M.R.Burleigh 2601/Unit 1 DEPARTMENT OF PHYSICS AND ASTRONOMY LIFECYCLES OF STARS Option 2601

M.R.Burleigh 2601/Unit 1

DEPARTMENT OF PHYSICS AND ASTRONOMY

LIFECYCLES OF STARSLIFECYCLES OF STARS

Option 2601Option 2601

M.R. Burleigh 2601/Unit 1

BooksBooks

Introductory Astronomy and Introductory Astronomy and AstrophysicsAstrophysics– Zeilik and GregoryZeilik and Gregory

Astrophysics I: starsAstrophysics I: stars– Bowers and DeemingBowers and Deeming

The Physics of StarsThe Physics of Stars– A.C. PhillipsA.C. Phillips


Stellar LifecycleStellar Lifecycle


StarbirthStarbirth


Young StarsYoung Stars


Globular ClustersGlobular Clusters


Star DeathStar Death








Aims and ObjectivesAims and Objectives

To introduce you to the underlying To introduce you to the underlying physics governing the properties of physics governing the properties of stars and their evolutionstars and their evolution


Lifecycles of StarsLifecycles of Stars

Unit 1 - Observational properties of Unit 1 - Observational properties of starsstars

Unit 2 - Stellar SpectraUnit 2 - Stellar Spectra Unit 3 - The SunUnit 3 - The Sun Unit 4 - Stellar StructureUnit 4 - Stellar Structure Unit 5 - Stellar EvolutionUnit 5 - Stellar Evolution Unit 6 - Stars of particular interestUnit 6 - Stars of particular interest

M.R.Burleigh 2601/Unit 1

DEPARTMENT OF PHYSICS AND ASTRONOMY

Unit 1Unit 1

Observational Properties of StarsObservational Properties of Stars


Observational Properties of StarsObservational Properties of Stars

The electromagnetic spectrumThe electromagnetic spectrum RadiationRadiation Flux, intensity and luminosityFlux, intensity and luminosity Stellar magnitudes and photometryStellar magnitudes and photometry Temperatures masses and radiiTemperatures masses and radii


The Electromagnetic The Electromagnetic SpectrumSpectrum


Atmospheric absorptionAtmospheric absorption


Wave nature:

Wavelength Frequency

The Nature of EM radiationThe Nature of EM radiation

Energy Planck’s constant


Energy ConversionsEnergy Conversions

1keV = 2.418 1018Hz

1keV = 11.60 106K

1keV = 1.24Å

1keV = 1.6 10-9erg

1J = 107erg


Solid angle

I

r

Normal

Spherical surface

a

A

Total energy flow from the surface of a star

Monochromatic intensityStellar Absolute Luminosity

Stellar distance


Output per unit area of source per second over the whole spectrum:

Stellar radius

Brightness (apparent luminosity) is sometimes termed as ‘flux at the Earth’:

Can also be considered as monochromatic luminosity or flux i.e. L(), F()

Surface flux of star (F): radiant Surface flux of star (F): radiant energyenergy

Inverse square law

Flux


Inverse Square LawInverse Square Law


Magnitude SystemMagnitude System

Comparison of stars wrt one anotherComparison of stars wrt one another Introduced by Hipparchus ~120BCIntroduced by Hipparchus ~120BC Catalogued >1000 naked eye stars in Catalogued >1000 naked eye stars in

order of importance (brightness)order of importance (brightness) 11stst magnitude = 1 magnitude = 1stst importance importance Extended by Ptolemy 180ADExtended by Ptolemy 180AD


Magnitude SystemMagnitude System

Modern scale dates from 1854, by Modern scale dates from 1854, by PogsonPogson

Showed that brightness scale is Showed that brightness scale is logarithmic, 1logarithmic, 1stst mag ~100 x 6 mag ~100 x 6thth mag mag

A step of 1 mag = 10 A step of 1 mag = 10 2/52/5 = 2.512 = 2.512 Can easily calculate differencesCan easily calculate differences


Magnitude system

Constant

Apparent magnitude (m):

Absolute magnitude (M):

Distance modulus

Parallax


Stellar MagnitudesStellar Magnitudes

Any detector (i.e the eye) is only Any detector (i.e the eye) is only sensitive to a limited wavelength rangesensitive to a limited wavelength range

Only sampling part of radiation from a Only sampling part of radiation from a starstar

Photographic film centred on ~420nm Photographic film centred on ~420nm (m(mpgpg))

Visual (eye) most sensitive ~550nm Visual (eye) most sensitive ~550nm (m(mvv))


UU BB VV RR II JJ HH KK LL MM NN

365365 440440 550550 700700 900900 12501250 1.651.65 2.22.2 3.63.6 4.84.8 10.210.2

nm m

Johnson system:

Magnitude DefinitionsMagnitude Definitions


(B – V)

(also U – B etc.)

B - VB - V -ve-ve forfor 20,000K20,000K

00 ForFor 10,000K10,000K (A0) e.g. Vega (A0) e.g. Vega

+ve+ve forfor 3,000K3,000K

Colour IndexColour Index


BC = -0.07 for the Sun (Teff = 6,500K)

Cannot observe mbol directly so use bolometric correction…

Bolometric MagnitudeBolometric Magnitude


Wien displacement law: c = 0.2898 cm deg

Stephan-Boltzmann law:

h is the Planck constant, k is Boltzmann’s constant

Temperature DefinitionsTemperature Definitions

Blackbody:

Stefan’s constant Effective temperature Te

Planck law:




Magnitude system

Constant

Apparent magnitude (m):

Absolute magnitude (M):

Distance modulus

Parallax


Stellar DistancesStellar Distances

The The ““ParallaxParallax”” method of measuring method of measuring distance…distance…

For nearest For nearest stars only stars only (<(<100pc100pc))


a = 1AU

d

(radians)(radians)

== a / da / d 1pc = 206,265AU1pc = 206,265AU

== 1 / d (pc)1 / d (pc) 1rad = 206,2651rad = 206,265

Stellar DistancesStellar Distances



Distances > 100pcDistances > 100pc

Use Sun’s motion through the nearby Use Sun’s motion through the nearby starsstars

Motions of relatively nearby star Motions of relatively nearby star clustersclusters


Michelson stellar interferometer

Angle in radians

Stellar physical diameter

Distance

Interference pattern depends upon angle between wavefronts from opposite limbs of the star

Measurement of RadiiMeasurement of Radii

Occultations/eclipses in binary starsOccultations of stars by the Moon


So What is a Star?So What is a Star?

Self-gravitating ball of gas radiating Self-gravitating ball of gas radiating energyenergy

Energy produced byEnergy produced by– Thermonuclear reactionsThermonuclear reactions– + gravitational/stellar collapse+ gravitational/stellar collapse

Star must produce enough energy to Star must produce enough energy to maintain internal pressure to counter maintain internal pressure to counter gravitational fieldgravitational field


Physical PrinciplesPhysical Principles

Atomic physics Atomic physics radiation radiation processes/spectral linesprocesses/spectral lines

Thermodynamics Thermodynamics behaviour of behaviour of gas/stellar structuregas/stellar structure

Nuclear physics Nuclear physics energy energy generation/creation of heavy elementsgeneration/creation of heavy elements

Atmospheres

Interior


Unit 1 Slides and NotesUnit 1 Slides and Notes

CCan be found at… an be found at… – www.star.le.ac.uk/~mbu/lectures.htmlwww.star.le.ac.uk/~mbu/lectures.html

In case of problems see me in lectures In case of problems see me in lectures or email me… [email protected] email me… [email protected]

Documents

M.R.Burleigh 2601/Unit 1 DEPARTMENT OF PHYSICS AND ASTRONOMY LIFECYCLES OF STARS Option 2601