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Register a new userPhotometric study of selected cataclysmic variables
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We present time-resolved photometry of five relatively poorly-studied cataclysmic variables: V1193 Ori, LQ Peg, LD 317, V795 Her, and MCT 2347-3144. The observations were made using four 1m-class telescopes for a total of more than 250 h of observation and almost 16,000 data points. For LQ Peg WHT spectroscopic data have been analysed as well. The light curves show a wide range of variability on different time scales from minutes to months. We detect for the first time a brightness variation of 0.05 mag in amplitude in V1193 Ori on the same timescale as the orbital period, which we interpret as the result of the irradiation of the secondary. A 20-min quasi-periodic oscillation is also detected. The mean brightness of the system has changed by 0.5 mag on a three-month interval, while the flickering was halved. In LQ Peg a 0.05 mag modulation was revealed with a period of about 3 h. The flickering was much smaller, of the order of 0.025 mag. A possible quasi-periodic oscillation could exist near 30 min. For this object, the WHT spectra are single-peaked and do not show any radial-velocity variations. The data of LD 317 show a decrease in the mean magnitude of the system. No periodic signal was detected but this is certainly attributable to the very large flickering observed: between 0.07 and 0.1 mag. For V795 Her, the 2.8-hour modulation, thought to be a superhump arising from the precession of the disc, is present. We show that this modulation is not stable in terms of periodicity, amplitude, and phase. Finally, for MCT 2347-3144, a clear modulation is seen in a first dataset obtained in October 2002. This modulation is absent in August 2003, when the system was brighter and showed much more flickering.
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We present time-series photometry of nine cataclysmic variables: EI UMa, V844Her, V751 Cyg, V516 Cyg, GZ Cnc, TY Psc, V1315 Aql, ASAS J002511+1217.12, V1315 Aql and LN UMa. The observations were conducted at various observatories, covering 170 hours and comprising 7,850 data points in total. For the majority of targets we confirm previously reported periodicities and for some of them we give, for the first time, their spectroscopic orbital periods. For those dwarf-nova systems which we observed during both quiescence and outburst, the increase in brightness was followed by a decrease in the amount of flickering. Quasi-periodic oscillations have either been discovered, or were confirmed. For the eclipsing system V1315 Aql we have covered 9 eclipses, and obtained a refined orbital ephemeris. We find that, during its long baseline of observations, no change in the orbital period of this system has occurred. V1315 Aql also shows eclipses of variable depth.
We report on the properties of 71 known cataclysmic variables (CVs) in photometric Halpha emission line surveys. Our study is motivated by the fact that the Isaac Newton Telescope (INT) Photometric Halpha Survey of the northern galactic plane (IPHAS) will soon provide r, i and narrow-band Halpha measurements down to r simeq 20 for all northern objects between -5 degrees < b < +5 degrees. IPHAS thus provides a unique resource, both for studying the emission line properties of known CVs and for constructing a new CV sample selected solely on the basis of Halpha excess. Our goal here is to carry out the first task and prepare the way for the second. In order to achieve this, we analyze data on 19 CVs already contained in the IPHAS data base and supplement this with identical observations of 52 CVs outside the galactic plane. Our key results are as follows: (i) the recovery rate of known CVs as Halpha emitters in a survey like IPHAS is simeq 70 per cent; (ii) of the simeq 30 per cent of CVs which were not recovered simeq 75 per cent were clearly detected but did not exhibit a significant Halpha excess at the time of our observations; (iii) the recovery rate depends only weakly on CV type; (iv) the recovery rate depends only weakly on orbital period; (v) short-period dwarf novae tend to have the strongest Halpha lines. These results imply that photometric emission line searches provide an efficient way of constructing CV samples that are not biased against detection of intrinsically faint, short-period systems.
The space density of the various classes of cataclysmic variables (CVs) could only be weakly constrained in the past. Reasons were the small number of objects in complete X-ray flux-limited samples and the difficulty to derive precise distances to CVs. The former limitation still exists. Here the impact of Gaia parallaxes and implied distances on the space density of X-ray selected complete, flux-limited samples is studied. The samples are described in the literature, those of non-magnetic CVs are based on ROSAT (RBS - ROSAT Bright Survey & NEP -- North Ecliptic Pole), that of the Intermediate Polars stems from Swift/BAT. All CVs appear to be rarer than previously thought, although the new values are all within the errors of past studies. Upper limits at 90% confidence for the space densities of non-magnetic CVs are $rho_{rm RBS} < 1.1 times 10^{-6}$ pc$^{-3}$, and $rho_{rm RBS+NEP} < 5.1 times 10^{-6}$ p$^{-3}$, for an assumed scale height of $h=260$ pc and $rho_{rm IPs} < 1.3 times 10^{-7}$ p$^{-3}$ for the long-period Intermediate Polars at a scale height of 120 pc. Most of the distances to the IPs were under-estimated in the past. The upper limits to the space densities are only valid in the case where CVs do not have lower X-ray luminosities than the lowest-luminosity member of the sample. These results need consolidation by larger sample sizes, soon to be established through sensitive X-ray all-sky surveys to be performed with eROSITA on the Spektrum-X-Gamma mission.
The quiescent periodic photometric modulations of two low-inclination cataclysmic variables observed in Kepler K2 Campaigns 0 and 1, KZ Gem and TW Vir, are investigated. A phase-correcting method was successfully used to detect the orbital modulations of KZ Gem and TW Vir and improve their orbital periods. The light curve morphologies of both CVs were further analyzed by defining flux ratios and creating colormaps. KZ Gem shows ellipsoidal modulations with an orbital period of 0.22242(1) day, twice the period listed in the updated RK catalogue (Edition 7.24). With this newly determined period, KZ Gem is no longer a CV in the period gap, but a long-period CV. A part of the quiescent light curve of TW Vir that had the highest stability was used to deduce its improved orbital period of 0.182682(3) day. The flat patterns shown in the colormaps of the flux ratios for KZ Gem demonstrate the stability of their orbital modulations, while TW Vir show variable orbital modulations during the K2 datasets. In TW Vir, the single versus double-peaked nature of the quiescent orbital variations before and after superoutburst may be related to the effect of the superoutburst on the accretion disk.
Strong selection effects are present in observational samples of cataclysmic variables (CVs), complicating comparisons to theoretical predictions. The selection criteria used to define most CV samples discriminate heavily against the discovery of short-period, intrinsically faint systems. The situation can be improved by selecting CVs for the presence of emission lines. For this reason, we have constructed a homogeneous sample of CVs selected on the basis of Halpha emission. We present discovery observations of the 14 CVs and 2 additional CV candidates found in this search. The orbital periods of 11 of the new CVs were measured; all are above 3 h. There are two eclipsing systems in the sample, and one in which we observed a quasi-periodic modulation on a sim 1000 s time-scale. We also detect the secondary star in the spectrum of one system, and measure its spectral type. Several of the new CVs have the spectroscopic appearance of nova-like variables (NLs), and a few display what may be SW Sex star behaviour. In a companion paper, we discuss the implications of this new sample for CV evolution.
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