2006A&A...450.1221B

This paper presents a consistent description of the formation and the subsequent evolution of gaseous planets, with special attention to short-period, low-mass hot-Neptune planets characteristic of µ Ara-like systems. We show that core accretion, including migration and disk evolution, and subsequent evolution, taking irradiation and evaporation into account, provides a viable formation mechanism for this type of strongly irradiated light planets. At an orbital distance due to the incident XUV stellar flux. In order to reach a µ Ara-like mass (∼14M_⊕) after ∼1Gyr, the initial planet mass must range from 166M_⊕ (∼0.52M_J) to about 20M_⊕, for evaporation rates varying by 2 orders of magnitude, which corresponds to 90% to 20% mass loss during evolution. The presence of a core and heavy elements in the envelope affects the structure and the evolution of the planet appreciably and yields ∼8%-9% difference in radius compared to coreless objects of solar composition for Saturn-mass planets. These combinations of evaporation rates and internal compositions translate into different detection probabilities and thus into different statistical distributions for hot-Neptunes and hot-Jupiters. These calculations provide an observable diagnostic, namely a mass-radius-age relationship to distinguish between the present core-accretion-evaporation model and the alternative colliding core scenario for the formation of hot-Neptunes.