The Monitor project: Data processing and light curve production
Monthly Notices of the Royal Astronomical Society 375:4 (2007) 1449-1462
Abstract:
We have begun a large-scale photometric survey of nearby open clusters and star-forming regions, the Monitor project, aiming to measure time-series photometry for > 10000 cluster members over > 10 deg2 of sky, to find low-mass eclipsing binary and planet systems. We describe the software pipeline we have developed for this project, showing that we can achieve peak rms accuracy over the entire data set of better than ∼2 mmag using aperture photometry, with rms < 1 per cent over ∼4 mag, in data from 2- and 4-m class telescopes with wide-field mosaic cameras. We investigate the noise properties of our data, finding correlated 'red' noise at the ∼1-1.5 mmag level in bright stars, over transit-like time-scales of 2.5 h. An important source of correlated noise in aperture photometry is image blending, which produces variations correlated with the seeing. We present a simple blend index based on fitting polynomials to these variations, and find that subtracting the fit from the data provides a method to reduce their amplitude, in lieu of using techniques, such as point spread function fitting photometry, which tackle their cause. Finally, we use the SYSREM algorithm to search for any further systematic effects. © 2007 RAS.The Monitor project: rotation of low-mass stars in the open cluster NGC 2516
Monthly Notices of the Royal Astronomical Society 377:2 (2007) 741-758
Abstract:
ABSTRACT We report on the results of an i-band time-series photometric survey of NGC 2516 using the Cerro Tololo Inter-American Observatory (CTIO) 4-m Blanco telescope and 8k Mosaic-II detector, achieving better than 1 per cent photometric precision per data point over. Candidate cluster members were selected from a V versus colour-magnitude diagram over (covering masses from down to below the brown dwarf limit), finding 1685 candidates, of which we expect ∼1000 to be real cluster members, taking into account contamination from the field (which is most severe at the extremes of our mass range). Searching for periodic variations in these gave 362 detections over the mass range. The rotation period distributions were found to show a remarkable morphology as a function of mass, with the fastest rotators bounded by, and the slowest rotators for bounded by a line of, with those for following a flatter relation closer to. Models of the rotational evolution were investigated, finding that the evolution of the fastest rotators was well reproduced by a conventional solid body model with a mass-dependent saturation velocity, whereas core-envelope decoupling was needed to reproduce the evolution of the slowest rotators. None of our models were able to simultaneously reproduce the behaviour of both populations. © 2007 The Authors. Journal compilation © 2007 RAS.The Monitor project: JW 380 - A 0.26-, 0.15-M⊙ , pre-main-sequence eclipsing binary in the Orion nebula cluster
Monthly Notices of the Royal Astronomical Society 380:2 (2007) 541-550
Abstract:
ABSTRACT We report the discovery of a low-mass (0.26 ± 0.02, 0.15 ± 0.01 M⊙) pre-main-sequence (PMS) eclipsing binary (EB) with a 5.3 d orbital period. JW 380 was detected as part of a high-cadence time-resolved photometric survey (the Monitor project) using the 2.5-m Isaac Newton Telescope and Wide Field Camera for a survey of a single field in the Orion nebula cluster (ONC) region in V and i bands. The star is assigned a 99 per cent membership probability from proper motion measurements, and radial velocity observations indicate a systemic velocity within 1σ of that of the ONC. Modelling of the combined light and radial velocity curves of the system gave stellar radii of 1.19+0.04-0.18 and 0.90 +0.17-0.03 R⊙ for the primary and the secondary, with a significant third light contribution which is also visible as a third peak in the cross-correlation functions used to derive radial velocities. The masses and radii appear to be consistent with stellar models for 2-3 Myr age from several authors, within the present observational errors. These observations probe an important region of mass-radius parameter space, where there are currently only a handful of known PMS EB systems with precise measurements available in the literature. © 2007 The Authors. Journal compilation © 2007 RAS.The Monitor project: Searching for occultations in young open clusters
Monthly Notices of the Royal Astronomical Society 375:1 (2007) 29-52
Abstract:
The Monitor project is a photometric monitoring survey of nine young (1-200 Myr) clusters in the solar neighbourhood to search for eclipses by very low mass stars and brown dwarfs and for planetary transits in the light curves of cluster members. It began in the autumn of 2004 and uses several 2- to 4-m telescopes worldwide. We aim to calibrate the relation between age, mass, radius and where possible luminosity, from the K dwarf to the planet regime, in an age range where constraints on evolutionary models are currently very scarce. Any detection of an exoplanet in one of our youngest targets (≲ 10 Myr) would also provide important constraints on planet formation and migration time-scales and their relation to protoplanetary disc lifetimes. Finally, we will use the light curves of cluster members to study rotation and flaring in low-mass pre-main-sequence stars. The present paper details the motivation, science goals and observing strategy of the survey. We present a method to estimate the sensitivity and number of detections expected in each cluster, using a simple semi-analytic approach which takes into account the characteristics of the cluster and photometric observations, using (tunable) best-guess assumptions for the incidence and parameter distribution of putative companions, and we incorporate the limits imposed by radial velocity follow-up from medium and large telescopes. We use these calculations to show that the survey as a whole can be expected to detect over 100 young low and very low mass eclipsing binaries, and ∼3 transiting planets with radial velocity signatures detectable with currently available facilities. © 2007 RAS.WASP-1b and WASP-2b: Two new transiting exoplanets detected with SuperWASP and SOPHIE
Monthly Notices of the Royal Astronomical Society 375:3 (2007) 951-957