Download General Module information

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General Module information
The Intermediate Physics Handbooks (for PHYS 2001 and 2901) contain important information,
including examination and assessment policies. Please read the Handbook carefully. Note that the
module designation for these lectures is “ISA.”
The Handbooks and further information are available from the WebCT pages for PHYS 2001
and 2901. These can be accessed from the Intermediate Physics webpages
http://www.physics.usyd.edu.au/ugrad/ijpc.html
or the Student Intranet site
http://intranet.usyd.edu.au/student/.
Access to some Intranet pages requires a Unikey username and password that is issued with your
confirmation of enrolment. The University provides computer facilities in the Access Centres
http://www.usyd.edu.au/su/is/labs/.
A brief introduction to help you with web access is available on the Intermediate Physics web page.
For further information contact the lecturer,
John O’Byrne
Room 568
School of Physics A28
University of Sydney, NSW 2006, Australia
email: [email protected]
telephone: +61-2-9351-3184
fax: +61-2-9351-7726
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Assessment and learning goals
This module will be assessed by an examination which will form one section of the final examination
in your Intermediate Physics unit of study.
The specific learning goals for this module are summarised below by chapter heading. Students
who have mastered the material in this module should be able to:
Introduction
Describe the overall features of the Solar System and be able to place the Solar System with
respect to the Milky Way galaxy.
Recognise and describe open star clusters, globular clusters, and gaseous nebulas.
You will be able to describe the various types of galaxies, including spiral, elliptical, starburst
and irregular galaxies.
Convert between standard SI units and the units commonly used in astronomy, including the
parsec, solar mass unit and light year.
Convert from sexagesimal (degree, minute, second) angular units to radian units, and be understand when each is to be used.
Astrophysical tools
Convert from wavelength to frequency and vice versa using the relation f = c and be able
to convert between photon energy, frequency and wavelength using the Planck-Einstein law,
E = hf . [assumed knowledge from Junior Physics]
Express energy either in SI units (joules) or electron volts (eV). [assumed knowledge from
Junior Physics]
Identify the parts of the electromagnetic spectrum of astrophysical interest, and know their
approximate wavelength, frequency, or energy ranges.
Understand what is meant by an atmospheric spectral window and why such windows are
important.
Understand qualitatively what is meant by the sensitivity of a telescope and detector and be
able to explain the limits to sensitivity. In particular, you will be able to describe the natural
and man-made sources of background radiation in the visible and at radiofrequencies.
Understand and use Rayleigh’s criterion in simple problems.
Understand how the Earth’s atmosphere sets practical limits to resolution.
Explain how an interferometer can achieve very high resolution and be able to calculate the
theoretical resolution of such instruments.
Have a qualitative understanding of what is meant by spectroscopy, photometry and multicolour photometry.
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Stellar magnitudes
Understand the concept of magnitude difference and be able to convert between magnitude
difference and flux ratio using the relation
mA ; mB = ;2:50 log10
fA
fB
Understand what is meant by the combined magnitude of two stars which are very close together on the sky, and determine their separate magnitudes when given the flux ratio between
them.
Explain qualitatively how magnitudes are determined using multi-colour photometry.
Know that U , B and V represent the magnitudes determined using the Johnson U, B, V filters
and are measured with respect to standard stars.
Know what the term colour index means in general and know that, unless stated otherwise,
the colour index means C = B ; V .
Explain qualitatively the cause of interstellar reddening, and, given the absorption A, be able
to calculate the corrected magnitude of a star using m0 = m ; A.
Explain what is meant by colour excess and use the colour excess to determine the true or
intrinsic colour index:
(B ; V )0 = (B ; V ) ; (AB ; AV ) = (B ; V ) ; E
Explain what is meant by the term bolometric magnitude, and, given the bolometric correction
BC , calculate the bolometric magnitude from the V magnitude.
Understand what is meant by absolute magnitude and be able to calculate the absolute magnitude of a star given its apparent magnitude and distance:
m ; M = 5 log10 d ; 5
where the distance d is measured in parsecs.
Stellar distances
Explain what is meant by stellar parallax and how it can be measured.
Know the relation between parallax (in arcseconds) and distance (in parsecs):
d = 1=.
Know what a Cepheid variable star is and be able to use the period luminosity law to determine
the absolute magnitude, and thereby the distance, to a Cepheid variable:
log10 + 0:394MV = ;0:657
Explain qualitatively what is meant by the cosmological red shift z and carefully distinguish
it from the Doppler effect.
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Stellar spectra
Explain qualitatively how a continuous spectrum or the continuum is formed. Explain what is
meant by a black body.
Use the Wien displacement law which relates the wavelength of the maximum of the Planck
distribution to the temperature of the black body.
;3
max
= 2:898 T 10
m
Understand and use the Stephan-Boltzmann relation between the emergent flux and temperature of a black body:
Z
F
=
1
0
B d = T 4
Define what is meant by the effective temperature of a star and know how to determine it,
given the bolometric flux at the Earth and the angular diameter of the star:
Teff4 = Fbol = 4fbol2
Define what is meant by luminosity and understand the relation between luminosity, emergent
flux, effective temperature, and the radius of a star:
L = 4R2Fbol = 4R2Teff4
Use the relation between luminosity and absolute bolometric magnitude:
Mbol = 4:72 ; 2:5 log10(L=L )
Explain qualitatively how spectral lines are formed in stellar atmospheres.
Explain qualitatively what is meant by excitation equilibrium and explain (in words) the significance of the Boltzmann equation.
Explain qualitatively what is meant by ionisation equilibrium and explain (in words) the significance of the Saha equation.
Explain qualitatively how these two competing equilibrium processes cause the emission of
spectral lines to be strongly temperature-dependent, and in particular explain why hydrogen
absorption lines are strongest for stars with effective temperatures of 10 000 K.
Explain what is meant by line broadening and explain qualitatively the mechanisms of line
broadening and when each may be significant:
– natural broadening
– Doppler broadening, including turbulence
– collisional or pressure broadening
– Zeeman effect
In the case of Doppler broadening, calculate its magnitude for a particular atomic species and
a given temperature:
s
= 2c
2kT + v2 ln 2
turb
m
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Spectral classification
Explain qualitatively what is meant by spectral classification.
Recognise that the spectral classes
OBAFGKM
form a temperature series and roughly estimate the effective temperature, given the spectral
class.
Explain what is meant by luminosity class, and in particular know the correspondences:
Luminosity class
Ia
Ib
II
III
V
wd
Description
Luminous supergiants
Less luminous supergiants
Bright giants
Normal giants
Dwarfs or main sequence stars
White dwarfs
The Hertzsprung-Russell (HR) Diagram
Draw an HR diagram and properly label its axes with appropriate units.
Sketch the following regions of interest on an HR diagram:
– The main sequence
– The red giant branch
– White dwarfs
– The turn-off point
– The horizontal branch
– The instability strip (refer to Variable Stars, below)
Explain why cluster HR diagrams are important and sketch examples of young and old cluster
diagrams.
The physics of stars (extra detail in ADV)
Explain, using words and diagrams, what is meant by hydrostatic equilibrium in a star.
Use the equation of hydrostatic equilibrium
to find P (r) in simple cases.
dP = ; GMr = ;g
dr
r2
Use the ideal gas equation of state P
kT in simple problems.
= m
H
Explain qualitatively how the equation of state is modified by radiation pressure.
Explain qualitatively what is meant by radiative transfer.
Explain qualitatively the effects of turbulence in stellar atmospheres.
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Explain why fusion of light nuclei releases energy in terms of the binding energy per nucleon
and its dependence on atomic mass.
Explain qualitatively what the “Gamow peak” is and why it occurs.
Recognise the equations for the three reaction processes: the p-p reaction, the CNO cycle and
the triple-alpha process.
Given a set of nuclear reactions, calculate the overall energy production per nucleon consumed. Given the overall energy production of a star, use this information to calculate the
amount of nuclear fuel consumed per second.
State, approximately, the ignition temperatures for the nuclear fuels: H, He, C, O, Si.
State, approximately, the temperature dependence of the reaction rates for the p-p, CNO and
triple-alpha processes.
In words, describe how one might construct a stellar model.
Stellar evolution
Qualitatively describe how protostars are formed and how they evolve to the main sequence.
Explain what is meant by a Hayashi track and sketch such a track on an HR diagram.
Explain qualitatively how planetary systems might form.
Explain what is meant by the zero age main sequence (ZAMS).
Explain in words the evolution of a star on the main sequence and know approximately how
the main sequence lifetime varies with mass.
Qualitatively describe the post-main sequence evolution of stars with mass greater than M . Important aspects of the evolution include:
– onset of hydrogen shell burning
– core collapse
– “first dredge up” phase
– the physical effects leading to the red giant branch
Qualitatively explain how the evolution of low mass stars differ from the above.
Explain qualitatively how the post-RGB evolution of low mass stars leads to the formation of
planetary nebulas and white dwarfs. Explain how the asymptotic giant branch is formed.
Explain qualitatively how the post-RGB evolution of massive stars differs from this. Explain
the processes leading to a supernova. Describe what happens after the supernova explosion.
Variable stars (ADV only)
In words, describe what is meant by the period-mean density relation and its physical cause.
Show how the period-mean density relation leads to the period-luminosity law for Cepheids.
Explain in words Eddington’s valve theory and why partial ionisation can act as such a mechanism.
Describe what is meant by helioseismology and asteroseismology, and why they are important.
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