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UNIVERSITY OFTORONTO ASTRONOMY 201H1S MIDTERM TEST THURSDAY, MARCH 15, 2012 DURATION: 45 MINUTES TOTAL MARKS: 35 NOAIDS ALLOWED UTORID: _________________________________ CIRCLE YOUR TUTORIALSECTION BELOW: Monday Tuesday Wednesday 10:00 0101 -- Nathan 0102 -- Snezana 0701 -- Liam 0702 -- Eric 1201 -- Stephanie 1202 – JD 11:00 0201 -- Yevgeni 0202 --Adam 0801 -- Nathan 0802 -- Eric 1301 -- Stephanie 1302 – JD 12:00 0301 – Sergei 0302 -- Liam 0901 -- Nathan 0902 -- Eve 1401 – Sergei 1402 – Stephen 13:00 0401 -- Sergei 0402 -- Snezana 1001 --Adam 1002 -- Eve 1501 – Stephanie 1502 – JD 14:00 0501 -- Yevgeni 0502 -- Stephen 1101 – Liam 1102 -- Snezana1601 – Eve 1602 – Stephen 15:00 0601 -- Yevgeni 0602 -- Eric - - - - Instructions: 1. ON THIS PAGE: Fill in your UTorID (e.g. smithm1) and circle your tutorial section. 2. ON THE NEXT PAGE: Fill in your name (as it appears on ROSI), your student number, and your UTorID (e.g. smithm1). 3. ON THE SCANTRON CARD: Fill in your last name, first initial, and student number in the spaces given and, using pencil, darkly shade in the corresponding bubbles. Then sign the card. 4. For each multiple choice question, mark your answer in pencil on the Scantron card by darkly shading the appropriate bubble. All answers to multiple choice questions must be transferred to the Scantron card. Under no circumstances will answers to multiple choice questions written on this paper be accepted. 5. Answer short answer questions in the spaces provided. Answers written in pencil will not be re- marked. 6. Mark values are indicated with each question. 7. Make sure that your midterm has 9 pages. AST 201 MIDTERM 2, FALL 2012 PAGE 1 OF 9 NAME: __________________________________ UTORID: ________________________________ STUDENT NUMBER: _____________________ Question Marks A1-A20 (MC) /20 B1 /3 B2 /3 B3 /3 B4 /6 Total /35 AST 201 MIDTERM 2, FALL 2012 PAGE 2 OF 9 PARTA: Multiple choice questions. CIRCLE THE MOST CORRECTANSWER (1 mark each) 1. Which of the following has the highest luminosity? (a) a main-sequence O star (b) a white dwarf (c) a main-sequence M star (d) a horizontal branch star (e) we can't be sure without knowing the distance to each star 2. Why are the spectral lines of hydrogen stronger inA-class stars than in other classes? (a) BecauseAstars are made of hydrogen (b) Because hydrogen is neither too cold nor too ionized in those stars. (c) BecauseAstars are extremely luminous. (d) BecauseAstars are very hot. 3. Which of the following correctly orders the spectral classes from coolest to hottest? (a) OBAFGKM (b) I, II, III, IV, V (c) MKGFABO (d) V, IV, III, II, I (e) K2V, K2IV, K2III, K2II, K2I 4. If we can detect that a star system is a binary system only by examining the Doppler shift of its absorption lines, it is called a: (a) eclipsing binary (b) Doppler-broadened binary (c) resolved binary (d) optical binary (e) spectroscopic binary 5. Which of the following statements about the colours and ages of stars is always correct? (a) All young stars are blue. (b) All stars which have almost exhausted the hydrogen in their cores are red. (c) Blue stars are younger than red stars. (d) As a star cluster ages, it should lose its blue stars first. (e) Stars begin their main-sequence lives at the red end, then move up the main sequence to the blue end over the course of their lives. AST 201 MIDTERM 2, FALL 2012 PAGE 3 OF 9 6. Which of the following objects has the highest average density? (a) the Sun (b) a white dwarf (c) the Earth (d) a neutron star (e) a red dwarf 7. Aplanetary nebula forms when: (a) Alow-mass star dies and ejects its outer layers into space. (b) Aforming star gathers material around itself and shapes it into a disk. (c) Aplanet has a close encounter with its parent star, leaving behind only a cloud of gas and dust. (d) Amassive star explodes, leaving behind a glowing cloud of gas. (e) Acarbon-detonation supernova occurs. 8. Consider a molecular cloud such as Barnard 68. Such a cloud will begin to form a star when: (a) a shock wave from a nearby supernova hits it, heating it up and beginning nuclear fusion reactions. (b) it cools enough that gravity can overwhelm internal pressure. (c) it becomes dense enough to initiate helium fusion. (d) it gains enough angular momentum to produce a protostellar disk. (e) it gains enough mass from a binary companion to trigger fusion reactions. 9. If the core of the Sun were to cool just slightly, what would happen? (a) The fusion rate would fall, gravity would win, and the star would collapse. (b) The fusion rate would increase, a hydrogen shell would ignite, and the star would become a red giant. (c) The fusion rate would fall, the core would contract, the core would increase in temperature and density, and the normal fusion rate would be restored. (d) The fusion rate would fall, the star would begin to crush itself, electron degeneracy pressure would kick in, and the star would become a white dwarf. (e) The core would rapidly become denser, it would begin fusing helium, and the star would move off the main sequence. 10. When a molecular cloud is collapsing, it spins faster and faster. Why? (a) It converts gravitational potential energy into thermal energy. (b) It converts gravitational potential energy into kinetic energy. (c) It conserves energy while shrinking. (d) It conserves angular momentum while shrinking. (e) It converts gravitational potential into angular momentum. AST 201 MIDTERM 2, FALL 2012 PAGE 4 OF 9 11. If we know a star's luminosity class and its spectral type, we can make accurate estimates of : (a) its luminosity, surface temperature, main-sequence lifetime, and its size (b) only its luminosity (c) only its luminosity and surface temperature (d) only its mass (e) only its luminosity, surface temperature, and main-sequence lifetime 12. Why do low-mass stars live longer than high-mass stars? (a) Bec
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