Monitor Project: Introduction

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Goals of the survey

  • To detect occultations (eclipses by stars or brown dwarfs, or transits by planets) in the light curves of young low-mass stars and brown dwarfs in open clusters and star forming regions, and thus
    • To detect transiting extra solar planets at young ages, and by measuring their periods, masses and radii, further our understanding of the formation and evolution of planetary systems.
    • To discover young low mass eclipsing binaries, for which we can measure dynamical masses and radii of both components, thereby constraining the mass-radius and mass-luminosity relationships for low mass stars and briown dwarfs at early ages.
  • To further our understanding of the angular momentum of young, low mass stars by measuring photometric rotation periods for large numbers of objects at a range of ages from the stellar birthline to the zero-age main sequence.
  • To characterize and understand other forms of intrinsic variability (e.g. flaring, micro flaring, accretion-induced variability, stellar cycles) present in our targets.


  • To understand the early lives of planetary systems. When do planets form around stars? How many of them survive this early phase? What is the role of environment? How fast do they cool down and contract?
  • To increase the number of low mass stars and brown dwarfs with dynamically measured masses, known radii and a well-constrained age estimate. These provide the only anchoring points for theoretical evolutionary models of these objects. Systematic searches for eclipsing binaries also provide information on the binarity properties of these objects, which are contain information on the star formation process.
  • To construct a much more extensive database of stellar rotation periods, much more complete than has been possible previously in terms of period range, stellar mass and stellar age, with sufficient numbers of objects to draw statistically significant conclusions, and to use these to improve our understanding of the way the angular momentum of young stars is redistributed and exchanged with their surroundings.


  • Eclipsing events are rare: they occur only if a star possesses a companion, if the inclination of the orbit is such that the companion crosses the line of sight to the star, and only once per orbital period. They can also be very shallow - of order 1% for Jupiter-like companions to Sun-like stars. To detect these events, we must therefore measure precise light curves for large numbers of objects.
  • For the detections to have maximum impact, we need to know as much as possible about the systems, and in particular, their age. We target open clusters and star forming regions because they provide the largest concentrations of young stars whose ages and chemical composition are relatively well known, and it is also relatively easy to obtain rough mass estimates for the objects from their apparent magnitude.
  • Large-format, mosaic CCD cameras on 2- and 4-metre class telescopes provide us with huge fields of view (up to one square degree). These telescope apertures give us the sensitivity we need to reach well into the brown dwarf regime in nearby young open clusters and star forming regions in typically a minute of integration.
  • High-cadence monitoring is required to accurately measure the shape of an event and improve our chances of detection.
  • Long-term monitoring is required to increase our chances of catching multiple events in the same system and to increase our sensitivity to longer period systems.


  • Data processing. A typical night's observing with the INT telescope returns 25 GigaBytes of data. At CFH this is more like 50 Gigabytes. We want to measure tens of clusters for weeks of time. This is a TeraByte project.
  • Accurate measurement of photometry to levels of a few millimagnitudes.
  • Stellar variabilty, though fantastically interesting and a major science goal, is a major hurddle when it comes to searching for sub-percent variations caused by planetary transits.
  • Light curves provide only an estimate of the period and the relative radii of the eclipsing systems we detect. In order to determine their component masses and make sure they really are young objects in the clusters we observed, rather than field objects that happened to fall in the field of view, multi-epoch medium and high-resolution spectroscopy is needed, and this can be challenging for the relatively faint objects we detect.

More details

  • For more on the motivation, the design of the survey, and its detection potential (including eclipse detection and spectroscopic follow-up), check out this paper.
  • For more on the data processing and the noise properties of our light curves, check out this paper.
  • For more on the technique we use to measure rotation periods, check out this paper.

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