Recent interferometric surveys of nearby main-sequence stars show a faint but significant near-infrared excess in roughly two dozen systems , i . e. around 10 \mathrm { \% } to 30 \mathrm { \% } of stars surveyed .
This excess is attributed to dust located in the immediate vicinity of the star , the origin of which is highly debated .
We used previously published interferometric observations to constrain the properties and distribution of this hot dust .
Considering both scattered radiation and thermal reemission , we modelled the observed excess in nine of these systems .
We find that grains have to be sufficiently absorbing to be consistent with the observed excess , while dielectric grains with pure silicate compositions fail to reproduce the observations .
The dust should be located within \sim 0.01 - 1 \mathrm { au } from the star depending on its luminosity .
Furthermore , we find a significant trend for the disc radius to increase with the stellar luminosity .
The dust grains are determined to be below 0.2 - 0.5 \mathrm { \text { \textmu } \textrm { m } } , but above 0.02 - 0.15 \mathrm { \text { \textmu } \textrm { m } } in radius .
The dust masses amount to ( 0.2 - 3.5 ) \times 10 ^ { -9 } \mathrm { M _ { \oplus } } .
The near-infrared excess is probably dominated by thermal reemission , though a contribution of scattered light up to 35 \mathrm { \% } can not be completely excluded .
The polarisation degree predicted by our models is always below 5 \mathrm { \% } , and for grains smaller than \sim 0.2 \mathrm { \text { \textmu } \textrm { m } } even below 1 \mathrm { \% } .
We also modelled the observed near-infrared excess of another ten systems with poorer data in the mid-infrared .
The basic results for these systems appear qualitatively similar , yet the constraints on the dust location and the grain sizes are weaker .