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Title: THE WHITE DWARF IN EM CYGNI: BEYOND THE VEIL

We present a spectral analysis of the Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of the eclipsing double-line spectroscopic binary EM Cygni (EM Cyg), a Z Cam DN system. The FUSE spectrum, obtained in quiescence, consists of four individual exposures (orbits): two exposures, at orbital phases {phi} {approx} 0.65 and {phi} {approx} 0.90, have a lower flux; and two exposures, at orbital phases {phi} = 0.15 and 0.45, have a relatively higher flux. The change of flux level as a function of the orbital phase is consistent with the stream material (flowing over and below the disk from the hot spot region to smaller radii) partially masking the white dwarf. We carry out a spectral analysis of the FUSE data, obtained at phase 0.45 (when the flux is maximal), using synthetic spectra generated with the codes TLUSTY and SYNSPEC. Using a single white dwarf spectral component, we obtain a white dwarf temperature of 40, 000 K {+-} 1000 K, rotating at 100 km s{sup -1}. The white dwarf, or conceivably, the material overflowing the disk rim, shows suprasolar abundances of silicon, sulphur, and possibly nitrogen. Using a white dwarf+disk composite model, we obtain that the white dwarf temperature could be evenmore » as high as 50,000 K, contributing more than 90% of the FUV flux, and the disk contributing less than 10% must have a mass accretion rate reaching 10{sup -10} M{sub sun} yr{sup -1}. The single white dwarf model fits the absorption lines better than the white dwarf+disk model, but the white dwarf+disk model fits better the continuum in the shorter wavelengths. In both cases, however, we obtain that the white dwarf temperature is much higher than previously estimated. We emphasize the importance of modeling the spectra of EM Cyg around phase {phi} < 0.5, when the white dwarf and disk are facing the observer, and we suggest that the discrepancy between the present analysis and previous spectral analysis might be due to the occulting effect of the stream veiling the white dwarf and disk.« less
Authors:
;  [1] ;  [2] ;  [3]
  1. Department of Astronomy and Astrophysics, Villanova University, Villanova, PA 19085 (United States)
  2. United States Naval Observatory, Washington, DC 20392 (United States)
  3. Department of Astronomy, University of Washington, Seattle, WA 98195 (United States), E-mail: patrick.godon@villanova.edu, E-mail: edward.sion@villanova.edu, E-mail: barrett.paul@usno.navy.mil, E-mail: linnell@astro.washington.edu, E-mail: godon@stsci.edu
Publication Date:
OSTI Identifier:
21333750
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 699; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/699/2/1229; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ACCRETION DISKS; FAR ULTRAVIOLET RADIATION; HOT SPOTS; NITROGEN; NOVAE; ORBITS; SILICON; SIMULATION; WHITE DWARF STARS