# Explain why B-V loses temperature sensitivity for these hot stars.

Set the temperature to approximately 8000 by using the slider bar (note the arrow keys on your keyboard can be used for fine temperature adjustment. What is the wavelength of the peak emission?
Now set the temperature to approximately 4000. What is the wavelength of the peak emission?
What is the ratio of the two wavelengths? (a ratio is two numbers divided by each other). Is this ratio what you expect? Explain why or why not.
What color would a star appear to be which has a temperature of 7000?
What color would a star appear to be which has a temperature of 4500?
Now click on the box that says “Draw Limits of Integration” -the white lines that appear there represent filter band passes of standard astronomical filters. To measure stellar temperatures, astronomers put filters in front of their digital cameras and measure the flux ratio between the two filters. For B (blue) and V (visual or green) this ratio is encoded as the index value B-V. The lower that number, the hotter the star (more flux is emitted in the B filter than the V filter. A value of B-V = 0.5 means that approximately the same amount of energy is emitted in the blue filter as the green filter.
What temperature produces a B-V value of 0.5?
Suppose that I can measure B-V to an accuracy of 10% (.1 in B-V). For the case of B-V = 0.5, what percentage change in temperature produces this 10% change in B-V? (i.e. B-V moves to 0.6 or 0.4 when you change the temperature)
Set T to 15000. At this temperature, what temperature change is required to change B-V by +/- 0.1?
Explain why B-V loses temperature sensitivity for these hot stars.
What kind of observations would you need to do perform in order to accurately measure the temperatures of very hot stars?