Early Evolution Of The 2006 Eruption Of The Recurrent Novae RS Oph

Classical novae occur frequently, but repeated outbursts of a KNOWN nova occurs rarely. These observed repeated outbursts render recurrent novae (RN) unique amongst all novae, and important astrophysical laboratories in which to study the outburst physics and chemical processing that occurs in novae (or at least this subclass). The primaries of RN are thought to be massive white dwarfs (1.3-1.4 solar masses, close to the Chandrasekhar limit). Consequently, their outbursts are quite brief, returning back to their quiescent state within just a few months. If the white dwarf (WD) retains a net gain in mass after each accretion-eruption cycle, this could eventually result in a Type Ia supernovae explosion. RS Oph is one of only a few known recurrent novae, itself having been observed to erupt in 1898, 1933, 1958, 1967, and 1985; roughly once a generation! RS Oph is further unique in that the secondary is a late-type ~M2III giant star in a long-period orbit of ~460 days. Thus, the hot WD is enshrouded within the extended wind of the giant companion. On 2006 February 12, RS Oph experienced yet another eruption, rising by about 6 mags to V~5. A high-dispersion spectroscopic campaign was initiated on RS Oph using the APO 3.5m telescope using the echelle spectrograph (R~37,500, continuous coverage from 0.35nm to 0.98nm, ~25 nights) complimented by lower-dispersion spectra obtained on the SMARTS 1.5m telescope at CTIO, and coordinated with various campaigns conducted with space observatories. We report initial results from the spectroscopic ground-based campaign, and compare with results found during previous eruptions. Though the 2006 eruption behaved qualitatively similar to the 1985 outburst, important differences are observed. For example, the 2006 eruption proceeded more rapidly than the 1985 outburst, likely a result of a larger envelope mass accreted before the thermonuclear runaway ensured. Broad hydrogen lines narrowed as the eruption evolved, while He I lines disappeared, replaced by He II lines as the ejecta became shock heated. Details of the evolving ionization state, kinematics, and equivalent widths will be discussed.