Exam 3 Chap 17-23 short study

The most common kinds of stars in the Galaxy have low luminosity compared to the Sun

most are faint low-mass red dwarfs

Astronomers identify the main sequence with what activity

hydrogen fusion in the core

In an H-R diagram where is spectral type shown

along the bottom horizontal axis

Star B is 3× farther than A with same luminosity

nine times fainter

A star moving toward the Sun will show

blueshift in spectral lines

Why astronomers prefer luminosity over brightness

it shows true energy output independent of distance

Why distant stars can look bright

they are intrinsically very luminous

A star that looks dim could be

far away low luminosity or obscured

Which color star is hottest

blue-violet

High luminosity but low temperature means

very large star

How far away is a star with parallax 0.2 arcsec

5 parsecs

Distance to M31 method

Cepheid period-luminosity relation

Why parallax wasn’t measured until 1838

shift too small to detect

Hotter interstellar cloud means

lower density

How fragile molecules survive

in dense dust clouds

Why some interstellar gas is very hot

shock waves from supernovae

Which property requires distance

luminosity

Parallax baseline

half Earth’s orbital diameter

Why some spectral lines don’t shift

from interstellar matter

Interstellar dust consists of

tiny solid grains

What determines a star’s position on the main sequence

its mass

First exoplanet detection method

Doppler shift method

Habitable zone of Proxima Centauri

closer to the star

The Orion Nebula is

a star-forming cloud of gas and dust

Telescope that found many planets

Kepler mission

Why Kepler missed small planets

dips too small to detect

Hotter star same luminosity moves

left on H-R diagram

First exoplanet surprise

very close 4-day orbit

Evidence of planet formation

gaps in dust disks

Planets in habitable zone

allow liquid water

Indicator of a cluster’s age

main-sequence turnoff point

Event that begins giant phase

core hydrogen runs out

Massive stars differ because

fuse heavier elements

Why Sun-like stars can’t fuse heavier elements

not hot enough

Why hydrogen shell fusion begins

core contraction heats outer layers

Cluster with old stars

globular cluster

Distribution of globular clusters

spherical halo

Where heavy elements form

in massive stars

First generation stars

little or no heavy elements

Stars that live longest

low-mass (K-type)

White dwarf vs main sequence same mass

smaller diameter

Why no recent Milky Way supernova seen

dust blocks light

Elements heavier than iron form in

supernova explosions

Most stable nucleus

iron

Why novae repeat

accretion from companion star

Fate of a Sun-like star

white dwarf

Why white dwarfs appear early

evolved from massive stars

Best wavelength for dusty regions

infrared

Density of a neutron star

like atomic nucleus

Crab Nebula motion measured by

Doppler shift

What is a selection effect

bright distant stars dominate observations

Visual vs spectroscopic binary

seen directly vs detected by Doppler shifts

How Kepler’s third law is used

finds total mass from orbit

Methods to measure star diameter

occultation or eclipsing binaries

What are brown dwarfs

too low mass for sustained fusion

Mass-luminosity relation

luminosity proportional to mass⁴

H-R diagram axes

luminosity up temperature left

Main sequence description

hydrogen fusion band set by mass

White dwarf location and traits

hot dim small dense lower left

What 90% on main sequence implies

stars spend most of life there