Instructor: Juhan Frank. Identify the correct answers by placing a check between the brackets ë ë.

Transcription

1 Name:... ASTRONOMY 1102 í 1 Instructor: Juhan Frank Third Test ífall 1999í Friday November 12 Part I í Multiple Choice questions è3 ptsèquestion; total = 60 ptsè Identify the correct answers by placing a check between the brackets ë ë. correct answers in the questions identiæed by a*. *1è Some are wrong; which are correct? ë ë The sun will die as a neutron star. ëxë The sun will die as a white dwarf. ëxë brown dwarfs and white dwarfs cool to become black dwarfs. ë ë low mass stars produce black holes. ëë A20Mæ star will die as a white dwarf. 2è The absolute magnitude of a star is a measure of the star's ëxë luminosity. ë ë surface temperature. ë ë mass. ë ë apparent brightness. ë ë density. 3è The apparent magnitude of a star is a measure of the star's ë ë luminosity. ë ë surface temperature. ë ë mass. ëxë apparent brightness. ë ë density. 4è As a star cluster ages ëxë the bluest MS stars are the ærst to evolve to red supergiants. ë ë the red dwarfs leave the MS ærst. ë ë the white dwarfs become red dwarfs. ë ë white dwarfs are produced before neutron stars. ë ë all stars experience the Helium æash sooner or later. 5è Cepheids are pulsating variables ë ë whose luminosity is the same for all periods. ë ë whose luminosity is smaller the shorter the period. ëxë whose luminosity is larger the longer the period. ë ë only found in globular clusters. ë ë because they are binary stars. 6è The net eæect of the CNO cycle is to fuse ëë 4 4 He 2! H. ëxë 4 1 H 1! 4 He. ë ë Carbon to Oxygen. ë ë Carbon to Iron. ë ë Carbon to Nitrogen and Nitrogen to Oxygen. A1 Check ALL

2 7è A binary that can be resolved by telescopes is known as ëxë a visual binary. ë ë a spectroscopic binary. ë ë an eclipsing binary. ë ë double-lined spectroscopic binary. ë ë a Cepheid. 8è The essence of the Algol Paradox in a binary is that ë ë the more massive star is more evolved. ëxë the less massive star appears more evolved. ë ë the more massive star is larger. ë ë the more massive star is more luminous. ë ë the donor is a blue star. 9è Which evolutionary stage occurs earlier in the life of a low mass star? ë ë Helium æash. ë ë Horizontal Branch èhbè. ë ë Asymptotic Giant Branch èagbè. ëxë Main Sequence èmsè. ë ë White Dwarf èwdè. 10è These processes immediately precede and lead to the formation of a neutron star: ë ë core degeneracy and Helium æash. ëxë photodisintegration, neutronization and bounce. ë ë conduction, radiation and convection. ë ë thermal pulses and the expulsion of a planetary nebula. ë ë core exhaustion of Hydrogen and the formation of a H-burning shell. *11è True statements about the evolution of high mass stars: ëxë they do not experience the Helium æash. ëxë the Fe core is surrounded by multiple shells burning diæerent fuels. ë ë they produce white dwarfs. ë ë they die in a Type I or Carbon detonation supernova. ëxë they die in a Type II or core collapse supernova. 12è A nova explosion occurs when ëë alow mass star produces a white dwarf. ëxë a white dwarf accretes enough H-rich material from a companion. ë ë a massive star collapses to yield a black hole. ë ë a neutron star accretes enough material from a companion. ë ë a neutron star forms. 13è The redder the main-sequence turnoæ, ëxë the older the cluster. ë ë the younger the cluster. ë ë the smaller the number of RGB stars in the cluster. ë ë the bluer the main-sequence. ë ë the more black holes form. A2

3 14è The internal structure of an asymptotic red giant: ëxë Inert C core, He shell burning, H shell burning, inert H-rich envelope. ë ë Inert He core, H shell burning, inert H-rich envelope. ë ë core He burning, H shell burning, inert H-rich envelope. ë ë core H burning, inert H-rich envelope. ë ë Inert C core, He shell burning, inert H-rich envelope. 15è A white dwarf is supported against its own gravity by ë ë the strong force. ë ë the neutron degenerate pressure. ëxë the electron degenerate pressure ë ë the thermal pressure of an ordinary gas. ë ë the electromagnetic force. 16è A Type I Carbon detonation supernova occurs when ë ë a HB star exhausts its He. ë ë the iron core of a massive star collapses. ëë every time a white dwarf has accreted a small amount of H-rich material. ëxë the mass of a white dwarf is driven over the Chandrasekhar limit by accretion. ë ë a black hole forms. 17è Single isolated pulsars are extraordinarily good, stable clocks, and yet as they age, ë ë they spin faster and the pulse period decreases. ëxë they spin slower and the pulse period increases until pulsed emission ceases. ë ë they are spun up again by accretion. ë ë they become red giants. ë ë their rotation frequency increases. 18è The absorption lines of hydrogen are strongest in stars of spectral class ë ë A because they are the hottest. ë ë O because they are the hottest. ë ë B because the temperature is just right. ëxë A because the temperature is just right. ë ë M because they are the coolest. 19è What is a black hole candidate? ë ë A massive star which is about to collapse. ëxë An X-ray binary where the mass of the accretor exceeds 3 Mæ.. ë ë An intermediate mass star. ë ë A cataclysmic variable. ë ë A supernova oftype I. 20è An X-ray burst occurs when ë ë enough H has accumulated on the surface of a white dwarf. ëxë enough He has accumulated on the surface of a neutron star. ë ë enough H has accumulated on the surface of a black hole. ë ë enough C has accumulated on a red dwarf. ë ë a massive star goes supernova. A3

4 Part II í Problems è10 ptsèproblem; total = 40 ptsè NO CALCULATORS! Problem 1: The H-R diagrams of four star clusters are shown schematically below. Based on these sketches, which one is the youngest and which is the oldest cluster Problem 2: The following table shows data for several well-known bright stars. Note that Mv is the absolute magnitude and mv is the apparent magnitude. Name mv Mv Spectral Type Canopus F0I æ Cen A G2V æ Sco M1I Sirius A1V Spica B1V æ Tau K5III aè Which of the stars appears brightest in the sky? Sirius: it has the smallest èmost negativeè APPARENT magnitude mv bè Which is the most luminous star? æ Sco: it has the smallest èmost negativeè ABSOLUTE magnitude Mv cè Which is the star with the largest radius? æ Sco: it is on the top right of the HRD. dè Which stars have exahusted H in their cores? Canopus, æ Sco, æ Tau: they are NOT MS stars. eè Which star has the highest surface temperature and appears bluest? Spica: is the leftmost spectral type listed. A4

5 Problem 3: On the diagram shown overleaf plot and label clearly the approximate position of the following stars: aè B9V bè M0V cè K5I dè A central star of a planetary nebula whose surface temperature is 10 5 K and whose luminosity is 1000 Læ. eè A white dwarf of spectral type A0. Problem 4: The diagram overleaf shows the luminosities of stars plotted against their surface temperature. The thick curved line with embedded arrows shows the evolutionary track of a star like the sun from protostar to white dwarf. Answer the following questions: 1.í What is the name given to this kind of diagram? HertzsprungíRussell Diagram èejnar Hertzsprung and Henry Norris Russellè 2.í Mark and label the point at which this star reaches the ZAMS. 3.í Mark and label the point at which this star experiences the He æash. 4.í Mark and label the point at which this star is burning steadily He to C in the core and H in a shell surrounding the core. 5.í Identify which portion of the track corresponds to the RGB. A5