Question

1. If you look at the CMD of NGC 6397 in the lower-right corner, what are the stars there? There are no stars here fainter

The following plots show two clusters, the Hyades cluster and NGC 6397. They are a bit different than the HR diagram shown in the app, because they show properties that we can observe; this type of plot is called colour-magnitude diagram or CMD. On the x axis, a CMD plots colour (in this case V - I) instead of temperature. However, colour is related to temperature: the quantities I and V are the apparent magnitudes of the stars in the infrared and visible, so a big value of V- I means that the star is cool. You can see the conversion between V - I and temperature in the table on the preceding page. On the y axis, a CMD shows the apparent magnitude of the star in one band (in this case infrared) instead of luminosity. Indicate for each cluster the location of the main sequence, red giants and white dwarfs. (You can check how different phases of stellar evolution look like on a CMD in the section of the book on globular clusters). Remember that along the main sequence stars get bluer as they get brighter and that in a cluster all the stars with temperatures greater than a certain value are gone, while usually when the different evolution stages are represented on an HR diagram, the entire main sequence is present! (a) Hyades (b) NGC 6397 1.5 1.5 2.0 3.0 1.5 1.0 1.5 2.0 3.0 V-I V -I

than I = 25. Why do you think this is? What is it telling us?

2.If you look at the CMD of NGC 6397 in the lower-left corner, what are the stars there? There are no stars here fainter

than I = 28. Why do you think this is? What is it telling us?

Answer 1

CMD of NGC - 6397 There are many more stars our there in each ring show at the right, except for the last ring (inside) as well as the ring number (above and left). The dotted lines indicate the border between CCD, (above) and CCD_2 (below) Total number of stars in the cluster is above 19300 plusorminus 19000 down to the limit of hydrogen burning NGC 6397 is one of the nearest GC's which makes its faint star more accessible than those of other more distant GC's and mettality (IC/4) = -1.99 plusorminus 0.02 Class of faint OV stars towards the cluster Centre is inconsistent with mass segregation missing star (fainter than observation data I = 25) we used the best converting fitting multichromatic isochrome. The parameter were obtained by Statical method compare the mean ridge line from (MD's using multiple colours four rigid of isochromes four Dartmouth stellar Evaluation database The best fatting parameter for NGC 6397 are an age of