AST201H1 Lecture Notes - Protostar, Hydrostatic Equilibrium, Orion Nebula

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skylocust785

13 Oct 2012

School

UTSG

Department

Astronomy & Astrophysics

Course

AST201H1

Professor

Marija Stankovic

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AST201H1 Full Course Notes

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Document Summary

In infrared we can see past the dust and see that behind dark regions there are lots of stars seeing what lies behind it: any longer wavelength will go over that dust. Short wavelength ligh will not pass but longer will. Star nurseries: orion constellation, orion nebula in visible light, colours added later and correspond to emission of different spectral lines. In infrared light we see that a very young cluster is embedded in the gas. If you have dust clouds that block light, then inside thick dust clouds there should be no light at all. Pressure decreases because of slow movement: gravity wins! Fragmentation of a cloud: this simulation begins with a turbulent cloud containing 50 solar masses of gas, initial cloud not uniform (greater densities in some area) If it got a little cooler, the pressure inside would fall and gravity would win ten new star.

Related Questions

Dust in the interstellar medium follows the normal extinction lawR=A/E(B-V)=3.1; however, dust in the immediate locality of an HIIregion may not. The environment around the HII region Sh2-121 isparticularly dusty; Sh2-121 seems to be enveloped by a dust cloudof its own. Three stars are seen ionizing the nebula. The distanceto Sh2-121 is known independent of the stellar information below,at 4.2 kpc from the Sum.

a. What the the average total extinction A toward the start in theHII region?

b. The foreground reddening E(B-V) to the nebula can be estimatedfrom the total hydrogen column density in the ISM towards thenebula, which I have measured for you N(HI+H2)=7.2X10^21 cm^-2.Using the mean ratio of total neutral hydrogen to colour excess inBohlin, Savage & Drake (1978, The Astrophysical Journal, no.224, p. 132) what is the foreground reddening to Sh2-121?

Info.

Star 1, V(mag)=14.91, B-V(mag)=1.86, Sp Type & LC=B0II

Star 2, V(mag)=15.44, B-V(mag)=1.76, Sp Type & LC=O4V

Star 3, V(mag)=15.48, B-V(mag)=1.76, Sp Type & LC=B2II

11. What makes a red giant star so large?
ARed giants are rapidrotators, and centrifugal force pushes thesurface of the staroutwards.
BThe star has many timesmore mass than the Sun.
CThe hydrogen-burningshell is heating the envelope and making itexpand.
DThe helium-rich core hasexpanded, pushing the outer layers of thestar outwards.

12. A red dwarf is a
Ahot and dim mainsequence star.
Bcool and bright mainsequence star.
Chot and bright mainsequence star.
Dcool and dim mainsequence star.

13. Some red dwarfs are fully
Aconductive.
Bconvective.
Cradiative.
Ddevoid of nuclearfusion.

14. Which of the following pieces of information do we NOT needtoinfer the density of a star?
Adistance
Bflux
Ctemperature
Dage
Emass

15. We can measure the age of a planetary nebula by
Adividing thenebula's size by its expansion speed.
Busing the mass-luminosityrelationship for the white dwarf at thecenter.
Cdividing its distance bythe speed of light.
Dlooking at the ages ofstars nearby.

16. The maximum mass of a white dwarf is
A1.4 solar masses andknown as the Oppenheimer-Volkov limit.
B1.4 solar masses andknown as the Chandrasekhar limit.
C3 solar masses and knownas the Oppenheimer-Volkov limit.
D3 solar masses and knownas the Chandrasekhar limit.

17. The interstellar medium is mostly _______ followedby________.
AHydrogen;Helium.
BHelium;Hydrogen.
CCarbon;Hydrogen.
DHydrogen;Carbon.
ECorbon; Oxygen.

18. The interstellar medium has a cool component measuredvia_________ observations and a hot component revealed by________observations.
AX-ray;optical
BX-ray; infrared
CX-ray;gamma-ray
Doptical; X-ray
Einfrared; X-ray

19. The interstellar medium has a cool component which is_______its hot component.
Adenserthan
Bless dense than
Cas dense as

20. Which of the following processes will NOT cause a gas cloudtocollapse?
Aionization fromyoung stars
Bsupernovaexplosions
Cgalacticrotation
Dthe expansion of theUniverse

1. The Jeans instability occurs when
Athe pressure in a gascloud is less than its gravitationalforce.
Bthe pressure in a gascloud is greater than its gravitationalforce.
Cthe temperature in acollapsing cloud is hot enough to fuseHydrogen.
Dthe temperature in acollapsing cloud is hot enough to fuse Helium.

2. At what stage in its life does a star pass through theprotostarphase?
AAfter condensationbut before nuclear reactions begin in itscore.
BWhile it is convertinghydrogen into helium in its core.
CAfter nuclear reactionsend in its core, but before the red giantphase.
DWhen it is expanding insize as a red giant or supergiant.

3. The characteristics of an open cluster of stars are
Aa few hundredmembers, often very young and still embedded in thegas and dustfrom which they were formed.
Bmany thousand members, ofdifferent ages.
Ca few dozen members, theremnant of a globular cluster of starsfrom which most of themembers have escaped.
Dhundreds of thousands ofmembers, all very old, and no or verylittle interstellar gas anddust.

4. What is a protostar?
AA star near the endof its life, before it explodes as asupernova.
BA sphere of gas aftercollapse from an interstellar cloud butbefore nuclear reactionshave begun.
CA small interstellarcloud, before it collapses to become astar.
DA shell of gas left behindfrom the explosion of a star as asupernova.

5. What is an H II region?
AA region of hot,ionized hydrogen around one or more O and Bstars.
BA region of molecularhydrogen inside a giant molecularcloud.
CA region of neutral,atomic hydrogen in interstellar space.
DA region of gas and dustformed by the explosion of a massive star.

6. The total time that the Sun will spend as a main sequencestaris
Aabout 4.5 millionyears.
Bat least 200 billion yearsyears.
Cabout 1 millionyears.
Dabout 10 billionyears.

7. How is a star's lifetime related to its mass?
AThe lifetimes ofstars are too long to measure, so it is not knownhow (or if) theirlifetimes depend on mass.
BA star's lifetime does notdepend on its mass.
CLower-mass stars runthrough their lives faster and have shorterlifetimes.
DHigher-mass stars runthrough their lives faster and have shorterlifetimes.

8. In the Hertzsprung-Russell diagram, how does the position ofatypical star change while it is at the main sequence phase ofitsevolution?
AA star's position onthe main sequence is determined only by itsmass and not its age,and so, stars do not move along the mainsequence duringevolution.
BMassive stars (4 solarmasses) move toward the upper left as theirluminosity increases,while lower-mass stars move toward the lowerright as theirtemperature decreases.
CStars move from upperright to lower left while they are on themain sequence.
DStars move from upper leftto lower right while they are on themain sequence.

9. Why does the core of the Sun contain more helium andlesshydrogen than does the surface of the Sun?
AHelium condenses moreeasily so, when the Sun was forming the corebecame helium-rich;vast quantities of hydrogen were added onlyafter the core becamemassive enough.
BThe hydrogen has beenlifted out of the core by the Sun's magneticfield.
CHelium is heavier thanhydrogen, and has sunk toward the center ina process of chemicaldifferentiation.
DThermonuclear reactionshave converted much of the originalhydrogen in the core intohelium.

10. In terms of nuclear reactions, what is the next stage ofastar's life after the end of hydrogen burning in thecore?
AHydrogen burning ina thin shell around the core.
BHelium burning in thecore.
CCarbon burning.
DDeath (it becomes eithera supernova or a white dwarf).