Evolution of the O I triplets (RMT 1, top, and 4, bottom). Triplet (1) is resolved in the narrow absorption at approximately −460 km s⁻¹. Together with triplet (1) we overplot the Hδ profile forcomparison (gray line) (see text for details; the H line has been arbitrarily offset in each subpanel; in the bottom subpanel it has also been scaled by a factor 0.5). The blue line of the Ca II triplet is included in the bottom panel; it shows similar behavior to the O I RMT 4. The Y -axis units are in erg cm⁻² s⁻¹ Å⁻¹. The colored vertical dotted lines have the usual meaning. The photometric state (min, max) of each spectrum is indicated in each subpanel.