Which of the stars (spectral type) below is hottest?

Harold Washington College, Chicago

Astronomy 201: Descriptive Astronomy

Final Exam- Spring 2019

Version B ________________________________________________________________________________________________

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Instructions

The exam consists of 60 Multiple-choice questions including 5 Bonus questions.

Read the question and all the answers carefully before choose your answer.

Choose the best answer and mark your answers with a number 2 pencil on a 5-answer scan sheet (only one answer per question).

Try all the questions and make your best effort. Good luck! _________________________________________________________________________________________

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

1) Which of the stars (spectral type) below is hottest? A) A B) G C) F D) M E) K

2) What is a planetary nebula? A) gas ejected from a low-mss star in the final stage of its life B) gas created from the remains of planets that once orbited a dead star C) interstellar gas from which planets are likely to form in the not-too-distant future D) the remains of a high-mass star that has exploded

3) If you were to come back to our solar system in 6 billion years, what might you expect to find? A) a black hole B) a rapidly spinning pulsar C) a white dwarf D) a red giant star E) Everything will be essentially the same as it is now.

4) On the main sequence, stars obtain their energy A) by fusing hydrogen to helium. B) from nuclear fission. C) from chemical reactions. D) by fusing helium to carbon, nitrogen, and oxygen. E) from gravitational contraction.

Descriptive Astronomy 201 Spring 2019

5) The main source of energy for a star as it grows in size to become a red giant is ________. A) hydrogen fusion in a shell surrounding the central core B) gravitational contraction C) hydrogen fusion in the central core D) helium fusion in the central core

6) Which of the following observatories/telescope is most likely to image a black hole in a galactic center? A) the Hubble Space Telescope B) Event Horizon Telescope (EHT) C) the Arecibo Radio Observatory D) the Chandra X-Ray Observatory E) the SOFIA airborne infrared observatory

7) To calculate the masses of stars in a binary system, we must measure their (a) spectral types (b) distance from Earth (c) orbital period (d) average orbital distance (e) luminosities

A) Both (b) and (e) B) Both (a) and (b) C) Both (c) and (d) D) Both (a) and (e)

8) What is the spectral type of the Sun? A) G B) K C) F D) M E) A

9) If the beam from a spinning neutron star hit Earth, A) we would call it a pulsar B) we would call it a gamma ray burst C) we would die D) nobody observe it E) we would call it a nebula

10) What is an ionization or an emission nebula? A) a clump of gas that will soon give birth to a new star B) a name sometimes used to describe spiral galaxies besides the Milky Way C) a region of very hot, low-density accreation gas surrounding a recent supernova D) a colorful glowing cloud of ionized gas by light from nearby hot stars

11) What kinds of objects lie in the disk of our galaxy? A) gas and dust clouds B) emmision and refelection nebulae C) open clusters D) all ages of stars E) all of the above

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Use the Hertzsprung-Russell (H-R) diagram below to answer from Question 12-16. The sketch below shows groups of stars on the H-R diagram.

12) Which group represents stars of the largest radii? A) A B) C C) D D) E E) E

13) Which group represents stars that are hot, extremely bright and emit most of their radiation as ultrviolet? A) A B) C C) D D) E E) F

14) Which group represents white dwarfs which have no ongloing nuclear fusion? A) a B) b C) c D) d E) e

15) On a Hertzsprung-Russell diagram, where would you find red giant stars? A) upper right B) lower right C) upper left D) lower left

16) The position of a star on an Hertzsprung-Russell diagram can tell you all of the following except? A) Temperature B) Luminosity C) Stellar radius D) Distanc from Earth E) Life time

17) Where does globular clusters lie in a galaxy? A) in cool gas clouds B) in spiral arms C) in the central buldge D) in the halo E) in the disk

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Use the H-R diagram below to answer from Question 18-21. The sketch below shows some labelled stars (A to H)on the H-R diagram.

18) Which group has only the main-sequence stars? A) A, B, C, D, F, G B) A, B, C, D, E, H C) A, B, C, D, E D) A, B, D, E, F, H E) All of them

19) Which main sequence star has the longest life time? A) A B) B C) C D) D E) E

20) On H-R diagram, Which main sequence star has the the greatest mass? A) A B) C C) D D) F E) H

21) Where would our own sun be placed on the above H-R Diagram? A) A B) B C) C D) D E) E

22) Where does most star formation occur in the Milky Way today? A) in the halo B) in the galactic center C) in the spiral arms D) in the bulge E) uniformly throughout the galaxy

23) The first gravitational waves were detected in 2015 by the LIGO observatories in Washington and Louisiana. What event was thought to cause these gravitational waves?

A) ripples in space-time left over from the Big Bang B) two black holes merging C) two neutron stars merging D) a hypernova

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24) How would the apparent brightness of Alpha Centauri change if it were two times farther away?

A) Its apparent brightness will increase by a factor of 2. B) Its apparent brightness will increase by a factor of 4. C) Its apparent brightness will decrease by a factor of 2. D) Its apparent brightness will decrease by a factor of 4.

25) Which type of galaxies have a clearly defined spheroidal (halo) component but do not have a clearly defined disk component ?

A) lenticulars B) spiral C) ellipticals D) all of the above

26) Spectral type of a star determines its ______________________________. A) Luminosity B) radius. C) surface temperature. D) mass E) core temperature.

27) What is the cause of short gamma-ray bursts? A) the collision of stars in the dense nuclei of distant galaxies B) very powerful supernovae occurring in distant galaxies C) the collision of two neutron stars or a neutron star with a black hole D) supernovae in the Milky Way E) new stars forming in the Milky Way

28) What happens when a star like the sun exhausts its core hydrogen supply? A) It contracts, becoming smaller and dimmer. B) It contracts, becoming hotter and brighter. C) Its core contracts, but its outer layers expand and the star becomes bigger but cooler and therefore remains

at the same brightness. D) Its core contracts, but its outer layers expand and the star becomes bigger and brighter. E) It expands, becoming bigger but dimmer.

29) Which of the following is closest in size (radius) to a neutron star? A) the Sun B) a small city C) a football stadium D) the Earth E) the solar system

30) A neutron star is ________. A) the remains of a star that died by expelling its outer layers in a planetary nebula B) an object that will ultimately become a black hole C) the core remnant of a star that died in a massive star supernova D) a star made mostly of elements with high atomic mass numbers, so that they have lots of neutrons

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31) The spectral sequence in order of decreasing temperature is A) OBAGFKM B) OABGMFK C) OABFGKM D) OBAFGKM E) OBAFKMG

32) What is the approximate range of masses required for a collapsing cloud fragment to become a main-sequence star, with hydrogen fusion at its core?

A) 0.1 to 150 solar masses B) 0.1 to 10 solar masses C) 1 to 150 solar masses D) 1 to 10 solar masses E) 0.1 to 1,500 solar masses

33) Which types of galaxies have a clearly defined disk component? A) irregulars only B) spirals only C) lenticulars only D) ellipticals only E) spirals and lenticulars

34) Which of the following is the most common type of main-sequence star? A) an O star B) an M star C) an F star D) a G star E) an A star

35) Astronomers have observed a 1.3 solar mass white dwarf and a 1.0 solar mass white dwarf. Which of the following must be true?

A) The 1.3 solar mass white dwarf has a higher surface temperature. B) The 1.3 solar mass white dwarf has a longer lifetime. C) The 1.3 solar mass white dwarf has a smaller radius. D) The 1.3 solar mass white dwarf has a larger radius.

36) If a protostar doesn’t have enough mass to become a true star, it becomes a A) brown dwarf which will remain as brown dwarf forever B) a planet C) a main-sequence star slowly over the time. D) white dwarf. E) brown dwarf which will become a main-sequence star later

37) A star’s luminosity depends primarily on its A) radius and surface temperature. B) distance from Earth. C) radius. D) surface temperature. E) mass and radius.

38) What object do we define as a black hole? A) an object that absorbs all light and emits radiation based only on its temperature B) any object made from dark matter C) a dead star that has faded from view D) an object with gravity so strong that not even light can escape

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39) What do we mean by the event horizon of a black hole? A) It is the very center of the black hole. B) It is the place where X-rays are emitted from black holes. C) It is the boundary beyond which light cannot escape. D) It is the distance from the black hole at which stable orbits are possible.

40) A typical white dwarf is ________. A) about the same size and mass as the Sun but much hotter B) about as massive as the Sun but only about as large in radius as Earth C) as massive as the Sun but only about as large in size as Jupiter D) as large in diameter as the Sun but only about as massive as Earth

41) As of our modern understanding, what is a nova? A) an explosion on the surface of a white dwarf in a close binary system B) the sudden formation of a new star in the sky C) a rapidly spinning neutron star D) the explosion of a massive star at the end of its life

42) Which of the following is not one of the galaxy classes? A) spiral galaxies B) irregular galaxies C) lenticular galaxies D) globular galaxies E) elliptical galaxies

43) After a massive-star supernova, what is left behind? A) always a neutron star B) always a white dwarf C) always a black hole D) either a white dwarf or a neutron star E) either a neutron star or a black hole

44) Which of the following types of galaxies have a disk and (spheroidal) halo component but lack spiral arms? A) lenticulars B) ellipticals C) irregulars D) all of the above

45) The age of stars in a cluster can be determined by A) finding pulsating variable stars in the cluster. B) finding spectroscopic binaries in the cluster. C) fitting the position of the main sequence to the Sun. D) counting the number of stars in each spectral class. E) determining the main-sequence turnoff point.

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46) If we measure the light emitted by a K spectral type main sequence star for several weeks and observe a graph of brightness verses time as the graph below.

Which of the graph below show how the graph of brightness verses time would look for a F spectral type star?

A) B)

C) D)

47) Where are most elements heavier than hydrogen and helium made? A) in the cores of stars and in supernovae B) in the cool atmospheres of red giant stars C) in white dwarfs D) in the interstellar medium E) All were made in the Big Bang, when the universe first began.

48) What kind of gas cloud is most likely to give birth to stars? A) a hot cloud of gas expelled by dying star B) a hot, dense gas cloud C) a cold, dense interstellar gas cloud called molecular clouds D) a cloud in which elements such as carbon, nitrogen, and oxygen are made

49) What kind of object do astronomers suggest lies at the center of our galaxy? A) a supermassive neutron star B) a super massive black hole C) globualr clusters D) an enormous collection of dark matter, explaining why we detect no light at all from the galactic center E) a dense cluster of young, hot stars

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50) What happens to the core of a star after the planetary nebula stage? A) It contracts from a protostar to a main-sequence star. B) It breaks apart in a violent explosion. C) It becomes a neutron star. D) It becomes a white dwarf. E) none of the above

51) If we could view our galaxy outside from a distance of several hundred thousand light-years, it would appear ________.

A) as a flattened disk with a central bulge and spiral arms B) as a single, bright star C) as a faint smudge barely visible to the unaided eye D) as a faintly glowing band of light stretching all the way around the sky

52) Compared to spiral galaxies, elliptical galaxies are A) redder and more round. B) bluer and flatter. C) redder and flatter. D) bluer and more round. E) always much smaller.

53) Which of the following best descibes a protostar? A) a star which is at the halo of a galaxy B) a star which is at the galactic plane C) a star that is still in the process of forming D) a star which is at the galactic center E) a main-sequence star

54) Which of the following statements about star clusters is/are true? (a) All stars in the cluster are approximately the same age. (b)All stars in the cluster are at same distance from Earth. (c) All stars in the cluster have approximately the same mass. (d) All stars in the cluster will havea similar life cycle.

A) Only (d) is true. B) Only (c) is true. C) Both (a) and (b) are true. D) All are true. E) None.

55) Which of the following sequences correctly describes the stages of life for a high- mass star? A) main-sequence, protostar, red supergiant, neutron star or blackhole B) planetary nebular, protostar, main-sequence, red giant, blackhole C) protostar, main-sequence, red supergiant, white dwarf, neutron star or blackhole D) protostar, main-sequence, red supergiant, neutron star or blackhole E) protostar, main-sequence, red supergiant, white dwarf

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Bonus Questions: Attempt all the bonus questions! 56) Use the table of star data to answer the following Questions 56-59.

STAR PARALLAX (ARCSEC)

SPECTRAL TYPE LUMINOSITY (L/L )

DENEB 0.0023 A2 I 196,000

ALDEBARAN 0.051 K5 III 518

TAU CETI 0.274 G8.5 V 0.52

SPICA 0.012 B1 V 2,200

PROCYON 0.286 F5 V 7.2

BETELGEUSE 0.005 M2 I 120,000

Determine which of the stars on the table is closest to the Earth, and which star is the farthest. A) Closest is Deneb and farthest is Tau Ceti. B) Closest is Procyon and farthest is Deneb. C) Closest is Spica and farthest is Betelgeus. D) Closest is Tau Ceti and farthest is Deneb. E) Closest is Spica and farthest is Deneb.

57) How do you know which star is the closest? A) The one with the smaller parallax angle is the closest. B) The one with the larger parallax is the closest. C) Can’t tell, since parallax angle has nothing to do with distance. D) The star which appears the brightest is the closest.

58) Which of these stars are main sequence stars? A) Betelgeuse and Deneb only B) Aldebaran only C) They are all main sequence stars D) Tau Ceti, Spica and Procyon only E) Deneb, Aldebaran and Betelgeuse only

59) Which of these stars are supergiants? A) Aldebaran only B) We can’t determine with this information C) Tau Ceti, Spica and Procyon only D) Deneb, Aldebaran and Betelgeuse only E) Betelgeuse and Deneb only

60) Astronomers can measure a star’s mass in only certain cases. Which one of the following cases might allow astronomers to measure a star’s mass?

A) The star is of spectral type A. B) The star is of spectral type G. C) The star is a member of a binary star system. D) We know the star’s luminosity and distance.

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