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Added by
Isabel De Jesus Lima
Publication date
2021
fields
Physics
and research's language is
English
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SW Sextantis systems are nova-like cataclysmic variables that have unusual spectroscopic properties, which are thought to be caused by an accretion geometry having part of the mass flux trajectory out of the orbital plane. Accretion onto a magnetic white dwarf is one of the proposed scenarios for these systems. To verify this possibility, we analysed photometric and polarimetric time-series data for a sample of six SW Sex stars. We report possible modulated circular polarization in BO Cet, SW Sex, and UU Aqr with periods of 11.1, 41.2 and 25.7 min, respectively, and less significant periodicities for V380 Oph at 22 min and V442 Oph at 19.4 min. We confirm previous results that LS Peg shows variable circular polarization. However, we determine a period of 18.8 min, which is different from the earlier reported value. We interpret these periods as the spin periods of the white dwarfs. Our polarimetric results indicate that 15% of the SW Sex systems have direct evidence of magnetic accretion. We also discuss SW Sex objects within the perspective of being magnetic systems, considering the latest findings about cataclysmic variables demography, formation and evolution.
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We present time-resolved spectroscopy and circular spectropolarimetry of the SW Sex star RX J1643.7+3402. We find significant polarisation levels exhibiting a variability at a period of 19.38 +- 0.39 min. In addition, emission-line flaring is found predominantly at twice the polarimetric period. These two findings are strong evidences in favour of the presence of a magnetic white dwarf in the system. We interpret the measured periodicities in the context of our magnetic accretion model for SW Sex stars. In contrast with LS Pegasi -the first SW Sex star discovered to have modulated circular polarisation- the polarisation in RX J1643.7+3402 is suggested to vary at 2(omega - Omega), while the emission lines flare at (omega - Omega). However, a 2omega/omega interpretation cannot be ruled out. Together with LS Peg and V795 Her, RX J1643.7+3402 is the third SW Sex star known to exhibit modulated circular polarisation.
We present optical photometry and spectroscopy of the new eclipsing Cataclysmic Variable MASTER OTJ192328.22+612413.5, discovered by the MASTER team. We find the orbital period to be P=0.16764612(5) day /4.023507(1) hour. The depth of the eclipse (2.9$pm$0.1 mag) suggests that the system is nearly edge on, and modeling of the system confirms the inclination to be between 81.3-83.6 degree. The brightness outside of eclipse varies between observations, with a change of 1.6$pm$0.1 mag. Spectroscopy reveals double-peaked Balmer emission lines. By using spectral features matching a late M-type companion, we bound the distance to be 750$pm$250 pc, depending on the companion spectral type. The source displays 2 mag brightness changes on timescales of days. The amplitude of these changes, along with the spectrum at the faint state, suggest the system is possibly a dwarf nova. The lack of any high excitation HeII lines suggests this system is not magnetically dominated. The light curve in both quiescence and outburst resembles that of Lanning 386, implying MASTER OTJ192328.22+612413.5 is a possible cross between a dwarf nova and a SW Sextantis star.
[Abridged] We report on time-resolved optical spectroscopy of ten non-eclipsing nova-like cataclysmic variables in the orbital period range between 3 and 4 hours. Of the ten systems so far observed, HL Aqr, BO Cet, AH Men, V380 Oph, AH Pic, and LN UMa are identified as new members of the SW Sex class. We present improved orbital period measurements for HL Aqr (Porb = 3.254 +- 0.001 h) and V380 Oph (Porb = 3.69857 +- 0.00002 h). BO Cet and V380 Oph exhibit emission-line flaring with periodicities of 20 min and 47 min, respectively. The Halpha line of HL Aqr shows significant blueshifted absorption modulated at the orbital period. Similarly to the emission S-wave of the high-inclination SW Sex stars, this absorption S-wave has its maximum blue velocity at orbital phase ~0.5. We estimate an orbital inclination for HL Aqr in the range 19 < i < 27 deg, which is much lower than that of the emission-dominated, non-eclipsing SW Sex stars (i ~ 60-70 deg). This gives rise to the interesting possibility of many low-inclination nova-likes actually being SW Sex stars, but with a very different spectroscopic appearance as they show significant absorption. The increasing blueshifted absorption with decreasing inclination points to the existence of a mass outflow with significant vertical motion. This six new additions to the SW Sex class increase the presence of non-eclipsing systems to about one third of the whole SW Sex population, which therefore makes the requirement of eclipses as a defining criterion for SW Sex membership no longer valid. The statistics of the cataclysmic variable population in the vicinity of the upper period gap is also discussed.
New time-resolved optical spectroscopic echelle observations of the nova-like cataclysmic variable RW Sextantis were obtained, with the aim to study the properties of emission features in the system. The profile of the H_alpha emission line can be clearly divided into two (`narrow and `wide) components. Similar emission profiles are observed in another nova-like system, 1RXS~J064434.5+33445, for which we also reanalysed the spectral data and redetermined the system parameters. The source of the `narrow, low-velocity component is the irradiated face of the secondary star. We disentangled and removed the `narrow component from the H_alpha profile to study the origin and structure of the region emitting the wide component. We found that the `wide component is not related to the white dwarf or the wind from the central part of the accretion disc, but is emanated from the outer side of the disc. Inspection of literature on similar systems indicates that this feature is common for some other long-period nova-like variables. We propose that the source of the `wide component is an extended, low-velocity region in the outskirts of the opposite side of the accretion disc, with respect to the collision point of the accretion stream and the disc.
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