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A Search for Transiting Extrasolar Planets in the Open Cluster NGC 4755

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A Search for Transiting Extrasolar Planets in the Open Cluster NGC 4755 ResearchOnline@JCU This file is part of the following reference: Jayawardene, Bandupriya S. (2015) A search for transiting extrasolar planets in the open cluster NGC 4755. DAstron thesis, James Cook University. Access to this file is available from: http://researchonline.jcu.edu.au/41511/ The author has certified to JCU that they have made a reasonable effort to gain permission and acknowledge the owner of any third party copyright material included in this document. If you believe that this is not the case, please contact [email protected] and quote http://researchonline.jcu.edu.au/41511/ A SEARCH FOR TRANSITING EXTRASOLAR PLANETS IN THE OPEN CLUSTER NGC 4755 by Bandupriya S. Jayawardene A thesis submitted in satisfaction of the requirements for the degree of Doctor of Astronomy in the Faculty of Science, Technology and Engineering June 2015 James Cook University Townsville - Australia i STATEMENT OF ACCESS I the undersigned, author of this work, understand that James Cook University will make this thesis available for use within the University Library and, via the Australian Digital Thesis network, for use elsewhere. I understand that, as an unpublished work, a thesis has significant protection under the Copyright Act and; I do not wish to place any further restriction on access to this work. 2 STATEMENT OF SOURCES DECLARATION I declare that this thesis is my own work and has not been submitted in any form for another degree or diploma at any University or other institution of tertiary education. Information derived from the published or unpublished work of others has been acknowledged in the text and list of references is given. --------------------------------- Signature Date 3 ACKNOWLEDGMENTS There are number of people without whom I would not have been able to achieve my childhood dream of studying astronomy, and I would like to thank them here. Firstly, I would like to thank Dr Graeme White, who willingly gave the opportunity to me to work for a Doctorate of Astronomy in my spare time. This work would not have been possible without the guidance of my supervisor from mid-2006, Dr David Blank for sparing a great deal of time answering my questions and acquiring NGC 4755 data. I would like to thank A. Prof. Andrew Walsh, Professor Ian Whittingham, Alex Hons, Dr Wayne Orchiston of JCU and other JCU staff for their support and encouragement for finishing this thesis. I do not forget to thank the members involved in REST, who have given me the hard-earned sky data, and Arie Verveer and James Biggs of Perth Observatory for giving me sky data of open cluster NGC 4755. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Centre/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This search has made use of the SIMBAD database, at CDS, Strasbourg, France and Kepler database of NASA. Finally, I thank my family, D, I and Y, who have perhaps unintentionally, conspired to make my life interesting. 4 ABSTRACT The search for ESP (extra-solar planets) has become a very popular astronomical research activity since the first discovery of ESP in 1995. Although, there are many ways of finding these exotic bodies, the transit method has become a widely used method; even amateurs have their opportunity to become planet hunters. This requires high precision time-series photometry and light curve analysis of large numbers of stars. When a planet transits, its radii ratio with the primary star can be determined accurately. Thus, combining this ratio with radial velocity data, the mass and radius of the planet can be realized, assuming the primary star’s radius is known. The information gained from the transiting planets makes it possible to unravel the structure and composition of ESPs, understand the formation and the evolution process, and find the physical properties of the planet. The detection of a weak, short, periodic transit signal in noisy light curves is a challenging task. As large numbers of light curves are to be analyzed, automation and an optimization of the search and analysis process is a necessity. The fluxes of stars on CCD (Charge Coupled Device) images are measured and the de-trended flux is used to draw the light curve. Normally, the search is done by a ground based detection system; hence the light curve is contaminated with noise components coming from atmospheric variations and systematic errors. To obtain high precision data without atmospheric noise, space based CCD cameras are already active. Based on the above transit theory, this search was first done by using REST (Really Embarrassing Small Telescope) at JCU for field stars in the solar neighbourhood, GL 581, HD 13445 and HD 27894. The CCD images of the stars were subjected to CCD data reduction, pre-processing, differential photometry and analyzing by transit identification algorithms. Differential photometry, the ratio of the target star flux and reference star flux was used to nearly nullify the atmospheric variations. The target open cluster for the main search is NGC 4755, which is widely known as the Jewel Box, in the constellation of the Southern Cross. The Perth Automatic Telescope, which can be remotely controlled, was used to obtain the data for the open cluster. 176 cluster stars brighter than 14th magnitude with published ‘B’ and ‘V’ magnitudes and another 994 faint stars in the 5 cluster frame have been analyzed. Several analytical signal-processing methods have been used to process the light curve to get the best light signal, having a SD (Standard Deviation) less than 5 milli-magnitudes. Later, fast wavelet transform was used to remove high frequency noise components and to produce an approximate signal which shows the long-term trend of the light curve and contain a possible transit. While no planetary transits have been identified in this cluster before, the ability to get light curves with standard deviation less than 5 milli-magnitudes is a significant achievement. The approximated light curves (using wavelets) are almost flat indicating that there are no signals with cycle time of 90 minutes or more. The PSD (Power Spectral Density) of the light curve gives the frequency components associated with the curve. As there is a limitation of using this FFT based method, the Lomb-Scargle method was used to generate PSD. This data was compared with 2MASS data to find closer brown dwarfs and a dozen possible candidates were found. Variable stars in the cluster can also be studied with the light curve of stars. As there are at least 19 known variable stars in the NGC 4755; this is an opportunity to study the known variable stars in the cluster as well as to discover additional ones. 6 Table of Contents Chapter 1 ......................................................................................................................................... 1 Introduction ..................................................................................................................................... 1 1.1 What is an extra-solar planet? ................................................................................................ 3 1.1.1 Classification of Extra-Solar Giant planets .................................................................... 4 1.2 Formation of gas giant planets ............................................................................................... 4 1.2.1 Formation by core-accretion ........................................................................................... 5 1.2.2 Gravitational collapse ..................................................................................................... 5 1.2.3 Planet migration.............................................................................................................. 6 1.3 General Properties of known ESP systems ............................................................................ 7 1.3.1 Properties of the planets ................................................................................................. 7 1.3.2 Properties of the parent stars .......................................................................................... 8 1.3.3 Planets in multiple systems ............................................................................................ 8 1.4 Extra-solar planet search methods .......................................................................................... 9 1.4.1 Direct imaging ................................................................................................................ 9 1.4.2 Radial velocity .............................................................................................................. 10 1.4.3 Pulsar timing ................................................................................................................. 11 1.4.4 Gravitational micro-lensing .......................................................................................... 11 1.4.5 Astrometry .................................................................................................................... 11 1.4.6 The transit method ........................................................................................................ 12 1.5 Search in open clusters ......................................................................................................... 23 1.6 Variable
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