UNIVERSE (LOOSELEAF):STARS+GALAXIES
6th Edition
ISBN: 9781319115043
Author: Freedman
Publisher: MAC HIGHER
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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 (LOOSELEAF):STARS+GALAXIES
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- Most 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_forwardIf the main-sequence mass lower limit is 0.08 solar mass and the brightest main-sequence stars are 1 million times more luminous than the Sun, what is the mass range along the main sequence in the figure below? (answer in solar masses)arrow_forwardAn 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_forward
- A 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_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_forwardMatch the spectral type and luminosity class to theletters shown on the Hertzsprung-Russell diagram 1) A WD (White Dwarf)2) G V (Main Sequence) 3) M V (Main Sequence)4) M I (Supergiant)5) G III (Giant)arrow_forward
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