The nearby eclipsing stellar system δ Velorum ^*

I. Origin of the infrared excess from VISIR and NACO imaging

¹ LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 Place Jules Janssen, 92195 Meudon, France e-mail: Pierre.Kervella@obspm.fr
² Université de Nice-Sophia Antipolis, Lab. Cassiopée, UMR 6202, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice, France
³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

Received: 10 July 2008
Accepted: 3 October 2008

Abstract

Context. The triple stellar system δ Vel system presents a significant infrared excess, whose origin is still being debated. A large infrared bow shock has been discovered using Spitzer/MIPS observations. Although it appears as a significant contributor to the measured IR excess, the possibility exists that a circumstellar IR excess is present around the stars of the system.

Aims. The objective of the present VISIR and NACO observations is to identify whether one of the stars of the δ Vel system presents a circumstellar photometric excess in the thermal IR domain and to quantify it.

Methods. We observed δ Vel using the imaging modes of the ESO/VLT instruments VISIR (in BURST mode) and NACO to resolve the A–B system (0.6´´ separation) and obtain the photometry of each star. We also obtained one NACO photometry epoch precisely at the primary (annular) eclipse of δ Vel Aa by Ab.

Results. Our photometric measurements with NACO (2.17 μm), complemented by the existing visible photometry allowed us to reconstruct the spectral energy distribution of the three stars. We then compared the VISIR photometry (8.6–12.8 μm) to the expected photospheric emission from the three stars at the corresponding wavelengths.

Conclusions. We can exclude the presence of a circumstellar thermal infrared excess around δ Vel A or B down to a few percent level. This supports the conclusions of Gáspár et al. (2008, ApJ, 672, 974) that the IR excess of δ Vel has an interstellar origin, although a cold circumstellar disk could still be present. In addition, we derive the spectral types of the three stars Aa, Ab, and B (respectively A2IV, A4V and F8V), and we estimate the age of the system around 400–500 Myr.