Other
Scientific paper
Oct 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004mast.conf..279s&link_type=abstract
Magnetic stars, Proceedings of the International Conference, held in the Special Astrophysical Observatory of the Russian AS, Au
Other
Accretion, Hu Aqr (Rxj2107-05), Cataclysmic Variables
Scientific paper
We present the results of optical time-resolved spectroscopy and photometry of the eclipsing polar HU Aquarii, obtained with the help of the scanner of the 6 m telescope in July, 1994 and the CCD photometer of the 1 m telescope in September, 2002. The parameters of Balmer and HeII emission lines in the spectra of HU Aqr have demonstrated significant variations with the phase of the orbital period on a time-scale of 5-10 min and from day to day. Spectral light curves (integrated flux in the range of wavelengths 4000-5000Å) have also shown significant variability. The bottom of the primary eclipses in the spectral light curves was 318±12 s with variable ingress (328-388 s) and egress (85-333 s). The form of the spectral light curves is strongly variable on a time-scale of 1-1.5 hours. The radial velocity curves on July 14, 1994 demonstrated deviation from a sinusoid near the orbital phase 0.5, which is considered to be the result of occultation of the magnetic part of the accretion stream by the white dwarf. At the same time, the spectral light curve showed several dips:
-- at phase 0, the eclipse of the white dwarf and the accretion stream by the secondary;
-- at phase ≈ 0.85, the pre-eclipse dip due to the eclipse of the accretion spot by the accretion stream;
-- at phase 0.5, the dip which, as we suppose, is caused by the eclipse of the accretion spot by the white dwarf;
-- at phase 0.46, the pre-eclipse dip due to the eclipse of the accretion spot by the magnetic part of the stream. The two pre-eclipse dips at phases 0.85 and 0.46 indicate that the accretion spot is located in the magnetosphere between two parts of the accretion stream coming from the spot along the field lines in approximately opposite directions. The direction of the field lines and the character of perturbation of the emission lines and the spectral light curve at phase 0.5 are indicative of a hot spot, where the horizontal or ballistic part of the stream is threaded onto the magnetic field lines of the white dwarf. The duration of the dip at phase 0.5 gives the upper limit for the distance of ≈ 12Rwd from the center of the white dwarf to the accretion spot. The location of the accretion spot is far from the base of the accretion column and should be considered as a second hot spot in the system. The hot spot is the principal source of the optical radiation of the system in the high state of accretion. The absence of the dips at phases 0.5, 0.46 and 0.85 on other neighboring dates of our observations is evidence of instability of the accretion geometry on a time-scale of 1 day.
Photometric observations during two nights in September 2002 found HU Aqr in the intermediate state, closer to the low state of brightness of the system. The light curve in the V band showed only the primary eclipse without the dips at phases 0.5 and 0.85.
Barsukova Elena A.
Bonnet-Bidaud Jean-Marc
Goranskij Vitalij P.
Somov Nicolai
Somova T. A.
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