Stellar Evolution and Spectral Classification

The stellar spectral sequence was originally based on which of the following? the strength of hydrogen lines in the spectra of stars Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________. less luminous, cooler, smaller, and less massive Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________. cooler and larger in radius Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________. hotter and smaller in radius The main-sequence lifetime of a spectral type O star is _______ the main-sequence lifetime of a spectral type A star. shorter than What is a white dwarf? the remains of a star that ran out of fuel for nuclear fusion What is the approximate chemical composition (by mass) with which all stars are born? Three quarters hydrogen, one quarter helium, no more than 2% heavier elements Which of the following statements about apparent and absolute magnitudes is true? All of the above are true. Which of the following statements about globular clusters is true? Most stars in the cluster are yellow or reddish in color. Which of the following comparisons between low-mass stars and high-mass main-sequence stars is true? Low-mass stars are cooler and less luminous than high-mass stars. What is the approximate luminosity of a main-sequence M star? 0.01 solar On an H-R diagram, stellar masses ________. can be determined for main sequence stars but not for other types of stars You observe a star cluster with a main-sequence turn-off point at spectral type G2 (the same spectral type as the Sun). What is the age of this star cluster? 10 billion years Suppose we wanted to represent all of these objects on the 1-to-10-billion scale from Chapter 1, on which the Sun is about the size of a grapefruit. Approximately how large in diameter would the star Aldebaran be on this scale? 6 meters (roughly the size of a dorm room) Approximately how large in diameter would the star Betelgeuse be on this same scale? 3 kilometers (the size of a small town) What is the approximate luminosity of a star whose mass is 10 times that of the Sun? 10,000LSun What is the approximate lifetime of a star whose mass is 10 times that of the Sun? slightly longer than 107 years What is the approximate luminosity of a star whose mass is 3 times that of the Sun? 100LSun What is the approximate lifetime of a star whose mass is 3 times that of the Sun? slightly shorter than 109 years What is the approximate luminosity of a star whose mass is twice that of the Sun? 10LSun What is the approximate lifetime of a star whose mass is twice that of the Sun? 109109 years Approximately how large in diameter would the star Procyon B be on this same scale? 1 millimeter (the size of a grape seed) This star map shows stars as we see them in our sky from Earth, centered around the constellation Canis Major. Larger dots represent brighter stars, and a few of the brightest stars are identified. From this view alone, what can you conclude about Sirius? It has the greatest apparent brightness of any star in this region of the sky. Why do some of the bright stars (such as the one indicated by the arrow) in this photo have crossshaped spikes over them? The spikes are an artifact of photography through a telescope. All the stars in this photo are at about the same distance from Earth (some 26,000 light-years away). Which stars in this picture are the largest in size (radius)? the bright red stars This graph shows how the apparent brightness of an eclipsing binary system changes with time. Which of the four labeled regions represents the system at a time when one star is eclipsing the other? both II and IV Study this H-R diagram. What is the spectral type of the star Sirius? A Study this H-R diagram. Which of the following stars is the most massive? Beta Centauri Study this H-R diagram. Which of the following stars is the largest in size (radius)? Antares Study this H-R diagram. Which of the following stars has (or had) the longest hydrogen burning lifetime? Barnard's star This photo shows an object located in the halo of our Milky Way galaxy. What kind of object is it? a globular cluster of star This photo shows an object located in the halo of our Milky Way galaxy. Notice the many bright red dots in the photograph. What are they? red giant stars On a Hertzsprung-Russell diagram, where would you find stars that are cool and have low luminosities? lower right The age of stars in a cluster can be determined by determining the main sequence turnoff point. What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us? It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age. The choices below each describe the appearance of an H-R diagram for a different star cluster. Which cluster is most likely to be located in the halo of our galaxy? The diagram shows main-sequence stars of spectral types G, K, and M, along with numerous giants and white dwarfs. How is the lifetime of a star related to its mass? More massive stars live much shorter lives than less massive star Star A and B have the same luminosity, but star B is 10 times farther from Earth than star A. How much brighter will star A appear? 100 times Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram? surface temperature on the horizontal axis and luminosity on the vertical axis Which of the following stars are brightest at ultraviolet wavelengths? O and B stars A main-sequence star's luminosity can directly inform us of the rate at which it converts hydrogen to helium. From hottest to coolest, the order of the spectral types of stars is _________. OBAFGKM A star's luminosity depends primarily on its radius and surface temperature. What is a star's luminosity class related to? its size (radius) What is the spectral type of the star with the strongest hydrogen absorption lines? A Determine the difference between open clusters and globular clusters in terms of their numbers of stars, ages, and locations in a galaxy. Open clusters are several thousand stars , are found in the galactic disk , and contain young . Globular clusters are more than a million stars , are found in the galactic halo , and contain old . Red Giant or Supergiant Starts: Very cool but very luminous Found in the uppper right of the H-R diagram Main-sequence stars: The majority of stars in our galaxy The Sun, for example A very hot and very luminous star White dwarfs: not much larger in radius than Earth Very hot but very dim Which of the following is the most numerous types of main-sequence star? an M star What does the apparent magnitude of a star tell us about that star? how bright it appears from Earth Which of the following facts about stars in a cluster make it possible to determine the approximate age of the cluster? all of the above Star X has an apparent magnitude of 3, and star Y has an apparent magnitude of 13. How do they compare in observed brightness? Star X is 10,000 times brighter than star Y. A star of spectral type B with a mass of 10 times the mass of the Sun will last approximately how long on the main sequence? 10 million years According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples? Its apparent brightness will decrease by a factor of 9. You observe a star and you want to plot it on an H-R diagram. You will need to measure all of the following, except the star's ________. mass Which of the following statements about spectral types of stars is true? All of the above are true. Which of the following statements about open clusters is true? All stars in the cluster are approximately the same age. On a Hertzsprung-Russell diagram, where on the main sequence would you find stars that have the greatest mass? upper left