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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.