Stars: Color Index
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Goal:

Determine the B-V color indices of a group of stars and plot results on a Color-Magnitude Diagram (similar to an HR Diagram)

Method:

• Choose a number of stars based on certain criteria using Software Bisque's TheSky (telescope control and planetarium software)
• Image selected star fields using Etscorn Campus Observatory Robotic Telescope
• Determine B-V color index using Software Bisques CCDSoft (camera control and data reduction software)
• Create Color-Magnitude Diagram based on results

Introduction Outline: 

• Stars are colored differently
• Color corresponds with temperature
• Color Index : Ratio of light intensity measured in two different wavelengths (colors) of light; color index related to star temperature
• B-V most common color index measurement. B = Blue, V = Visual (yellow-green)
• Images taken through filter that only lets one color of light pass through
• Star magnitudes are logarithmic; ratio of light intensities determined from apparent magnitude in blue (mB) and visual (mV)
• Measure star intensity in blue and visual; subtract V from B to get star's B-V color index
• Positive B-V value indicates redder, and therefore cooler, star
• Positive B-V means B value higher; larger numbers represent fainter stars in the stellar magnitude scale; less blue light than visual light
• B-V value derived from apparent magnitude is same as that derived from absolute magnitudes, therefore distance information not necessary to determine color index
• For stars on the main sequence, those with like B-V color indices have same absolute magnitude
• Stars can be plotted on a graph using B-V color index as x-axis and absolute magnitude as y-axis