Important Notes


As a user, you are responsible for ensuring that the grid on which the radiative transfer is carried out is adequate to resolve density and temperature gradients. In the case of the AnalyticalYSOModel class, Hyperion tries to optimize the gridding of the inner disk to ensure that it is properly resolved, but you still need to ensure that the number of cells you specificy is adequate.

Number of photons

Similarly to the Gridding, you are responsible for choosing an adequate number of photons to carry out the radiative transfer. You can read the Choosing the number of photons wisely page for advice, and this page will be expanded in future, but the best way to ensure that you have enough photons is to check yourself that the results (temperature, images, SEDs) have converged if you increase the number of photons.

Dust and/or Gas?

While Hyperion is a dust continuum radiative transfer code, you should take care when specifying densities, accretion rates, etc. as to whether to include the contribution from gas. The guidelines are as follows:

  • The core Fortran code does not make any assumptions regarding gas - it simply computes optical depths from the densities and opacities provided. Therefore, dust opacities and densities have to be consistent as to whether they are per unit dust mass, or per unit dust+gas mass, and what gas-to-dust ratio they assume.

    For example, if the dust opacities are provided per unit dust mass, then the densities specified in the model should be dust densities. If the dust opacities are provided per unit dust+gas mass, then the densities specified in the model should be dust+gas densities. For the dust models provided in Library of dust models, each dust model explicitly states whether it includes gas in the opacities or not. When setting up your own dust models, you should be aware of whether they are given per unit dust or dust+gas mass and what gas-to-dust ratio was assumed.

  • For the UlrichEnvelope density structure, the infall rate provided is directly related to the density, so that if the dust opacities are per unit dust mass, the infall rate should be the infall rate of dust.

  • For the AlphaDisk density structure, the accretion rate provided does not relate to the density in the model, but it used to add a source of luminosity. Therefore, it should include the total mass of dust+gas regardless of how the opacities are expressed. However, the mass or density of the disk should be given depending on the units of the opacity, as described above.