Channel 1 and 2 Flashcards
What is stellar structure?
core - radiation zone - convection zone
What can we observe from nearby stars?
temperature and brightness
What can we observe from binary systems?
mass of a star
What does a colour-magnitude diagram measure?
The apparent brightness of stars in two different wavebands e.g B-lue and V-isual
The difference is a measure of colour and surface temperature.
What happens to apparent brightness if stars are at the same distance?
It is a measure of intrinsic brightness
What is a star cluster?
A group of stars bound together by gravity and formed out of the same material and at the same time
What are galactic or open clusters?
they are not well defined
distance to them is not well known
blue stars
What are globular clusters?
well defined
distance known reasonably well
crowded
yellow stars
What are extragalactic clusters?
distance well known
unresolved
How much is 1 mili arcsec?
1/1000 arcsec
How much is 1 arcsec?
1/3600 degrees
How can the position of a star be measured?
By looking at the declination and right ascension of the star (both in miliarcsecs)
What is the parallax of an object used to approximate?
The distance to an object
What is the equation for parallax?
D = 1/p (p = parallax angle observed and D is actual distance measured in parsecs)
What is a parsec?
The distance at which an object has a parallax of 1 arcsecond
What is luminosity?
The total power integrated over all wavelengths
What is flux?
Energy crossed unit area per unit time integrated over all wavelengths arriving at Earth
(Jm-2s-1 or Wm-2)
How is the effective temperature of a star measured?
Directly from analysis of stellar spectrum
What is the mass luminosity relationship?
L is proportional to M to the power 3.3
How much hydrogen does a star which is 10x as massive as the Sun burn?
How quickly does it use up its fuel?
10x as much
as it is 10^3.3 times brighter, 10^3.3/10 = 200 times more quickly
What the relationship between time and Mass?
t is proportional to M^-2.3
Where do most stars lie on a CMD/HR diagram?
Most stars are on the MS
Which characteristics do more massive stars have?
Brighter, bluer and have shorter lives
What is the CMD/HR diagram?
The prime medium through which stellar evolution models are compared with observations
What do clusters with short lived bright blue stars lack?
They have very few red giants
What do clusters with many red giants lack?
They have no short-lived blue MS stars
If we look at stellar clusters what do they show us?
Clues to stellar evolution
Which assumptions are made about stars in order to study their structure?
STEADY STATE
equilibrium and not changing with time
SPHERICAL GEOMETRY
all variables are function of r only, rotational forces negligible, no magnetic forces
INITIAL COMPOSITION IS HOMOGENEOUS
What affects the expected lifetime of a star?
Gravitational potential energy
(millions of years)
Chemical energy
(thousands of years)
Nuclear fusion of light elements
(billions of years)
How much mass of a star has conditions that allow nuclear burning?
typically 10% of mass
In a fusion reaction of H into He, how much of the mass if converted into energy?
0.7%
What is a nuclear timescale?
Nuclear energy available divided by luminosity
What is a thermal timescale?
The energy released is due to gravitational contraction
The thermal timescale is then the gravitational potential energy divided by luminosity
What happens at several times in evolution?
star pressure-gravity imbalance occurs
Which timescale dominates evolution of a star?
Nuclear timescale
