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View of the Interior Structure UNIVERSITY OF CINCINNATI Date: 17-Sep-2010 I, Benjamin Frank Bubnick , hereby submit this original work as part of the requirements for the degree of: Master of Science in Physics It is entitled: Massive Stellar Clusters in the Disk of the Milky Way Galaxy Student Signature: Benjamin Frank Bubnick This work and its defense approved by: Committee Chair: Margaret Hanson, PhD Margaret Hanson, PhD 10/4/2010 1,102 Massive Stellar Clusters in the Disk of the Milky Way Galaxy A Thesis submitted to the Graduate School of the University of Cincinnati in partial fulfillment of the requirements for the degree of Master of Science in the Department of Physics of the College of Arts and Sciences 2010 by Benjamin Bubnick Committee Chair: Margaret Hanson ABSTRACT Title of thesis: Massive Stellar Clusters in the Disk Of the Milky Way Galaxy Benjamin Bubnick, Master of Science, 2010 Thesis directed by: Professor Margaret Hanson Department of Physics This thesis outlines successful efforts for identifying and characterizing the stellar content of two Galactic disk star clusters using near-infrared observations. Astronomers have a great wealth of knowledge about globular clusters. They are easy to see as most lie outside the plane of the galaxy in the halo. Extinction is low, the stellar population is dense in the cluster, and they are fairly common. However, in the plane of the galaxy, relatively little is known of the open cluster population. Galactic disk open clusters, such as the two discussed in this thesis, are hidden behind gas, dust, and projected against a multitude of field stars. Through the use of near-infrared broad-band photometry and spectroscopy, the distance, age and approximate mass of two disk clusters has been determined. c Copyright by Benjamin Bubnick 2010 Acknowledgments I want to thank everyone who provided me with scientific and moral support through the writing of this thesis. Foremost, my sincere gratitude goes to my adviser, Dr. Margaret Hanson, who assisted me invaluably in the data analysis and who provided me with the tools necessary to write this work. I owe much to the University of Cincinnati, and in particular the Physics Department, for for the support and education that has brought me to this point. I owe gratitude also to Dr. Richard Gass and Aaron Eiben for the discussions that helped me organize my ideas for this work. I appreciate the contributions from Lori Beerman and Yara Beshara to the astrometry analysis for the two clusters. And finally my thanks goes out to my family for the moral support they have given me. My parents’ dedication to my education gave me the drive to pursue study in physics, and my wife’s love and support gave me the drive to finish. Thank you all. ii Table of Contents List of Tables v List of Figures vi List of Abbreviations vii 1 Introduction 1 1.1WhyNIRAstronomyisuseful...................... 1 1.1.1 Stars,Telescopes,andtheInterstellarMedium......... 2 1.1.2 DimmingandReddeningbytheISM.............. 4 1.2StellarEvolution............................. 8 1.2.1 HRDiagram............................ 9 1.2.2 MSLifetime............................ 12 1.2.3 Metallicity . ............................ 12 1.3TheInfraredTelescopes......................... 13 1.3.1 NIRTechnology.......................... 13 1.3.2 IRTF................................ 14 1.3.3 VLT................................ 15 1.3.4 NTT................................ 15 1.4StellarClusters.............................. 16 1.4.1 GlobularClusters......................... 17 1.4.2 OpenClusters........................... 19 1.4.3 SuperStarClusters........................ 20 1.4.4 TheNearInfraredSkySurveys................. 21 1.5ToolsoftheObservationalAstronomer................. 22 1.5.1 Photometry............................ 22 1.5.2 Spectroscopy........................... 23 1.6DefinitionofBasicTerms......................... 25 1.6.1 CelestialCoordinates....................... 25 1.6.2 EquatorialCoordinates...................... 25 1.6.3 GalacticCoordinates....................... 26 1.6.4 Resolution............................. 26 1.6.5 Seeing............................... 27 1.6.6 TelluricContamination...................... 27 2 The Open Cluster [BDS2003]107 28 2.1Astrometry................................ 29 2.1.1 StarLocations........................... 30 2.1.2 RadialVelocity.......................... 32 2.2Photometry................................ 44 2.2.1 STARFINDPhotometry..................... 44 2.2.2 MagnitudeSplitting....................... 45 2.2.3 LimitingMagnitudes....................... 47 iii 2.2.4 Color-MagnitudeDiagram.................... 48 2.2.5 Color-ColorDiagram....................... 48 2.2.6 TheFieldStar#23........................ 50 2.2.7 FalseColorImage......................... 52 2.3ClusterCharacteristics.......................... 52 3 The Super Star Cluster Westerlund1 55 3.1Astrometry................................ 56 3.2Westerlund1Cross-ReferenceChart.................. 60 3.3Photometry................................ 65 3.3.1 DAOPHOTPhotometry..................... 65 3.3.2 LimitingMagnitudes....................... 66 3.3.3 Color-MagnitudeDiagram.................... 66 3.3.4 Color-ColorDiagram....................... 69 3.3.5 FalseColorImage......................... 69 3.4ClusterCharacteristics.......................... 69 4 Massive Cluster Research 72 4.1ImportanceofMassiveClusterResearch................ 72 4.2FutureofMassiveClusterResearch................... 74 4.3ImprovementsonMassiveClusterResearch............... 76 4.3.1 TheRadialVelocityofCluster107............... 76 4.3.2 BetterCalibratedPhotometry.................. 77 Bibliography 80 iv List of Tables 1.1Zero-MagnitudeFlux........................... 4 1.2TheProton-ProtonChain........................ 9 1.3AbsoluteSolarMagnitudes........................ 10 1.4PhotometricBands............................ 23 2.1Cluster107StarsObserved........................ 33 2.2Cluster107StarsObserved........................ 34 2.3Cluster107StarsObserved........................ 35 2.4Cluster107StarsObserved........................ 36 2.5FalseColorImageColorRanges..................... 54 3.1Wd1StarsObserved........................... 57 3.2Wd1StarsObserved........................... 58 3.3Wd1StarsObserved........................... 59 3.4Wd1CrossReferences.......................... 62 3.5Wd1CrossReferences.......................... 63 3.6Wd1CrossReferences.......................... 64 v List of Figures 1.1EMWaveScattering........................... 6 1.2ExtinctionCurve............................. 7 1.3HRDiagram................................ 11 1.4Color-MagnitudeDiagram........................ 18 1.5JHKTransmissionCurve......................... 24 2.1FindingChart............................... 37 2.2Star#23Spectra............................. 38 2.3FluxDifference.............................. 40 2.4RadialVelocity.............................. 41 2.5MilkyWayRotationCurve........................ 42 2.6AverageFluxDifference......................... 43 2.7Color-MagnitudeDiagram........................ 49 2.8Color-ColorDiagram........................... 51 2.9ColorCompositeImage.......................... 53 3.1FindingChart............................... 61 3.2Color-MagnitudeDiagram........................ 67 3.3Color-MagnitudeDiagram........................ 68 3.4Color-ColorDiagram........................... 70 3.5ColorCompositeImage.......................... 71 4.1SpiralGalaxy............................... 73 4.2MilkyWayGalaxy............................ 75 4.3ExtremelyNoisySpectra......................... 78 vi List of Abbreviations 2MASS Two Micron All Sky Survey Aλ Monochromatic Extinction α Right Ascension BII Galactic Latitude CCD Color-Color Diagram CMD Color-Magnitude Diagram Dec. Declination δ Declination EM Electromagnetic ESO European Southern Observatory Fλ Monochromatic Flux Density FWHM Full Width at Half Maximum GLIMPSE Galactic Legacy Infrared Mid-Plane Survey Extraordinaire Gyr Giga-year (109 years) HgCdTe Mercury Cadmium Telluride HR Hertzsprung-Russell HWHM Half Width at Half Maximum InSb Indium Antimode IPAC Infrared Processing and Analysis Center IRAF Image Reduction and Analysis Facility IRTF Infrared Telescope Facility ISAAC Infrared Spectrometer and Array Camera ISM Interstellar Medium kWaveNumber kpc Kiloparsec LII Galactic Longitude Lλ Monochromatic Luminosity λ Wavelength M Mass of the Sun Mλ Monochromatic Absolute Magnitude mλ Monochromatic Apparent Magnitude MS Main Sequence Myr Mega-year (106 years) μm Micron or Micrometer vii NASA National Aeronautics and Space Administration NIR Near Infrared NSF National Science Foundation NTT New Technology Telescope PbS Lead Sulfide pc Parsec PSF Point Spread Function R.A. Right Ascension SOFI Son of ISAAC (Infrared Spectrometer and Array Camera) Teff Effective Temperature TT Terrestrial Time τMS Main Sequence Timescale VISTA Visible and Infrared Survey Telescope for Astronomy VLT Very Large Telescope VVV VISTA Variables in The Via Lactea W Watts Wd1 Westerlund 1 viii Chapter 1 Introduction 1.1 Why NIR Astronomy is useful In order to understand the structure of the Milky Way, we need to develop an accurate, unbiased census of star formation in the inner Galaxy[63]. This would be very easy if not for a phenomenon called extinction, which is a result of the interstellar medium (ISM) that lies in the galactic plane. The ISM is the gas and dust that permeates the galaxy between the stars and is responsible for extinction, the dimming of starlight making it more difficult for observation. At visible
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