Main order band 。 The stars on the main sequence belt are called Main sequence star 。 Siderogenic Molecular cloud It is the area at the extreme right of the figure, but as the molecular cloud begins to shrink, its temperature begins to rise, and it will slowly move to the main sequence band. When the star is dying, it will leave the main sequence belt, and the star will move to the upper right. Here is Red Giant and Red supergiant The area of surface temperature A low but luminous star. Passing the red giant but not happening Supernova explosion The star will cross the main sequence band and move to the lower left. This is the area with high surface temperature and low luminosity White dwarf The area where the Black dwarf 。

Chinese name: Herotu
Foreign name: Hertzsprung-Russell diagram
Presenter: Herzpoon ， Russell

Proposed time: 1911 1913
Applied discipline: Stellar astronomy
Abbreviation: H-R diagram

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historical background

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In the 19th century, the Harvard University Observatory conducted a large-scale photographic spectral survey of stars, obtained the spectra of hundreds of thousands of stars, classified them, and finally completed the Henry Draper Catalog. Antonia Murray She participated in one part of the work according to Spectral line Herzpoon pointed out that stars described by narrow spectral lines are smaller than other stars of the same spectral type. He thought it was that stars with narrow spectral lines had greater luminosity indication, and calculated some groups of Long-term parallax , so that he can estimate its absolute magnitude.^[1-2]

In 1910, Hans Rosenberg published a chart to plot the apparent magnitude of stars in the Pleiades cluster with the strength of calcium lines relative to the two Palmer lines of hydrogen^[3] 。 These spectral lines act as Stellar temperature Agent for, yes Spectral classification The early form of. In the same star cluster, the apparent magnitude of stars is equal to their absolute magnitude, so this early picture is actually a luminosity map related to temperature. Even today, the same type of image is still used to display the stars in the cluster without knowing their distance and brightness^[4] Herzpoon has also used this type of chart, but it was not until 1911 that he first showed it in his publications. This is also the pattern of using the apparent magnitude map of star clusters with the same distance.^[5]

The figure of Russell's early version (1913) includes giant stars classified by Antonia Murray and confirmed by Herzpoon, as well as close stars with measured parallax at that time, Hyades (nearby open star clusters) and some Moving constellation Stars in; All of these are OK Measuring distance To obtain the absolute magnitude of these stars.^[6]

Form of graph

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There are several types of Herloths, but they are not well defined in terms of naming. All types have a common general layout: bright stars are distributed at the top of the figure, surface temperature High stars are distributed on the left side of the image.

The original image is in horizontal axis Display the spectral type of the star on the vertical axis Absolute apparent magnitude 。 The spectral type is not a numerical quantity, but its sequence reflects the monotonic sequence of the star surface temperature. The modern observational version of the chart replaces the spectral type with the color index (in the 20th century chart, the most common is that of stars B-V color index ）。 This type of chart is often referred to as the observational Herot chart, or special Chromatic light Figure (CMD, color–magnitude diagram）， And usually Observer When using a known star at the same distance (such as Stellar cluster CMD is usually used to describe the stars in the cluster vertical axis Apparent magnitude of apparent star. For members of clustering, it is assumed that there is a single additive constant difference between the apparent magnitude and the absolute magnitude (called distance modulus) of all star clusters. Early to nearby Open cluster (like the Hyades and Pleiades ）Herzpoon and Rosenberg obtained the first CMD map Russell Collect All Siderogram Comprehensive data can determine the absolute magnitude of stars.^[7]

Another form of the diagram is to plot the effective surface temperature of the star on one axis and the luminosity of the star on the other axis, and almost all of them use a double logarithmic coordinate system. Stellar structure and Stellar evolution The results of theoretical calculation and observation are consistent. This kind of diagram is called "temperature photometry", but this name has hardly been used; When distinguishing, this form is replaced by the name of "theoretical Herlotto". The characteristic of this form of Herot chart is that the temperature is plotted from high temperature to low temperature, which is helpful to compare with the chart of observation type.

Although the two pictures are similar, astronomers have made a clear distinction between them. The reason for this distinction is that it is not easy to accurately convert from one diagram to another. stay Effective temperature The conversion between and color requires a color temperature relationship, which is difficult to construct; It is well known that this is a function of star composition and is subject to other factors (e.g Stellar rotation ）Impact. When the luminosity or absolute full band magnitude（ Hot magnitude ）Convert to Apparent magnitude Or absolute visual magnitude, which may or may not have the same correlation with the color temperature map. In addition, it is also necessary to know the effect of the observed object (i.e. distance modulus) and interstellar occlusion, which have an impact on both color (reddening) and apparent magnitude (the effect is called extinction). Distortion (including reddening) and extinction (shading) of color are significant Periplanetary dust It is also obvious on the star. It is ideal to compare the theory of stellar evolution directly with the observation, because the conversion between theory and observation will generate additional Uncertainty 。^[8]

Picture analysis

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The distribution of most stars in the map is called the main sequence zone diagonal Regional. The life stage of these stars in the main sequence belt nuclear fusion The reaction is hydrogen fusion. The stars concentrated in the next stage are Horizontal branch (At the core is Helium fusion , hydrogen fusion takes place in the shell surrounding the core). Another prominent feature is that it is located in the region between spectral types A5 and G0, and between absolute magnitude+1 and - 3 Herschel gap (That is, between the top of the main sequence belt and the giant star of the horizontal branch). On the left side of the gap is called Unstable zone The interval of RR Lyrae variable The stars of. Cepheid variable It also falls in the area with higher luminosity on the unstable zone.

Astronomers can roughly measure star clusters or Galaxy How far is it from the earth. This can be achieved by Apparent magnitude With known distance (or model star) Absolute magnitude Compare to achieve. Then move the whole group in the vertical direction until the main sequence bands of the two overlap. in order to Match two Group bridged the magnitude The difference is called Distance modulus , that is direct measurement Distance out (ignored extinction Factors). This technique is called main sequence fitting, which is the spectrum parallax One of. Not only can turning points in the main sequence be used, Red Giant The tip of the branch can also be used^[9-10]

Scientific application

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Right Chart The thinking of the "red giant" led astronomers to speculate that it might prove the evolution of stars, and the main argument is that the red giant fell from dwarf star And then move down the main sequence during its lifetime. Therefore, stars are believed to convert gravitational energy into radiation through the Kelvin Helm or z mechanism Radiant energy 。 This mechanism results in the age of the sun being only tens of millions of years solar system Astronomers and biologists and geologist There was a conflict between them, and they had evidence that the earth was much older than this. By the 1930s, when nuclear fusion It can be solved only when it is determined as the energy source of the star.

At Russell in Royal Astronomical Society After introducing the picture at the 1912 conference, Arthur Eddington was inspired to use it as a development Stellar physics The foundation of thought. In 1926, he explained how stars fit into the physics of pictures in his book The Internal Structure of Stars.^[11] This paper anticipates the later discovery nuclear fusion , and correctly proposed that the power source of stars is hydrogen fusion into helium, releasing huge energy. This is a leap of opportunity, because the energy source of the star has not been solved at that time, and the existence of the star has not been proved thermonuclear Energy, even though it has not been found that stars are mainly hydrogen (see Amount of metal ）。 Eddington managed to avoid the problem, Concentrate attention In the star Internal energy Of thermodynamics 。^[12]

Figure 1

(Related terms: Stellar nucleosynthesis )

Apply formula

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When physicists studied the thermal radiation spectrum, they found the relationship between brightness and temperature on a unit area. The higher the temperature High brightness The brighter. Therefore, once we can determine the absolute magnitude and spectral type of a planet, we can estimate its size.

Heat radiation energy and temperature released in unit area per unit time Quartic Is proportional.

For example, F=σ T ∨ (a=5.67 × 10 ¯ erg s ¯¹ cm ¯² K ¯) (σ is Stephen· Boltzmann constant ）

Brightness as unit time Internal heat The energy emitted by radiation, so multiply the above equation by the total area of the planet, assuming that the planet is spherical:

L=4πR²σT⁴

So on the Herotu, we can also put the same Surface area The location of the planet is marked with a line. As we can see, at the top right of Figure 1, it is a very large planet with low temperature and high brightness. The higher the temperature and lower the brightness, the smaller the volume.^[7]

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