First L band detection of hot exozodiacal dust with VLTI/MATISSE

Abstract

For the first time we observed the emission of hot exozodiacal dust in L band. We used the new instrument MATISSE at the Very Large Telescope Interferometer to detect the hot dust around $\hat{I}º$ Tuc with a significance of 3$\ddot{I}ƒ$ to 6$\ddot{I}ƒ$ at wavelengths between 3.37 and 3.85 $\hat{I}¼$m and a dust-to-star flux ratio of 5 to 7 %. We modelled the spectral energy distribution based on the new L band data alone and in combination with H band data published previously. In all cases we find 0.58 $\hat{I}¼$m grains of amorphous carbon to fit the $\hat{I}º$ Tuc observations the best, however, also nanometre or micrometre grains and other carbons or silicates reproduce the observations well. Since the H band data revealed a temporal variability, while our L band data were taken at a different epoch, we combine them in different ways. Depending on the approach, the best fits are obtained for a narrow dust ring at a stellar distance in the 0.1 to 0.29 au range and thus with a temperature between 940 and 1430 K. Within the 1$\ddot{I}ƒ$ uncertainty dust location and temperature are confined to 0.032 - 1.18 au and 600 - 2000 K.

Accepted by MNRAS Letters. Author accepted manuscript. Accepted on 04/09/2020. Deposited on 04/09/2020. 6 pages, 4 figures