The young B-star quintuple system HD 155448^⋆,⋆⋆

¹ European Southern Observatory, Alonso de Cordova 3107, Santiago 19, Chile
e-mail: oschuetz@gmail.com
² Universidad Autónoma de Madrid, Departamento de Física Teórica C-XV, 28049 Madrid, Spain
³ ISDC Data Centre for Astrophysics, University of Geneva, chemin d’Ecogia 16, 1290 Versoix, Switzerland
⁴ Observatoire de Genève, University of Geneva, chemin des Maillettes 51, 1290 Sauverny, Switzerland
⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

Received: 23 December 2010
Accepted: 11 May 2011

Abstract

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  ~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 μm, most circumstellar emission is located at distances between  ~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 μm. 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.