Physics & Astronomy 307
Autumn 2010 Homepage
Univ.
Louisville
Instructor: Dr. Gerard
Williger, NS 206, tel 852-0821
e-mail:
williger@*
where
*=
physics.louisville.edu
(please
do
not
e-mail
to
my Groupwise
acct)
My
homepage
is
here
Office hours: after
class (12:30-1:30pm) and by appointment;
I will not entertain questions on problem
sets on the day they are
due
Lectures: NS 312 and
NS313,
Tue/Thu 11am-12:15pm
We'll use NS313 at the beginning but will use NS312 (across the hall,
with a computer) for some lectures.
Text: Foundations of Astrophysics,
Ryden & Peterson, 1st ed., Addison-Wesley (2010)
The course objective is to learn basic the basic physics of
astronomical phenomena. A mastery of calculus and
introductory (calculus-based)
college physics is assumed. Differential equations will help, but if you
have not had them, you can pick up what you will need. The
lectures will begin on Tuesday, Aug
24.
A password-enabled protected
site will contain answers to homework and midterm problems, if I do
not
pass them out in class. I may also put commentaries on common
homework errors there as well.
Finally, all the PowerPoint files for my Astro 107 class from Spring
2008, plus animation files,
are on the protected site. They're an excellent overview for the
material in this course, and I
highly recommend your looking at the files. We'll try to cover
roughly
chapters 1-18 from that course,
but not do too much on the planets.
Special
dates on semester calendar for this class:
Tue 7 Sep **IN PLANETARIUM** (tentatively)
Thu 7 Oct and Thu 2 Dec: midterms
Midterm 1, 7 Oct 2010: up through Chapter 7, HW6 and qualitatively
cover Chap 8-9 (material covered in lecture on 5 Oct).
Midterm 2, 2 Dec 2010: from Chap 8-9 on through lecture on 30 Nov,
covering HW7-12. Material on 30 Nov (Chap 18) will be
mainly qualitative.
Here are links
for supplemental material and additional explanations
Reading:
24-26 Aug: Chap 1-2
31 Aug - 2 Sep: Chap 3
7-9 Sep: Chap 3-4
14-16 Sep: Chap 4-5
21-23 Sep: Chap 7 (We'll skip Chap 6)
28-30 Sep: Chap 8-9 (we'll go fast, pay attention to the physics)
05 Oct: Chap 8-9 (we'll go fast, pay attention to the physics)
12-14 Oct: Chap 10-12 (again, going fast; we're concentrating on the
physics given in lecture)
19-21 Oct: Chap 13
26-28 Oct: Chap 14-15
02-04 Nov: Chap 15
09-11 Nov: Chap 16
16-18 Nov: Chap 17
23 Nov: Chap 17
30 Nov: Chap 18
Homework:
due
at
beginning
of
class;
answers
in
units
given in the problem e.g.
SI units OR standard
astronomical units (like AU or pc for distance, solar masses for mass,
years for time
etc.)
unless noted, following the format below.
Solutions will always be provided and you are responsible for
all homework problems.
However, I reserve the right to
grade only some of the problems,
those being graded to be announced when the homework is collected.
Problems are indicated as chapter.problem (e.g. 1.5 is chapter 1,
problem 5).
YOU MUST
SHOW YOUR WORK (INCLUDING ORIGINS OF ALL NUMBERS) SO
THAT I CAN
FOLLOW YOUR CALCULATIONS AND GIVE
PARTIAL CREDIT.
HW01, due Tue 31 Aug: 1.3, 1.6, 1.8, 2.4 STATS: 17 done,
mean=2.7, std dev=0.9, range=1.3-4.0
HW02, due Tue 07 Sep: 2.6, 2.7, 3.2, 3.3 STATS: 15 done, mean=2.8, std
dev=0.6, range=1.8-4.1
HW03, due Tue 14 Sep: 3.9, 4.3, 4.5, 4.8 STATS: 16 done, mean=2.7, std
dev=1.0, range=0.5-3.9
HW04, due Tue 21 Sep: 4.9, 5.5, 5.7, 5.8 STATS: 16 done, mean=2.6, std
dev=0.7, range=0.9-3.9
HW05, due Tue 28 Sep: 5.4, 5.6, 5.A,5.B (see below) STATS: 15 done,
mean=2.5, std dev=0.8, range=0.8-3.7
For the following, _ denotes a subscript (like in Latex)
5.A: To understand the relative importance of the different parameters
in the Saha equation,
perform the following experiment. Assume that T=5000K, N_e=1e15
cm-3, and chi=12eV.
By what factor does the ionization ratio (N_+/N_0) change when we
separately
(a) double the temperature? (Which is more important during the
temperature change, the exponential
term or the T^3/2 term?)
(b) double the electron density?
(c) double the ionization potential?
5.B Let N_2 be the number of second-level (first excited state) H atoms
and N_1 be the number in the
ground state. Using Fig. 5.13, find the excitation ratio (N_2/N_1)
and the excited fraction (N_2/N) for each of the following stars.
Give the results in log and in exponential forms.
(a) Sirius, T=10000K
(b) Rigel, T=15000K
(c) the Sun, T=5800K
Which star will exhibit the strongest Balmer lines? Why are the
Balmer lines in each of the other two
stars weaker?
HW06, due Tue 5 Oct: 7.6,7.8,7.9,7.A (below)
7.A (a) Given that the photosphere is at a temperature of 6000K, would
you expect collisional or radiative
excitations to be more important in exciting H atoms to the second
(n=2) level?
(b) Would you expect the Ly-alpha line to appear in emission or
absorption? Explain.
HW07, due Tue 19 Oct: 8.6, Van Allen pblm, 9.9, 9.10
Van Allen pblm: (a) Use the strength of the magnetic field at the
Earth's surface
to estimate the strength of each of the two Van Allen belts.
(b) Use this estimate to calculate the radius of curvature of a 50-MeV
proton
in each of the belts.
HW08, due 26 Oct: 11.2,13.1,13.4, 8.A (below)
8.A (a) Compute the Planck function in wavelength for 4400A, 5500A,
6200A and 7700A (roughly
the centroids for B,V,R,I), for temperatures 2900K, 5800K, 9000K,
15000K. The temperatures
correspond to M, G, A and B stars. Using the Planck curves as
fluxes (dlambda=1 A is fine),
compute the colors in terms of B-V and R-I, all as a function of
temperature.
(b) Why do astronomers tend to use B-V as a main reference for colors
of spectral types rather
than R-I? Explain in detail. Use graphics for the
explanations if this would be helpful to your argument.
HW09, due Thu 04 Nov: 13.7,14.6, Eclipsing Binary Pblm, Radial Velocity
Pblm (both below)
Eclipsing Binary Pblm: The star
Sirius A has a surface temperature of 10,000K
a radius 1.8 Rsun and M_bol=1.4;
the radius of its white dwarf companion, Sirius B
is 0.01 Rsun and M_bol=8.6.
a) What is the ratio of their
luminosities?
b) What is the ratio of their
effective temperatures?
c) If they orbit at i=90 deg,
which star is eclipsed at primary minimum
d) If your photometer can measure
magnitudes to an accuracy of 0.001, would you be
able to detect the hypothetical
eclipse? (Hint: Use log10(1+x)~x/2.3 for x<<1).
Radial Velocity Pblm:
(A) Use the
radial velocity calculator from U. Washington linked here
for this problem.
Your job:
EXPLORE PARAMETER SPACE TO FIND OUT HOW RADIAL VELOCITY VARIES WITH
VARIOUS PARAMETERS.
TEST OUT A GRID OF VALUES FOR EACH PARAMETER.
VARY THE PARAMETERS ONE BY ONE, SYSTEMATICALLY FROM LOW TO HIGH VALUES.
START WITH THE DEFAULT VALUES AND EXPLORE THE
POSSIBILITIES.
THEN, REPORT ON THE EFFECTS ON THE RADIAL VELOCITY CURVE.
Use 5 system parameters:
1) mass ratio (default: 1:1)
2) semi-major axis a (default: 1
AU)
3) eccentricity e (default: e=0)
4) inclination i (default: i=90
deg)
5) angle to line of apsides w
(default: w=0)
Observe these characteristics of
radial velocity curve:
a) maximum radial velocity v_r
b) ratio of v_{r,1}/v_{r,2}
c) period P
d) FWHM of maximum, minimum v_r
(as a function of time) for a given star
e) symmetry of v_r curve at
maximum, minimum v_r for a given star
f) time from v_{r,max} to
v_{r,min} compared to v_{r,min} to v_{r,max}
for a
given star
g) does v_{r,max}=-v_{r,min} for a
given star?
How does each system parameter
affect each observable? Some system
parameters
will affect more observables than others.
Make 7x5 grid for
presentation, so each parameter-observable combination has some
description.
Be sure to test the elliptical case (e>0) as well as the circular
case (e=0) whenever you can!
HW10, due 11 Nov: 15.5,15.9,15.10,He-burning lifetime pblm (below)
He-burning lifetime pblm: Estimate the energy available and the
lifetime for the He-burning phase in a 1 Msun star.
(a) Calculate the energy released per net reaction 3 He-4 -> C-12.
(b) What fraction of the available mass of 3 He nuclei is liberated
in the form of energy in the triple-alpha reaction? Compare this to the
fraction of available mass liberated in the p-p reaction.
(c) Assume that approximately 10% of the original mass of the star is
in the
form of He-4 in the stellar core during the He-burning phase. Estimate
the
total energy available from the triple-alpha process.
(d) During the He-core-burning phase, some H burning is also occurring
in a shell. Thus the star's luminosity is not due only to He-burning.
Keeping
this in mind, assume that the typical luminosity from He-burning is 100
Lsun.
Estimate the lifetime of the He core burning phase (in Myr or Gyr).
HW11, due 18 Nov: 16.2,16.5,16.6,16.9
HW12, due 30 Nov: 17.A HR Evolution (below, worth 2 pts), 17.B Star formation
paper (below, worth 2 pts)
NB: I originally assigned pblm 17.7, which doesn't exist, therefore I threw I'm
only assigning 2 problems.
17.A HR Evolution
Assuming that a star radiates as a blackbody during all hases of its
evolution, use the Stefan-Boltzmann Law
to determine the radius (in units of Rsun) of a 1 Msun star at all main
stages in this HR diagram figure.
(Note: Both axes are logarithmic.)
Fill in a table like this:
STAGE
log(L/Lsun) L/Lsun log(Teff) Teff T/Tsun R/Rsun
1) main sequence
2) 1st dredge-up
3) RGB
4) He flash
5) He->C+O
6) AGB
7) Thermal pulses
8) PN ejection
9) to white dwarf
17.B Star formation paper (2-point reading assignment):
read http://arxiv.org/abs/astro-ph/0605088
and answer these questions:
a) What most likely formed HI holes in other galaxies? What
mechanisms
appear unlikely?
b) Explain the post-T-Tauri problem and the current questions we
have about it.
You are particularly welcome to work with one other person on
the reading assignment. Just note
with whom you are working. I will give equal and
full credit to each participant. But,
please do not work together in groups of more than two.
EXTRA CREDIT: BULLITT LECTURE THU 14 OCT 7PM
Attend the
Bullitt Lecture, Thu 14 Oct at 7pm in the Planetarium. In a
maximum of 200-250 words,
summarize the talk. Then, in a maximum of 200-250 more words,
describe one of the telescopes
discussed by Don York: history, construction, design, wavebands used,
discoveries made with it (and by whom) etc.
Document your references. Credit: +1 homework problem on the
homework grades.
We will get an online version of the talk up ASAP. See me if you cannot
make the lecture in person and want to do the project. This is
worth a bonus of +1 to the homework
grade (equivalent to one problem). DEADLINE: TUE 2
NOV.
EXTRA CREDIT: JOSH PEPPER SEMINAR FRI 22
OCT 3PM
Attend the
Josh Pepper's seminar, Fri 22 Oct at 3pm in the Nat. Science
Bldg. In 300 words,
summarize the talk. This is worth a bonus of +1 to the homework
grade (equivalent to one problem). DEADLINE: TUE 2
NOV.
The participation grades are
subjective and are subject
to change. Generally, if you
come to class and ask an
average number of questions, you'll
get a 7 out of 10.
If you just sit there, you'll get
around a 5. If you skip class
(which I can note in any way,
including not
picking up homework) then you can
get <5. I also am less
likely to be generous with
participation if you habitually don't
turn in homework, since doing
homework generates questions
and feedback on common
misconceptions.
GRADING:
Your grades are composed of 3 parts:
homework avg, midterms, final,
participation.
All three parts are required for
completing the course.
The lowest homework grade is dropped.
Your grade is:
0.3*HW+0.3*MIDTERM1+0.3*MIDTERM2+0.10*PARTICIPATION
Partial Credit:
Homework and tests will have partial
credit available. You MUST
show
your work, in particular the
equations which are used to begin a
calculation, to get any credit at
all. You must keep track
of significant
digits. If the least accurate
number going into a calculation has
n
significant digits, then the answer
should have that number, also.
If you happen to do the wrong
homework problem instead of an assigned
one, you will typically not get
credit for it.
Leaving a question blank gets no
credit, ever.
Scientists
need to check their own work. To this end,
you are expected to have an idea
what a reasonable answer is, even
though
you might not get the correct answer.
A
reasonable answer has the correct units
-- use dimensional analysis!
It also has an order of magnitude
which is not wildly inconsistent
with information given in the problem
or common
knowledge. For example,
calculating a core temperature of the Sun
to
be 3K is a nonsense (unreasonable)
answer, because its surface and even
Earth are much hotter than
that. If your answer is way off
and you note it
and attempt to
explain where the problem might be,
I will take it into consideration.
If you give
a nonsense answer due to simple
arithmetic or mathematical
errors and do not catch it, you may
not get partial credit for setting
up the
problem correctly.
Here are also links (from an
Astronomy 107 links site) for recent
discoveries,
(simple) equations
used
in
that
class and supplemental
material.
Planned
Syllabus
(subject
to
modification;
links
for supplemental material are provided),
with a short summary.
Topics
covered:
time, celestial coordinates,
celestial mechanics, Earth-Moon dynamics,
interplanetary dust, E-M radiation and matter, the Sun, stellar
distances/magnitudes,
binaries, Hertzsprung-Russell diagram, interstellar medium, stellar
structure/evolution,
stellar remnants, possibly Galactic structure
Additional
material from other
chapters and books will be added as needed.
If you miss a midterm and you give
me a
week's
advance notice with a documentable
reason, the make-up will be
a one hour
oral exam.
General test policy is that once you
leave the room, you can't come
back in.
The worst homework grade will be
dropped.
You are permitted to help each other
in groups, but you must turn in
your own work.
A subjective score for class
participation (including
improvement)
will also count for 10% of the
grade. Grading will be done on a curve.
There is no fixed
percentile for grades, nor any absolute standard for letter
grades. The
plus-minus grading system (A, A-, B+ etc.) will be used.