HD 42927 and HD 126341 : two pulsating B stars surrounded by circumstellar dust ?

We have performed an infrared study of pulsating B stars. The main conclusion is that none of the 163 (non-)radial pulsators shows an IR excess flux due to free-free emission, despite the fact that the sample contains several rapid rotators. Two β Cep stars and two slowly pulsating B stars do exhibit an unexpected infrared colour excess at 12 μm. The small IR excess of the B 2 IV β Cep star HD 126341 (τ1 Lup) is not accompanied by H α emission nor by a near-IR excess. It follows an energy distribution described by a powerlaw that points to dust emission. An optically thin dust model is fitted to the IR data and leads to the presence of circumstellar dust which is situated very far from the star. The infrared data of the star HD 42927 also point towards the presence of (hotter) dust which is situated close to the star. We have gathered follow-up photometry and high-resolution spectroscopy that confirm the Hipparcos classification of the star as a new slowly pulsating B star. We briefly discuss the connection between these two pulsating stars and the occurrence of circumstellar dust around main-sequence stars.