Lab6_HR_Diagram

Name: Lab 6: HR Diagram – Worksheet 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. Enter your answers to each question in the data tables and yellow highlighted areas below. When completed, please save and upload this file to the assignment submission link in Canvas. Question 1: The table below summarizes the relationship between spectral type, temperature, and color for stars. Fill in the missing blanks in the table. 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 K1 red sun 5800 G2 Yellow Procyon A 6530 F5 Yellow-White Sirius A 9940 A1 White Rigel A 11,000 B8 blue white Delta Orionis 29500 O9 blue - ov Question 2: Complete the following table related to stellar luminosities in solar units using the equation L ∝ R 2 T 4 . Radius (R ⊙ ) Temperature (T ⊙ ) Luminosity (L ⊙ ) 1 1 1 1 2 16 1 1 9

1 1/2 .0625

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: Place an "X" in the appropriate box for each region of the HR diagram corresponding to the description below. ● Drag the active location around on the HR Diagram once again. This time focus on the Size Comparison panel. Question 5: Place an "X" in the appropriate box for each region of the HR diagram corresponding to the description below. Description Upper Left Upper Right Lower Right Lower Left Large Blue stars are found at the: x Small Red stars are found at the: x Small Blue stars would be found at the: x Really Large Red stars are found at the: x ● 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.

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 π R 2 σ T 4 So, this equation is basically saying that a star's brightness, or luminosity, is directly related to how big it is (its radius) and how hot it is (its temperature). The Stefan-Boltzmann constant is just a number that scientists figured out to make the equation work. ● 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? top- large and hot stars, lifetime of few million middle- stars like our sun, lifetime of 10 billion years bottom-small and cool stars, lifetime of trillions ● 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? The masses of the stars generally increases as we move from left to right, most massive stars being located at the upper left and the least massive at the lower right

● Uncheck show luminosity classes and check show instability strip . Note that this region of the HR Diagram indicates where pulsating stars are found such as RR Lyrae stars and Cepheid variable stars. These stars vary in brightness because they are pulsating – alternately growing bigger and smaller – which changes their radii and surface temperatures and resulting their luminosities. m Question 10: Describe the characteristics of stars that are found in the instability strip. You should cover their range of temperatures, colors, luminosities, and sizes. (Hint: Comparing them to the sun is useful.) Are variable stars necessarily on the main sequence? temperatures are greater than the suns, size as big as sun, colors are yellow white ish, temperatures range from 3000k to 50000k and the luminosity ranges from 1L to 9L. they are necessarily on the main sequence. ● Check the plotted stars option the nearest stars . You should cover their range of temperatures, colors, luminosities, and sizes. Question 11: Describe the characteristics of the nearest stars. most nearby stars are small and faint where as most of the brightest stars are large and bright. Question 12: Do you think these stars are rare or very common among all of the stars of our galaxy? Explain your reasoning. Are any assumptions involved in your reasoning? the nearest star term is a bit rare when it comes to all the stars in the galaxy. ● Uncheck the plotted stars option the nearest stars and check the brightest stars . Why are these stars the brightest in the sky? Three students debate this issue:

Student A: “I think it’s because these stars must be very close to us. That would make them appear brighter to us in the sky.” Student B: “I think it’s because these stars are very luminous. They are putting out a tremendous amount of energy.” Student C: “I think it’s because these stars are very close and very luminous.” Question 13: Use the tools of the HR Diagram to support the views of one of the three students. Why are the stars we perceive as bright in the night sky really bright?” (hint: You may find the options labeled both the nearest and brightest stars and the overlap useful.) the star has more luminosity and less distance from us so it seems brighter in the sky. Question 14: Do you think that these bright stars are very common (make up a large percentage of all stars in general)? Explain your reasoning. It is not very common because there is such a large number of stars with high luminosity but they are very far from us its a little less than half percent.

G 160000 100 2 H 625 100 0.5