Radionuclide Ionization in Protoplanetary Disks: Calculations of Decay Product Radiative Transfer
Aug 30, 20136 pages
Published in:
- Astrophys.J. 777 (2013) 28
- Published: Oct 10, 2013
e-Print:
- 1309.0018 [astro-ph.SR]
View in:
Citations per year
Abstract: (IOP)
We present simple analytic solutions for the ionization rate ζSLR arising from the decay of short-lived radionuclides (SLRs) within protoplanetary disks. We solve the radiative transfer problem for the decay products within the disk, and thereby allow for the loss of radiation at low disk surface densities; energy loss becomes important outside R 30 AU for typical disk masses Mg= 0.04 M☉. Previous studies of chemistry/physics in these disks have neglected the impact of ionization by SLRs, and often consider only cosmic rays (CRs), because of the high CR-rate present in the interstellar medium. However, recent work suggests that the flux of CRs present in the circumstellar environment could be substantially reduced by relatively modest stellar winds, resulting in severely modulated CR ionization rates, ζCR, equal to or substantially below that of SLRs (ζSLR 10–18 s–1). We compute the net ionizing particle fluxes and corresponding ionization rates as a function of position within the disk for a variety of disk models. The resulting expressions are especially simple for the case of vertically Gaussian disks (frequently assumed in the literature). Finally, we provide a power-law fit to the ionization rate in the midplane as a function of gas disk surface density and time. Depending on location in the disk, the ionization rates by SLRs are typically in the range ζSLR ~ (1-10) × 10–19 s–1.Note:
- 7 pages, 4 figures, accepted to ApJ
- stars: pre-main sequence
- radiative transfer
- circumstellar matter
- accretion, accretion disks
References(27)
Figures(4)