THE CARBON UNDERABUNDANCE OF THE SECONDARY OF V356-SAGITTARII

We report observations of visual and near-infrared C I, N I, and O I l ines in the A2 II secondary of V356 Sagittarii made during a total ecl ipse of the primary. We confirm the weakness of the secondary's C I li nes first seen in ultraviolet observations. Based on a marginal detect ion of the 9100 angstrom C I lines we estimate that relative to a stan dard star (HR 7145; A0 II) of similar spectral type the [C/Fe] abundan ce ratio of the secondary is -1.7 +/- 0.3 dex. The secondary is not si gnificantly underabundant in N or O. We interpret the C deficiency of the secondary as a result of mass transfer, which has removed its oute r layers and exposed its CN-processed interior.