Hubble Space Telescope Time-resolved Ultraviolet Spectroscopy of ST Leonis Minoris and UZ Fornacis: Resolving the Accretion Stream

Abstract

view Abstract Citations (28) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hubble Space Telescope Time-resolved Ultraviolet Spectroscopy of ST Leonis Minoris and UZ Fornacis: Resolving the Accretion Stream Stockman, H. S. ; Schmidt, Gary D. Abstract Time-resolved, low-resolution ultraviolet spectroscopy of the magnetic cataclysmic variables ST LMi and UZ For was obtained with the Hubble Space Telescope during periods near eclipse and self-eclipse egress, respectively. The UZ For data indicate three eclipsing components: the white dwarf; a hot, presumably photo spheric emission region on the white dwarf; and the UV-bright accretion stream. The latter is observed in both continuum bands and in strong resonance lines: C IV λ1549 and He II λ1640. ST LMi is at lower inclination and displays a "self-eclipse" as the accretion shock and lower portion of the accretion column rotate over the limb. A broad, warm (T > 30,000 K) spot is identified as the principal source of far-UV emission through an analysis of the ST LMi self-eclipse egress. In both UZ For and ST LMi, the accretion stream provides the majority of UV emission at longer wavelengths. The eclipse behavior for UZ For is used to bound the size and location of the accretion region. These bounds place the majority of the UV emission in the accretion stream between the white dwarf surface and Rcirc of the Lubow and Shu model. The general properties of the stream can be explained by a two-phase model. Low filling factor, dense clumps are photoionized by the soft and hard X-ray radiation from the accretion shock and cool through line emission in the mid-UV and Lyman and He II freebound continua. The "interclump" medium is shocked and compressed to high temperatures and confines the dense clumps. Variations in the UV continuum are strongly correlated with similar variations in the emission lines. Time lags between the UV line and continuum emission are observed, with essentially zero lag between the primary UV continuum and line-emission flickering components. A secondary line-emission flickering component lags the primary component by ∼40-80 s. Publication: The Astrophysical Journal Pub Date: September 1996 DOI: 10.1086/177744 Bibcode: 1996ApJ...468..883S Keywords: ACCRETION; ACCRETION DISKS; STARS: BINARIES: ECLIPSING; STARS: INDIVIDUAL CONSTELLATION NAME: UZ FORNACIS; STARS: INDIVIDUAL CONSTELLATION NAME: ST LEONIS MINORIS; STARS: MAGNETIC FIELDS; ULTRAVIOLET: STARS; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (12) MAST (1) ESA (1)