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TOPIC: Hertzsprung-Russell diagram
Blobrana


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RE: Hertzsprung-Russell diagram
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Hertzsprung Russell diagrams and cepheid variables to estimate distance in astronomy



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Blobrana


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The HR Diagram
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In the prime of their lives, when stars burn hydrogen in their core, there's a clear and simple relationship between a star's colour and brightness. Nearly a century ago, astronomers developed a way to illustrate this relationship with what's now called the H-R Diagram, a critical tool for understanding how stars evolve. Here's how it works.

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Blobrana


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Stellar parameters
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Title: The relations between main stellar parameters
Authors: B.V.Vasiliev

The relations between masses, radii and surface temperatures of stars are considered. It is shown that calculated values of these relations are in a satisfactory agreement with measuring data.

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Blobrana


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Star Colours
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Like most scientists, astronomers love to classify things.  In the late 19th century, Harvard astronomers developed a system to classify stars according to the strength by which hydrogen gas absorbed light at particular wavelengths.  The star classes were labelled A to N in order of decreasing hydrogen absorption strength.  After a time, the classes were simplified to O, B, A, F, G, K, and M.  This is the Harvard spectral classification, which is still used today.

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Blobrana


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RE: Hertzsprung-Russell diagram
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Project Universe - Red Giants and White Dwarfs (1)
Project Universe - Red Giants and White Dwarfs (2)



Project Universe - Red Giants and White Dwarfs (3)



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Blobrana


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The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude diagram, or CMD) shows the relationship between absolute magnitude, luminosity, classification, and effective temperature of stars. The diagram was created circa 1910 by Ejnar Hertzsprung and Henry Norris Russell, and represented a huge leap forward in understanding stellar evolution, or the 'lives of stars'.

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Blobrana


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The Hertzsrung-Russell Diagram (HR Diagram)
as related to Stellar Radius and Temperature Engage!


spacer.gif Hertzsrung-Russell Diagram

Hertzsrung-Russell Diagram
The HR Diagrams plots stellar brightness versus surface temperature
  • Luminosity vs. Surface Temperature
  • Absolute Magnitude vs. Colour Index
  • Absolute Magnitude vs. Spectral Class
Radius: The radius of the star's photosphere
Luminosity: L

Temperature: The temperature of the surface of the photosphere that give the total luminosity by Planck's Blackbody radiation
Bolometric Magnitude: The total Luminosity expressed in Magnitudes relative to the sun [Mbol(sun) = +4.75]
Colour Index: B - V The stars colour as given by its blue magnitude minus visible magnitude. Since magnitudes are smaller for larger brightness, a brighter blue star will have a more negative Colour Index.
Spectral Class of Star
Class Color Temperature
O blue-white 35,000 degrees C HeII lines visible; lines from highly ionised species, for
example, CIII, NIII, OIII, SiIV ; H lines relatively weak;
strong ultraviolet continuum.
B blue-white 21,000 degrees C HeI lines strong; attain maxmimum at B2; HeII lines absent;
H lines stronger; lower ions, for example, CII, OII, SiIII
A White 10,000 degrees C H lines attain maxmimum strength at A0 and decrease toward later
types; MgII, SiII strong; CaII weak and increasing in strength
F Creamy 7,000 degrees C H weaker, CaII stronger; lines of neutral atoms and first ions
of metals appear prominently
G Yellow 6,000 degrees C Solar-type spectra; CaII lines extremely stron; neutral metals
prominent, ions weaker; G band (CH) strong; H lines weakening
K Orange 4,500 degrees C Neutral metallic lines dominate; H quite weak; molecular bands
(CH,CN) developing; continuum weak in blue
M Red 3,000 degrees C Strong molecular bands, particularly TiO; some neutral lines for
example, CaI quite strong; red continua
C(R,N) Red
Carbon stars; strong bands of carbon compounds C ,CN,CO;
TiO absent; temperatures in range of 2 classes K and M
S Red
Heavy-element stars; bands of ZrO, YO, LaO; neutral atoms strong
as in classes K and M; overlaps these classes in temperature range
W Wolf-Rayet

Subtypes

Within each stellar type, stars are placed into subclasses (from 0 to 9) based on its position within the scale.
Ia-0 Most extreme supergiants
Ia Luminous supergiants
Iab Moderate supergiants
Ib Less luminous supergiants
II Bright giants
III Normal giants
IV Subgiants
V Dwarfs (main sequence)
VI Subdwarf (below main sequence, extreme metal poor. )
VII White dwarfs



Only
Bored Astronomers
Find
Gratification Knowing Mnemonics

General we can narrow the range on stars down to those within the F, G, and K class as being most likely to be capable of sustaining life. The reason concerns the age of such stars and their temperature. F stars have a temperature of 7000 C. G stars have a temperature of 6000 C. And K stars have an average temperature of 4500 C. These stars all fit within the main sequence area. They are rather long lived and they provide decent habital ranges for planets.






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