Spectral Mapping of the Intermediate Polar DQ Herculis

摘要

We report an eclipse-mapping study of the intermediate polar DQ Her based on time-resolved optical spectroscopy (Δλ ~ 3800-5000 ?) covering four eclipses. The spectra were sliced into 295 narrow passbands in the continuum and in the lines, and the corresponding light curves were analyzed to solve for a set of monochromatic maps of the disk brightness distribution and for the flux of an additional uneclipsed component in each band. Eclipse maps of the He II λ4686 line indicate that an azimuthally and vertically extended bright spot at disk rim is an important source of the reprocessing of X-rays from the magnetic poles. The disk spectrum is flat with no Balmer or Helium lines in the inner regions, and shows double-peaked emission lines in the intermediate and outer disk regions, while the slope of the continuum becomes progressively redder with increasing radius. The inferred disk temperatures are in the range T bsime; 13500-5000 K and can be reasonably well described by a steady-state disk with mass accretion rate of M = (2.7 ± 1.0) x 10~(-9) M_⊙ yr~(-1). A comparison of the radial intensity distribution for the Balmer lines reveals a linear correlation between the slope of the distribution and the transition energy. The spectrum of the uneclipsed light is dominated by Balmer and He I lines in emission (probably from the extended nova shell) with narrow absorption cores (likely from a collimated and optically thick wind from the accretion disk). The observed narrow and redshifted Ca II λ3934 absorption line in the total light spectra plus the inverse P-Cygni profiles of the Balmer and He II λ4686 emission lines in spectra of the asymmetric component indicate radial inflow of gas in the innermost disk regions and are best explained in terms of magnetically controlled accretion inside the white dwarf magnetosphere. We infer projected radial inflow velocities of ~200-500 km s~(–1), significantly lower than both the rotational and the free-fall velocities for the corresponding range of radii. A combined net emission He II plus Hβ low-velocity eclipse map reveals a twisted dipole emitting pattern near disk center. This is interpreted as being the projection of accretion curtains onto the orbital plane at two specific spin phases, as a consequence of the selection in velocity provided by the spectral eclipse mapping.