BEXCO - Room F(201/202/203/204)
[SH155] The ionising effect of low energy protostellar cosmic rays in protoplanetary disks
- Donna RODGERS-LEE
- Donna RODGERS-LEE (University of Hertfordshire, UK; Dublin Institute for Advanced Studies, Ireland)
Young low-mass stars are typically more magnetically active than our Sun making it reasonable to assume that they accelerate particles to energies of ~GeV, as the Sun itself is an effective MeV accelerator. These low energy cosmic rays may prove to be an important source of ionisation for the very weakly ionised protoplanetary disks surrounding young stars. If angular momentum transport in these disks is mediated by magnetic fields then the ionisation rate in the disk is one of the most important quantities to consider. Until recently it had been assumed that the dominant sources of ionisation for these systems were stellar X-rays and galactic cosmic rays. As pointed out by Cleeves et al. (2013), since the Sun's heliosphere shields us from galactic cosmic rays out to ~100au, the protostellar analogue of the heliopshere could potentially suppress galactic cosmic rays out to ~1000au thus eliminating an important source of ionisation from the protoplanetary disk. Here, based on the assumption that young low-mass stars accelerate protons to ~GeV, we estimate the ionising effect of these low energy stellar cosmic rays in protoplanetary disks. We solve their transport equation by treating the propagation of the cosmic rays as diffusive. We will present our results which investigate the influence of a number of parameters, such as the diffusion coefficient of the cosmic rays, the mass density profile of the disk and the energy of the protostellar cosmic rays on the resulting ionisation rate. We compare the ionisation rate from the cosmic rays with that expected from stellar X-rays. We find that, generally, the high mass density in the inner region of the protoplanetary disk prevents the cosmic rays from significantly ionising the outer regions of the disk at the midplane. We discuss further ways of investigating the ionising effect from low energy protostellar cosmic rays.