Spectrally-resolved accretion disk maps of the dwarf nova IP~Peg during outburst

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Session 21 -- Cataclysmic Variables, Dwarf Novae
Display presentation, Monday, 9, 1995, 9:20am - 6:30pm

[21.07] Spectrally-resolved accretion disk maps of the dwarf nova IP~Peg during outburst

C.A. Haswell (Columbia Univ.), R. Baptista (STScI), G. Thomas (Columbia Univ.)

Spectrally-resolved eclipse maps of the accretion disk in the dwarf nova IP~Peg are presented and discussed. The analysis is based on time-resolved optical spectroscopic observations covering one eclipse during the 1993 May outburst.

The trailed spectrogram was divided into passbands ($\sim 50$ \AA ~in the continuum and $\sim 600$ Km/s in the emission lines) and light curves were extracted for each one. Velocity-resolved light curves in H$\alpha$ show minima progressively displaced towards later phases as one moves from blue to red, signaling a rotational disturbance in this emission line. Eclipse mapping techniques were used to solve for a map of the disk brightness distribution and for the flux of an additional uneclipsed component in each band. In contrast to other dwarf novae in outburst, the radial temperature profiles derived from these maps are in clear disagreement with the radial dependence predicted by the steady state disk model ($T \propto R^{-3/4}$). The flat profiles obtained are quite similar to those observed in quiescent dwarf novae, with temperatures ranging from 4,000\,K to 6,500\,K.

Spatially-resolved disk spectra show that the H$\alpha$ and the He\,I $\lambda 5876$ and $\lambda 6678$ lines are in emission at all disk radii. This is in marked contrast with the results obtained for the nova-like variable UX~UMa, where the lines progressively transition from absorption in the inner disk to emission in the outer disk (Rutten et al. 1994; Baptista et al. 1994). This result suggests that the currently accepted view that nova-like systems are similar to dwarf novae in a permanent outburst state has to be revised.

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