Merging Recent and Historic Spectra of ∊ Aurigae: Properties of the System’s Components, and Discovery of a Mass Transfer Stream
This study of new CCD spectra of ∊ Aur recorded in the blue and near-UV during the 2010 eclipse has been reinforced and extended by the inclusion of some 130 digitized historic spectra from Mount Wilson (dating back to the 1930s) and from the DAO (dating from 1971). The precise repetition of disk-related spectral-line changes during three successive eclipses indicates that the structure of the disk does not alter appreciably on a time-scale of a least a century. We deduce that the disk has an extensive but optically thin outer layer, and a flat structure that is tilted near to edge-on. We discover that it is receiving from the supergiant a very confined stream of material that is enriched in rare-earth elements. The stream has an approach velocity very similar to the projected rotational velocity of the F star; it has an extremely small velocity dispersion, and is only visible between specific egress phases. We surmise that the F star is a horizontal-branch star though its own photosphere appears, on average, to have a solar composition. We also uncover variable broad emission in the system and find a possible correlation with the F-star’s Cepheid-like ∼67-day pulsations that cause its photometric variations.