The nearby eclipsing stellar systemδVelorum

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.

The nearby eclipsing stellar systemδVelorum

“…This simple computation, however, does not take into account that the observer faces the coldest (equatorial) part of the system. The apparent magnitudes of the eclipsing pair synthesized by the ROCHE code (including all proximity effects and gravity darkening), U = 1.98 ± 0.02, B = 1.94 ± 0.02, V = 1.95 ± 0.02, and K = 1.86 ± 0.02 are in very good agreement with the observations: Kervella et al (2009) found V (Aab) = 2.00 ± 0.02 and K (Aab) = 1.86±0.09.…”

“…The components are of similar temperature, however, both very probably being of spectral type A1V. This is strongly supported by a close agreement with the synthetic depth of the primary minimum in the K passband Δmag I = 0.430, while Kervella et al (2009) determined Δmag I = 0.440 ± 0.011 from the NACO imaging during the primary eclipse; -there is no apsidal motion in the system observed during the six-year time-series of the SMEI data as indicated by the observed times of the minima;…”

“…Therefore, the systemic velocity of δ Velorum may be offset from its true value. According to the VLT/NACO imaging of Kervella et al (2009), the separation of the optical pair A-B was about 0.6 in 2008. Because of a PSF of 3-5 at the HPT, both visual components were included in the fiber entrance.…”

“…This very large structure, ∼1 , was explained by the authors as a result of the heating and compression of the interstellar medium by the photons from δ Velorum as the trio moves through the interstellar medium. Kervella et al (2009) resolved the wide visual pair AB using the VISIR and NACO instruments at the VLT and obtained independent photometry of each of the Aa, Ab, and B components. Their photometry did not infer the large radii of the components, found by Kellerer et al (2007).…”

The nearby eclipsing stellar systemδVelorum

“…The presence of interstellar material was also reported by Hempel & Schmitt (2003), who observed two red-shifted absorbing components in absorption in the Ca II K line of probably interstellar origin. In Paper I of the present series, Kervella et al (2009) confirmed that the infrared excess is essentially emitted by the bow shock, and not warm circumstellar material located close to the stars. In the framework of a search for resolved emission from debris disks, Moerchen et al (2010) obtained thermal infrared images of δ Vel using the Gemini South telescope and the T-ReCS instrument, and detected a marginally resolved emission at λ = 10.4 μm.…”