Intermediate polars as low-field magnetic cataclysmic variables
Abstract
Detailed calculations are presented of the polarization properties of extended accretion shocks on the surface of a magnetic white dwarf, where allowance is made both for field spread and for the change in shock height as a function of specific accretion rate. These results are used to show conclusively that the null detection of circular polarization in most IPs imply fields of less than 5 MG. The X-ray properties of MCVs depends critically on the fractional area of the white-dwarf surface over which accretion occurs, and on the type of accretion (smooth or clumpy). In the known IPs, accretion occurs via a disk. The accretion flow is smooth and a strong shock forms making them a powerful source of hard X-rays. There is a new class of MCV distinct from the IPs, where the white dwarf is asynchronous and accretes without a disk in which the accretion is clumpy and the radiation is mainly in the EUV region. A significant fraction of the IPs above the period gap evolve into such systems below the gap and not into AM Hers, as some workers have previously proposed. Any IP-AM Her transitions occur mainly above the period gap at P(O) greater than 4 hr.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 1991
- DOI:
- 10.1093/mnras/249.3.460
- Bibcode:
- 1991MNRAS.249..460W
- Keywords:
-
- Cataclysmic Variables;
- Magnetic Stars;
- Polarization Characteristics;
- Stellar Magnetic Fields;
- White Dwarf Stars;
- Accretion Disks;
- Bremsstrahlung;
- Circular Polarization;
- Cyclotron Radiation;
- Magnetic Moments;
- Astrophysics