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ASTR1040 Spring, 2005
Due date: Tuesday, April 26
The table below provides data on measurements of apparent magnitudes and observed wavelengths of the Ca II K line (rest wavelength 3933.663Å) for a number of galaxies.
(a) Your main job is to use these data to derive the value of Ho, the Hubble constant. To do so, you will have to convert the given wavelengths into recession velocities and the apparent magnitudes into distances (for this assume that all of the galaxies have the same absolute magnitude, MV = -21.0). Then make a plot of velocity versus distance, draw a straight line through the data points and find the slope of the line (in units of km/sec/Mpc), which will be your value of Ho. If you are familiar with statistical methods, you could find the straight line by doing a least-squares fit through the points (demanding that the line pass through zero); otherwise, just make an eyeball fit using a ruler.
(b) Use your value of Ho to find the age of the universe (applying the traditional 2/3 correction factor to what you get from 1/Ho). How does your value compare with the estimated age of the galaxy, based on globular cluster ages? How does your answer change if you adopt the more modern correction factor of 0.9 instead of 2/3?
Here are the data:
mV Wavelength mV Wavelength
11.12 3961.032 13.32 4007.522
10.70 3954.567 13.64 4019.836
13.60 4023.457 12.79 3992.052
13.40 4013.540 8.60 3939.568
6.39 3936.418 12.21 3983.942
12.96 4004.984 13.82 4033.938
13.20 4010.998 13.17 4005.251
12.27 3979.163 10.55 3955.754
11.94 3975.318 9.19 3946.402
10.05 3951.800 13.82 4030.038
13.25 4005.384 12.91 3997.113
12.39 3983.278 10.15 3949.429
13.45 4018.496 11.83 3969.021
11.64 3970.550 12.55 3993.383
12.67 3987.264 13.49 4016.084
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