Intro to Astronomy - Prof. Duffin - Midterm II Review

What could happen after a low mass star becomes a white dwarf?

1. can simply fizzle out and get cooler
2. "nova, nova, nova": material gets sucked from the red giant and infills into the accretion disk resulting in a small carbon detonation
3. can become a Type I supernova with a close and massive neighbor

Type 1 Supernova

a fast, massive transfer of material from a red giant leading to carbon detonation and explosions

Why does a sun-like star stop expanding?

Because when the core reaches 100 million K a helium flash occurs, helium to carbon fusion begins, and the star only shrinks after

What wavelength of hydrogen is used to see sunspots?

H-alpha (the strongest wavelength)

What is the spectral class of the sun?

G2

solar constant

1.4 kw/m^2 or 1400 J/s/m^2

Dimensions of the Sun

Core: r = 200 million km
Radiation Zone: r = 300 million km
Convection Zone: r = 200 million km
Photosphere: n/a
Corona: n/a

Temperatures of the Sun

Core: T = 15 million K
Radiation Zone: n/a
Convection Zone: n/a
Photosphere: T = 6,000 K
Corona: T = 1-2 million K

solar cycle

the 11 year period where the regions of magnetic polarity get a different charge; creates the butterfly pattern

butterfly pattern

the pattern created when sunspot pairs move towards the equator while their polarity regions do the same; over time more pairs are created and each pair lasts 3 cycles

solar maximum

the month and year where the sun has the most amount of sun spots during a solar cycle

solar minimum

the month and year where the sun has the least amount of sun spots during a solar cycle

Helium to Hydrogen Fusion

Input: 4 hydrogen
Output: 1 helium, 2 neutrinos, 1 gamma ray

How to Tell Where a Sunspot Event Occurs

split the sun into degrees (counter-clockwise: O° at N, 90° at E, 180° at S, 360° at W) and use Universal Standard Time (UT/UST) and radius; ex: "event happened at 90° and .45 solar radii at 05:00 UT"

How long does the sun take to rotate?

26 days

How many times does the sun rotate in one Earth year?

12 times

granulation

when small sells push (convect) plasma, and therefore heat, out of and back into the sun's photosphere from the convection zone

coronal holes

the source of solar wind through open field lines; winds are 400 km/s at the equator and 800 km/s at the poles

coronograph

a regular camera with a dark disk in front so that the disk of the sun is blocked and you can see sun's corona (atmosphere)

sunspots

seen in H-alpha wavelengths; they are the footprints of coronal loops

coronal loop

a thick bundle of magnetic field lines that is in a ring-like shape and goes from the convection zone up through the photosphere; we see plasma running up and down through field lines; can become a coronal mass ejection (CME)

coronal mass ejection (CME)

when a coronal loop accelerates out from the sun's interior making the tension too strong when at a point the plasma cuts off

Two Main Solar Events

1. from the whole disk: Solare Flares
2. from the limb: Coronal Mass Ejections (CME)

solar flare

when radiation is emitted from the sun in large quantities; higher mass particles are damaging to humans and electronics

hydrostatic equilibrium

when a star's radiation pressure is equal to the pressure of its gravity

parallax

an measure to help find the distance of a star from earth or from the sun; D(in parsecs) = 1 / parallax angle (in arc seconds)

parallax example

parallax angle = 0.05° --> 1 / 0.05° = 20 parsecs

absolute luminosity

luminosity at 10 parsecs as shown on the HR diagram

apparent luminosity

luminosity measured from Earth

Distance of 1 Parsec

1 parsec = 3.26 light years

What is the nearest star to us?

Proxima Centauri, at 1.3 parsecs away (4.2 light years)

blackbody curve

shows how much of each wavelength of light an object produces

Inverse Square Law

I(N) = I(1)/N^2

Inverse Square Law Example

"intensity at 10 parsecs is 100 solar luminosities, what is the intensity at 50 parsecs?"

I(1) = 100, N = 5 (50 is 5x more than 10) --> I = 100 / 5^2 = 4 solar lum.

spectroscopic parallax

method of finding the distance to a star

1. look at absorption spectra to determine spectral class and luminosity class; the elemental content determines spectral class and the thickness of lines determines luminosity class (big line = little star and vice versa)
2. look at place on HR diagram and read off absolute luminosity
3. measure apparent luminosity from Earth
4. use inverse square law to determine distance

Star Evolution Process

MS to RG: helium ash compacts as the hydrogen shell burns and
H-->He fusion begins. The temperature increases to 100 million K so the star expands to release heat and He-->C fusion begins after a helium flash
RG to HB: the star shrinks until radiation pressure is equal to gravity and the temperature of the core is 250 million K
HB to SRG: carbon ash compacts as density, T(core), and R(star) increase while the R(core) decreases
SRG to PN: the He and H shell burns and when R(star) = 500 solar radii the star's atmosphere moves away
PN to WD: the core becomes C and O while T(surface) increases and L(star) decreases, becoming a white dwarf

Is the mass of the average star smaller than that of our sun?

Yes

open cluster

a cluster of younger, blue and white colored stars formed in the spiral arm of galaxies with many other smaller, unseen stars in the cluster

globular cluster

a cluster of mostly older, mostly red and white stars located in random orbits in the halo of a galaxy (ex: Pleides)

dark cloud

the dark cloud of gas and dust where star formation occurs

emissions nebula

appear red/orange in color; found near stars emitting lines of hydrogen (i.e. strong radiation) in the dust lanes (regions of more dust where stars form); key: red = hydrogen and star formation

reflections nebula

appear blue/white in color; close-by starlight reflects off the dark cloud; key: blue = helium and light reflection