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Lab Comments• Age of Pleiades

• All stars in a cluster are the SAME age. Blue live shorter lives while red live longer before exhausting their hydrogen. Do not confuse red supergiants with just red stars.

• Collecting more photons at each wavelength allows the signal to overcome the statistical noise

• Take the difference of your observed spectra with known spectra. How much it deviates allows you to estimate a spectra uncertainty range.

• The estimate the uncertainty in the age, look at your uncertainty in spectral type to create a min and max age.

• Stars do not move up and down the main sequence line. They stay at one brightness and spectral type until they die, at which point they fall off the main sequence line. So in 2 billion years, everything right of about A5 is going to stay exactly where it was.

How do we know the distances to star

clusters?

•Stellar parallax is only reliable up to 3,000 light-years

•For more distant objects we must use the standard candle technique such main sequence fitting.

•A Standard Candle is an object of known luminosity

•We can take advantage of the inverse-square law!

Apparent Magnitude and the color (spectral type) of a star can be found through photometry

Absolute Magnitude can be found from an H-R diagram

Your Task•Measure the APPARENT B and V magnitudes of several

stars in Pleiades

• Subtract B-V to determine the color (spectral type) of each star

• Plot V vs. B-V on the H-R diagram

• The difference between the APPARENT main sequence and the ABSOLUTE main sequence gives you the distance

• Some of the stars we give you will not be Main Sequence stars but they will still be cluster stars

• Some of the stars we give you will not even be in the Pleiades star cluster

Warning!