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Register a new userAn Absence of Hot Jupiter Planets in 47 Tucanae: Results of a Wide-Field Transit Search
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David T.F Weldrake RSAA
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We present the results of a comprehensive wide field search for transiting ``Hot Jupiter planets (1d<P<16d) in the globular cluster 47 Tucanae. Motivated by the core null result of Gilliland and coworkers, this work further addresses the question of giant planet frequency in 47 Tuc by observing, from the ground, a 52x52 field centered on the cluster for 30.4 nights. Hence this work is most sensitive to the uncrowded outer regions of the cluster and concentrates on 21,920 main sequence stars (~solar in mass). This work comprises the largest ground-based transit search of a globular cluster to date. Monte Carlo simulations predict that seven planets should be present in our dataset, if 47 Tuc has the same planetary frequency observed in the solar neighbourhood. A detailed search with a custom developed detection algorithm found no transit events. Being consistent with the cluster core null detection of Gilliland and coworkers, our result indicates that system metallicity is the dominant effect inhibiting Hot Jupiter formation in this environment.
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We present a short progress report of a comprehensive search for variability in the globular cluster 47 Tucanae. Using the MSSSO 40 telescope and a combined V+R filter, we are searching for variability across a 52x52 field centered on the cluster. The main aim is to search for transiting Hot Jupiter planets, the results of which are still being produced, but a natural side product is a deep catalogue of variable stars within the cluster field. The experiment samples the whole of the cluster (except the inner 5), thus probing the uncrowded outer regions where the stellar densities are lower, increasing the prospects for the survivability of planetary systems. Half of the currently identified variable stars are new discoveries. We have data for 36,000 stars with masses similar to that of the Sun for the main transit search.
Using images from the Hubble Space Telescope Wide-Field Camera 3, we measure the rate of diffusion of stars through the core of the globular cluster 47 Tucanae using a sample of young white dwarfs identified in these observations. This is the first direct measurement of diffusion due to gravitational relaxation. We find that the diffusion rate $kappaapprox 10-13$ arcsecond$^2$ Myr$^{-1}$ is consistent with theoretical estimates of the relaxation time in the core of 47 Tucanae of about 70 Myr.
We report the first wideband observations of pulsars C, D and J in the globular cluster 47Tucanae (NGC 104) using the Ultra-Wideband Low (UWL) receiver system recently installed on the Parkes 64 m radio telescope. The wide frequency range of the UWL receiver (704-4032 MHz), along with the well-calibrated system, allowed us to obtain flux density measurements and polarization pulse profiles. The mean pulse profiles have significant linear and circular polarization, allowing for determination of the Faraday rotation measure for each pulsar. Precise measurements of the dispersion measures show a significant deviation in the value for pulsar D compared to earlier results. Searches for new pulsars in the cluster are on-going and we have determined optimal bands for such searches using the Parkes UWL receiver system.
We present the results of a comprehensive search for stellar variability in the globular cluster 47 Tucanae. Using the Mount Stromlo 40-inch (1m) telescope at Siding Spring Observatory and a combined V+R filter, we have detected 100 variable stars across a 52$times52$ field centered on the cluster. Here we present the V+R lightcurves and preliminary investigations of the detected variables, which comprise 28 Eclipsing Binaries (21 contact binaries and 7 detached systems), 45 RR Lyrae stars (41 of which belong to the SMC and four seemingly to the Galactic Halo), and 20 K-giant Long Period Variables (LPVs). We also detected four $delta$ Scuti stars, one TypeI Cepheid, and one TypeII Cepheid. One variable appears to be a dust-enshrouded SMC star with a short period pulsation. Of these 100 variables, 69 are new discoveries. Our eclipsing binary sample indicates a radial segregation in period, and includes two binaries that are seemingly orbited by low-luminosity stellar companions. One RR Lyrae star shows a Blahzko effect with remarkable regularity.
Aims. Hot Jupiters are thought to belong to single-planet systems. Somewhat surprisingly, some hot Jupiters have been reported to exhibit transit timing variations (TTVs). The aim of this paper is to identify the origin of these observations, identify possible periodic biases leading to false TTV detections, and refine the sample to a few candidates with likely dynamical TTVs. Methods. We present TTV frequencies and amplitudes of hot Jupiters in Kepler Q0--6 data with Fourier analysis and a frequency-dependent bootstrap calculation to assess the false alarm probability levels of the detections. Results. We identified 36 systems with TTV above four standard deviation confidence, about half of them exhibiting multiple TTV frequencies. Fifteen of these objects (HAT-P-7b, KOI-13, 127, 183, 188, 190, 196, 225, 254, 428, 607, 609, 684, 774, 1176) probably show TTVs due to a systematic observational effect: long cadence data sampling is regularly shifted transit-by-transit, interacting with the transit light curves, introducing a periodic bias, and leading to a stroboscopic period. For other systems, the activity and rotation of the host star can modulate light curves and explain the observed TTVs. By excluding the systems that were inadequately sampled, showed TTV periods related to the stellar rotation, or turned out to be false positives or suspects, we ended up with seven systems. Three of them (KOI-186, 897, 977) show the weakest stellar rotation features, and these are our best candidates for dynamically induced TTV variations. Conclusions. Those systems with periodic TTVs that we cannot explain with systematics from observation, stellar rotation, activity, or inadequate sampling may be multiple systems or even exomoon hosts.
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