# ps07 - Astronomy 10 Fall 2008 Homework 7 40 points total...

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Astronomy 10, Fall 2008 Homework 7 - 40 points total Due in the boxes in the basement of Campbell Hall by 5pm Tuesday, October 28 . Be sure to include your name, SID, Section Number, and GSI name on your homework, and staple it together. 1. Clouds of Gas (9 points) Looking out into the sky, you can ﬁnd lots of clouds of dense gas and dust from which stars form. One such cloud (called Barnard 68) is shown below. In general for this problem, you can assume the cloud is (very roughly) a sphere. (a) The diameter of the cloud is measured to be 200 arcseconds on the sky, and the cloud is known to be at a distance of about 500 light-years. What is the actual diameter of the cloud? (2 points) (b) Using a handy radio telescope you happen to have nearby, you measure how much ﬂux is being emitted by the carbon monoxide gas (CO) in the cloud, f = 5 × 10 - 14 erg s - 1 cm - 2 . What is the total luminosity of the cloud in radiation from CO? (2 points) (c) For temperatures and densities typical of clouds like this, it turns out that one kilogram of CO would emit about 350 erg of radiation each second. We also know that in these molecular clouds, the ratio of the mass of hydrogen (H 2 ) to that of CO is about M H 2 /M CO 10 4 . Using this information, what is the total mass of the cloud (in solar units)? (3 points)

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(d) Given your results from (a) and (c), what is the overall density of the cloud? (2 points)
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## This note was uploaded on 07/09/2010 for the course ASTRO 10 taught by Professor Norm during the Fall '06 term at Berkeley.

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ps07 - Astronomy 10 Fall 2008 Homework 7 40 points total...

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