A light curve of the eclipsing binary CM Draconis has been analyzed for the presence of transits of planets of size º2.5 Earth radii with periods of 60 days or less, and in coplanar orbits around the (R E ), binary system. About 400 million model light curves, representing transits from planets with periods ranging from 7 to 60 days, have been matched/correlated against these data. This process we call the "" transit detection algorithm ÏÏ or TDA. The resulting "" transit statistics ÏÏ for each planet candidate allow the quantiÐcation of detection probabilities, and of false-alarm rates.Our current light curve of CM Dra has a coverage of 1014 hr with 26,043 individual points, at a photometric precision between 0.2% and 0.7%. Planets signiÐcantly larger than would constitute a 3R E "" supranoise ÏÏ detection, and for periods of 60 days or less, they would have been detected with a probability greater than 90%. "" Subnoise ÏÏ detections of smaller planets are more constrained. For example, planets with 10 day periods or less would have been detected with an 80% probability. The neces-2.5R E sity for predicted observations is illustrated with the nine top planet candidates that emerged from our TDA analysis. They are the planet candidates with the highest transit statistics from the 1994È1998 observing seasons, and for them transits for the 1999 observing season were predicted. Of the seven candidates that were then observationally tested in 1999, all were ruled out except one, which needs further observational conÐrmation. We conclude that the photometric transit method is a viable way to search for relatively small, inner extrasolar planets with moderate-sized telescopes using CCD photometry with a matching-Ðlter analysis.
Aims. Our objective is to elucidate the physical process that causes the observed observed-minus-calculated (O-C) behavior in the M4.5/M4.5 binary CM Dra and to test for any evidence of a third body around the CM Dra system. Methods. New eclipse minimum timings of CM Dra were obtained between the years 2000 and 2007. The O-C times of the system are fitted against several functions, representing different physical origins of the timing variations.Results. Using our observational data in conjunction with published timings going back to 1977, a clear non-linearity in O-C times is apparent. An analysis using model-selection statistics gives about equal weight to a parabolic and to a sinusoidal fitting function. Attraction from a third body, either at large distance in a quasi-constant constellation across the years of observations or from a body on a shorter orbit generating periodicities in O−C times is the most likely source of the observed O−C times. The white dwarf GJ 630.1B, a proper motion companion of CM Dra, can however be rejected as the responsible third body. Also, no further evidence of the shortperiodic planet candidate described by Deeg et al. (2000, A&A, 358, L5) is found, whereas other mechanisms, such as period changes from stellar winds or Applegate's mechanism can be rejected. Conclusions. A third body, being either a few-Jupiter-mass object with a period of 18.5 ± 4.5 years or an object in the mass range of 1.5 M jup to 0.1 M with periods of hundreds to thousands of years is the most likely origin of the observed minimum timing behavior.
We report on detection of negative superhumps in KR Aur which is the representative member of the VY Scl stars. The observations were obtained with the multi-channel photometer during 107 h. The analysis of the data clearly revealed brightness variations with a period of 3.771 +/- 0.005 h. This is 3.5 per cent less than the orbital period, suggesting it is a negative superhump. Negative superhumps in VY Scl stars are widely spread. The discovery of powerful soft X-rays from V751 Cyg demonstrates that VY Scl stars may contain white dwarfs, at which nuclear burning of the accreted material occur. If this suspicion is correct, we then can suppose that the powerful radiation emerging from the white dwarf may cause the tilt of the accretion disk to the orbital plane, and its retrograde precession may produce negative superhumps in VY Scl stars.Comment: 6 pages, 6 figures, will be published in MNRA
We report the results of photometry of the intermediate polar V515 And. Observations were obtained over 33 nights in 2008 and 2009. The total duration of the observations was 233 h. We clearly detected two oscillations with periods of 465.484 93 ± 0.000 07 and 488.618 22 ± 0.000 09 s, which may be the white dwarf spin period and the orbital sideband. The semi‐amplitudes of the oscillations are accordingly 25 and 20 mmag. The oscillation with a period of 465.484 93 s has a stable smooth asymmetric pulse profile, whereas the pulse profile of the oscillation with a period of 488.618 22 s reveals significant changes from a quasi‐sinusoidal shape to a shape somewhat resembling a light curve of an eclipsing binary. Two detected oscillations imply an orbital period of 2.73 h. V515 And is one of the most rapidly spinning intermediate polars with orbital periods less than 3 h and may not be in spin equilibrium. This could be proved by future observations. For this purpose, we obtained oscillation ephemerides with a formal shelf life of about 100 yr (a 1σ confidence level).
Abstract. We present results of our photometry of the Z Camelopardalis-type dwarf nova AT Cnc. The observational data were obtained during 13 nights in February and March 2003 when AT Cnc was in its long standstill. Two sets of our data reveal brightness variations with quasi-periods of (4.65 ± 0.02) and of (4.74 ± 0.02) h. The semiamplitude of these variations was observed in the range 5-9 mmag, showing changes from night to night. This signal varies in period and in phase on a time-scale of weeks, as is typical of superhumps. A comparison with the orbital period obtained by Nogami et al. (1999) from the radial velocity measurements of AT Cnc, which equals (4.826 ± 0.014) h, shows that this signal can be a negative superhump since the average period of brightness variations is approximately 3% shorter than the orbital period. These results make AT Cnc a permanent superhump system with a rather large orbital period and a large mass ratio. This is also the first detection of superhumps in a Z Camelopardalis-type system. In addition, we have found signs of an unstable signal with a period of about 2.3 h, which may represent the second harmonic of the 4.7-h signal or the second orbital sideband of the wobble frequency of the tilted precessing accretion disc. The average power spectrum of AT Cnc reveals a broad hump at frequencies in the range 0.4-0.7 mHz, which is evidence of quasiperiodic oscillations. The hump crest corresponds to a period of 1700-1800 s, which is remarkably close to 10% of the orbital period. This may indicate that this system contains a magnetic white dwarf creating the tilted accretion disc.
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