Exercise 4 - Measurement of the Age and Distance of a Globular Star Cluster
We measure blue (mB) and green (visual, mV) magnitudes
of selected stars in the outer regions of a globular cluster shown on VLT images,
convert the (mB-mV) values into stellar surface temperatures
(T) and plot the mV values as a function of the T values on a Hertzsprung-Russell
diagram. The cluster's Main Sequence, seen in the plotted diagram, is compared
with a distance-calibrated standard Main Sequence from the nearby Hyades cluster.
The distance to the cluster can be determined by Main Sequence fitting and using
the distance modulus. The cluster's age, which incidentally places a lower limit
on the age of the Universe, can be estimated from the position of the turn-off
point on the Main Sequence.
Two FITS files and one Excel file with additional data for this exercise
can be downloaded here.
To get a printed version or a CD-ROM with PDF-files and images,
please contact one of the contact persons.