Thermal desorption of Na in meteoroids - Dependence on perihelion distance of meteor showers

Context. The observed sodium abundance of meteoroids in meteor showers might differ from the original abundance because of processing in interplanetary space after ejections from their parent bodies. Among various processes, thermal alteration of alkali silicate is most likely the major process of Na depletion. Aims. We clarify at which perihelion distances the thermal desorption alters the Na content of meteoroids that are observed as meteor showers. Methods. We compile Na abundances of meteoroids in meteor showers at each perihelion distance and compare them to the sublimation temperatures of alkali silicates. Results. Na abundances of meteoroids do not depend on their perihelion distances at 0.14 <= q <= 0.99AU. No Na depletion in these distances constrains the temperature of meteoroids at q = 0.14AU to be lower than the sublimation temperature of alkali silicates similar to 900 K. Conclusions. Meteoroid particles are characterized as large, compact, blackbody-like particles. On orbit with perihelion distances q < 0.1 AU, meteoroids would show evidence of thermal desorption of metals, in particular, Na.