Astronomy Midterm 2

Front 1

Kirchoff's Laws of Spectroscopy

Back 1

1. hot solid or hot, dense gas produces an emission-line spectrum (rainbow)

2. a hot, low-density gas produces an emission-line spectrum (black w/ color lines)

3. a continuous spectrum viewed through a cool gas produces an absorption-line spectrum (rainbow w/ black lines)

Front 2

continuous blackbody spectrum

Back 2

emitted by a hot solid or hot, dense gas

Front 3

emission-line spectrum

Back 3

produced by hot, low-density gas

Front 4

absorption-line spectrum

Back 4

continuous spectrum viewed through cool gas

Front 5

distance ladder

Back 5

find distances of stars

using radar or parallaxes

Front 6

closer stars have _____ parallax angles

Back 6

larger

Front 7

further stars have _____ angles

Back 7

smaller

Front 8

limitations of parallax methods:

Back 8

hard to measure stars when they are far away

Front 9

luminosity

Back 9

rate at which a light source emits energy

-use apparent brightness to measure

B = L/4(pi)d^2

L = 4(pi)R^2(theta)T^4

Front 10

stellar spectra

Back 10

the hot, dense photosphere at a star is surrounded by a thin, slightly cooler atmosphere

Front 11

OBAFGKML

Back 11

spectra determined by temperature, O is hottest, L is coolest

Front 12

HR Diagram

Back 12

luminosity v temperature

Front 13

Main Sequence

Back 13

where ~85% of stars lie;

3000K - 50,000K

the Sun is a MS star

Front 14

giant

Back 14

brighter than MS stars of same temp, have larger R;

Front 15

supergiants

Back 15

top of the HR diagram

Front 16

white dwarfs

Back 16

fainter than MS of same temp, smaller R; bottom right corner of HR

Front 17

4 physical parameters

Back 17

luminosity (L): derived from App Brightness and Distance

temperature (T): color of spectrum

mass (M): measure for binary stars using Newton's version of Kepler's 3rd Law

radius (R): direct imaging for giants and SG or other methods (eclipse)

Front 18

what keeps stars from flying apart?

Back 18

gravity

Front 19

when a star contracts, the radius goes down and the star becomes more ___ bound?

Back 19

gravitationally

Front 20

hydrostatic equilibrium

Back 20

the balance between gravity and pressure

results in core/envelope structure

Front 21

the lifetime of a star equation:

Back 21

internal energy / luminosity

Front 22

energy sources:

Back 22

chemical, gravitational, nuclear

Front 23

chemical energy:

Back 23

burning by oxidation, muscle power

Front 24

gravitational energy:

Back 24

water running downhill, heat from meteorite impacts

Front 25

nuclear energy:

Back 25

fusion of H into Helium

sun powered primarily by Proton-Proton chain nuclear fusion reaction

Front 26

Kelvin-Holmes Mechanism:

Back 26

way to use gravitational binding energy to power the Sun

chemical and gravitational energy not enough to power the sun

Front 27

nuclear fusion happens two ways:

Back 27

1. P-P chain: low core, low temp; 4 H --> 1 He

2. CNO cycle: high core, high temp; C acts as a catalyst to fuse 4 H into 1 He nucleus w/ N and O as intermediate products

Front 28

Hydrostatic thermostat:

Back 28

controls nuclear fusion in stellar cores

Front 29

if fusion is too fast:

Back 29

core heats, increase pressure, core expands, core cools, and fusion slows

Front 30

energy is transported to the surface 3 ways:

Back 30

1. radiation: energy carried by photons

2. convection: when hot buoyant gas rises faster than it can radiate its heat away

3. conduction: when heat is transported from atom-to-atom in a dense medium

Front 31

thermal equilibrium

Back 31

occurs when energy generation is balanced by the transport of the energy to the surface to be radiated away

Front 32

red dwarfs

Back 32

lowest mass in MS, fully convective; p-p chain

Front 33

lower MS

Back 33

have radiative cores and collective envelopes; p-p chain

Front 34

upper MS

Back 34

convective cores and radiative envelopes; CNO cycle

Front 35

thermal equilibrium

Back 35

energy generation = luminosity

Front 36

low mass MS

Back 36

burns fuel slow so should last a long time (civic)

Front 37

high mass MS

Back 37

burns fuel quickly so should leave MS in shorter time (Jeepy)

Front 38

3 stages of formation:

Back 38

1. protostar phase: built up mass by accretion (hydrostatic eq)

2. pre-main sequence phase: energy from gravitational contraction (thermal eq)

3. zero-age main sequence: energy from core H fusion (Hydrostatic and Thermal Eq)

Front 39

GMC

Back 39

giant, cold interstellar clouds of molecular hydrogen (H2)

supported by internal gas pressure, weak magnetic fields and gas motion

Front 40

how to trigger a collapse of GMC:

Back 40

1. cloud-cloud collision

2. shocks from nearby supernova explosions

3. passage through a spiral arm of the galaxy

Front 41

low-mass star evolution

Back 41

Pre-MS, MS, RG, HB, AG, WD

Front 42

Pre-MS energy source (LM)

Back 42

gravity

Front 43

MS energy source (LM)

Back 43

core H fusion

Front 44

RG energy source (LM)

Back 44

shell H fusion

Front 45

HB energy source (LM)

Back 45

He core and H shell fusion

Front 46

AG energy source (LM)

Back 46

He shell and H core fusion

Front 47

WD energy source (LM)

Back 47

residual internal heat

Front 48

white dwarf

Back 48

remnants of a low-mass star

C-O WD or O-Ne-Mg WD

Front 49

white dwarf thermonuclear supernovae

Back 49

when the mass of a white dwarf exceeds 1.44, electron degeneracy fails and WD collapses and explodes as supernova

Front 50

how WD exceeds 1.44?

Back 50

1. binary accretion: WD gets matter from donor

2. double WD merger: double WD close binary and they converge -- BOOM too heavy

Front 51

neutron stars

Back 51

collapsed cores left after core collapsed supernova of massive stars

Front 52

pulsars

Back 52

pulsating radio sources

Front 53

black hole

Back 53

when a neutron star collapses, the remnant core becomes a black hole! a BH is the most extreme object, super strong gravity

Front 54

event horizon

Back 54

point of no return for objects near the black hole

Front 55

gravitational lensing

Back 55

bent light because of strong gravitational field of black hole

Front 56

continuous blackbody spectrum

Back 56

hot, dense gas

Front 57

star clusters

Back 57

groups of stars moving together through space; share common properties (distance, age, etc)

Front 58

open clusters

Back 58

space clusters containing 100s to 1000s of stars

many hot, blue MS stars

Front 59

globular clusters

Back 59

rich spherical clusters w/ 10^5 or 10^6 stars

many red giants, no blue, hot MS