skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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

Abstract

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

Citation Formats

Godon, Patrick, Sion, Edward M., Barrett, Paul E., and Linnell, Albert P. THE WHITE DWARF IN EM CYGNI: BEYOND THE VEIL. United States: N. p., 2009. Web. doi:10.1088/0004-637X/699/2/1229; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Godon, Patrick, Sion, Edward M., Barrett, Paul E., & Linnell, Albert P. THE WHITE DWARF IN EM CYGNI: BEYOND THE VEIL. United States. doi:10.1088/0004-637X/699/2/1229; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Godon, Patrick, Sion, Edward M., Barrett, Paul E., and Linnell, Albert P. Fri . "THE WHITE DWARF IN EM CYGNI: BEYOND THE VEIL". United States. doi:10.1088/0004-637X/699/2/1229; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
@article{osti_21333750,
title = {THE WHITE DWARF IN EM CYGNI: BEYOND THE VEIL},
author = {Godon, Patrick and Sion, Edward M. and Barrett, Paul E. and Linnell, Albert P.},
abstractNote = {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 even 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.},
doi = {10.1088/0004-637X/699/2/1229; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)},
journal = {Astrophysical Journal},
number = 2,
volume = 699,
place = {United States},
year = {Fri Jul 10 00:00:00 EDT 2009},
month = {Fri Jul 10 00:00:00 EDT 2009}
}
  • Time-resolved spectroscopy of V1500 Cyg are presented from 1981, when the nebular lines from the nova ejecta had faded sufficiently to permit reliably radial velocity measurements on emission lines from the binary remnant. The spectra possess a typical AM Herculis signature. The wavelength region 3800-5100 A contains a number of strong lines, in particular the Balmer series and He II 4686 A. All lines show periodic velocity changes with the same period as the photometric variations. On the first night the lines are relatively weak and narrow, are in phase with the photometric cycle, and suffer extreme modulation; two monthsmore » later they are strong and broad, are roughly 90 deg out of phase with the photometric cycle, and have relatively less variation in their line fluxes. These features support the suggestion that the remnant is an AM Her system. The observed radial velocity of the secondary is 193 + or - 9 km/s. Various constraints suggest that the magnetic white dwarf in this system has a mass over 0.9 solar. 32 refs.« less
  • We have carried out a combined Hubble Space Telescope (HST/GHRS) and Far Ultraviolet Spectroscopic Explorer (FUSE) analysis of the prototype dwarf nova SS Cygni during quiescence. The FUSE and HST spectra were obtained at comparable times after outburst and have matching flux levels where the two spectra overlap. In our synthetic spectral analysis, we have used SS Cygni's accurate HST fine guidance sensor parallax giving d = 166 pc, a newly determined mass for the accreting white dwarf (WD) of M{sub wd} = 0.81 M{sub sun} (lower than the previous widely used 1.2 M{sub sun}) and the reddening (E{sub B-V})more » values 0.04 and 0.07 derived from the 2175 A absorption feature in the IUE LWP spectra. From the best-fit model solutions to the combined HST + FUSE spectral energy distribution, we find that the WD is reaching a temperature T{sub eff}{approx} 45,000-55,000 K in quiescence, assuming log(g) = 8.3 with a solar composition accreted atmosphere. The exact temperature of the WD depends on the reddening assumed and the inclusion of a quiescent low mass accretion rate accretion disk. Accretion disk models alone fit badly in the FUSE range while, and if we take the distance to be a free parameter, the only accretion disk model that fits well is for a discordant distance of at least several hundred parsecs and an accretion rate ({approx}10{sup -8} M{sub sun} yr{sup -1}), which is unacceptably high for a dwarf nova in quiescence. We discuss the implications of the WD's temperature on the time-averaged accretion rate and long-term compressional heating models.« less
  • We show that scalar perturbations of the eternal, rotating Banados-Teitelboim-Zanelli (BTZ) black hole should lead to an instability of the inner (Cauchy) horizon, preserving strong cosmic censorship. Because of backscattering from the geometry, plane-wave modes have a divergent stress tensor at the event horizon, but suitable wave packets avoid this difficulty, and are dominated at late times by quasinormal behavior. The wave packets have cuts in the complexified coordinate plane that are controlled by requirements of continuity, single-valuedness, and positive energy. Due to a focusing effect, regular wave packets nevertheless have a divergent stress energy at the inner horizon, signalingmore » an instability. We propose that this instability, which is localized behind the event horizon, is detected holographically as a breakdown in the semiclassical computation of dual conformal field theory (CFT) expectation values in which the analytic behavior of wave packets in the complexified coordinate plane plays an integral role. In the dual field theory, this is interpreted as an encoding of physics behind the horizon in the entanglement between otherwise independent CFTs.« less