LAB 9 HR DIAGRAM.pdf

Name: Faith Berry HR Diagram – Student Guide Background Information Work through the background sections on Spectral Classification, Luminosity, and the Hertzsprung-Russell Diagram. Then complete the following questions related to the background information. Question 1: The table below summarizes the relationship between spectral type, temperature, and color for stars. Note that the surface temperature of the stars in the table increases. Star Surface Temperature K Spectral Type Color Betelguese 3500 M2 Orange-red Arcturus 4,300 K2 Orange 5770 G2 Yellow Procyon A 6530 F5 Yellow-White Sirius A 9940 A1 White Rigel A 11,000 B8 Blue-white Delta Orionis 18,400 O9 Blue-white

Question 2: Complete the following table related to stellar luminosities in solar units using the equation 2 4 L RT ∝ . Radius (R ⊙ ) Temperature (T ⊙ ) Luminosity (L ⊙ ) 1 1 1 1 2 16.8 3 1 9 1 1/2 1/16 NAAP – HR Diagram Explorer 1/9 Question 3: The mass luminosity relation 3.5 L M ∝ describes the mathematical relationship between luminosity and mass for main sequence stars. It describes how a star with a mass of

2 M ⊙ would have a luminosity of _____16________ L ⊙ while a star with luminosity of 3,160 L ⊙ would have an approximate mass of ______10__________ M ⊙ . HR Diagram Explorer Open the HR Diagram Explorer . Begin by familiarizing yourself with the capabilities of the Hertzsprung-Russell Diagram Explorer through experimentation. ∙ An actual HR Diagram is provided in the upper right panel with an active location indicated by a red x. This active location can be dragged around the diagram. The options panel allows you to control the variables plotted on the x-axis: (temperature, B V, or spectral type) and those plotted on the y-axis (luminosity or absolute magnitude). One can also show the main sequence, luminosity classes, isoradius lines, or the instability strip. The Plotted Stars panel allows you to add various groups of stars to the diagram. ∙ The Cursor Properties panel has sliders for the temperature and luminosity of the active location on the HR Diagram. These can control the values of the active location or move in response to the active location begin dragged. The temperature and luminosity (in solar units) are used to solve for the radius of a star at the active location. ∙ The Size Comparison panel in the upper left illustrates the star corresponding to the active location on the HR Diagram. Note that the size of the sun remains constant. NAAP – HR Diagram Explorer 2/9 Exercises ∙ Drag the active location around on the HR Diagram. Note the resulting changes in the temperature and luminosity sliders. Now manipulate the temperature and luminosity sliders and note the corresponding change in the active location.

Question 4: Check the appropriate region of the HR diagram corresponding to each description below. HOT STARS ARE FOUND AT THE: Left FAINT STARS ARE FOUND AT THE: Bottom LUMINOUS STARS ARE FOUND AT THE : Top COOL STARS ARE FOUND AT THE: Right ∙ Drag the active location around on the HR Diagram once again. This time focus on the Size Comparison panel. Question 5: Check the appropriate region of the HR diagram corresponding to each description below. Description Upper Left Upper Right Lower Right Lower Left Large Blue stars are found at the: Yes Small Red stars are found at the: Yes Small Blue stars would be found at the: Yes Really Large Red stars are found at the: Yes ∙ Check show isoradius lines. Note that at each point on a green line, stars have the same value of radius. Use these isoradius lines to check your answers in the table above. NAAP – HR Diagram Explorer 3/9 Question 6: The equation below describes the luminosity of a star in terms of its radius and temperature. Use this equation to explain the results you found in the table of the previous question. Radius, temperature, and luminosity determine the placement on the HR and is used to

determine where stars fall on the HR diagram. Luminosity is dependent on the size and temperature of the star itself. 2 4 L = 4 π R T σ ∙ In addition to the isoradius lines, check show luminosity classes . This green region (dwarfs V) is known as the main sequence and contains all stars that are fusing hydrogen into helium as their primary energy source. Over 90% of all stars fall in this region on the HR diagram. Move the active cursor up and down the main sequence and explore the different values of stellar radius. Question 7: Describe the sizes of stars along the main sequence. What are stars like near the top of the main sequence, the middle, and the bottom? The top is the big blue hot stars. The middle is yellow-whiteish cooler stars. The bottom is organeish-red cooler stars. They get smaller as you go down. ∙ The background pages of this module talked about the mass-luminosity relationship for stars on the main sequence: 3.5 L M ∝ Question 8: What can you conclude about the masses of stars along the main sequence? As mass decreases, luminosity decreases.

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