1994PASP..106..365T

We report observations of visual and near-infrared C I, N I, and O I lines in the A2 II secondary of V356 Sgr made during a total eclipse of the primary. We confirm the weakness of the secondary's C I lines first seen in ultraviolet observations. Based on a marginal detection of the 9100A C I lines we estimate that relative to a standard star (HR 7145; A0 II) of similar spectral type the [C/Fe] abundance ratio of the secondary is -1.7 ± 0.3 dex. The secondary is not significantly underabundant in N or O. We interpret the C poorness of the secondary as a result of mass transfer, which has removed its outer layers and exposed its CN-processed interior.