SIMBAD references

The Hipparcos photometric observations carried out over 37 months have been investigated in detail for ∼250 Miras. This leads to an unexpected by-product of the mission that we already suspected from ESOC real-time reductions: the first detection from space of photometric short-term brightness variations in Mira-type variables. Altogether, 51 events in 39 M-type Miras are detected and no similar variations are found for S and C-type Miras. Their amplitude ranges from 0.23 mag up to 1.11 mag and their duration extends from 2 hours up to almost 6 days. These events seem to occur preferentially in late spectral types. We suggest that they might be related to molecular opacity effects.