Can the Rapid Braking of the White Dwarf in AE Aquarii Be Explained in Terms of the Gravitational-Wave Emitter Mechanism?
The spin-down power of the white dwarf in the close binary AE Aquarii significantly exceeds the bolometric luminosity of the system. The interpretation of this phenomenon in terms of the gravitational-wave emitter mechanism has been recently suggested by Choi & Yi. The basic assumption of their interpretation is that the spatially limited blobs or mounds of mass δm ~ 10-3 M☉ are present at the magnetic poles of the white dwarf. We show that the mounds of this mass can be confined by the magnetic field of the white dwarf only if the dipole magnetic moment of the star exceeds 4 × 1037 G cm3. Under these conditions, however, the magnetodipole losses of the white dwarf would exceed the evaluated spin-down power by 6 orders of magnitude. On this basis, we discard the possibility that the observed rapid braking of the white dwarf in AE Aqr can be explained in terms of the mechanism proposed by Choi & Yi.
On the Rapid Spin-down and Low-Luminosity Pulsed Emission from AE Aquarii
AE Aqr is an unusual close binary system with a very short white dwarf spin period, a high spin-down rate, a relatively low quiescent luminosity, and clear pulse signals. The exact nature of the large spin-down power has not been well explained mainly because the observed luminosities in various energy ranges are much lower than the spin-down power. We consider an unconventional picture of AE Aqr in which an accreting white dwarf, modeled as a magnetic dipole whose axis is misaligned with the spin axis, is rapidly spun down via gravitational radiation emission and therefore the spin-down power is not directly connected to any observable electromagnetic emission. The rapid spin-down is caused by the nonaxisymmetric polar mounds of accreted material slowly spreading away from the magnetic poles over the surface of the star. The effectiveness of the spin-down driven by the gravitational radiation depends on complex diffusion and thermonuclear burning of the accretion mound material. The accretion proceeds at high altitudes toward the magnetic poles of the white dwarf, while a large fraction of the inflowing material is ejected in a propeller-like manner. Based on the observed quiescent X-ray and UV emission, the magnetic field strength is estimated as ~1 × 105η G and the mass accretion rate as ~1 × 1015η g s-1, where ηX < 1 is the X-ray radiative efficiency. A large fraction of the accreted mass is flung out by the propeller action, and ~50% of the accreted material arrives at the magnetic poles. The electromagnetic dipole emission is expected at the level of ~1 × 1029η ergs s-1, which suggests that, for ηX ~ 0.1, the observed radio luminosity could be well accounted for by dipole radiation.
APPLICATION OF SATELLITE PHOTOGRAPHS IN A MORPHOTECTONIC STUDY OF THE CENTRAL ALBORZ, IRAN
This paper introduces a study of morphotectoni c structure in the Central Alborz Basin, Mazandaran province of Iran (about 1200 square kilometer), using Russian KFA-1000 satellite photography and sequential air photographs. The KFA-1000 metric camera has better ground resolution than SPOT and LANDSAT for the whole of the study area. Results are provided from one pair of 30×30 cm. photos, which provided easy interpretation and better results than other data. Areas identified from these images as being of significance were examined in greater detail through the use of aerial photographs (at scales of 1:5000, 1:10000 and 1:60000 were available).