Stars

Question 1

What is Pogson’s relation?

Answer 1

ratio of power 2.5logf1/f2=m2-m1

Question 2

What is apparent brightness related to?

Answer 2

Vega. It’s apparent magnitude is 0.

Question 3

How do you find absolute magnitude?

Answer 3

Apparent brightness depends on luminosity and distance. A reference distance of 10pc is used to find the absolute magnitude. m-M=5logd-5

Question 4

How are the colours of stars measured?

Answer 4

The flux in a blue band and a visible band are measured.
If the mB>mV then the star is red, as the spectrum is shifted more to the red end.
If mB<mV then the star is blue.
The magnitude is relative to Vega which is zero magnitudes in all wavelengths.

Question 5

How do absorption lines arise?

Answer 5

When a hot source is viewed through a cool gas, the cool gas absorbs photons with energy equal to the electronic transitions. When these photons are released, they are released in all directions.

Question 6

What is the Balmer series?

Answer 6

It is the electronic transition between n=2 energy level and above. The H(alpha) line is between n=2 and n=3.

Question 7

What does absorption line strength depend on?

Answer 7

Temperature, density of gas, abundance - number of particles in the lower state.
The strength of particular transitions- atomic physics

Question 8

How does temperature effect absorption line strength?

Answer 8

The distribution of populations among energy levels in an atom depends on temperature. In higher temperatures, electrons populate higher energy levels or can be ionized completely. An absorption line for a species will have a maximum strength at a particular temperature. At lower temperatures, most species will be in the ground state. At higher temperatures most species will be ionized, which have another spectra.

Question 9

How are stars temperatures classified?

Answer 9

OBAFGKM

O is hot young stars, and M is cool stars. The sun is G2.

Question 10

How are stars luminosity classified?

Answer 10

More luminous stars with the same temperature must be larger, so density will be lower. Lower density causes the spectral lines to be thinner, due to less collisions with atoms.
Roman numerals are used. The larger the number, the smaller the star.

Question 11

Where are the locations of star types on the HR diagram?

Answer 11

Main sequence is on a curve. Red giants are above the curve. Supergiants are at the top. White dwarfs mirror the main sequence curve below it.

Question 12

What is the mass luminosity relationship in main sequence stars?

Answer 12

L is proportional to M. l=M^3.3

Question 13

What is the range of main sequence stars?

Answer 13

0.08 solar masses. Below that, it will not burn hydrogen.

100 solar masses. Above that radiation pressure will blow the star apart.

Question 14

What is the lifetime - mass relationship in main sequence stars?

Answer 14

Lifetime = energy/luminosity. Energy is proportional to mass. Luminosity is proportional to M^3.3 so lifetime = M^-2.3

Question 15

How do low mass stars develop?

Answer 15

Evolve into red giant, and then eject their outer layers as planetary nebulae leaving behind a white dwarf

Question 16

How do high mass stars develop?

Answer 16

Evolve into supergiants, then explode as a supernovae leaving behind a neutron star or blackhole.

Question 17

What is a star cluster?

Answer 17

A collection of stars concentrated in space that formed at the same time, out of the same cloud.

Question 18

What is an open cluster?

Answer 18

1000 members. Not gravitationally bound, found in the spiral arms. Consist of young, hot, blue MS stars.
The colour magnitude diagram, is between 0-10 magnitudes, and 0-1 B-V and a smooth curve.

Question 19

What is a globular cluster?

Answer 19

10^5 stars, gravitationally bound, found in the galactic halo, made of old, cool red stars.
The colour magnitude diagram, is between 10-20 magnitudes and colour between .5-1.

Question 20

Why are population 1 stars more metal rich?

Answer 20

The first stars were made of material from the big bang. As the hydrogen underwent nucleosynthesis in the stars, more metals were created, which were returned to the interstellar medium through planetary nebulae and supernovae explosions. Therefore successive generations become progressively more enriched in heavy elements.

Question 21

What are the features of a population 1 star?

Answer 21

Young (less than a billion years), very large, metal rich, from recent star formation, spiral arms, new generation stars

Question 22

What are the features of a population 2 star?

Answer 22

Older than a billion years, metal poor, no star formation for a long time eg globular clusters

Question 23

How is stellar mass determined?

Answer 23

Using a binary system. Circular motion is equated to gravitational force, and centre of mass is used.

Question 24

How can Keplers third law be applied to binary stars?

Answer 24

period^2 x(mass of two stars/solar mass)= distance between stars in au ^3

Question 25

What are real orbits like?

Answer 25

Elliptical

Question 26

What is orbital inclination?

Answer 26

The orbital plane of a binary system will be inclined at an angle i

Question 27

What are visual binaries?

Answer 27

Where the two stars are spatially resolves in the sky and orbit around each other

Question 28

What are spectroscopic binaries?

Answer 28

When the stars are not spatially resolved, but orbital motion is revealed through periodic doppler shifts in spectral lines

Question 29

How is mass determined from visual binaries?

Answer 29

The angle from the centre of mass to the stars can be determined.

Question 30

How is mass determined from double lined spectroscopic binaries?

Answer 30

The radial velocity of the stars are used.

Question 31

How is mass determined from single lined binaries?

Answer 31

The velocity of one star is assumed to be unknown so it is eliminated. The mass of one star is estimated to limit the mass of the other star.