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Register a new userThe period-gap cataclysmic variable CzeV404 Her: A link between SW Sex and SU UMa systems
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Context: We present a new study of the eclipsing cataclysmic variable CzeV404 Her (Porb = 0.098 d) that is located in the period gap. Aims: This report determines the origin of the object and the system parameters and probes the accretion flow structure of the system. Methods: We conducted simultaneous time-resolved photometric and spectroscopic observations of CzeV404 Her. We applied our light-curve modelling techniques and the Doppler tomography method to determine the system parameters and analyse the structure of the accretion disk. Results: We found that the system has a massive white dwarf M_WD = 1.00(2) M_sun a mass ratio of q = 0.16, and a relatively hot secondary with an effective temperature T_2 = 4100(50) K. The system inclination is i = 78.8{deg}. The accretion disk spreads out to the tidal limitation radius and has an extended hot spot or line region. The hot spot or line is hotter than the remaining outer part of the disk in quiescence or in intermediate state, but does not stand out completely from the disk flux in (super)outbursts. Conclusions: We claim that this object represents a link between two distinct classes of SU UMa-type and SW Sex-type cataclysmic variables. The accretion flow structure in the disk corresponds to the SW Sex systems, but the physical conditions inside the disk fit the behaviour of SU UMa-type objects.
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We conducted a spectroscopic and photometric study of SDSS J075653.11+085831. X-ray observations were also attempted. We determined the orbital period of this binary system to be 3.29 hr. It is a deep eclipsing system, whose spectra shows mostly single-peaked Balmer emission lines and a rather intense He II line. There is also the presence of faint (often double-peaked) He I emission lines as well as several absorption lines, Mg I being the most prominent. All of these features point towards the affiliation of this object with the growing number of SW~Sex-type objects. We developed a phenomenological model of an SW~Sex system to reproduce the observed photometric and spectral features.
We present time-resolved optical spectroscopy and photometry of the nova-like cataclysmic variable V348 Puppis. The system displays the same spectroscopic behaviour as SW Sex stars, so we classify V348 Pup as a new member of the class. V348 Pup is the second SW Sex system (the first is V795 Herculis) which lies in the period gap. The spectra exhibit enhanced HeII 4686 emission, reminiscent of magnetic cataclysmic variables. The study of this emission line gives a primary velocity semi-amplitude of K1 ~= 100 km/s. We have also derived the system parameters, obtaining: M1 ~= 0.65 Msun, M2 ~= 0.20 Msun (q ~= 0.31), i ~= 80 deg and K2 ~= 323 km/s. The spectroscopic behaviour of V348 Pup is very similar to that of V795 Her, with the exception that V348 Pup shows deep eclipses. We have computed the ``0.5-absorption spectrum of both systems, obtaining spectra which resemble the absorption spectrum of a B0 V star. We propose that absorption in SW Sex systems can be produced by a vertically extended atmosphere which forms where the gas stream re-impacts the system, either at the accretion disc or at the white dwarfs magnetosphere (assuming a magnetic scenario).
We report results of an extensive world-wide observing campaign devoted to the recently discovered dwarf nova SDSS J162520.29+120308.7 (SDSS J1625). The data were obtained during the July 2010 eruption of the star and in August and September 2010 when the object was in quiescence. During the July 2010 superoutburst SDSS J1625 clearly displayed superhumps with a mean period of $P_{rm sh}=0.095942(17)$ days ($138.16 pm 0.02$ min) and a maximum amplitude reaching almost 0.4 mag. The superhump period was not stable, decreasing very rapidly at a rate of $dot P = -1.63(14)cdot 10^{-3}$ at the beginning of the superoutburst and increasing at a rate of $dot P = 2.81(20)cdot 10^{-4}$ in the middle phase. At the end of the superoutburst it stabilized around the value of $P_{rm sh}=0.09531(5)$ day. During the first twelve hours of the superoutburst a low-amplitude double wave modulation was observed whose properties are almost identical to early superhumps observed in WZ Sge stars. The period of early superhumps, the period of modulations observed temporarily in quiescence and the period derived from radial velocity variations are the same within measurement errors, allowing us to estimate the most probable orbital period of the binary to be $P_{rm orb}=0.09111(15)$ days ($131.20 pm 0.22$ min). This value clearly indicates that SDSS J1625 is another dwarf nova in the period gap. Knowledge of the orbital and superhump periods allows us to estimate the mass ratio of the system to be $qapprox 0.25$. This high value poses serious problems both for the thermal and tidal instability (TTI) model describing the behaviour of dwarf novae and for some models explaining the origin of early superhumps.
We report photometric and spectroscopic observations of the eclipsing SU UMa-type dwarf nova ASASSN-18aan. We observed the 2018 superoutburst with 2.3 mag brightening and found the orbital period ($P_{rm orb}$) to be 0.149454(3) d, or 3.59 hr. This is longward of the period gap, establishing ASASSN-18aan as one of a small number of long-$P_{rm orb}$ SU UMa-type dwarf novae. The estimated mass ratio, ($q=M_2/M_1 = 0.278(1)$), is almost identical to the upper limit of tidal instability by the 3:1 resonance. From eclipses, we found that the accretion disk at the onset of the superoutburst may reach the 3:1 resonance radius, suggesting that the superoutburst of ASASSN-18aan results from the tidal instability. Considering the case of long-$P_{rm orb}$ WZ Sge-type dwarf novae, we suggest that the tidal dissipation at the tidal truncation radius is enough to induce SU UMa-like behavior in relatively high-$q$ systems such as SU UMa-type dwarf novae, but that this is no longer effective in low-$q$ systems such as WZ Sge-type dwarf novae. The unusual nature of the system extends to the secondary star, for which we find a spectral type of G9, much earlier than typical for the orbital period, and a secondary mass $M_2$ of around 0.18 M$_{odot}$, smaller than expected for the orbital period and the secondarys spectral type. We also see indications of enhanced sodium abundance in the secondarys spectrum. Anomalously hot secondaries are seen in a modest number of other CVs and related objects. These systems evidently underwent significant nuclear evolution before the onset of mass transfer. In the case of ASASSN-18aan, this apparently resulted in a mass ratio lower than typically found at the systems $P_{rm orb}$, which may account for the occurrence of a superoutburst at this relatively long period.
We report the discovery of a new eclipsing polar, CRTS J035010.7+323230 (hereafter CRTS J0350+3232). We identified this cataclysmic variable (CV) candidate as a possible polar from its multi-year Catalina Real-Time Transient Survey (CRTS) optical light curve. Photometric monitoring of 22 eclipses in 2015 and 2017 was performed with the 2.1-m Otto Struve Telescope at McDonald Observatory. We derive an unambiguous high-precision ephemeris. Strong evidence that CRTS J0350+3232 is a polar comes from optical spectroscopy obtained over a complete orbital cycle using the Apache Point Observatory 3.5-m telescope. High velocity Balmer and He II $lambda$4686{AA} emission line equivalent width ratios, structures, and variations are typical of polars and are modulated at the same period, 2.37-hrs (142.3-min), as the eclipse to within uncertainties. The spectral energy distribution and luminosity is found to be comparable to that of AM Herculis. Pre-eclipse dips in the light curve show evidence for stream accretion. We derive the following tentative binary and stellar parameters assuming a helium composition white dwarf and a companion mass of 0.2 M$_{odot}$: inclination i = 74.68$^{o}$ ${pm}$ 0.03$^{o}$, semi-major axis a = 0.942 ${pm}$ 0.024 R$_{odot}$, and masses and radii of the white dwarf and companion respectively: M$_{1}$ = 0.948 $^{+0.006}_{-0.012}$ M$_{odot}$, R$_{1}$ = 0.00830 $^{+0.00012}_{-0.00006}$ R$_{odot}$, R$_{2}$ = 0.249 ${pm}$ 0.002 R$_{odot}$. As a relatively bright (V $sim$ 17-19 mag), eclipsing, period-gap polar, CRTS J0350+3232 will remain an important laboratory for the study of accretion and angular momentum evolution in polars.
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