RX J1914.4+2456 exhibits a light curve with a strong modulation at 569 s: this period is characteristic of the white dwarf spin period in intermediate polar (IP) systems. However, the X‐ray light curve is difficult to reconcile with current models for IP emission. We argue that a simpler explanation is that the system is a polar with a degenerate secondary star, which would make it the first known system of its kind. As such it should contain the first example of an He‐dominated radial accretion flow on to the white dwarf surface, and RX J1914.4+2456 would have the shortest known orbital period of any binary system.

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A detailed analysis of simultaneous photometric and spectroscopic observations of the optical counterpart of the LMC \supersoft" X-ray source RX J0513.906951 (identied with HV 5682) is presented. The spectrum is dominated by He II emission lines and H + He II blends; no He I is observed but several higher ionization emission features, especially O VI (3811, 3834, and 5290 A) are prominent. Radial velocity measurements suggest a binary period of 0: d 76. If the small velocity amplitude, K11 km s 01 , is interpreted as orbital motion, this implies that the binary system contains a somewhat evolved star plus a relatively massive compact object, viewed nearly pole-on. No orbital photometric variations were found, although irregular brightness changes of 0:3 mag occurred. Unusual emission lines are observed which cannot be identied except as high velocity (4000 km s 01 ) bipolar outows or jets. These outows are seen in H and He II at the same positive and negative velocities. They were relatively stable for periods of 5 days, but their velocities appear to have been 250 km s 01 smaller in 1992 than in 1993 or 1994.

A B S T R A C TWe apply our technique for indirect imaging of the accretion stream to the polar HU Aquarii, using eclipse profiles observed when the system was in a high accretion state. The accretion stream is relatively luminous, contributing as much as the accretion region on the white dwarf, or more, to the overall system brightness. We model the eclipse profiles using a model stream consisting of a ballistic trajectory from the L1 point followed by a magnetically channelled trajectory that follows a dipole field line out of the orbital plane. We perform model fits using two geometries: a stream that accretes on to both footpoints of the field line, and a stream that accretes only on to the footpoint of the field line above the orbital plane. The stream images indicate that the distribution of emission along the stream is not a simple function of the radial distance from the white dwarf. The stream is redirected by the magnetic field of the white dwarf at a distance 1X0±1X3 Â 10 10 cm from the white dwarf; this implies a mass transfer rate in the range 8±76 Â 10 16 g s 21 . The absorption dips in the light curve indicate that the magnetically entrained part of the stream moves from 428 to 488 from the line of centres over the three nights of observation. This is in close agreement with the results of the one-footpoint models, suggesting that this is the more appropriate geometry for these data. The stream images show that, in almost all sections of the stream, the flux peaks in B and is successively fainter in U, V and R.

Schwope et al (1997) suggested that the newly discovered Polar RX J2115-5840 is a near-synchronous system. We have obtained circular polarisation observations of RX J2115-5840 which show that the spin and orbital periods differ by 1.2%. We find the first direct evidence of `pole-switching' in a near-synchronous Polar. Further our data requires that the accretion flow must be directed onto the same magnetic field line at all spin-orbit beat phases implying that at some phases the flow must follow a path around the white dwarf before accreting.Comment: To be published in Proc Annapolis workshop on magnetic CVs, held in July 199

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We present near-infrared (NIR) spectra for Type Ia supernovae at epochs of 13 to 338 days after maximum blue light. Some contemporary optical spectra are also shown. All the NIR spectra exhibit considerable structure throughout the J-, H-and K-bands. In particular they exhibit a flux 'deficit' in the J-band which persists as late as 175 days. This is responsible for the well-known red J-H colour. To identify the emission features and test the 56 Ni hypothesis for the explosion and subsequent light curve, we compare the NIR and optical nebularphase data with a simple non-LTE nebular spectral model. We find that many of the spectral features are due to iron-group elements and that the J-band deficit is due to a lack of emission lines from species which dominate the rest of the IR/optical spectrum. Nevertheless, some emission is unaccounted for, possibly due to inaccuracies in the cobalt atomic data. For some supernovae, blueshifts of 1000-3000 km/s are seen in infrared and optical features at 3 months. We suggest this is due to clumping in the ejecta. The evolution of the cobalt/iron mass ratio indicates that 56 Co-decay dominates the abundances of these elements. The absolute masses of iron-group elements which we derive support the basic thermonuclear explosion scenario for Type Ia supernovae. A core-collapse origin is less consistent with our data.