Quiz #5 There are two stars, star A and star B. Star A is approaching the Earth at 100 km/s and Star B is moving away from the Earth at 200 km/s. Compare the Doppler shift for these two stars by explaining how the spectra will be shifted and by how much. (I am not looking for a number here, just a qualitative comparison)

BUT, what happens when atoms, with electrons attached, are packed really close together? The electrons from the neighboring atoms can have a small effect on the standing wave of each of the atom’s electrons.

In a supergiant star (luminosity class I) the star has a huge volume In a supergiant star (luminosity class I) the star has a huge volume. That means the atoms are not close to each other near the surface. They have virtually no effect on the given energy levels. In a giant star (luminosity class III) the star has a large radius but not as large as the supergiant. The atoms near the surface interact more with each other. In a main-sequence star (luminosity class V) the radius is much smaller and atoms are packed closely together near the surface.

Luminosity classes in stars.

The amount of pressure broadening is related to the radius of the star The amount of pressure broadening is related to the radius of the star. When the pressure is high, (luminosity class V) the pressure broadening is large and the radius of the star is small. When the pressure is low (luminosity class I) the broadening is small and the radius of the star is big. We can calculate the radius of the star in this fashion.

How do we now find the distance? We can calculate it from B = σT4(R2)/d2 Here is a visual example of how it works. We know the properties of the H-R diagram for the near by stars.

NGC 3370 Spiral Galaxy

Galaxies currently produce stars In order for stars to form, gas and dust has to be compressed to densities greater than 10 times the normal density in a gas cloud. This happens in the spiral arms of galaxies where the density is higher. Once the density is high enough, gravity can begin to collapse the cloud.

M 51 The Whirlpool Galaxy

The interstellar medium (ISM) The ISM contains both gas and dust. Dust are small grains, about the size of cigarette smoke particles. The gas is mostly hydrogen. When hydrogen atoms are close together they usually form a diatomic molecule, H2 Density of atoms in ISM ~ 1 atom/cm3 In molecular clouds density ~ 10 atoms/cm3 In the air around us density ~ 1 x 1021 atoms/cm3

NGC 6357 D = 8000 light years

Sharpless 171 D=3000 light years

Center of M8 – Lagoon Nebula

Eagle Nebula (M 16) Already formed star cluster Star formation Molecular cloud

Infrared Observations show dust which is warm and glowing Infrared Observations show dust which is warm and glowing. Large area is the Orion molecular cloud

Proto-stars with tails. The tails point away from Trapezium.

Debris disk around young star

Stellar Wind and Radiation pressure Stellar wind is comprised of charged particles which are shot out of a star and move with very high speeds out into space When stellar wind particles hit gas outside the star, it causes the gas move rapidly away from the star. Radiation (light) being emitted by stars can also effect material outside of a star. When dust absorbs the light, dust particles respond by moving away from the star.

Proto-planetary Survivors

New star in the vicinity of a high mass O-star.

The same effect occurs with comets and our Sun

Gas tail Dust tail

When the comet leaves the Sun, will it look like this…. 1)

Or this? 2)

Please make your selection... 30 30 Choice One Choice Two 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

It’s this one 2)

In the vacuum of space the only thing pushing on the tail is the solar wind and the light coming from the Sun. The tail has to always point away from the Sun, regardless of how the comet moving.

Star pushing back with its own, weaker wind Direction of intense light and stellar wind from high mass stars

Eagle Nebula (M 16)

Self-sustained star formation Very massive O-type stars and drive away all the gas and dust near them. When the material collides with other gas and dust in the molecular cloud, the gas and dust becomes compressed and new star formation begins. This is why most star forming regions have stars forming, and nearby a cluster of stars with hot O- stars that are driving the new formation.

Perseus Double Cluster

This is also why, not all of the star forming regions in a galaxy are found in the spiral arms. Some are in between the spiral arms. Because of self-sustained star formation.

M 51 The Whirlpool Galaxy