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تسجيل مستخدم جديدEstimating the binary fraction of planetary nebulae central stars
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During the past 20 years, the idea that non-spherical planetary nebulae (PN) may need a binary or planetary interaction to be shaped was discussed by various authors. It is now generally agreed that the varied morphologies of PN cannot be fully explained solely by single star evolution. Observationally, more binary central stars of planetary nebulae (CSPN) have been discovered, opening new possibilities to understand the connections between binarity and morphology. So far, simeq 45 binary CSPN have been detected, most being close systems detected via flux variability. To determine the PN binary fraction, one needs a method to detect wider binaries. We present here recent results obtained with the various techniques described, concentrating on binary infrared excess observations aimed at detecting binaries of any separation.
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precision free from the observational gaps dictated by weather and lunar cycles, we are able to detect companions at much larger separations and with much smaller radii than ever before. We have been awarded observing time to obtain light-curves of the central stars of the six confirmed and possible planetary nebulae in the Kepler field, including the newly discovered object Kn 61, at cadences of both 30 min and 1 min. Of these six objects, we could confirm for three a periodic variability consistent with binarity. Two others are variables, but the initial data set presents only weak periodicities. For the central star of Kn 61, Kepler data will be available in the near future.
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resented. We examined the light curves of all `possible, `likely and `true PNe in every {it Kepler/K2} campaign (0 through 19) to identify CS variability that may indicate a binary CS. For Campaigns 0, 2, 7, 15, and 16 we find 6 likely or confirmed variables among 21 PNe. Our primary effort, though, was focused on Campaign 11 which targeted a Galactic bulge field containing approximately 183 PNe, in which we identified 30 candidate variable CSs. The periods of these variables range from 2.3~h to 30~d, and based on our analysis, most are likely to be close binary star systems. We present periods and preliminary classifications (eclipsing, double degenerate, or irradiated systems) for the likely binaries based on light curve shape. From our total sample of 204 target PNe, with a correction for incompleteness due to magnitude limits, we calculate a binary fraction of PN central stars to be 20.7 percent for all the observed PNe, or 23.5 percent if we limit our sample only to `true PNe. However these fractions are almost certainly lower limits due to the large angular size of the emph{Kepler} pixels, which leads to reduced sensitivity in detecting variability, primarily as a result of dilution and noise from the nebula and neighbouring stars. We discuss the binary population of CSs based on these results as part of the total known sample of close binary CSs.
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