AAS 201st Meeting, January, 2003
Session 40. Normal and Dwarf Novae
Poster, Tuesday, January 7, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[40.14U] A Synthetic Spectral Analysis of the Far UV Spectra of the Dwarf Novae TW Vir, CH UMa and IR Gem During Quiescence

M. Dulude, E.M. Sion (Villanova University)

We have selected three dwarf novae, the U Gem-type systems CH UMa and TW Vir and the SU UMa type systems IR Gem with archival IUE spectra during their quiescence for a study of their behavior, disk properties (e.g. accretion rates), relative contributions of the accretion disk and white dwarf to the far UV flux and, if possible, the properties of the underlying white dwarfs. CH UMa may contain a very massive white dwarf and has very strong N V disk emission and extremeyl; weak C IV emission. After applying the Massa-Fitzpatrick flux calibration correction to the archival NEWSIPS spectra and masking out strong emission lines, we compared the spectra to a grid of model accretion disks with vertical structure covering the range of accretion rates 1E-8.5 to 1E-10.5 Msun/yr, inclination angles 18 degrees to 81 degrees and white dwarf masses from 0.55 to 1.2 Msun. In addition, we compared their IUE spectra wih high gravity model atmospheres computed with TLUSTY and SYNSPEC. Finally we took the best-fitting white dwarf model atmosphere for each system and combined it with the best-fitting disk. We varied the accretion rate of the accretion disk until the combined white dwarf plus disk yielded the least chi2 value. In all three systems, the quiescent accretion disk contributes over 90 light and only upper limits to the white dwarf temperatures are derived. We find accretion rates of 10-10.5 Msun/yr, 10-11.5 Msun/yr and 10-9.9 Msun/yr for IR Gem, CH UMa and TW Vir, respectively. We present the results of our analysis and discuss implications for disk and white dwarf properties during quiescence.

This work was supported by NSF grant 9901955 and summer research support from the NASA Delaware Space Grant Consortium

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