Spectroscopy of infrared flares from the microquasar GRS 1915+105

We present near-infrared medium-resolution (R similar to 875) spectra of the microquasar GRS 1915+105 on 1997 August 13-15 UTC from the Hale 5 m telescope. The spectra show broad emission lines of He I (2.058 mu m) and H I (2.166 mu m; Br gamma), which are consistent with previous work. On August 14 UTC, we took spectra with an similar to 6 minute time resolution during infrared flaring events similar to those reported in Eikenberry et al., which appear to reveal plasma ejection from the system. During the flares, the emission-line fluxes varied in approximately linear proportionality to the IR continuum flux, implying that the lines are radiatively pumped by the flares. We also detected a weak He II (2.189 mu m) emission line on August 14 UTC. The nature of the line variability and the presence of the He rr feature indicate that the emission lines in GRS 1915+105 arise in an accretion disk around the compact object rather than in the circumstellar disk of a proposed Oe/Be companion. The radiative line pumping also implies that the flare emission originates from ejecta that have moved out of the accretion disk plane.