Vertical soundings of the atmospheric ion production rate have been obtained from Geiger counters integrated with conventional meteorological radiosondes. In launches made from Reading (UK) during 2013–2014, the Regener–Pfotzer ionisation maximum was at an altitude equivalent to a pressure of (63.172.4) hPa, or, expressed in terms of the local air density, (0.10170.005) kg m . The measured ioni...

We analyse the evolution of the fractional ionisation in a steady-state protoplanetary disc over 10 yr. We consider a disc model with a vertical temperature gradient and with gas-grain chemistry including surface reactions. The ionisation due to stellar X-rays, stellar and interstellar UV radiation, cosmic rays and radionuclide decay is taken into account. Using our reduction schemes as a tool ...

In this Letter, we argue that the standard analytical derivations of properties of HII regions, such as the speed, shape and asymptotic position of ionisation fronts require a more precise treatment. These derivations use the on the spot approximation , which in effect ignores the diffuse component of the radiation field. We show that, in fact, HII regions are diffusion dominated. This has as a...

Context. The wings of Balmer lines are often used as effective temperature diagnostics for late-type (F, G, K) stars under the assumption they form in local thermodynamic equilibrium (LTE). Aims. Our goal is to investigate the non-LTE excitation and ionisation of hydrogen and the formation of Balmer lines in late-type stellar atmospheres, to establish if the assumption of LTE is justified. Furt...

This paper considers the chemistry in a protoplanetary accretion disk during the viscous stage. The model calculation extends our previous work by including in the chemical reaction network the ionisation processes due to cosmic rays and especially the ionisation due to the extinct radio-nuclides 26Al and 60Fe which are known to have been present at the time of formation of our own solar system...

1964 B E C K E Y reported about a combined field ionisation/electron impact source1 the commercial version of which is shown in Fig. 1 2. Vhe vapour to be analyzed enters the source via an inlet line. However such inlet is suitable only for sampes of not too low volatility. For the qualitative analysis of organic compounds of very low volatility evaporation out of an oven (direct inet) in the i...

We use velocity map imaging of photoelectrons in coincidence with molecular cations to determine which ionic states are populated via strong field ionisation, and whether the ionisation to excited ionic states proceeds indirectly via the ground ionic state or directly from the neutral. We carry out measurements on a series of molecules that have different energy gaps between the ground ionic st...

We use a combination of analytic and numerical arguments to consider the impact of quasar photo-heating during He II reionisation on the thermal evolution of the intergalactic medium (IGM). We demonstrate that rapid (∆z < 0.1–0.2), strong (∆T > 10 K) photo-heating is difficult to achieve across the entire IGM unless quasar spectra are significantly harder than implied by current observational c...