David K. Lynch

A new probe of the planet-forming region in T Tauri disks

We present new observations of the far-ultraviolet (FUV; 1100-2200 A) radiation field and the near- to mid-IR (3-13.5 μm) spectral energy distribution (SED) of a sample of T Tauri stars selected on the basis of bright molecular disks (GM Aur, DM Tau, and LkCa 15). In each source we find evidence for Lyα-induced H2 fluorescence and an additional source of FUV continuum emission below 1700 A. Comparison of the FUV spectra to a model of H2 excitation suggests that the strong continuum emission is due to electron impact excitation of H2. The ultimate source of this excitation is likely X-ray irradiation that creates hot photoelectrons mixed in the molecular layer. Analysis of the SED of each object finds the presence of inner disk gaps with sizes of a few AU in each of these young (~1 Myr) stellar systems. We propose that the presence of strong H2 continuum emission and inner disk clearing are related by the increased penetration power of high-energy photons in gas-rich regions with low grain opacity.

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 novas 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.

The Early Spectrophotometric Evolution of V1186 Scorpii (Nova Scorpii 2004 No. 1)

We report optical photometry and optical through mid-infrared spectroscopy of the classical nova V1186 Sco. This slowly developing nova had a complex light curve with multiple secondary peaks similar to those seen in PW Vul. The time to decline 2 mag, t2, was 20 days, but the erratic nature of the light curve makes determination of intrinsic properties based on the decline time (e.g., luminosity) problematic, and the often-cited relationship of maximum magnitude versus the rate of decay of the light curve of Della Valle & Livio fails to yield a plausible distance. Spectra covering 0.35-35 μm were obtained in two separate epochs during the first year of outburst. The first set of spectra, taken about 2 months after visible maximum, are typical of a CO-type nova with narrow-line emission from H I, Fe II, O I, and He I. Later data, obtained between 260 and 380 days after maximum, reveal an emerging nebular spectrum. Spitzer spectra show weakening hydrogen recombination emission with the emergence of [Ne II] (12.81 μm) as the strongest line. Strong emission from [Ne III] (15.56 μm) is also detected. Photoionization models with low effective temperature sources and only marginal neon enhancement (Ne ~ 1.3 Ne⊙) are consistent with these IR fine-structure neon lines indicating that V1186 Sco did not occur on a ONeMg white dwarf. In contrast, the slow and erratic light-curve evolution, spectral development, and photoionization analysis of the ejecta imply that the outburst occurred on a low-mass CO white dwarf. We note that this is the first time strong [Ne II] lines have been detected so early in the outburst of a CO nova and suggest that the presence of mid-infrared neon lines is not directly indicative of a ONeMg nova event.

0.8–2.5 μm Spectroscopy of Novae

We present new infrared results on a number of recent novae including V2274 Cyg (Nova Cygni 2001), CI Aquilae, and V723 Cas (Nova Cassiopeiae 1995), and review some of the outstanding aspects of their infrared spectra. The discussion includes the identification of coronal lines and their interpretation and structure in the CO emission band at 2.3 μm.