For the case of the neutron star RBS 1223, present the answer to these questions on the whiteboard:
- What makes you believe that the blackbody model curve is a better fit to the observed spectrum?
- Predict properties of this NS, given distance of 1200 parsecs: Flux (ergs/cm2/sec), Temperature (in Kelvin, using conversion of 1keV= 1.1 x 107 K), Luminosity (ergs/sec)
- Compare to another, hypothetical, neutron star with same temperature (1.13 x 106 K), but higher luminosity (1.5 x 1033 ergs/sec). How is this hypothetical star different from RBS1223? Can you say anything about their relative size? (luminosity is 50% more, and temperature is the same, so the hypothetical star would have a larger radius.
- Image of project assignment: (investigation 3 assessment prompt)
- Images of student whiteboard presentations: (neutron star presentation 1, neutron star presentation 2)
- If more time or a more challenging wrap up is desired, have students predict the luminosity of the hypothetical star: give students values for distance (= 1470 pc, further), temperature (= 1.13 x 106 K, same) and flux (= 5.5 x10-12 ergs/cm2/sec, same) for hypothetical neutron star. Via calculation, students obtain the luminosity given above (= 1.5 x 1033 ergs/sec, about 1.5 times the luminosity of RBS 1223)
- Also, with extra time or for students done early, have them calculate the radii of the two neutron stars, using the relation L = sigma*T4 * 4 * pi * R2. Hypothetical star radius will only be larger by a factor of 1.13, or 13% ( = square root of 1.5)
Assessment ideas: None