Mass-Luminosity and Stellar Lifetimes WS

Transcription

1 Name Mass-Luminosity and Stellar Lifetimes WS The graph shows the Mass-Luminosity Relationship for main sequence stars. Use it to answer questions ) A star with a mass of 0.5 solar masses would be how luminous? 2) A star with 10 solar masses would be how luminous? 3) What mass would a star have to have to be 10 times more luminous than the sun. Show your calculations for the following questions. 4) How luminous would a star be that has a mass of 15 solar masses? 5) How long would the star in question 4 live? 6) How luminous would a star be that has a mass of 0.25 solar masses? 7) How long would the star in question 6 live? 8) Explain why stars that are more massive than the sun have lifetimes that are shorter than the sun s lifetime, although they have more fuel to consume than the sun does. (2 pts)

2 Key to Mass-Luminosity and Stellar Lifetimes WS 1) about 0.09 L sun (determined graphically) 2) about 9 x 10 3 or 1 x 10 4 (9000 to 10,000) L sun (determined graphically) 3) about 1.9 to 2.0 M sun (determined graphically) 4) (15M sun / 1M sun ) 4 = 50,625 L sun 5) (1 / 15 3 ) x (1 x years) = about 2.96 million years (3 million years) 6) (0.25M sun / 1M sun ) 2.3 = L sun Pretty faint! 7) (1 / ) x (1 x years) = about 60 billion years 8) A star that is more massive than our sun does have more H fuel to fuse to He, but it would use it up at a rate that is proportional to its mass to the 4 th power faster than our sun. A star of 3 solar masses has 3 times more H fuel available, but uses it up at a rate of 3 4 or 81 times faster than our sun consumes H, and therefore lives a shorter time.

3 Name Stellar Properties WS (A general review of the information in starlight) 1) At 4 light years distance, the brightness of a star is ¼ as much as it is at light years distance. 2) The larger (more positive) the magnitude of a star, the ( brighter / dimmer ) it is. 3) Star distances can be accurately measured by parallax out to a distance of only light years. 4) A star with m = 8.4 and M = -3.9 is how far away in parsecs? Show your calculation. 5) Differences in spectra from one star to another are caused by differences in the stars : luminosity magnitude temperature distance 6) Betelgeuse is a star: red dwarf blue supergiant red main sequence red supergiant 7) Rigel is a star: white dwarf blue supergiant blue main sequence red supergiant 8) Our sun is what spectral class? 9) Is a G star ( hotter / cooler ) than an F star? 10) The hottest stars have almost no dark absorption lines from H in their spectra because most of their hydrogen: a) is ionized b) has been used up c) is metallic 11) A star like our sun shows strong absorption lines from this metallic element: ( Fe / Ca / U ) 12) On the HR diagram, the hottest stars are in the half of the diagram. ( top / bottom / left / right ) 13) On the HR diagram, a star near the top right would be: ( small & hot / small & cool / large & hot / large & cool ) 14) A star in the previous would be called a star. 15) Most of the stars closest to our sun are stars. 16) Stars that are more massive than our sun will have ( a longer / a shorter / the same ) life expectancy. 17) If a star has a small parallax, it means that the star is: very distant very close not very bright very small in size 18) What is the name for the apparent motion of a star against the distant background that is actually due to the motion of the star through space? 19) Orange stars have this spectral class ( B / M / K / F ) 20) A star with a mass 3.5 times our sun s mass would have a life expectancy of how many years. Show your calculation. 21) The vertical axis of the HR diagram has units of ( temperature or color / luminosity or brightness / distance ). 22) On the HR diagram, stars with small masses would be found in the half of the diagram. ( top / bottom / left / right ) 23) A star with a mass 3 times the sun s mass would be how many times brighter than the sun: ( 3 / 9 / 27 / 81 ) 24) A small red dwarf star with a mass of 0.15 solar masses would (show your calculations) a) have what luminosity compared to the sun? b) have what lifetime compared to the sun?

4 25) Sirius is about 20 times brighter than the sun. a) Sirius ( is more massive / is less massive / has the same mass ) as/than our sun. b) Sirius is ( hotter / cooler / about the same temperature ) as/than our sun. c) Sirius will live for a ( shorter time / longer time / similar time ) as/than our sun. d) Sirius is burning its fuel ( more slowly / about the same rate / faster ) as/than our sun. 26) Astronomers believe that only stars with spectral classes similar to our sun s could have planets on which life may have evolved. Give an explanation of why hotter stars are not expected to have life on their planets, even if they could have planets at the proper distances (so that the total amount of sunlight was right for life.)

5 Key to Stellar Properties WS (A general review of Ch. 14) 1) 2 LY 2) dimmer 3) 300 light years. 4) 10^[(8.4-(-3.9)+5)/5] = 10^[(17.3)/5] = 10^3.46 = 2884 pc. 5) temperature 6) red supergiant 7) blue supergiant blue main sequence (both these are correct!) 8) G2 9) cooler 10) a) is ionized 11) Ca 12) left 13) large & cool 14) red supergiant 15) main sequence or red dwarf 16) a shorter 17) very distant 18) Proper motion 19) K 20) (1 / ) x 10,000,000,000 = 233,000,000 years 21) luminosity or brightness 22) bottom 23) 81 24) a) = times the sun s brightness. b) (1 / ) x 10 billion = 118,000,000,000 years 25) a) more massive b) hotter c) shorter time d) faster 26) Hotter stars just don t live long enough for complex life to evolve.