Transcript powerpoints - Georgia Southern University Astrophysics

GEARS Workshop Thursday
2011
Warm Up
• Howdy!
• Please add some more thoughts to paper
evals
• Please complete your morning warmup
Concepts
• Astronomers make 3 color diagrams to represent
3 pieces of information visually. For example, 3
different emission line features.
• Spectral lines are like fingerprints, they are
unique to the element or molecule that emitted
(or absorbed) them due to the unique electronic
energy levels in each.
• Type Ia and Type II supernova remnants may
appear similar in size and shape but have
different spectral signatures due to the different
progenitors.
Elements in us
• Most of the heavy elements (everything except
hydrogen and helium) in the Earth were produced
a) by stars that burned out before the Solar System
formed.
b) in chemical reactions in the primitive oceans and
atmosphere.
c) in nuclear reactions in the Sun.
d) in the hot, dense, early universe.
Where do the elements come
from?
• Big Bang = energy forms neutrons, protons,
electrons and overwhelmingly hot and dense
conditions are such that Hydrogen (which is
only a proton anyway…), Deuterium, and
Helium and Lithium nuclei form
• http://map.gsfc.nasa.gov/universe/bb_tests_e
le.html
All other elements
• Formed in main sequence stars
• Or formed in explosions of stars called
supernova (supernovae is plural)
• The supernova are needed to spread the
fusion products into space – otherwise
trapped in stellar cores
http://imagine.gsfc.nasa.gov/docs/teachers/elemen
ts/
Fusion – summary of chain of
reactions – not the exact reaction
• Main sequence:
4 (1H) --> 4He + 2 e+ + 2 neutrinos + energy
• Hydrogen in core expended – fusion ends,
collapse begins, heating and …
• 3 (4He) --> 12C + energy (Sun ends here…)
• Helium in core expended – fusion ends,
collapse begins, heating and …
• 12C + 12C --> 24Mg OR 12C + 4H --> 16O
E=mc2
• Where does the energy come from ?
• Mass of four 1H > Mass of one 4He
Low Mass vs High Mass
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Really massive stars
High Mass
Why is Fe so special?
• Examining the binding curve in detail.
MIT OpenCourseware
Formation of the elements
• Most of the heavy elements (everything except
hydrogen and helium) in the Earth were produced
a) by stars that burned out before the Solar System
formed.
b) in chemical reactions in the primitive oceans and
atmosphere.
c) in nuclear reactions in the Sun.
d) in the hot, dense, early universe.
Suppose the universe contained only low-mass stars.
Would elements heavier than carbon exist?
a. Yes, all stars create heavier elements than carbon when they
become a supernova.
b. Yes, but there would be far fewer heavier elements because
high-mass stars form elements like iron far more prolifically
than low-mass stars.
c. No, the core temperatures of low-mass stars are too low to
fuse other nuclei to carbon, so it would be the heaviest
element.
d. No, heavy elements created at the cores of low-mass stars
would be locked away for billions of years.
e. No, fission reactions would break down all elements heavier
than carbon.
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Where does Uranium come
from?
How does the iron get out of the core?
Explosions
Are all explosions created equally?
Explosions leave a mess
Mess (nebula) can be swept up into new stars
Nebula
Tying back to yesterday
• We saw S, Si, Mg, O, Fe in the supernova remnants
• Tycho – Type Ia (115)
• The oxygen-rich supernova G292.0+1.8 contains a
pulsar. Type II
• Type Ia and Type II remnants because the progenitors are
different. Type Ia remnants - from white dwarfs - usually show
relatively strong Si, S, Ar, Ca, and Fe, and weak O, Ne, and Mg
lines; Type II remnants - from massive stars - generally have
the reverse pattern.
• (http://chandra.harvard.edu/xray_sources/pulsar_java.html )
• http://chandra.harvard.edu/edu/formal/stellar_ev/story/index.html
Core Collapse
• http://en.wikipedia.org/wiki/Type_II_superno
va
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http://hyperphysics.phy-astr.gsu.edu/hbase/astro/snovcn.html
Classification
• They are classified as Type I if they have no
hydrogen lines in their spectra. The subclass
type Ia refers to those which have a strong
silicon line at 615 nm. They are classified as Ib
if they have strong helium lines, and Ic if they
do not. Type II supernovae have strong
hydrogen lines. These spectral features are
illustrated below for specific supernovae.
• http://chandra.harvard.edu/edu/formal/snr/bg.html
• The elements and their relative abundances are different for Type Ia and
Type II remnants because the progenitors are different. Type Ia remnants from white dwarfs - usually show relatively strong Si, S, Ar, Ca, and Fe, and
weak O, Ne, and Mg lines; Type II remnants - from massive stars generally have the reverse pattern. In addition to the composition of the
ejecta, spectroscopy can show how much of the stellar material was
convectively mixed during the supernova event by calculating the density
and temperature of the ionizing gas that generates the spectral lines.
However, spectroscopy of supernova remnants is not clear cut and
drawing conclusions is complicated; it is sometimes difficult to determine
if a remnant is Type II or Type Ia. The Chandra and XMM-Newton missions
have inaugurated the era of true spatially resolved X-ray spectroscopy.
Spectrum on top of
Brehmsstrahlung
Chandrasekhar limit
• The maximum mass that can be supported by
electron degeneracy pressure against gravity
• Chandrasekhar won Nobel Prize in 1983 with
William Fowler
• http://nobelprize.org/nobel_prizes/physics/la
ureates/1983/chandrasekhar-autobio.html
Other parking lot
• Related to stellar evolution
Switching GEARS
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Search for extra solar planets
This is looking for planets around other stars
Not looking for objects orbiting the Sun
There is an app for that
And the resource for all things planet searchy:
http://planetquest.jpl.nasa.gov/
Engage: Demonstration
• Take a look at ONE of these ways to represent
a star with a planet as seen from a distant
observer on Earth
• Brainstorm ways to find planets based on this
information
Engage: Planet demos
• Brainstorm how you might detect planets.
http://www.youtube.com/watch?v=WApazS6-mu4
[email protected]
[email protected] after May 1
Kepler Mission
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Staring at a part of the sky for 3.5 years
Watching the brightness of stars
Looks for dimming of light from star
Periodically!
Make some predictions
• Think about why you are making your predictions
• Spend less than 7 minutes on your predictions
Which type of system make it easier to find
planets using this technique. If it doesn't
matter, write EQUAL CHANCE
1. Less massive stars or more massive stars.
2. Planets with orbits that are closer to circular
or highly elliptical orbits.
3. Face-on orbits or edge-on orbits.
4. Small diameter planets or large diameter
planets.
5. Small mass planets or large mass planets.
6. Planets close to star or planets far from star.
Explore: Transit Simulator
• Semi-major axis – average distance from star – see
ellipse definition
• Eccentricity – ellipticity – or deviation from round –
see ellipse definition
• Inclination – how much plane of orbit tilts as seen
from Earth. Face-on = 0 degrees. Edge on = 90.
• Longitude – angle that plane of orbit seen by earth –
think 2-D ellipse that you aren’t looking at from short
or long axis – but at an angle
Discuss
• What definition did your group use for easier to find?
• % flux change – bigger easier to see
• Frequency of dip – must balance between the orbital
period (e.g. 100 years vs. 1 year) and the fraction of
the orbital period the star is blocked.
• Need to discuss normalized flux – 100% of star light
seen vs 99%.
• Other simulator used 0.1 instead of .99 to represent
a 1% drop.
After play with sim
• Create a hypothesis
• Write a hypothesis in the form of "If xxx
massive stars make it easier to find planets
then I expect to see ________." What is your
independent variable? What is your
dependent variable? What are your controlled
variables?
• Hypothesis: If it is easier to find massive
planets then I expect to see more massive
planets.
• Testable with simulator or no?
• Discuss Testable hypotheses vs. Good
questions to ask.
Elaborate: Kepler Flash
• Assign multiple people to examine same star
to be able to compare answers.
• Form to complete for answers.
Evaluate: Graphing Kepler
Data in Excel
Kepler - Period
• Multiple ways to decide the period.
• Group discussion about what those methods
are.
Kepler Peer Review
• Compare results with other participants who
had the same planet.
• Provide a formal review of their results on
your whiteboard.
Kepler Planet - answers
The Atlas
• http://planetquest.jpl.nasa.gov/atlas/atlas_se
arch.cfm?Sort=Star&SorDir=ASC&Planet_Type
=Kepl
• Sounds like hundreds of new candidates
announced at end of May at American
Astronomical Society Meeting. Confirmation is
after ground based followup – so still only 16
confirmed
% difference, % error
• Is it appropriate to calculate the percent
difference or % error of your results with the
astronomically published results in this case?
• Discuss in groups.
Citizen Science & Kepler data
• http://www.planethunters.org/
• Kepler data for your own investigations – published quarterly
• A list (in Excel format) of candidates is published (as of Apr
2011) in directory:
http://archdev.stsci.edu/pub/kepler/catalogs/
Kepler candidates
• Or from link on News page
http://archive.stsci.edu/kepler/
• If you visit the html version – you can click on the
candidate and plot the light curves from publicly
accessible data. (Only the EX – not the STKS)
Corrected, Uncorrected
Demonstration #2
• Brainstorm some ways to detect planets using
this demonstration as inspiration.
• Hand out set of demonstrations for each
person.
Radial velocity
• Vs. tangential
• Video – introduction
• http://planetquest.jpl.nasa.gov/Planet_Finder
/planetfinder.html
• And Radial velocity
• Requires sound
Doppler Shift
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Introduction to Doppler shift of light
Redshift
Blueshift
From radial velocity link in Planet Quest video
Must use spectral lines – otherwise is just
continuous shift to continuous…
• http://hyperphysics.phyastr.gsu.edu/hbase/sound/dopp.html#c3
Doppler Shift Lecture Tutorial
• Complete this exercise in groups of 2 to 3.
• This is designed to be completed while you
are discussing with other people.
• This is not designed to be completed on your
own.
Doppler Shift Misconception
• Summarize – depending on where are
– ABC red, yellow, blue stars
– Or spacecraft/planets
Habitable Zone
• Define it based on your understanding from
the simulation
• Whiteboard and defend your definition
Scientific definitions
• Mutually agreed upon by many
Habitable zone
• Defined as location in a solar system in which
a planetary surface could support liquid water
• Does not include greenhouse effect heating
(like on Earth)
• Does not include tidal heating – such as on
Europa
Why liquid water?
• Ties to other disciplines – chemistry, biology
Other speculations
• What else might be required for life?
• Might we find life?
• How might we look?
Carbon based/Silicon based
• How can a discussion of habitable zone be
used in biology, chemistry, physics?
In 2020, a spacecraft lands on Europa and melts its way through the ice into the
Europan ocean. It finds numerous strange, living microbes, along with a few
larger organisms that feed on the microbes.
a.
b.
c.
d.
This is likely because biosignatures were already detected on Europa by the
Voyager 2 spacecraft.
This could happen because there is evidence for an ocean underneath the icy
surface of Europa and water is a good place to look for life.
This is fantasy because it would take more than 10 years for a spacecraft to reach
Jupiter using current rocket technology.
This is fantasy because the X-ray emission from Jupiter has effectively sterilized
all the moons around it.