Early Infrared Spectral Development of V1187 Scorpii (Nova Scorpii 2004 No. 2)

We report on an unprecedented infrared time series of spectra of V1187 Sco, a very fast ONeMg nova. The observations covered a 56 day period (2004 August 6-September 30) starting 2 days after the nova's peak brightness. Time evolution of the spectra revealed changing line strengths and profiles on timescales of less than a day to weeks as the nova evolved from early postmaximum to early coronal phases. When our ground-based optical and Spitzer Space Telescope data were combined, the wavelength coverage of 0.38-36 μm allowed an accurate spectral energy distribution to be derived when it was about 6 weeks after outburst. Developing double structure in the He I lines showed them changing from narrow to broad in only a few days. Using the O I lines in combination with the optical spectra, we derived a reddening of E(B - V) = 1.56 ± 0.08 and a distance of 4.9 ± 0.5 kpc. Modeling of the ejected material strongly suggested that it was geometrically thick with ΔR/R = 0.8-0.9 (more of a wind than a shell) and a low filling factor of order a few percent. The line shapes were consistent with a cylindrical jet, bipolar, or spherical Hubble flow expansion with a maximum speed of about -3000 km s-1. The central peak appeared to be more associated with the spherical component, while the two peaks (especially in Hβ) suggested a ring with either a lower velocity component or with its axis inclined to the line of sight.