Upload
eleanor-barber
View
225
Download
2
Embed Size (px)
Citation preview
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
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
Wave nature:
Wavelength Frequency
The Nature of EM radiationThe Nature of EM radiation
Energy Planck’s constant
M.R. Burleigh 2601/Unit 1
Energy ConversionsEnergy Conversions
1keV = 2.418 1018Hz
1keV = 11.60 106K
1keV = 1.24Å
1keV = 1.6 10-9erg
1J = 107erg
M.R. Burleigh 2601/Unit 1
Solid angle
I
r
Normal
Spherical surface
a
A
Total energy flow from the surface of a star
Monochromatic intensityStellar Absolute Luminosity
Stellar distance
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
Magnitude system
Constant
Apparent magnitude (m):
Absolute magnitude (M):
Distance modulus
Parallax
M.R. Burleigh 2601/Unit 1
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))
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
(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
M.R. Burleigh 2601/Unit 1
BC = -0.07 for the Sun (Teff = 6,500K)
Cannot observe mbol directly so use bolometric correction…
Bolometric MagnitudeBolometric Magnitude
M.R. Burleigh 2601/Unit 1
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:
M.R. Burleigh 2601/Unit 1
Magnitude system
Constant
Apparent magnitude (m):
Absolute magnitude (M):
Distance modulus
Parallax
M.R. Burleigh 2601/Unit 1
Stellar DistancesStellar Distances
The The ““ParallaxParallax”” method of measuring method of measuring distance…distance…
For nearest For nearest stars only stars only (<(<100pc100pc))
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
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
M.R. Burleigh 2601/Unit 1
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]