Spectroscopic Observations of V616 Mon (A0620-00)

Abstract

We report on spectroscopic observations made in March 1976 at the time of the optical and X-ray secondary maximum of V616 Mon (A0620-00). The three highest signal-to-noise-ratio spectra, having a resolution of 3 Å and covering the spectral interval λλ 3900–5600 Å were obtained near phase ø = 0.5 (maximum flux) in the 8-day cycle (Chevalier, Janot-Pacheco, Mauder and Ilovaisky 1976) when the object was near B = 13.65, B-V = 0.32, U-B = −0.50. The spectra were obtained at the coudé focus of the 1.52−m European Southern Observatory reflector using the Echelec spectrograph in single-spectrum mode and a 30−mm Lallemand electronographic camera. After digital processing with a PDS microphotometer, the three best spectra were numerically added. The composite spectrum shows the following weak (10% of the continuum), broad (50 Å) features: (a) Balmer lines (H_β,H_γ,H_δ,H_ε) in absorption, with narrow, weak emission cores; (b) He II λ4686 Å in emission with structure in the blueward wing, probably due to weaker CIII-NIIII λλ 4630–4650 Å emission; (c) He I absorption lines at λ 5015 Å and λ4471 Å, the latter certainly blended with the diffuse interstellar absorption band near λ 4430 Å. Radial velocity measurements, though somewhat uncertain due to the weakness and shallowness of the lines, indicate no evidence whatever for an expansion velocity greater than about 150 km s⁻¹. We note satisfactory agreement with spectra taken in January 1976 with the 3.9−m AAT reflector and a Wampler-Robinson IDS (Whelan et al. 1976).