STELLAR
PROPERTIES
|
What do we want to know? |
Method used to determine the desired quantity |
What do we have to know? |
Equations |
|
How far away is it? Distance d (measured from
the Sun) |
(1)
parallax (nearby stars) (2)
standard candle (distant stars) |
(1)
parallax angle, baseline (2)
luminosity L, apparent brightness B |
|
|
What is its intrinsic brightness? Luminosity
L |
(1)
inverse square law for light (2)
spectral class |
(1)
apparent brightness B and distance d (2)
spectrum |
|
|
How hot is it? Temperature
T |
(1)
Wien’s law (2)
spectral class |
(1)
color (peak wavelength) (2)
spectrum |
|
|
What is its mass? Mass
M |
(1)
Kepler’s third law (2)
Mass-luminosity relation (main sequence stars) |
(1)
distance and period of a binary system (2)
spectrum and luminosity |
|
|
What is its radius? Radius
R |
(1)
Stefan-Boltzman Law (2)
Eclipsing binary |
(1)
Color (= temperature) (2)
binary revolving edge-on to our line-of-sight |
|
|
What is it made out of? Chemical
composition |
(a) atmosphere deduced from spectral analysis (b) total composition deduced from density |
(a) spectrum (b) mass, diameter |
|
|
How long will it last as a “normal” (main sequence) star? Projected
lifetime TL |
Rate
of fuel consumption (H ® He) and fuel (H)
available in the core |
Mass
(for a main sequence star mass is related to luminosity) |
|
