Issue |
A&A
Volume 402, Number 1, April IV 2003
|
|
---|---|---|
Page(s) | 201 - 209 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20030235 | |
Published online | 07 April 2003 |
Cyclotron spectroscopy of HU Aquarii*
1
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
2
Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85740 Garching, Germany
3
Universitäts-Sternwarte München, Scheinerstr. 1, 81679 München, Germany
Corresponding author: A. D. Schwope, aschwope@aip.de
Received:
30
October
2002
Accepted:
13
February
2003
We present the results of a combined analysis of
low-resolution spectroscopy and
high-speed optical photometry of the bright eclipsing polar
HU Aqr, obtained in its high accretion state. Cyclotron harmonic
emission in a field of MG
became evident and could be traced through the whole
optical bright phase. The cyclotron harmonics display an asymmetric
motion as a function of phase which requires a certain forward tilt
of the magnetic field lines in the emission region.
The optical bright phase is more
extended than the bright phase in soft X-rays suggesting a more
extended emission region. Also, ingress into and egress from the
optical eclipse last much longer in the optical than at X-ray wavelengths.
These observations require the existence of an accretion arc
with total extent of about 20°. The soft X-ray accretion spot
is located at the far end of the arc, where the bulk of matter
is accreted. The arc is likely to be more extended
than the foot-line of field lines connecting to the ballistic
accretion stream in a dipolar geometry. This together with the
required tilt of the accreting field lines suggest a more
complex magnetic geometry than a simple dipole.
Key words: accretion, accretion disks / stars: binaries: eclipsing / magnetic fields / stars: individual: HU Aqr
© ESO, 2003
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