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Transcript
INTRODUCTION
On the evening of November 11, 1572, Danish astronomer Tycho
Brahe noticed a new, very luminous object in the constellation
Cassiopeia. This object became bright enough (as bright as
Venus!) to be observed for several weeks during the day. Over the
next year and a half, it dimmed by a factor of about 10,000 until it
was no longer visible to the naked eye, even at night.
Tycho’s Uraniborg (castle of the heavens)
Cassiopeia
“If it were a star, then the immutable heavens had changed, and the basic contrast between the
superlunary region and the corruptible earth was in question. If it were a star, the earth might more easily
be conceived as a planet, for the transitory character of terrestrial affairs would now have been
discovered in the heavens as well. Brahe and the best of his contemporaries did conclude that the visitor
was a star. Observations … indicated that it could not be located below the sphere of the moon or even
close to the sublunary region. Probably it was among the stars for it was observed to move with them.
Another cause for cosmological upheaval had been discovered.“
from The Copernican Revolution, Thomas Kuhn
Tycho’s “Stella Nova”, however, was
not the birth of a star as he had
thought, but the death of a star or a
supernova.
ROSAT Images of Tycho's SNR
BACKGROUND INFORMATION
A light curve reconstructed from Brahe’s
observations has shown that this supernova is
a Type 1a. A star can have different fates
depending upon its mass. A star with about
the same mass as the Sun will turn into a
white dwarf. If this white dwarf is in a binary
system, it can accrete enough mass so that it
cannot support its own weight. The star
collapses and temperatures become high
enough for carbon fusion to occur. Fusion
begins throughout the white dwarf almost
simultaneously and an explosion occurs.
Type Ia Supernova
Tycho’s SNR
"To make an apple pie from scratch,
you must first invent the universe."
~Carl Sagan
“The elements have their ultimate origins in cosmic events. Further, different elements come
from a variety of different events. So the elements that make up life itself reflect a variety of
events that take place in the Universe.
The hydrogen found in water and hydrocarbons was formed in the moments after the Big
Bang. Carbon, the basis for all terrestrial life, was formed in small stars.
Elements of lower abundance in living organisms but essential to our biology, such as
calcium and iron, were formed in large stars.
Heavier elements important to our environment, such as gold, were formed in the explosive
power of supernovae.
And light elements used in our technology were formed via cosmic rays.
The solar nebula, from which our solar system was formed, was seeded with these elements,
and they were present at the Earth's formation. Our very existence is connected to these
elements, and to their cosmic origin.”
(coded according to the dominant processes
which produce the elements)
What elements are in Tycho’s SNR and how are they distributed?
What tools do scientists use to answer these questions?
NASA's Chandra X-ray Observatory, which was launched and deployed by the Space
Shuttle Columbia on July 23, 1999, is the most sophisticated X-ray observatory built to date.
Incoming X-rays are focused by the mirrors to a tiny spot (about half as wide as a human
hair) on the focal plane, about 30 feet away. The focal plane science instruments, ACIS and
HRC, are well matched to capture the sharp images formed by the mirrors and to provide
information about the incoming X-rays: their number, position, energy and time of arrival.
Two additional science instruments provide detailed information about the X-ray energy, the
LETG and HETG spectrometers.
ds9 software (available as a free download
from the Chandra Ed website) allows
educators, students, amateur astronomers
and the general public to perform X-ray
astronomy data analysis using data sets
from the Chandra X-ray Observatory.
Your “color-by-number” image of a supernova remnant
from the activity “Decoding Starlight? ds9 makes
images in a similar way. What can ds9 analysis tell you
about the elements in Tycho’s SNR? Let’s find out!
PURPOSE
To use ds9 software to analyze the X-ray spectrum of the Tycho Supernova Remnant,
determine the elements present, and investigate the distribution of these elements in the
remnant.
HYPOTHESIS
Use prior knowledge about stellar
evolution to predict which elements you
might expect to see in a Type 1a
supernova remnant and how those
elements might be distributed in the
remnant.
Where would the heavier
elements be? Where would the light
elements be? Explain your reasoning.
You may wish to read more first.
PROCEDURE
A supernova remnant can have a temperature of
millions of degrees Kelvin. Bremsstrahlung
radiation occurs in such a hot gas where many
electrons are stripped from their nuclei, leaving a
population of electrons and positive ions. When an
electron passes close to a positive ion, the strong
electric forces cause its trajectory to change. The
acceleration of the electron in this way causes it to
radiate electromagnetic energy - this radiation is
called bremsstrahlung and produces a continuous
X-ray spectrum.
In addition, emission lines can appear superimposed on this spectrum, corresponding to the
ejection of K and L shell electrons knocked out of atoms by collisions with high-energy
electrons. Higher energy electrons then fall into the vacated energy state in the outer shell,
and so on, emitting X-ray photons. The energies of these emissions lines can be matched to
energies in the CHIANTI Atomic Database to identify the elements in plasmas such as
supernova remnants.
9.
Enlarge the graph by dragging the lower right corner. Either on the screen or
on a printout of the graph, measure the distance between O and 1 keV to the
nearest tenth of a centimeter (mm). This gives your scale in cm/keV.
10. Measure the distance in cm (to the nearest 1/10 cm) from 0 keV to the center of
each peak (X- ray emission line).
11. Divide the distance to each peak (cm) by your scale (cm/keV) to get the energy
(keV) of each emission line.
An alternative way of getting the energy of each
emission line is to create a zoom box by holding the
left mouse button down and dragging a box around the
line. When you click again, a zoom will appear. Right
clicking the mouse returns you to the original graph.
element
Energy
(KeV)
element
Energy
(KeV)
0
0.18
Si
1.98
Mg
0.25
Si
2.13
Mg
0.27
S
2.42
C
0.31
S
2.44
C
0.37
S
2.60
O
0.64
S
2.88
O
0.66
S
2.95
Fe
0.80
Ar
3.10
Fe
0.81
Ar
3.32
Ne
0.92
Ar
3.69
Ne
0.93
Ca
3.86
Ni
0.95
Ca
3.89
Ni
0.98
Ca
4.11
Ne
1.02
Ca
4.95
Mg
1.33
Fe
6.47
Mg
1.45
Fe
6.54
Fe
1.66
Fe
6.97
Fe
1.67
Fe
7.80
Si
1.84
Fe
8.26
Si
1.87
12. Identify the elements for each X-ray emission
line using the chart to the left. If you have lines
whose energy is not close to that of one of the
elements in the chart, leave that line
unidentified.
13. You may wish to use the CHIANTI database to
get possible candidates for unidentified lines.
You will need to convert energies in KeV to
wavelengths in angstroms using E = hc/l where
h = 6.626X10-34 js, c = 3 X 10-8 m/s,
1 A = 1.6 X10-10 m and 1 keV = 1.6 X10-16 j.
Si
Fe
0.8 keV
1.8 keV
Mg
S
1.3 keV
2.4 keV
Ar
3.1 keV
Ca
3.9 keV
Fe
6.4 keV
0.1-10 keV
0.7-0.9 keV (in the region of Fe)
Contour interval – 750 counts
Contour interval – 200 counts
14. Reload Obs id 115 (Tycho SNR) into ds9.
15. Analysis>Display Contours
16. If you wish to see the contour intervals – Analysis>Contours Parameters
17. Use Chandra Ed Analysis Tools>Energy Cut to view the Tycho SNR in an energy band close to the energy
values of each peak (choose a hi and lo of 0.1 keV on either side of the line energy). This will help you see
the distribution of the elements. Analysis>Display Contours is useful here.
18.
0.1-10 keV
4-6 keV continuum
Contour interval – 750 counts
Contour interval – 19 counts
On your bremsstrahlung spectrum, there is an energy continuum where there are no spectral
lines. Do an energy cut for this energy interval. Think about what this area might represent and
why there are no spectral lines in this region.
0.1-10 keV
1.2-1.4 keV (Mg)
1.7-1.9 keV (Si)
2.3-2.5 keV (S)
3.0-3.2 keV (Ar)
3.8-4.0 keV (Ca)
6.3-6.5 keV (Fe)
0.7-0.9 keV (Fe)
4-6 keV continuum
Si
Fe
Mg
S
Ar
19.
Ca
Using various shaped regions, enclose areas of interest from your energy cuts and create
bremsstrahlung spectra as you did for the whole Tycho
SNR.
Si
Fe
Mg
S
Ar
Ca
Si
Fe
Mg
S
Ar
Ca
Fe
Mg
Si
S
Ar
Si
Fe
Mg
S
Ar
20.
Find a region that contains each of the elements in the whole remnant as well as part of the
shockwave.
CONCLUSIONS
1. Do the results of your ds9 analysis support
your hypothesis? Why or why not?
2. How do the spectra of different regions you
investigated within the Tycho SNR
compare to each other? What are their
similarities and differences?
3. Describe the shape of the region for the
energy cut of the continuum that contained
no spectral lines.
What could this
represent? Why doesn’t it contain spectral
lines?
4. Describe the features and shape of the
Tycho SNR.
XMM-Newton, ESA
FURTHER INVESTIGATIONS
1. Conduct a similar investigation of other types of supernova. Go to Analysis>Virtual
Observatory>Chandra Ed Archive Server. At the bottom of the page that comes up, click
“Unofficial Chandra Public Archive”. On this form, do a search by ObsID or the name of the
supernova. Clicking on the title of choices that come up in the search will load the FITS
image into ds9. You can view various supernovae in the Chandra Supernova Photo Gallery.
Two suggestions for further study would be Cas A, a type
II supernova remnant with a central neutron star, and
W49B, a prime candidate for being the remnant of a
gamma ray burst involving a black hole collapsar.
How do the types and distributions of elements and the
structures in other types of supernova compare to that of
Tycho’s SNR?
Cas A
W49B
2. Research recent Hubble images that may have located
the runaway binary companion to the white dwarf that
exploded in Tycho’s supernova.
3. Investigate why Type 1a supernova can be used as
standard candles (objects whose absolute magnitude is
thought to be very well known and can, therefore, be
used to find distances to galaxies that contain these
objects).
Hubble Image – Tycho’s companion?
X-Rays - Another Form of Light
X-ray Sources: Supernovas & Supernova Remnants
Chandra's View of Tycho's Supernova Remnant
Chandra Education Data Analysis Software & Activities
XMM-Newton observation of the Tycho Supernova Remnant
Chandra Observations of Tycho's Supernova Remnant
(Astronomy & Astrophysics)
(Journal of Astrophysics & Astronomy
The CHIANTI atomic database
Chandra Images by Category - Supernovas & Supernova Remnants
Chandra Supernova Remnants Catalog
Universe Today - Survivor Found From Tycho's Supernova
Special thanks for assistance with the development of this project to Dr. Frederick Seward of the
Smithsonian Astrophysics Observatory.