Astronomers study the temperatures of other stars using a graph called a color-color diagram. To make a color-color diagram, find two colors of a single star; for example, g-r and u-g. Then, make a graph with u-g on the x-axis and g-r on the y-axis. The star you found will plot into a point on the diagram. Find colors of several other stars and plot them on the same graph. The image at the right shows what a hypothetical color-color diagram might look like.
Explore 5. Use SkyServer’s Object Explorer to find the stars with the following object IDs in the SDSS database. Click on one of the Object IDs to open the Object Explorer. Write down each object’s ID and its magnitudes through SDSS’s five filters – they are the quantities u, g, r, i, and z in the second row on the right of the object’s image.
Record your data in this workbook.
| Object ID | ra | dec |
|---|---|---|
| 1237655130384631215 | 261.53089 | 27.8252 |
| 1237659326573642860 | 259.45503 | 26.13354 |
| 1237663783128006843 | 10.01782 | -0.75441 |
| 1237663784211054802 | 31.16766 | 0.16188 |
| 1237648720144367845 | 151.18504 | -0.92994 |
| 1237648702968430736 | 187.87919 | -1.08739 |
| 1237648704042893633 | 189.45609 | -0.29485 |
| 1237659896710562048 | 262.90111 | 57.66249 |
| 1237663783142359239 | 42.6732 | -0.75043 |
| 1237648720689496156 | 169.97091 | -0.53913 |
| 1237655503501722501 | 261.36639 | 27.56075 |
| 1237648720715186525 | 228.71353 | -0.4823 |
| 1237648704582058231 | 194.75972 | 0.1813 |
| 1237648704049184997 | 203.88511 | -0.32011 |
| 1237657191447527658 | 12.51927 | 0.39023 |
| 1237648721785717058 | 221.42084 | 0.32477 |
Open a spreadsheet program such as Excel. Enter all the data you just collected. Find the g-r, r-i, u-g, and i-z colors of each of the 16 stars in the above list. Make a graph for the 16 stars with g-r on the x-axis and r-i on the y-axis.
If you need help with using Excel, see SkyServer’s Graphing and Analyzing Data tutorial.
Question 3. Where on your diagram are the hotter stars? Where are the cooler stars? How do you know?