UNIVERSITY OF HERTFORDSHIRE MASTERS BY RESEARCH THESIS Searching for Young Substellar Companions to Gaia Stars Supervised by: Author: Prof. David J. PINFIELD Matthew J. RICKARD Dr. Federico MAROCCO Centre for Astrophysics Research School of Physics, Astronomy and Mathematics University of Hertfordshire Submitted to the University of Hertfordshire in fulfilment of the requirements of the degree of Masters by Research. June 2018 Abstract The aim of this thesis is to select young ultra-cool dwarf (UCD, spectral type later than M7) candidates that are likely companions to primary stars within the Tycho-Gaia Astrometric Solu- tion (TGAS) catalogue. The intention is to identify a sample of “benchmark” UCDs for which youth and age constraints can be established through association with well understood primary stars. Candidate UCDs are identified through searches of two large-area optical surveys, the Sloan Digital Sky Survey (SDSS) and the Panoramic Survey Telescope and Rapid Response System (PanSTARRS), and two large-area infrared surveys, the UKIRT Infrared Deep Sky Sur- vey (UKIDSS) and the VISTA Hemisphere Survey (VHS). Potential benchmark pairings are selected using a cone-search around each TGAS star with a search radius of 10,000 AU at the distance of each TGAS star. Photometric (colour and magnitude) requirements are imposed on possible associations through comparison, in colour magnitude diagrams (CMDs), with the location of established parallax samples of young and normal UCDs. A set of complementary approaches has been implemented to identify indications of youth in both the UCD and the pri- mary components, the results of which have been brought together into a prioritisation scheme which has been used to guide and plan follow-up observing runs during the project. These diagnostics included unusual UCD colours in the near-infrared and optical, main-sequence life- time constraints for the primaries, and primary over-brightness (as a function of [M/H] and Teff) indicative of pre-main sequence evolution. A broad range of database information on the stellar components is also gathered providing additional age limitations. UCD proper motion constraints are determined using multi-epoch astrometry from the search-surveys as well as archival motions from the SuperCOSMOS Science Archive. This extensive search and anal- ysis generated a sample of 1,623 candidate young benchmark associations, twenty-four that already evidence strong youth diagnostics in both UCD and primary star components, fifty that are common-proper-motion associations, thirty where the pairs are in close proximity to each other (< 6 arcseconds), and 348 where the primary candidate has high proper motion leading to expectation that the companion candidate can be rapidly motion-tested. Narrow band near- infrared observations are also presented for ten of the candidate UCD components, in an attempt to search for established H-band morphological indicators of extreme youth. With three of these candidates showing Hs-Hl and J-J3 colours consistent with synthesized predictions using previ- ously known young objects. Finally, high priority followup plans and additional development aimed at near-future Gaia DR2 exploitation are considered as future work. Declaration I declare that no part of this work is being submitted concurrently for another award of the University or any other awarding body or institution. This thesis contains a substantial body of work that has not previously been submitted successfully for an award of the University or any other awarding body or institution. The submission is my own work. Matthew J. RICKARD February 2018 ii Acknowledgements My thanks to my wife, Anna, for the love and support as I began a new career. Thanks to Alex, Max and Thomas for keeping me sane in the office. Thanks to David and Federico for their time and patience. Section 2.5 method was carried out and developed further under my supervision by Paaryn Vadgama, a student completing his A-Levels in Summer 2018 who worked on this project as part of a four week Nuffield Research Placement1. Radostin Kurtev of the Universidad de Valpara´ıso submitted numerous observing proposals as part of the observation program of this work and conducted the observing program in November 2017. Research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. This research made use of the cross-match service provided by CDS, Strasbourg. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Sci- ence. The SDSS-III website is listed in the footnote2. SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, University of Cambridge, Carnegie Mellon University, University of Florida, the French Partic- ipation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins Uni- versity, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York Univer- sity, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University. The Pan-STARRS1 Surveys (PS1) have been made possible through contributions of the Insti- tute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins Univer- sity, Durham University, the University of Edinburgh, Queen’s University Belfast, the Harvard- Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued 1http://www.nuffieldfoundation.org/nuffield-research-placements/ 2http://www.sdss3.org/ iii through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation under Grant No. AST-1238877, the University of Maryland, and Eotvos Lorand University (ELTE). Guoshoujing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope LAM- OST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission. LAM- OST is operated and managed by the National Astronomical Observatories, Chinese Academy of Sciences. Funding for RAVEhas been provided by: the Australian Astronomical Observatory; the Leibniz- Institut fuer Astrophysik Potsdam (AIP); the Australian National University; the Australian Re- search Council; the French National Research Agency; the German Research Foundation (SPP 1177 and SFB 881); the European Research Council (ERC-StG 240271 Galactica); the Istituto Nazionale di Astrofisica at Padova; The Johns Hopkins University; the National Science Foun- dation of the USA (AST-0908326); the W. M. Keck foundation; the Macquarie University; the Netherlands Research School for Astronomy; the Natural Sciences and Engineering Research Council of Canada; the Slovenian Research Agency; the Swiss National Science Foundation; the Science & Technology Facilities Council of the UK; Opticon; Strasbourg Observatory; and the Universities of Groningen, Heidelberg and Sydney. The RAVE website is given in the foot- notes3. This work is based in part on data obtained as part of the UKIRT Infrared Deep Sky Survey. Based on observations obtained as part of the VISTA Hemisphere Survey, ESO Program, 179.A- 2010 (PI: McMahon). This work has made use of data from the European Space Agency (ESA) mission Gaia4, pro- cessed by the Gaia Data Processing and Analysis Consortium (DPAC5). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research has made use of data obtained from the SuperCOSMOS Science Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This research has benefitted from the SpeX Prism Spectral Libraries, maintained by Adam Bur- gasser6 of the Department of Physics of UC San Diego. 3https://www.rave-survey.org 4https://www.cosmos.esa.int/gaia 5https://www.cosmos.esa.int/web/gaia/dpac/consortium 6http://pono.ucsd.edu/~adam/browndwarfs/splat/ Contents Abstract i Acknowledgements iii Contents v List of Figures viii List of Tablesx List of Abbreviations xi 1 Introduction1 1.1 Brown Dwarfs and Exoplanets..........................2 1.2 Ultracool Dwarfs: Definition and Classification.................3 1.2.1 Absorption Features of UCD Spectral Types...............3 1.2.2 Colours and Magnitudes of UCDs....................9 1.3 Ultracool Dwarfs: Evolution........................... 11 1.4 Photometric and Spectral Indicators of Young Ultracool Dwarfs........ 11 1.4.1 Spectral Features