S. Kafka

New Complexities in the Low-State Line Profiles of AM Herculis

When accretion temporarily ceases in the polar AM Her, the emission-line profiles are known to develop several distinct components, whose origin remains poorly understood. The new low-state spectra reported here have a more favorable combination of spectral resolution (R ~4500), time resolution (~3 minute exposures), and S/N than earlier work, revealing additional details of the orbital dependence of the line profiles. The central strong feature of Hα is found to be composed of two components of similar strength, one having K ~ 100 km s^−1 and phased with the motion of the secondary star, the other having little or no detectable radial velocity variations. We attribute the central line component to gas near the coupling region, perhaps with a contribution from irradiation of the secondary star. The two satellite components have radial velocity offsets of ~±250 km s^−1 on either side of the central strong Hα peak. These satellites most likely arise in large loops of magnetically confined gas near the secondary star due to magnetic activity on the donor star and/or interactions of the magnetic fields of the two stars. Doppler maps show that these two satellite features have concentrations at velocities that match the velocity locations of L4 and L5 in the system.

Low-state Magnetic Structures in Polars: Nature or Nurture?

We present an orbit-resolved study of the magnetic cataclysmic variable (MCV) BL Hyi in its low state, and we explore the origin of its Hα emission line components, their properties, and their possible formation mechanism. We tentatively associate one of the line components with a high-velocity component also seen in the high state. We propose a scenario in which streaming prominence-like magnetic loops (super-prominences) are kept in place by magnetic field interactions between the white dwarf and the donor star and are responsible for the high-velocity line components in the Balmer lines. We also discuss how this is in accord with the standard scenario of the secular evolution for MCVs. Finally, we offer an observational test of our ideas and present challenges for future theoretical studies.

Observations of V592 Cas -— an Outflow at Optical Wavelengths

We present new red optical spectra of V592 Cas aimed at exploring the properties of the outflow of this system in a spectral region where the underlying white dwarf and the accretion disk do not contribute significantly to the observed absorption components of the Hα and He I line profiles. We use the Hα emission line to study the wind, which appears as pronounced blueshifted P Cygni absorption troughs whose low velocity end contaminates the blue side of the emission line profile. The wind appears to be episodic in nature, with multiple events reaching velocities of 5000 km s^–1 in Hα. Similar (but weaker) wind signatures appear in the He I 5876 A line but are absent in He I 6678 A. Our data suggest that during wind episodes the wind is phase dependent and is visible for half of the orbit of the system. Considering that V592 Cas is viewed almost face-on, the symmetry axis of the outflow cannot be orthogonal to the disk and/or the outflow must have some other inherent asymmetry in outflow geometry. A possible origin of the wind is in a disk hotspot, either at the initial impact point of the accretion stream on the disk edge or as a result of disk overflow (similar to SW Sextantis stars). Simultaneous optical photometry during one night of our spectroscopic observations indicate that there is no clear relationship between the optical brightness variations and the strength of the outflow in this system.

ORBIT-RESOLVED PHOTOMETRY AND ECHELLE SPECTROSCOPY OF THE CATACLYSMIC VARIABLE ST LMi DURING A 2007 HIGH STATE

We present high-resolution echelle spectra and contemporaneous photometry of the polar ST LMi during a high state in 2007 March. Emission lines at Hα, He I λ5876, and He I λ7065 show similar line profiles over orbital phase and have narrow and broad components. These profile changes with phase are very similar to those reported in earlier high-state studies of ST LMi. The radial velocity curves from double Gaussian fits to the line profiles are interpreted as two crossing curves, neither of which is coincident with the orbital motion of the secondary star. We attribute one component to infall motions near the white dwarf and the other to a gas streaming along magnetic field lines connecting the two stars.

What's Cool About Hot Stars? Infrared Observations of Cataclysmic Variables with the Spitzer Space Telescope

Cataclysmic variables have been extensively observed at optical, ultraviolet, and Xray wavelengths, where their white dwarf primary stars and bright accretion disks dominate their emitted luminosity. Comparatively little is known about the infrared properties of cataclysmic variables. The assumption that infrared observations would reveal only the “uninteresting” secondary star has been shown to be false: recent infrared observations of cataclysmic variables have instead shown that cool dust in these interacting binaries is possibly the most important contributor to their spectral energy distributions at long wavelengths. We present recent results from infrared observations of the cataclysmic variable EF Eridani obtained with the Spitzer Space Telescope.