Glossary

• Luminosity

  • Unit: Joules/Second (or Watts)
  • Amount of energy released by a star per unit time. Often expressed in units of the sun, which has luminosity 3.846×1e26 J/S.
  • Celeste model:
    • this value, along with temperature, enter into the likelihood function to determine band specific flux values that are then convolved with a point spread function.
    • 'brightness' of a star = b(\ell_s, d_s) = c_L ell_s / d_s^2.
      • \ell_s: luminosity of source s
      • d_s^2 : squared distance to source
      • c_L = .25 * .75 * 1.25^2 meters^2 (area of lens) * 54 seconds (length of exposure)
      • "the amount of energy entering the telescope during an exposure"
  • Can be inferred by:
    • Size and effective temperature:
    • Brightness and distance:

• Spectrum

  • The stars in the SDSS catalog will come with a graph of its spectrum.
  • Roughly, for an ideal black body, we can get a ballpark for it's temperature by using Wien's Approximation, which states

  T_effective = 2.9e-3 / lambda_max (Kelvin)

  Where 2.9e-3 is a constant (meters * kelvin), and lambda_max is the maximizing value of that star's spectral density (in meters). For example, our sun's spectrum peaks at around lambda_max = 500 nanometers (green). We can get a rough estimate of it's effective temperature as T_eff = 2.9e-3 / 500e-9 = 5795.5 Kelvin (actually 5778, so pretty close).