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

M.R. Burleigh 2601/Unit 1 Books  Introductory Astronomy and Astrophysics –Zeilik and Gregory  Astrophysics I: stars –Bowers and Deeming  The Physics of Stars –A.C. Phillips

M.R. Burleigh 2601/Unit 1 Stellar Lifecycle

M.R. Burleigh 2601/Unit 1 Starbirth

Young Stars

M.R. Burleigh 2601/Unit 1 Globular Clusters

M.R. Burleigh 2601/Unit 1 Star Death

M.R. Burleigh 2601/Unit 1 Star Death

M.R. Burleigh 2601/Unit 1 Star Death

M.R. Burleigh 2601/Unit 1 Star Death

M.R. Burleigh 2601/Unit 1 Aims and Objectives To introduce you to the underlying physics governing the properties of stars and their evolution

M.R. Burleigh 2601/Unit 1 Lifecycles of Stars  Unit 1 - Observational properties of stars  Unit 2 - Stellar Spectra  Unit 3 - The Sun  Unit 4 - Stellar Structure  Unit 5 - Stellar Evolution  Unit 6 - Stars of particular interest

M.R.Burleigh 2601/Unit 1 DEPARTMENT OF PHYSICS AND ASTRONOMY Unit 1 Observational Properties of Stars

M.R. Burleigh 2601/Unit 1 Observational Properties of Stars  The electromagnetic spectrum  Radiation  Flux, intensity and luminosity  Stellar magnitudes and photometry  Temperatures masses and radii

M.R. Burleigh 2601/Unit 1 The Electromagnetic Spectrum

M.R. Burleigh 2601/Unit 1 Atmospheric absorption

M.R. Burleigh 2601/Unit 1 Wave nature: Wavelength Frequency The Nature of EM radiation Energy Planck’s constant

M.R. Burleigh 2601/Unit 1 Energy Conversions 1keV =  Hz 1keV =  10 6 K 1keV = 1.24Å 1keV = 1.6  erg 1J = 10 7 erg

M.R. Burleigh 2601/Unit 1 Solid angle I r Normal Spherical surface aa   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 energy Inverse square law Flux

M.R. Burleigh 2601/Unit 1 Inverse Square Law

M.R. Burleigh 2601/Unit 1 Magnitude System  Comparison of stars wrt one another  Introduced by Hipparchus ~120BC  Catalogued >1000 naked eye stars in order of importance (brightness)  1 st magnitude = 1 st importance  Extended by Ptolemy 180AD

M.R. Burleigh 2601/Unit 1 Magnitude System  Modern scale dates from 1854, by Pogson  Showed that brightness scale is logarithmic, 1 st mag ~100 x 6 th mag  A step of 1 mag = 10 2/5 =  Can 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 Magnitudes  Any detector (i.e the eye) is only sensitive to a limited wavelength range  Only sampling part of radiation from a star  Photographic film centred on ~420nm (m pg )  Visual (eye) most sensitive ~550nm (m v )

M.R. Burleigh 2601/Unit 1 UBVRIJHKLMN nm mm Johnson system: Magnitude Definitions

M.R. Burleigh 2601/Unit 1 (B – V) (also U – B etc.) B - V -vefor20,000K 0For10,000K (A0) e.g. Vega +vefor3,000K Colour Index

M.R. Burleigh 2601/Unit 1 BC = for the Sun (T eff = 6,500K) Cannot observe m bol directly so use bolometric correction… Bolometric Magnitude

M.R. Burleigh 2601/Unit 1 Wien displacement law:c = cm deg Stephan-Boltzmann law: h is the Planck constant, k is Boltzmann’s constant Temperature Definitions Blackbody: Stefan’s constant Effective temperature T e 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 Distances The “Parallax” method of measuring distance… For nearest stars only (<100pc)

M.R. Burleigh 2601/Unit 1 a = 1AU d   (radians) = a / d 1pc = 206,265AU     = 1 / d (pc) 1rad = 206,265  Stellar Distances

M.R. Burleigh 2601/Unit 1

Distances > 100pc  Use Sun’s motion through the nearby stars  Motions of relatively nearby star clusters

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 Radii Occultations/eclipses in binary stars Occultations of stars by the Moon

M.R. Burleigh 2601/Unit 1 So What is a Star?  Self-gravitating ball of gas radiating energy  Energy produced by –Thermonuclear reactions –+ gravitational/stellar collapse  Star must produce enough energy to maintain internal pressure to counter gravitational field

M.R. Burleigh 2601/Unit 1 Physical Principles  Atomic physics  radiation processes/spectral lines  Thermodynamics  behaviour of gas/stellar structure  Nuclear physics  energy generation/creation of heavy elements Atmospheres Interior

M.R. Burleigh 2601/Unit 1 Unit 1 Slides and Notes  Can be found at… –  In case of problems see me in lectures or me…