Hertzsprung-Russel diagram

Figure 1.2 The Hertzsprung-Russell diagram for stars with known luminosities and spectra.

Fig. 3.3. Theoretical Hertzsprung-Russell diagram. The right-hand scale shows in absolute bolometric magnitude what the left-hand scale expresses as the logarithm of the intrinsic luminosity in units of the solar intrinsic luminosity (Lq = 4 x 10 erg s ). On the horizontal axis, the logarithm of the effective temperature, i.e. the temperature of the equivalent blackbody, is put into correspondence with the spectral type of the star, as determined by the observer. This temperature-luminosity diagram shows the lifelines of the stars as strands combed out like hair across the graph. With a suitable interpretation, i.e. viewed through the explanatory machinery of nuclear physics, it opens the way to an understanding of stellar evolution and its twin science of nucleosynthesis. (Courtesy of Andre Maeder and co-workers.)...

Fig. 3.4. Observed Hertzsprung-Russell diagram. Luminosity is given in absolute magnitude (about +5 for the Sun). The point marked Sanduleak is the progenitor star of the 1987A supernova as it was observed before the cataclysm. On the horizontal axis, the spectral type is given instead of temperature. (After Kaler 1997.)...

For a whole range of stellar masses between 1 and 100 times the mass of the Sun, evolutionary tracks are traced out in the temperature-luminosity plane, also known as the Hertzsprung-Russell diagram, so frequently referred to by astronomers. 

Figure 1 Mass loss over the Hertzsprung-Russell diagram. The numbers give values of -log ( M) for individual stars, to one decimal. The lines are interpolation lines according to a formula given by De Jager et al. (1987).

The uppermost part of the Hertzsprung-Russell diagram is of particular interest since the stars in that area are apparently close to their limit of existence, which is shown by their stochastic variability, pulsations, large rate of mass loss and occasional episodic mass loss. The curve above which no stars appear to exist is called the Humphreys-Davidson limit (Humphreys and Davidson 1979 De Jager, 1980) cf. Figure 2. Stars close to that limit exhibit many of the properties listed above. In that area one also finds the Luminous Blue Variables, which are stars that erratically expell a large amount of mass. At some distance from the star the gas condenses into dust particles and thus the star becomes reddened. Sometimes the expelled gas is optically... 

Figure 4 Proposed solar wind mechanisms in the Hertzsprung-Russell diagram. R = radiation driven winds W = wave-(turbulence-) driven D = dust-driven T = thermal (coronal) winds.

Fig. 1 - Hertzsprung-Russell diagram for stars of 15 and 20 M and composition appropriate to the LMC (Z /4) (solid lines) and to the sun (dashed lines) evolved through hydrogen, helium, and carbon burning. The location of the presupernova stars are indicated. The four-pointed star indicates the best estimated properties of SK-202-69. 

Figure 12.7 Schematic representation of a Hertzsprung-Russell diagram. (From C. E. Rolfs and W. S. Rodney, Cauldrons in the Cosmos, Chicago University Press, Chicago, 1988.)...

Fig. 4. The pre-main sequence evolution of 0.5 to 1.5 solar mass stars in the Hertzsprung-Russell diagram. The lines represent theoretical evolutionary tracks, while the dots represent observational data for T Tauri stars (Cohen and Kuhi, 1979). The corresponding ages and ratios of UV flux to present solar UV flux are indicated for a solar-mass star.

The key features of stars which are of interest to astronomers are their mass, their luminosity, their surface temperature, and their distance from us. These parameters are used to classify stars and place them into an evolutionary sequence. A widely used classification diagram, based on optical data for stars, is the Hertzsprung-Russell Diagram (the H-R diagram) which is a plot of stellar luminosity versus effective surface temperature. The luminosity of a star is a function of its radius and effective temperature. The surface temperature is determined from its color and is vastly different from temperatures in the core of the star. For example, our sun has a surface temperature of about 5,700 K but a core temperature of 14 million K. 

Data from nearby stars measured by the Hipparcos satellite and displayed on a Hertzsprung-Russell Diagram show four main groups of stars (Fig. 2.4). These are the following ... 

The cycle of birth-life-death for a star may be charted on a Hertzsprung-Russell diagram as illustrated in Fig. 2.4. Most stars evolve onto the main sequence and then into the Dwarf stage as follows (Lewis, 2004) ... 

The Hertzsprung-Russell diagram is a snapshot of a group of stars at some given moment in time. It shows what the luminosities and temperatures of those stars were at the moment that snapshot (set of observations) was taken. What the H-R diagram does not tell is anything about the evolution of those stars, the way their temperatures and luminosities have changed over time. For example, the Sun was not born with the temperature and luminosity shown by its current position on the Main Sequence. 

John Maddox, editor of the journal Nature, later explained the importance of B2FH. First, he said, it provided the best explanation then available for the way elements are produced in stars. Second, it settled the ongoing dispute as to the changes that take place in stars as they move across the Hertzsprung-Russell diagram. Finally, it provided a basis for calculating the composition of stars and predicting their ultimate fate. 

Hayashi track The line on a Hertzsprung-Russell diagram during which a star s luminosity stays relatively constant, while its temperature continues to decrease, helium burning A series of nuclear reactions in which helium nuclei fuse to make larger atomic nuclei, helium flash A period of very rapid helium burning that occurs in the core of a star with low mass. 

Hertzsprung-Russell diagram A graph that plots the color of stars against their luminosity. 

Main Sequence The region on a Hertzsprung-Russell diagram occupied by stars that are fusing hydrogen into helium in their cores. 

T-TIuiri star A young star that is approaching the main sequence on the Hertzsprung-Russell diagram, terrestrial planets Solar system planets that are relatively small and dense compared with the gas giants, including Mercury, Venus, Earth, and Mars sometimes referred to as the minor planets. 

Fig. 1. Hertzsprung-Russell diagram a plot of luminosity (absolute magnitude) against the colours of the brightest stars ranging from the high-temperature blue-white stars on the left side of the diagram to the low temperature red stars on the right side. Original image by Richard Powell licensed for derivative works and redistribution under the Creative Commons Attribution Share Alike 2.5 License...

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