H-R Diagram.notebook

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October 22, 2013

The H-R Diagram:

Represents one of the great observational syntheses in astrophysics

Ejnar Hertzsprung (1911) & Henry Norris Russell (1913)

Absolute magnitude plotted verses Spectral type: the two most observable intrinsic properties of stars

Absolute magnitude (MV) (original-traditional)

Luminosity (log[L/L ]) (theoretical)

Apparent magnitude (V) (observational color-magnitude diagram; all plotted stars at the same distance)

Spectral type (original-traditional)

Surface Temp. (log[T/T ]) (theoretical)

Color-index (observational color-magnitude diagram; all plotted stars at the same distance)

log[L/L ] log[T/T ]

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October 22, 2013

Absolute magnitude:

Plot Sirius A & B on diagram:

Sirius A: mV = -1.44 r = 2.63 pc Sp = A1

Sirius B: mV = 8.44 r = 2.63 pc Sp = A2

Determine the abs. mags using the dist. modulus - distance relation:

First diagram used stars with classified spectral type, measured apparent mags, and parallaxes.

Example:

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

0 1 2 3 4 5 6 7 8 90°

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HHH H

**(See exercise 6)**

Spectral type and Color index:

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Color index:

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Note: V = "visual" filter = green bandpass

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October 22, 2013

Note: V = "visual" filter = green bandpass

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October 22, 2013

Note: V = "visual" filter = green bandpass

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H-R Diagram; relative no.s of types of stars; sequences of stars on the diagram

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October 22, 2013

H-R Diagram; Types of stars

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H-R Diagram; Types of stars

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H-R Diagram; Sequences of stars

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October 22, 2013

H-R Diagram; Sequences of stars

Red Giant Branch

Main Sequence

White Dwarfs

Note: mass measurements from binary stars shows that the MS is a "mass sequence". i.e.: the cool, low luminosity stars are low mass stars and as we go up the MS to greater surface temperatures and higher luminosity stars, the mass of MS stars increases.

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October 22, 2013

H-R Diagram: How come "Giant" or "Dwarf"? (radii of stars)

Red Giant Branch

Main Sequence

White Dwarfs

Compare Sirius A & B:

Sirius A: MV = 1.47 Sp = A1

Sirius B: MV = 11.34 Sp = A2

For the purpose of the example, assume both A & B are same spectral type

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October 22, 2013

Red Giant Branch

Main Sequence

White Dwarfs

H-R Diagram: How come "Giant" or "Dwarf"? (radii of stars)

Compare Sirius A & B:

Sirius A: MV = 1.47 Sp = A1

Sirius B: MV = 11.34 Sp = A2

For the purpose of the example, assume both A & B are same spectral type

note:

From S-B law:

A is much brighter (more luminous) than B:

A is much larger in radius than B:

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October 22, 2013

H-R Diagram: How come "Giant" or "Dwarf"? (radii of stars)

From S-B law: Note: total radiative power of star is its luminosity

Sun:

Above result shows that lines of constant radius would be straight lines with a slope of 4 as plotted on a theoretical H-R Diagram.

(See next page.)

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October 22, 2013

log[L/L ]

log[T/T ]