Astronomy 100 Spring 2006 Lecture Questions Twelve Weeks Review

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1 Astronomy 100 Spring 2006 Lecture Questions Twelve Weeks Review 16-1 Fusion in the Sun The solar corona has temperatures roughly the same as temperatures in the Sun's core, where nuclear fusion takes place. Fusion doesn't occur in the corona because A. the density in the corona is too low. B. the corona has too many free electrons. C. atoms in the corona are mostly ionized. D. the corona has more heavy atoms than the core. E. Two of the above Stellar stability Suppose the fusion reactions in the core of Sun went out tomorrow. A. the Sun would explode immediately B. the light from the Sun would vanish immediately C. the neutrinoes would vanish immediately D. the Sun would collapse immediately 18-1 Heliocentric Parallax Sirius is 2.5 pc away. The angular radius of Earth's orbit as seen from Sirius is A. 2.5 arcsec B. 1 arcsec C. 0.4 arcsec D. cannot be determined from this information 18-2 Magnitudes Pluto has an apparent magnitude of 13.5, and the faintest star you can see with your eyeballs is apparent magnitude 6. Pluto s apparent brightness is how much fainter than you can see? A. 7.5 B. 10 C. 100 D Luminosity Practice Recall that Sirius is 2.5 pc away (parallax 0.4 arcsec). It is about 4 times as bright as Vega (apparent magnitude -1.5), but Vega has a distance of 7.5 pc and a Luminosity of 24 L sun. Sirius Luminosity is A. 4 x Vega (200 L sun ) B. 1/3 x Vega (9 L sun ) C. 4/9 x Vega (12 L sun ) D. 9/4 x Vega (58 L ) sun

2 19-2 Stellar Spectra This stellar spectrum is A. Type M B. Type A C. Type G D. Impossible 20-1 Size, temperature, and Luminosity Betelgeuse (M2, T = 3000) has a size 100 times Spica (B1, T = 30,000). How do their luminosities compare? L(Spica) / L(Betelgeuse) = A. 1/100 B. 1/10 C. 1 D. 10 E Mass of a Binary Star Suppose a binary star has a period of 2 years and an orbital size ( semi-major axis ) of 2 AU. A. The sum of their masses is 1/2 M sun B. Each star has a mass of 1/2 M sun C. The sum of their masses is 2 M sun D. Each star has a mass of 2 M sun 21-2 Observing Binary stars Suppose nearby two stars are in a circular orbit oriented such that the plane of the orbit is perpendicular to our line of sight (a "plan view"). In such a case A. it could be observed as a spectroscopic binary but not a visual binary B. it could be observed as a visual binary but not a spectroscopic binary C. It could be observed as either a visual or spectroscopic binary 22-1 Pre Main Sequence Stars If pre-main sequence stars are collapsing out of large gas clouds, where would you first expect to see them on the HR diagram? A. upper left B. upper right C. lower left D. lower right

3 24-1 Star Clusters Suppose the Sun were part of a star cluster. What kind of star would we be surprised to see in our cluster? A. An M type main sequence star B. A B type main sequence star C. A and B D. a pre-main sequence star E. B and D 25-1 Planetary Nebula shape Why are many Planetary Nebulae not round? A. The non-round ones come from binary star systems B. The non-round ones come from rapidly rotating stars C. Magnetic fields funnel the nebula D. The flow is distorted by interstellar gas and dust around the star E. All of the above suggestions are possible 25-2 Sirius A & B scenario We found in the problem that Sirius A, a Main sequence A star, has a mass of 2 M sun, and Sirius B, a White Dwarf, has a mass of 1 M sun. What is a possible mass for Sirius B when the Sirius system was born? A. 0.5 M sun (M star) B. 1 M sun (G star) C. 1.4 M sun (F star) D. 3 M sun (A star) E. 9 M (B star) sun 27-1 Where to look for pulsars There are some pulsars seen in globular clusters. Does this fit with the formation scenario we just talked about? A. No. A globular cluster would be disrupted by a supernova B. No. Supernovae in globular clusters would all make black holes C. No. All the neutron stars in a globular cluster would long ago have spun down D. Yes. There should be a lot of neutron stars in a globular cluster Algol "Paradox" In some close binary stars, we see a main sequence star that is more massive than its red giant companion. How is that possible? A. Not a problem. The red giant ran out of Hydrogen first B. Not possible. The more massive star must run out of Hydrogen first C. The more massive star was born later D. The red giant lost enough mass to become the less massive object

4 29-1 Radio Rotation Curve Using a radio emission line for Hydrogen, if we look along a line of sight that passes inside the solar orbit, we see a maximum redshift for the gas on one side of the center, and a maximum blueshift in the other. If the gas orbits with the stars, A. This is gas near the sun B. This is the gas that is nearest the center C. This is gas at the Sun's orbit on the other side of the galaxy D. This is gas way beyond the solar orbit 30-1 Population III Population III candidates have been very hard to identify. Why do you suppose this is? A. they have all become white dwarfs B. they are all far away C. they are all intrinsically very faint D. they are hidden by interstellar gas and dust E. B and C

5 ANSWERS 16-1 A 17-1 C 18-1 C 18-2 D 19-1 C 19-2 D (ignoring the possibility of interstellar reddening) 20-1 C 21-1 C 21-2 B 22-1 B 24-1 E 25-1 E 25-2 D 27-1 C 28-1 D 29-1 B 30-1 E