Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Question
Chapter 20, Problem 18Q
To determine
(a)
The reason to have two pair of gas shells as shown in the image of Planetary nebula IC 418.
To determine
(b)
The reason to have a very thick outer shell around the edges than near the middle of planetary nebula IC 418.
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If the hottest star in the Carina Nebula has a surface temperature of 51,000 K, at what wavelength (in nm) does it radiate the most energy?
Hint: Use Wien's law:
?max =
2.90 ✕ 106 nm · K
T
How does that compare with 91.2 nm, the wavelength of photons with just enough energy to ionize hydrogen?
-The wavelength calculated above is shorter than 91.2 nm. Photons at this calculated wavelength will have more than enough energy to ionize hydrogen.
-The wavelength calculated above is longer than 91.2 nm. Photons at this calculated wavelength will have more than enough energy to ionize hydrogen.
-The wavelength calculated above is shorter than 91.2 nm. Photons at this calculated wavelength will not have enough energy to ionize hydrogen.
-The wavelength calculated above is longer than 91.2 nm. Photons at this calculated wavelength will not have enough energy to ionize hydrogen.
A planetary nebula expanded in radius 0.3 arc seconds in 30 years. Doppler measurements show the nebula is expanding at a rate of 35 km/s. How far away is the nebula in parsecs?
First, determine what distance the nebular expanded in parsecs during the time mentioned. Δd = vpc/sTs
So we first need to convert the rate into pc/s and the time into seconds:
vpc/s = vkm/s (1 pc / 3.09 x 1013km)
vpc/s = ?
Ts = (Tyr)(365 days/yr)(24 hrs/day)(3600 s/hr)
Ts = ? s
Δd= vpc/sTs
Therefore, Δd = ? pc
A cloud of mean number density n ~ 3000 cm-3 and radius 3 pc has an ionising
source with luminosity at 13.6 eV of L13.6eV = 2.18 x 109 erg s- at the centre.
(a) What is the size of the HII region in pe? [og = 2 x 10-13 cms-].
%3D
(b) What assumptions are involved in part
a)
(c) Discuss why the HII region will drive a shock into the rest of the cloud, and
calculate the post-shock density.
(d) Show why this HII region will destroy the cloud.
Chapter 20 Solutions
Universe: Stars And Galaxies
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