An Unexpected Outcome from Disentangling

Extract

During our recent spectroscopic study of ε Aur (Chadima et al. 2011), we made an attempt to detect weak spectral lines of the secondary, hidden in a dark disk, using the spectral disentangling technique of Simon & Sturm (1994) and Hadrava (1995, 1997, 2004). We used the Dominion Astrophysical Observatory (DAO) and Ondřejov (OND) red electronic spectra, which cover more than one half of the orbital period. To our surprise, two different programs that disentangled the spectrum in Fourier space, KOREL (Hadrava 1995, 2004) and FDBINARY (Ilijić et al. 2001), both yielded apparently good, similar reconstructions of two well-defined spectra for mass ratios near unity. The results (Solution 1) are shown in Fig. 1 (left panels) and Table 1 (left column). This result is hard to accept as real given the existing knowledge about the system: ε Aur is an F-type star with an unseen companion embedded in a cool, dark disk (temperature ~ 500–600 K). A detailed search for any trace of spectral signatures of the secondary in the spectra was carried out (see Bennett et al., these proceedings). Although they found line profile variations that were correlated with orbital phase, these variations were not consistent with the presence of a secondary.