An anomaly detector with immediate feedback to hunt for planets of Earth mass and below by microlensing

University of Cambridge, Cambridge, England, United Kingdom
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 06/2007; 380(2). DOI: 10.1111/j.1365-2966.2007.12124.x
Source: arXiv


(abridged) The discovery of OGLE 2005-BLG-390Lb, the first cool rocky/icy exoplanet, impressively demonstrated the sensitivity of the microlensing technique to extra-solar planets below 10 M_earth. A planet of 1 M_earth in the same spot would have provided a detectable deviation with an amplitude of ~ 3 % and a duration of ~ 12 h. An early detection of a deviation could trigger higher-cadence sampling which would have allowed the discovery of an Earth-mass planet in this case. Here, we describe the implementation of an automated anomaly detector, embedded into the eSTAR system, that profits from immediate feedback provided by the robotic telescopes that form the RoboNet-1.0 network. It went into operation for the 2007 microlensing observing season. As part of our discussion about an optimal strategy for planet detection, we shed some new light on whether concentrating on highly-magnified events is promising and planets in the 'resonant' angular separation equal to the angular Einstein radius are revealed most easily. Given that sub-Neptune mass planets can be considered being common around the host stars probed by microlensing (preferentially M- and K-dwarfs), the higher number of events that can be monitored with a network of 2m telescopes and the increased detection efficiency for planets below 5 M_earth arising from an optimized strategy gives a common effort of current microlensing campaigns a fair chance to detect an Earth-mass planet (from the ground) ahead of the COROT or Kepler missions. The detection limit of gravitational microlensing extends even below 0.1 M_earth, but such planets are not very likely to be detected from current campaigns. However, these will be within the reach of high-cadence monitoring with a network of wide-field telescopes or a space-based telescope. Comment: 13 pages, 4 figures and 1 table. Accepted for publication in MNRAS

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Available from: Lukasz Wyrzykowski, May 07, 2015
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    • "Burgdorf et al. 2007; Tsapras et al. 2009) pioneered the use of automated event prioritization algorithms (Horne et al. 2009) with robotic-telescope observations, and a pilot study within the MiNDSTEp (Microlensing Network for the Detection of Small Terrestrial Exoplanets; campaign (Dominik et al. submitted) has recently demonstrated the readiness to detect signatures of Earth-mass planets with a fully deterministic monitoring strategy involving automated anomaly detection (Dominik et al. 2007), realized by means of the ARTEMiS (Automated Robotic Terrestrial Exoplanet Microlensing Search; system (Dominik et al. 2008). "
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    ABSTRACT: Although Einstein originally judged that 'there is no great chance of observing this phenomenon', the 'most curious effect' of the bending of starlight by the gravity of intervening foreground stars--now commonly referred to as 'gravitational microlensing'--has become one of the successfully applied techniques to detect planets orbiting stars other than the Sun, while being quite unlike any other. With more than 400 extra-solar planets known altogether, the discovery of a true sibling of our home planet seems to have become simply a question of time. However, in order to properly understand the origin of Earth, carrying all its various life forms, models of planet formation and orbital evolution need to be brought into agreement with the statistics of the full variety of planets like Earth and unlike Earth. Given the complementarity of the currently applied planet detection techniques, a comprehensive picture will only arise from a combination of their respective findings. Gravitational microlensing favours a range of orbital separations that covers planets whose orbital periods are too long to allow detection by other indirect techniques, but which are still too close to their host star to be detected by means of their emitted or reflected light. Rather than being limited to the Solar neighbourhood, a unique opportunity is provided for inferring a census of planets orbiting stars belonging to two distinct populations within the Milky Way, with a sensitivity not only reaching down to Earth mass, but even below, with ground-based observations. The capabilities of gravitational microlensing extend even to obtaining evidence of a planet orbiting a star in another galaxy.
    Full-text · Article · Aug 2010 · Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences
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    • "On top of the ordinary brightening of the observed source star during a microlensing event, a planetary companion to the lens star can cause a further short blip or dip. A super-Jupiter was the first planet detected by this technique [6], but its sensitivity even reaches below the mass of Earth, even for ground-based observations [7] [8]. Here, we discuss another channel for revealing the existence of extra-solar planets from the study of microlensing light curves [9]. "
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    ABSTRACT: One of the successful techniques for the detection of exoplanets relies on the magnification of an observed star resulting from microlensing by a foreground star orbited by a planetary companion. We propose an alternative method for the detection of exoplanets by microlensing, in which the orbital motion of a planet around the source star induces a small motion of the star around the common barycentre, which leads to detectable deviations from the ordinary symmetric microlens-ing light curve. We show that favourable events for such deviations to occur involve lenses close to the source star and Einstein-radius crossing times substantially larger than the planet's orbital period. From a Monte-Carlo simulation, we find that a monitoring programme of Galactic bulge stars, capable of providing a 2-hour sampling and 2 % photometric accuracy, can detect planets of Jupiter mass with a detection efficiency of around 1 %.
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    ABSTRACT: Besides their capability for obtaining a census of sub-Neptunian planets orbiting Galactic disk or bulge stars, existing microlensing campaigns still face the chance of yielding the first discovery of an Earth-mass planet. In order to make this likely to happen in the short term, a well-coordinated effort of survey, follow-up and anomaly monitoring is required. From 2008, ARTEMiS (Au-tomated Robotic Terrestrial Exoplanets Microlensing Search) will merge strategy and tools that have been used by PLANET and RoboNet, and make these publicly available, thereby providing an independent open platform for rapid interchange of information. Embedding its expert system into eSTAR will moreover allow communication by means of standardized protocols with robotic telescopes that form part of the Heterogeneous Telescopes Networks (HTN) consortium. Based on the capabilities, availability, commitment, and strategic preferences associated with individ-ual observing sites, and taking into account data-sharing agreements, ARTEMiS will be able to recommend the optimal target to be observed at any given time. The SIGNALMEN anomaly de-tector, an integral part, has already demonstrated its power in 2007, where crucial data on several planet candidate events have been taken as response to notifications by its alert mechanism. The up-to-the-minute visualization and interpretation of ongoing events not only guides observers, but moreover offers an excellent opportunity for impactful public outreach, allowing the live commu-nication of discoveries.
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