Color-Color Diagrams

Figure 4 shows the Color-Color Diagrams for both our cluster and the control field. The thick solid line is the main sequence plotted from the intrinsic colors of main sequence stars from Table 4 of the lab handout. The dashed lines are the reddening lines of the main sequence. The region between these two lines determine the points on the color-color diagram that are main sequence stars that undergo ``normal extinction.'' This line was found by using Equation 7 using the extinction values found on Table 3 in the lab handout.

$$\mbox{reddening vector} = \frac{A_{J}-A_{H}}{A_{H}-A_{K}} = \frac{0.282-0.175}{0.175-0.112}=1.69841$$ (7)

Figure 4: Above are plots of the color-color diagram for IC348 and the control field. The solid line on the left of the points is the main sequence. The dashed lines are the reddening lines.

We can see that in our cluster, most of the stars lie inside the region between the two reddening lines but above the main sequence line. This displacement from the main sequence indicates that the stars are main sequence stars that are reddened due to extinction from the molecular cloud that is contained within the cluster. The stars located on the upper left hand part of the color-color diagram are physically impossible to reach according to Lada & Adams (1992) so we can disregard any points that lie in any of those regions as bad data. There are also several stars located outside and to the right of the reddening region. The stars in this region are stars that exhibit infrared excess emission revealing, possibly, T Tauri stars or proto-stellar accretion disks (Lada & Adams 1992). About 15% of the stars in our cluster, through examination of this plot, are T Tauri stars or proto-stellar disks.

Examining the control field data, we see that about half of the data points lie inside the reddening band, while the other half lie outside and to the right of the reddening bands. This is most likely an indication that our control field contains some faulty data as we should not be seeing proto-stars forming outside young clusters. However, in comparing the control field color-color diagram with that of the cluster field, we see that the stars in the control field lie closer to the main sequence within the reddening bands than the stars within the cluster. This shows that the stars inside our control field are less reddened than those of the cluster. This serves as a good check on our cluster since our cluster should be more reddened than stars at any other random point in the sky due to its contained molecular cloud.