Accretion Halos Research Articles

Intrinsic Properties of the Young Stellar Object SU Aurigae

Intensive long-term photometric Q1 observations of the archetypical young G2 IIIe stellar object SU Aurigae are analyzed to determine many of its photometric and physical properties. Combining nearly 2000 Stromgren uvby measures obtained using the 0.8 m Four College Automatic Photoelectric Telescope, previously published photometry, and recently obtained high-resolution echelle spectra has led to the deter- mination of its effective temperature, surface gravity, luminosity, mass, age, rotation period, and absolute radius. Since the disk of SU Aur is seen at a high inclination angle (i.e., nearly edge-on), this complicates the observations with significant (DVDyd0:80 mag), and apparently random, drops in observed mean light. These are possibly due to the transits of protoplanetary bodies, protocomets, or associated accretion halos. In this study, an effort has been made to separate the contributions of the circumstellar disk from the intrinsic properties of the stellar core itself. Furthermore, photometry has been simultaneously obtained for the nearby young A0 Vpe stellar companion AB Aurigae. Analysis has shown that SU Aur and AB Aur are a coeval proper-motion pair. Also included are certain photometric and physical properties of AB Aur. Q2

Phase‐resolved spectroscopy and photometry of the eclipsing polar EP Draconis (=H1907+690)

AbstractWe present phase‐resolved optical spectroscopy and CCD photometry of the faint eclipsing polar EP Dra (H1907+690). A revised ephemeris is derived which connects all 32000 binary cycles since its discovery by Remillard et al. (1991). We found no difference between spin and and orbital periods of the white dwarf. Changes in the light curve morphology are attributed to a different beaming behaviour which might change on timescales as short as one or several orbital periods. Optical light curve modelling was used to estimate the co‐latitude of the accretion spot, which must be larger than 40°. We have detected Zeeman absorption lines of Hα originating in an accretion halo in a field of 16 MG. The low‐resolution spectra reveal no indication of resolved cyclotron harmonics, which is also suggestive of a relatively low field strength in the accretion region. The Balmer emission lines contain significant contributions from the UV‐illuminated hemisphere of the companion star, whereas the Hell λ4686 emission originates predominantly from the accretion stream. The emission lines have a multi‐component structure and we could single out a narrow emission line in the Hβ and Hγ lines. It radial velocity amplitude suggests a low mass for the white dwarf, if the lines are interpreted as being of reprocessed origin from the whole illuminated hemisphere of the companion star.

The accretion halo in AM Herculis systems

Previous phase-resolved spectropolarimetric observations of the AM Herculis systems V834 Centauri (E1405-451) and EF Eridani have shown broad, Zeeman-shifted absorption features during the bright phases. These features are thought to be nonphotospheric in origin, and to arise from a cool 'halo' of unshocked gas surrounding the accretion shock on the surface of the white dwarf primary. Preliminary models for the accretion halo region are presented and these models are used to perform a more detailed analysis of the relevant data for these two systems than has previously been done. To explain the observed halo Zeeman features, geometries which are consistent with the presence of linearly extended cyclotron emission regions are required. Such regions have previously been deduced from different considerations by other investigators. The estimated masses for the accretion halo are comparable to the mass of the cyclotron emission region.

Optical properties of AM Her stars

We review the optical properties of AM Her systems. We consider first the photometric, polarimetric and spectroscopic observations and what can be deduced from them. We then consider some topics of current interest; these include accretion halos, the dynamics of the accretion stream and the evidence for synchronous rotation of the primary.