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Color-Color Diagrams

Click on the image for a larger view

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.

Object ID

ra

dec

587729409159726385

261.53089

27.8252

587729652355957714

259.45503

26.13354

588015508200030302

10.01782

-0.75441

588015509283012681

31.16766

0.16188

588848898826305740

151.18504

-0.92994

587722981743526024

187.87919

-1.08739

587722982817988795

189.45609

-0.29485

587725576963162456

262.90111

57.66249

588015508214317186

42.6732

-0.75043

588848899371434096

169.97091

-0.53913

587729782276817397

261.36639

27.56075

588848899397124437

228.71353

-0.4823

587722983357153451

194.75972

0.1813

582093484364529699

205.48587

0.47954

587722982824280273

203.88511

-0.32011

587731186746261653

12.51927

0.39023

588848900467654983

221.42084

0.32477

Launch the Object Explorer

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 17 stars in the above list. Make a graph for the 17 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?