Visual photometry for the Be star {mu} Centauri

We present the nine near-IR spectra we obtained in an epoch of relative photometric quiescence prior to an outburst of {Delta}V=0.4 magnitude. Visual estimates during the epoch of our L-band spectroscopy are also presented for the first time, together with the unpublished complete visual light curve between the years 1998 and 2014.

We observe significant and monotonic changes in emission line strength of Bracket-{alpha} and Pfund-{gamma} lines relative to Humphreys lines, and also in the continuum slope. We interpret these observed changes in terms of important changes to the column density of the line emitting regions, moving from an optically thin to an optically thick stage just prior to a major outburst. For each observing date, we provide estimates for the column density and relative extension of the line emitting region.