PX282 - A3 - luminosity and flux

see PX158 - D1 - luminosity and flux
physical properties of a star:
- fundamental premises: mass, radius, temperature, luminosity
- observable quantities: magnitude/brightness, colour/spectrum

luminosity, $L$

it is the energy transfer/total energy emitted by an object
units: $[J s^{- 1}]$

flux, $F$

note:
- $F$ is flux on the surface of star
- $f$ is flux at a distance, $d$ /the observed flux
it is the energy emitted per unit area/energy flux through a 3D surface
units: $[J s^{- 1} m^{- 2}]$
luminosity can be written as:

L = 4 π R_{*}^{2} F

where, both $L$ and $F$ are across all $λ$

at a distance, $d$ , the flux is given by:

f = \frac{L}{4 π d^{2}} = F {(\frac{R}{d})}^{2}

for the sun, $f = 1370 J s^{- 1} m^{- 2}$ , $d = 1 A U$ , $R_{⊙} = 7 \times 10^{8} m$
- $F = 6.3 \times 10^{7} J s^{- 1} m^{- 2}$
- $L = 3.9 \times 10^{26} J s^{- 1}$
$d$ is very important as it gives information about:
- where stars are
- how bright stars intrinsically are