Birth and fate of hot-Neptune planets

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摘要：

This paper presents a consistent description of the formation and thesubsequent evolution of gaseous planets, with special attention toshort-period, low-mass hot-Neptune planets characteristic of $\mu$ Ara-likesystems. We show that core accretion including migration and disk evolution andsubsequent evolution taking into account irradiation and evaporation provide aviable formation mechanism for this type of strongly irradiated light planets.At an orbital distance $a \simeq$ 0.1 AU, this revised core accretion modelleads to the formation of planets with total masses ranging from $\sim$ 14$\mearth$ (0.044 $\mjup$) to $\sim$ 400 $\mearth$ (1.25 $\mjup$). The newlyborn planets have a dense core of $\sim$ 6 $\mearth$, independent of the totalmass, and heavy element enrichments in the envelope, $M_{\rm Z,env}/M_{\rm env}$, varying from 10% to 80% from the largest to the smallest planets. We examinethe dependence of the evolution of the born planet on the evaporation rate dueto the incident XUV stellar flux. In order to reach a $\mu$ Ara-like mass($\sim$ 14 $\mearth$) after $\sim $ 1 Gyr, the initial planet mass must rangefrom 166 $\mearth$ ($\sim$ 0.52 $\mjup$) to about 20 $\mearth$, for evaporationrates varying by 2 orders of magnitude, corresponding to 90% to 20% mass lossduring evolution. The presence of a core and heavy elements in the envelopeaffects appreciably the structure and the evolution of the planet and yields$\sim 8%-9%$ difference in radius compared to coreless objects of solarcomposition for Saturn-mass planets. These combinations of evaporation ratesand internal compositions translate into different detection probabilities, andthus different statistical distributions for hot-Neptunes and hot-Jupiters.

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关键词：

planetary systems : formation stars : individual : mu Ara

DOI：

10.1051/0004-6361:20054040

被引量：

152

年份：

2005