The young B-star quintuple system HD 155448

Until now, HD 155448 has been known as a post-AGB star and listed as a quadruple system. In this paper, we study the system in depth and reveal that the B component itself is a binary and that the five stars HD 155448 A, B1, B2, C, and D likely form a comoving stellar system. From a spectroscopic analysis we derive the spectral types and find that all components are B dwarfs (A: B1V, B1: B6V, B2: B9V, C: B4Ve, D: B8V). Their stellar ages put them close to the ZAMS, and their distance is estimated to be similar to 2 kpc. Of particular interest is the C component, which shows strong hydrogen and forbidden emission lines at optical wavelengths. All emission lines are spatially extended in the eastern direction and appear to have a similar velocity shift, except for the [O I] line. In the IR images, we see an arc-like shape to the northeast of HD 155448 C. From the optical up to 10 mu m, most circumstellar emission is located at distances between similar to 1.0" and 3.0" from HD 155448 C, while in the Q band the arc-like structure appears to be in contact with HD 155448 C. The Spitzer and VLT/VISIR mid-IR spectra show that the circumstellar material closest to the star consists of silicates, while polycyclic aromatic hydrocarbons (PAH) dominate the emission at distances >1" with bands at 8.6, 11.3, and 12.7 mu m. We consider several scenarios to explain the unusual, asymmetric, arc- shaped geometry of the circumstellar matter. The most likely explanation is an outflow colliding with remnant matter from the star formation process.