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Transcript for Ds9 Decoding Starlight 2015 Webinar

Slide 1:
I am Donna Young and I work with the NASA/Chandra X-Ray Center outreach office. This is an overview and introduction to the Decoding Starlight – From Photons to Pixels activity developed by the Chandra mission. Decoding Starlight is an introductory activity to help students understand images and how numbers are converted to images. Decoding Starlight has both a middle and a high school version – the only difference between the two is that there is less missing data to fill in for the middle school version. Decoding Starlight is based on reduced data for the Cas A supernova remnant and the ds9 software is not required. Screen shots from ds9 are used to compare the student results with the ds9 version.

This activity is an introduction to the ds9 image analysis software that allows educators and students to perform X-ray astronomy data analysis using data sets from the Chandra X-Ray Observatory, and the ds9 image display program and software analysis tools. Decoding Starlight does not require using the ds9 software; however, it does use screen shots from the software. Teachers may have students download and use ds9 after the activity.

Slide 2:
The Chandra X-Ray Observatory is in an extreme orbit that ranges from 16,000 km at closest approach to Earth to more than a third of the distance to the moon. The highly inclined orbit takes 64 hours with 55 uninterrupted hours of observing time. The 2 sets of 4 nested hyperbolic/parabolic mirrors match the grazing incidence of the incoming X-Ray photons and direct them to a focal point at the end of the spacecraft. The photons are detected by one of two scientific instruments – the HRC (high resolution camera) or ACIS (advanced CCD imaging spectrometer). A high energy transmission grating is lowered into the focal plane with the ACIS and a low energy transmission grating for the HRC.

Slide 3:
The photons are detected, converted to a voltage and recorded. Every 8 hours there is a data download to the Deep Space Network (DSN) in Spain, Australia or Goldstone in Barstow, CA. The data is then transmitted through the system to Cambridge, MA where the data is analyzed by Chandra scientists. Unique to X-Ray observations and the mirror/grating/scientific instruments aboard the Chandra spacecraft, for each individual X-ray photon detected the amount of energy, the position (x-y coordinates) and time arrival are known – resulting in a high resolution analysis of the objects being observed.

Slide 4:
The extensive teachers guide and the introduction and background gives complete instructions for this activity. This is the high school version student handout. Students have the task of filling in the missing data to calculate the average number of photons from 5 different observations of a supernova remnant. Missing data is a common occurrence for scientists. Depending on the student composition, the missing data can be filled in using the average of the data that is available, or taking the mean, or even putting the information into an Excel spreadsheet to determine a formula. Students can use any method they choose. Once the average number of photons is calculated they are filled in on the numbered grid. Students look at the range of data and determine how the data is going to be binned – grouped together into 5 groups of numbers. The legend shows 3 different ways that the data can be binned. Any range of bins for the average number of photons is correct.

Slide 5: Once the bin values have been entered into the legend, color values need to be assigned for each bin, and then the grids are colored in according to the colors in the legend. This slide shows a sample with one set of bin values and assigned colors. The data in this activity is reduced from the actual observational data for the Cas A supernova remnant. Even with this small amount of data – 121 pixels – structural features of the remnant can be determined - the central neutron star and the inner and outer shock waves. The also gives students an idea of the power of image analysis software – because the HRC on the Chandra spacecraft has 9 million pixels!

Slide 6:
This shows 6 different student grids of binned and colored average photon intensities. Notice that the 3 samples in the top row all have the same bin ranges, but look very different because of the difference in color selection. The 3 in the bottom row all have different bin ranges. All of the samples show the basic structure of the supernova, only some structures are more obvious due to the colors assigned to the bin values. All of these results are correct!

Slide 7:
This slide shows 4 of the student samples with screen shots from the Cas A remnant from the ds9 toolbox. There is a scale menu that shows the remnant in different scale values. Four different scales are shows under the student samples that they resemble. The students probably did not realize that by binning and assigning color values with different contrast that what they were actually doing was devising a scale. The 4 scales shows here are all used by scientists depending on what part of the Cas A remnant they are interested in studying. The Log scale is used to show every single photon in the remnant, the Square Root scale is used is all the major features are being considered, the Linear scale shows the bright and intermediate bright parts of the remnant, and the Squared scale is used to study only the most bright energetic parts of the remnant.

Slide 8:
The download instructions for the ds9 software are located at http://chandra-ed.harvard.edu/. The software can be downloaded to Windows, MacOSX or Linux environments. The website also has self-guided tutorials and activities to learn how to use the software and the analysis tools. All the instructions and websites are in the teacher guides, and students do not need to access this website as will be explained further on. The software can be downloaded and the Cas A supernova data displayed in the software to show the students that the beautiful Cas A public release image is really just a grid of binned and colored squares – there are just 9,000,000 of them instead of 121.

Slide 9:
This slide is a series of zooms of the Cas A supernova remnant to show the students that astronomical images really are grids of binned numbers that are assigned color values. Students can download and use the ds9 software and easily use this feature.

Slide 10:
Students can also use the color menu to display the Cas A remnant in a variety of different colors, can zoom in and out and change the bias and contrast to see how the image changes. The important point is that the observational data never changes. It can be displayed in a variety of ways, but the numbers beneath the manipulation are the same – no matter what the final selected image looks like.

Slide 11:
The public release images of supernova remnants are beautiful. This is where art and science come together to produce an image that will catch the imagination of the public. All of these images of artistic renditions that use colors that emphasize the structures and features within the remnants. Remember that the numbers that these images are based on is not changed. The colors are selected to represent different photon energies or different wavelengths, or special features. This activity can also be used as a STEAM lesson – adding art to science, technology, engineering and mathematics.

Slide 12:
Students need to produce an artistic rendition of their results – an image that would be used to accompany a press release to the public. The colored grid needs to be turned into an artistic version pleasing to the eye for the public. This is one example from a student.

Slide 13:
This is another student example of an artistic public release version from a binned and colored grid for the Cas A data.

Slide 14:
The Chandra educational materials website has excellent supporting resources for multiwavelength astronomy and stellar evolution. You can request available ancillary classroom materials using the materials request form. If you have any questions, please email me.