Lab_6-_HR_Diagram_2023.pdf

Names: Astrophysics Lab 6- HR Diagrams 1 / 12 Astrophysics Lab 6 HR Diagrams A- Background material You will again be using the NAAP by either opening the NAAP app on your computer or by going to https://astro.unl.edu/naap/ . Open the Hertzsprung-Russell Diagram Lab and work through the Spectral Classification , Luminosity , and Hertzsprung-Russell Diagram background sections. Then complete the following questions. Question 1: The table below summarizes the relationship between spectral type, temperature, and color for stars. Fill in the blank entries. Star Surface Temperature K Spectral Type Color Betelgeuse M2 Arcturus 4300 G2 Yellow Procyon A F5 Yellow-White Sirius A A1 White Rigel A 11000 Delta Orionis O9

Astrophysics Lab 6- HR Diagrams 2 / 12 Question 2: Complete the following table related to stellar luminosities in solar units using the equation L ~ R 2 T 4 . Question 3: The mass luminosity relation L ~ M 3.5 d escribes 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 _____________ L ⊙ while a star with luminosity of 3160 L ⊙ would have an approximate mass of ________________ M ⊙ . B- 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. • 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. Radius (R ⊙ ) Temperature (T ⊙ ) Luminosity (L ⊙ ) 1 1 1 2 1 9 1 1/2

Astrophysics Lab 6- HR Diagrams 3 / 12 Question 4: Check the appropriate region of the HR diagram corresponding to each description below. • 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. • 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. Description Top Right Bottom Left Hot stars are found at the: Faint stars are found at the: Luminous stars are found at the: Cool stars are found at the: Description Upper Left Upper Right Lower Right Lower Left Large Blue stars are found at the: Small Red stars are found at the: Small Blue stars would be found at the: Really Large Red stars are found at the:

Astrophysics Lab 6- HR Diagrams 4 / 12 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. L= 4 πR 2 σT 4 • In addition to the isoradius lines, check show luminosity classes . The green region 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?

Astrophysics Lab 6- HR Diagrams 5 / 12 • The background pages of this module talked about the mass-luminosity relationship for stars on the main sequence: L ~ M 3.5 Question 8: What can you conclude about the masses of stars along the main sequence? Question 9: Use the results from the previous 5 questions to construct a “conceptual” HR Diagram. You simply want to draw arrows showing the direction in which variables are increasing. a) Draw in an arrow on the y axis showing the direction of increasing “intrinsic luminosity” of the stars. (This is already completed for you.) b) Draw in an arrow on the x-axis showing the direction of increasing surface temperature of the stars. c) Draw in an arrow showing the direction of increasing radius on the diagram. (hint: think of the relationship between this line and the isoradius lines.) d) Draw in an arrow showing the direction of increasing mass for main sequence stars on the diagram. (Note that this arrow only applies to main sequence stars, but these represent over 90% of all stars.)

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