Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 22, Problem 9Q
To determine
To explain:
The reason,O or B main-sequence stars are found in the galactic disk but not in globular clusters.
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If the RR Lyrae stars in a globular cluster have average apparent magnitudes of +19, how far away (in pc) is the cluster? (Hints: See the following figure, and use the magnitude-distance formula: d = 10(mv - My+5)/5.)
Туре
(Classical)
Cepheids
104
103
Туре II
Cepheids
102
RR Lyrae stars
0.3
1
10
30
100
Pulsation perlod (days)
pc
Absolute magnitude
Luminosity, L L.
Question 41
.Suppose you are looking at H-R diagrams of two similar star clusters. The most luminous main
sequence stars in the Porcini cluster are much more luminous than the most luminous main
sequence stars in the Morel cluster. What can you conclude?
O the Porcini cluster is younger than the Morel cluster
O the Porcini cluster is farther away than the Morel cluster
O the Porcini cluster is lower in metallicity than the Morel cluster
O the Porcini cluster is larger in diameter than the Morel cluster
If we plot the apparent brightnesses of stars in a globular cluster versus their surface temperatures in a similar way as in the HR diagram , there will be a horizontal branch . Which of the following statements about these horizontal branch stars is wrong ? (A)They have the same absolute magnitude . (B)They have different sizes . (C)Their sole source of energy is hydrogen shell burning . (D)They can help us estimate the distance of the globular cluster from us .
Chapter 22 Solutions
Universe: Stars And Galaxies
Ch. 22 - Prob. 1QCh. 22 - Prob. 2QCh. 22 - Prob. 3QCh. 22 - Prob. 4QCh. 22 - Prob. 5QCh. 22 - Prob. 6QCh. 22 - Prob. 7QCh. 22 - Prob. 8QCh. 22 - Prob. 9QCh. 22 - Prob. 10Q
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- Consider the following five kinds of objects: open cluster, giant molecular cloud, globular cluster, group of O and B stars, and planetary nebulae. A. Which occur only in spiral arms? B. Which occur only in the parts of the Galaxy other than the spiral arms? C. Which are thought to be very young? D. Which are thought to be very old? E. Which have the hottest stars?arrow_forwardIf the Sun were a member of the cluster NGC 2264, would it be on the main sequence yet? Why or why not?arrow_forwardYou can use the equation in Exercise 22.34 to estimate the approximate ages of the clusters in Figure 22.10, Figure 22.12, and Figure 22.13. Use the information in the figures to determine the luminosity of the most massive star still on the main sequence. Now use the data in Table 18.3 to estimate the mass of this star. Then calculate the age of the cluster. This method is similar to the procedure used by astronomers to obtain the ages of clusters, except that they use actual data and model calculations rather than simply making estimates from a drawing. How do your ages compare with the ages in the text? Figure 22.10 NGC 2264 HR Diagram. Compare this HR diagram to that in Figure 22.8; although the points scatter a bit more here, the theoretical and observational diagrams are remarkably, and satisfyingly, similar. Figure 22.12 Cluster M41. (a) Cluster M41 is older than NGC 2264 (see Figure 22.10) and contains several red giants. Some of its more massive stars are no longer close to the zero-age main sequence (red line). (b) This ground-based photograph shows the open cluster M41. Note that it contains several orange-color stars. These are stars that have exhausted hydrogen in their centers, and have swelled up to become red giants. (credit b: modification of work by NOAO/AURA/NSF) Figure 22.13 HR Diagram for an Older Cluster. We see the HR diagram for a hypothetical older cluster at an age of 4.24 billion years. Note that most of the stars on the upper part of the main sequence have turned off toward the red-giant region. And the most massive stars in the cluster have already died and are no longer on the diagram. Characteristics of Main-Sequence Starsarrow_forward
- In which of these star groups would you mostly likely find the least heavy-element abundance for the stars within them: open clusters, globular clusters, or associations?arrow_forwardCalculate the mass-to-light ratio for a globular cluster with a luminosity of 106LSunand 105 stars. (Assume that the average mass of a star in such a cluster is 1 MSun.)arrow_forwardWould the Sun more likely have been a member of a globular cluster or open cluster in the past?arrow_forward
- In the HR diagrams for some young clusters, stars of both very low and very high luminosity are off to the right of the main sequence, whereas those of intermediate luminosity are on the main sequence. Can you offer an explanation for that? Sketch an HR diagram for such a cluster.arrow_forwardWhy is star formation more likely to occur in cold molecular clouds than in regions where the temperature of the interstellar medium is several hundred thousand degrees?arrow_forwardYou have discovered two star clusters. The first cluster contains mainly main-sequence stars, along with some red giant stars and a few white dwarfs. The second cluster also contains mainly main-sequence stars, along with some red giant stars, and a few neutron stars-but no white dwarf stars. What are the relative ages of the clusters? How did you determine your answer?arrow_forward
- QUESTION 16 Use the figure shown below to complete the following statement: A low-mass protostar (0.5 to 8M the mass compared to our sun) remains roughly constant in decreases in until it makes a turn towards the main sequence, as it follows its evolutionary track. Protostars of different masses follow diferent paths on their way to the main sequence. 107 Luminosity (L) 10 105 10 107 10² 101 1 10-1 10-2 10-3 Spectral type 0.01 R 0.001 Re 60 M MAIN SEQUENCE 40,000 30,000 20 Mau 10 Mgun 5 Mun 0.1 Run Ren radius; temperature luminosity; radius 3 Min. 05 BO temperature; luminosity Oluminosity: temperature radius: luminosity 1 M 10,000 6000 Surlace temperature (K) 1,000 Rs 2 M STAR L 0.8 M B5 AO FOGO КБ МБ -10 +10 3000 Absolute visual magnitude andarrow_forwarda) Calculate the period of the solar system's orbit around the Milky Way. Assume that we are 8.5 kpc from the galactic center and assume that the mass of the Milky Way interior to our orbit is ~ 10¹¹ solar masses. Alpha Centauri is a multiple star system only 1.34 parsecs away. The apparent magnitudes of the two main stars are: a Cen A: my = +0.01; a Cen B: my = +1.33. b) Calculate the ratio of the flux we receive in the V filter from a Cen A to the flux we receive from a Cen B. c) Calculate the absolute magnitude My of a Cen B.arrow_forwardFor the PP chain 0.7% of the mass participating in nuclear fusion is liberated as energy which produces a star's luminosity. Assume that the core of a main sequence star consists of 10% of its total mass. Hence, estimate the lifetime of a star on the main sequence in terms of its luminosity L/L. Give your answer in years. You may use the observed mass-luminosity relation L x M³.5, where M is the star's total mass. Using typical values, calculate estimates for the main sequence lifetime of a KO star and a 05 star. Describe briefly why your estimate might be more accurate for K stars compared to O stars.arrow_forward
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