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Lab 08

Astronomy 105 Laboratory. Lab 08. Lab Quiz 08. The H-R diagram is a graph of. apparent magnitude vs. spectral type. apparent magnitude vs. color. absolute magnitude vs. spectral type. color vs. temperature. luminosity vs. absolute magnitude. The apparent magnitude of a star depends on the.

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Lab 08

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  1. Astronomy 105 Laboratory Lab 08

  2. Lab Quiz 08

  3. The H-R diagram is a graph of • apparent magnitude vs. spectral type. • apparent magnitude vs. color. • absolute magnitude vs. spectral type. • color vs. temperature. • luminosity vs. absolute magnitude.

  4. The apparent magnitude of a star depends on the • temperature of the star. • size of the star. • distance to the star. • all of the above • both 1 and 2

  5. The absolute magnitude of a star depends on the • temperature of the star. • size of the star. • distance to the star. • all of the above • both 1 and 2

  6. In today’s lab you will work with stellar data from which star cluster? • Prasepe. • Pleiades. • M76. • M11. • NGC6705.

  7. How is distance modulus defined? • mv – Mv • ka3 • 1/d2 • M1M2 / d2

  8. Lab 08 The Distance to the Pleiades

  9. Open or Galactic Cluster • Finding a Star’s Distance • Stellar Parallax • Main-Sequence Fitting M13 - Globular Cluster Distance-23,000 ly Size-150 ly

  10. 2.512 Faintest stars visible to naked-eye Brightest stars in the night sky Measuring a Star’s Brightness Magnitude Scale 1 2 3 4 5 6 Brighter Dimmer

  11. Magnitude • Stellar Brightness • Apparent Magnitude (mv) - Brightness from Earth • Absolute Magnitude (Mv) - Brightness from 10 pc

  12. 100 W 100 W 100 W √100 = 10 Apparent Brightness and the Inverse-Square Law of Light 40 meters 1/16 Apparent Brightness  1/d2 30 meters 1/9 20 meters 10 meters 1/4 100 W If this 100 Watt light bulb were observed to be 100 times fainter compared to the 10 meter distance; how far away is it? Photometer (measures brightness) 10 times farther away or 10 x (10 meters) = 100 m

  13. Apparent Brightness and the Inverse-Square Law of Light 1370 1370 ____ ____ 55 343   4 25 Apparent Brightness  1/d2 1370 watts/m2 55 watts/m2 343 watts/m2 1 AU = 25 = 4 = 5 = 2 5 AU 2 AU

  14. ? 10 pc √100 Mv = 5 G2 V Distance Modulus = m - M mv = 10 Is the star closer than 10 pc or farther away than 10 pc? If m-M > 0 then star’s distance > 10 pc. If m-M = 0 then star’s distance = 10 pc. If m-M < 0 then star’s distance < 10 pc. How much farther? Distance Modulus. = 10 – 5 = +5 Brightness Difference = 2.5125 = 100 Inverse-Square Law - Apparent Brightness ~ 1/d2 = 10 or 10 X 10 pc = 100 pc Star is 10x farther away than 10 pc

  15. Finding a Star’s Distance • Brightness at standard distance (10 pc) • Absolute magnitude • Measure apparent brightness • Apparent magnitude • Use inverse-square law of light to find distance

  16. Main-Sequence Fitting Pleiades Star Cluster • Stars in a Cluster • Common Properties • Distance • Age • Different Properties • Spectral Types (temperature) • Luminosity Class (size) Taurus Hyades Star Cluster

  17. = 2.73 √7.5 Main-Sequence Fitting Pleiades stars have the same luminosities as the Hyades stars. Why are the Pleiades stars 7.5 times dimmer? They are farther away! How much farther? The Pleiades is 2.73 times farther away!

  18. Interstellar Dust • Reddens Light (stars appear cooler) • Dims Light (stars appear further away)

  19. temperature Color Index = 0.415 mv = 9.8

  20. Using the average distance modulus from several stars, calculate the distance to the Pleiades star cluster. • Use the main-sequence fitting technique to find the distance modulus and calculate the distance to the Pleiades again. mv – Mv = 9.8 - 3.6 = +6.2 Color Index = 0.415 mv = 9.8 Mv = 3.6

  21. The End

  22. Stars in a Cluster • Common Properties • Distance • Age • Different Properties • Spectral Types (temperature) • Luminosity Class (size) Pleiades - Open Cluster

  23. HR Diagram Absolute Magnitude Main-sequence O B A F G K M -0.4 color index 1.3 d >10 pc { DM d <10 pc Apparent Magnitude -0.4 color index 1.3 Star Cluster 10 pc Color-Magnitude Diagram d <10 pc 10 pc Distance Modulus = m - M The difference between the absolute magnitude and the apparent magnitude can be used to find the distance to a star cluster. d >10 pc

  24. Main-Sequence Fitting Pleiades Star Cluster • Find distance to Hyades stars (measure parallax) • Measure apparent brightness of Hyades main-sequence stars • Calculate luminosity of Hyades main-sequence stars (standard candles) Taurus Luminosity = (apparent brightness) x (4 x distance2) • Main-Sequence fitting Hyades Star Cluster

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