WHY STUDY ASTROPHYSICS?  To gain an understanding of our universe and our role in it Learn about how the universe operates --> modern science  Observations lead to Laws such as Newtonian mechanics, which had applications for machines, construction and Industrial Revolution  Space technology gives us communication satellites, accurate weather forecasts, GPS, minerals exploration, long term monitoring of earth  Study of our solar system allows us to study data from other planets and assess the nature of our planet, its origins and our resources Technology (e.g. medicine, materials, techniques) developed for space have valuable uses on earth

the light-gathering power of the telescope (directly proportional to the square of the diameter of the objective) the minimum angular separation between two equal point sources such that they can be just barely distinguished as separate sources

ASTROPHYSICS n Resolution –Atmospheric seeing n Defocusing –atmospheric ‘cells’ act as concave or convex lenses, changing focal length n Image motion or blur –‘wedges’ of air moving along change refractive index and position of image Limitations of ground-based astronomy

ASTROPHYSICS Improving resolution and sensitivity of ground-based systems n Adaptive optics –position of star measured and corrected via computer and moving mirrors –size compared to a point source and changes corrected to maintain focus n Interferometry –combine signals from 2 or more radio telescopes to create a resolution equivalent to a telescope of diameter equal to antennae separation –different distances travelled cause destructive or constructive interference –antennae separations of 20 km give resolutions of 0.1 arc seconds –VLBI can give arc secs (1,000,000 x optical telescope) n Lightweight Mirrors –can give bigger diameters without problems of bending and flexing under own weight –multimirrors also counteract this problem

ASTROPHYSICS n PARALLAX n PARSEC n LIGHT YEAR n astronomical unit d = 1/p Limitations of trigonometric parallax need to measure within 0.01 arc seconds, so atmospheric seeing restricts observations of stars beyond 100 pc because to measured angle is too small to accurately determine Hipparcos orbital satellite is unaffected by atmospheric seeing measured the parallaxes of 1000’s of stars with extremely high accuracy enabled astronomers to determine higher stellar distances (out to several hundred parsecs) much more accurately

Caroline Chisholm College Many sources show a continuous spectra across wavebands Emission spectra Elements in hot gases or plasma produce characteristic bright emission lines at various wavelengths Absorption spectra Gas atoms between a continuum source and the observer absorb characteristic wavelengths

Technology nFnFnFnFilters –P–P–P–Pass light over a broad range of wavelengths nSnSnSnSpectrographs –S–S–S–Slit and collimator light parallel beams –d–d–d–dispersing element colours –c–c–c–camera and detector (e.g. CCD then data is fed to a computer for analysis) nSnSnSnSpectroscopic surveys –o–o–o–optical fibres can observe several spectra at once

TYPES OF SPECTRA Stars n underlying continuous spectra n absorption lines

Types of spectra Emission Nebulae emission lines in the radio - UV range continuous components Planetary Nebulae strong emission lines - UV,visible,radio waves Supernovae strong emission spectra in visible and UV black body continuum

Types of spectra Normal galaxies have red continuous spectra and calcium absorption lines Galaxies undergoing massive star formation have strong emission lines Active galaxies (with black holes) have broad emission spectra and strong synchrotron radiation

Key features of stellar spectra Spectral TYPE is based on ABSORPTION spectra Chemical Composition Absorption lines can be matched to absorption and emission spectra from known elements There may be a number of overlapping ‘fingerprints’ of elements in the spectrum of a star

Key features of stellar spectra Temperature Ionised Hydrogen means there are no absorption lines in O and B stars (hot)( K). At lower than 10000K, Balmer absorption lines are produced, so Hydrogen absorption is a maximum in A2 stars Different elements produce strong absorption lines at different temperatures. Therefore, observing the strong absorption lines for elements indicates the temperature Using Wien’s Law we can calculate the surface temperature from the wavelength of maximum intensity

Key features of stellar spectra Pressure Low pressure gives narrow absorption lines High pressure gives broad absorption lines Large diameter Low pressure Broad lines Large surface area Narrow lines High pressure Small diameter Small surface area Low luminosity High luminosity

Key features of stellar spectra Recessional velocity Doppler effect over a period of time shows velocity variation Rotational velocity Red shifted spectra shows star is moving away from observer Blue shifted spectra shows star is moving towards observer THE WIDER THE GAP BETWEEN RED SHIFTED AND BLUE SHIFTED POSITION, THE HIGHER THE ROTATIONAL SPEED

Stefan’s Law Total power produced at all wavelengths from a black body: 4 24 so... Stars with similar temperatures can have very different luminosities depending on radii i.e. giants and supergiants may have similar temperatures to main sequence stars but much higher luminosities