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 19, Problem 30Q
To determine
The reason forastronomers to attribute the observed Doppler shifts of a Cepheid variable to pulsation rather than to some other cause, such as orbital motion.
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Why are Cepheid variables important?
O Cepheids variables are pulsating stars whose pulsation periods are directly related to their true luminosities.
Therefore they can be used as distance indicators.
O Cepheids variables are supermassive stars that are on the verge of becoming supernovae. Therefore they
allow us to choose candidates to watch if we hope to observe a supernova.
O Cepheid variables are stars that vary in brightness because they harbor a black hole. Therefore, they provide
direct evidence for black holes.
O Cepheids variables are a type of irregular galaxy, much more common in the early universe. Therefore they
help to understand how galaxies formed.
For a main sequence star with luminosity L, how many kilograms of hydrogen is being converted into helium per second? Use the formula that you derive to estimate the mass of hydrogen atoms that are converted into helium in the interior of the sun (LSun = 3.9 x 1026 W).
(Note: the mass of a hydrogen atom is 1 mproton and the mass of a helium atom is 3.97 mproton. You need four hydrogen nuclei to form one helium nucleus.)
What is the free-fall time of a 10 MSun main-sequence star?
O 100 hours
O 10 hours
O 1 hour
O 0.1 hours
Chapter 19 Solutions
Universe: Stars And Galaxies
Ch. 19 - Prob. 1QCh. 19 - Prob. 2QCh. 19 - Prob. 3QCh. 19 - Prob. 4QCh. 19 - Prob. 5QCh. 19 - Prob. 6QCh. 19 - Prob. 7QCh. 19 - Prob. 8QCh. 19 - Prob. 9QCh. 19 - Prob. 10Q
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- The star HD 93250 in the Carina Nebula is a bright O-type star. It has a reported apparent magnitude in the V band of mV = 7.41 and V band absolute magnitude of MV = −6.14. Using these values calculate the distance to HD 93250 in parsec. The distance to HD 93250 has been measured by other means as 2350 pc. Compare your calculated value of the distance with the measured value, and give a possible explanation for any difference. Calculate the value of the interstellar extinction in the V band AV that would account for the difference in the distances. The parameter E(B − V ) = AB − AV , where AB and AV are the extinctions in the B and V bands, is often used to characterize interstellar extinction. For the star HD 93250 the value E(B − V ) = 0.48 has been measured. Given the above value of E(B − V ) for HD 93250, calculate the extinction in the B band, and explain why the parameter E(B − V ) is often called the “reddening.” The B band apparent magnitude of HD 93250 is mB = 8.12. Calculate…arrow_forwardMost stars (Main sequence) generate light through the same mechanism. Because of this, there is an empirical relation between their mass, M, and their Luminosity, L. This relation could be written in the form L/Lsun = (M/Msun, This relation is shown in the log-log diagram below. Find the value of a and round it to the nearest integer. 10 104 102 10-2 10-4 0.1 1.0 2.0 0.2 0.5 5.0 10.0 20.0 Mam (solar masses) Luminosty (solar units)arrow_forwardYou measure a star to have a parallax angle of 0.12 arc-seconds What is the distance to this star in parsecs? 8.33 Hint: d = 1/p What is the parallax angle of a different star that is twice as far away as the star from the previous problems? [answer in arc-seconds without including the unit]arrow_forward
- An O8 V star has an apparent visual magnitude of +5. Use the method of spectroscopic parallax to estimate the distance to the star (in pc). (Hints: Refer to one of the H–R diagrams in the chapter, and use the magnitude–distance formula, d = 10(mV − MV + 5)/5 where d is the distance in parsecs, mV and MV are the apparent and absolute visual magnitude respectively.)arrow_forwardA star has a period of P = 37 days. It has a radius of 5.7 times the radius of the sun. Calculate it's equatorial speed Vrot. Answer: Okm/s Om/s Check A star has a radius of 5.7 times the radius of the sun and a mass of 18 times the mass of the sun. It rotates at 0.7 of the critical speed W, the speed at which it's surface at the equator is actually in orbit. Recall Vrot is calculated at the equator and W= Vrot/Vorb Calculate it's period P. Answer: Odays Ohours Oseconds Checkarrow_forward(Astronomy) (Part A) White Dwarf Size II. The white dwarf, Sirius B, contains 0.98 solar mass, and its density is about 2 × 106 g/cm3. Find the radius of the white dwarf in km to three significant digits. (Hint: Density = mass⁄volume, and the volume of a sphere is 4/3πr3). (Part B) Compare your answer with the radii of the planets listed in the Table A-10. Which planet is this white dwarf is closely equal to in size?arrow_forward
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