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Transcript for Analyzing X-Ray Pulses from Stellar Cores

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 DS9 Analyzing X-Ray Pulses from Stellar Cores investigation developed by the Chandra mission. For a more comprehensive introduction to the DS9 image analysis software and individual investigations, please watch the short webinar introduction at the beginning of the imaging section. This investigation is an application of basic physics content related to rotational motion.

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:
There is an extensive teachers guide for this investigation and an answer key, as well as both a pencil and paper version and the version that requires the use of the ds9 image analysis software. The student handout provides all the information necessary for the investigation.

Slide 5:
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. However, all the Ds9 instructions are included within the Analyzing X-Ray Pulses from Stellar Cores student handout, so students do not need to learn the software beforehand, or use the tutorials or activities unless the teacher requires it.

Slide 6:
The student handout describes different types of stellar cores that result from the core collapse of massive stars – including white dwarfs and neutron stars (pulsars). These objects are embedded within accretion disks, and sometimes in binary systems with accretion disks. The dynamic interactions of these systems are often unstable, producing X-ray emissions from hot spots within the system.

Slide 7:
When light emissions change over time the resulting plot is a light curve, such as this animation of an X-ray binary system. The resulting light curve of the rotation of these hot spots can be used determine the rate of rotation which can then be used to determine the type of stellar core that is producing the emissions.

Slide 8:
Students plot and analyze light curves from GK Per and Cen X3 to determine what type of stellar core object they are – white dwarf or neutron star. These are screen shots from the Ds9 image analysis software that are used for the pencil and paper version of this investigation.

Slide 9:
Students analyze the light curve with the power spectrum and period fold tools to calculate the periods of GK Per and Cen X3.

Slide 10:
Students then apply basic physics concepts and a series of conversions and basic physics relationships and equation to determine the rotation rates. From this the centripetal acceleration of the materials on the stellar core can be determined. If the centripetal acceleration of material on the stellar core surface is greater than the acceleration due to gravity the rotational rate is too fast and the gravitational force is not strong enough to hold the material on the stellar core and it would fly apart.

Slide 11:
A task specific scoring rubric has been provided as an assessment tool for student understanding of the process and the basic physics principles, as well as the ability to communicate that understanding.

Slide 12:
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.