Volume 533, September 2011
|Number of page(s)||17|
|Section||Interstellar and circumstellar matter|
|Published online||26 August 2011|
The young B-star quintuple system HD 155448⋆,⋆⋆
European Southern Observatory,
Alonso de Cordova 3107,
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
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.
Key words: stars: pre-main sequence / ISM: general / circumstellar matter / stars: emission-line, Be / stars: individual: HD 155448
Based on observations collected at the European Southern Observatory (programme IDs 075.C-0091(B) and 075.C-0091(C), together with archival and technical data).
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2011
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