text: ---
  author:
  - JASMINA BLECIC
  bibliography:
  - 'chap-intro.bib'
  title: |
      OBSERVATIONS, THERMOCHEMICAL CALCULATIONS,\
      AND MODELING OF EXOPLANETARY ATMOSPHERES
  ---
  
  INTRODUCTION {#chap:intro}
  ============
  
  The exoplanetary field began its endeavor in 1992 with the first discovery of planets outside of our Solar system [@wolszczan1992planetary]. Soon after, in 1995, the detection of an extrasolar planet around a Sun-like star [@MayorQueloz1995Nature-fisrtExoplanet-mainSequence] led to the discovery that planets similar to the ones in our solar neighborhood are common [@FressinEtal2013ApJ-frequency]. In 2002, the first discovery of an exoplanetary atmosphere [@CharbonneauEtal2002apjnadet], gave us hope that we have come closer to answering the ultimate question: “Is there life out there?"
  
  Since then, the exoplanetary field has become one of the most rapidly developing fields in astronomy. Today, there are around 1500 confirmed planets and more than 3500 candidates (August 2015, [www.exoplanets.org](www.exoplanets.org)). The response of the scientific community to such a large number of exoplanets is the number of different techniques employed to analyze their data [e.g., @MoralesEtal2006-intraPixel; @DemingEtal2006-ramp; @Knutson2007; @PontEtal2008-HST; @PontEtal2009-HST; @SwainEtal2009-HD209458b; @SwainEtal2009-HD189733b; @Desert2009-intraPixel; @KnutsonEtal2009ApJ-Tres4Inversion; @CarterWinn2010; @StevensonEtal2012-BLISS; @deWitEtal2012aapFacemap; @DemingEtal2015-PixelDecorelation]. In addition, serious efforts have been made to characterize their atmospheres [e.g., @CharbonneauEtal2005apjTrES1; @DemingEtal2005natHD209458b; @HarringtonEtal2007natHD149026b; @Knutson08; @Fortney2008; @Tinetti2007Nature; @TinettiEtal2010-XO-1b; @BurrowsEtal2006; @Anderson2011-Ch24-WASP17b; @ShowmanEtal2009ApJ-Circulation; @MadhusudhanSeager2009ApJ-AbundanceMethod; @LeeEtal2012-CF; @BennekeSeager2012-Retrieval; @LineEtal2014-Retrieval-I]. The analyses revealed that the diversity of extrasolar planets is astonishing, and surprisingly, some of them are very different from the ones in our Solar system.
  
  In the past decade, exoplanetary research was mostly centered on hot Jupiters, gaseous giant planets. These planets, located very close to their host stars, are usually found on circular orbits, expected to be facing their stars with the same side. Although hot Jupiters are in fact less frequent than hot Neptunes and super Earths [@HowardEtal2012-panetOccurance], current technological limitations and instrumental systematics have directed us to use them to teach ourselves how to analyze exoplanets until more advanced instruments become available [@SeagerDeming2010; @hansen2014features; @Burrows2014-review]. Due to their large radii and small semimajor axes, these objects have provided the strongest signal-to-noise ratios and become the best targets for ground- and space-based observations, allowing us to get the first insights into exoplanetary atmospheres .
  
  To learn about an exoplanetary atmosphere, we need to study the planetary spectrum, a thermal emission caused by the planet’s intrinsic temperature, shaped as a Planck function (a black-body curve), which carries spectral features of molecular species present in its atmosphere. Each molecule has its unique signature (a set of absorption and emission lines) connected to specific wavelength locations. Thus, by distinguishing the spectral features in the planetary spectrum, we can say which molecules are present in the planetary atmosphere. In addition, the depth and the width of each feature tells us the abundance of a certain molecule and the local temperature in the atmosphere.
  
  The most fruitful technique for observing and studying planetary atmospheres, thus far, is the transit method. As seen from Earth, transiting planets pass in front of and/or behind their stars, revealing the most fundamental parameters of the planet-star system and providing a view into the planetary atmosphere. Being very far away from us (the closest confirmed exoplanet is \~4 light years away, [@Dumusque2012Nature-closestExoplanet]), the majority of planet-star systems appear as point sources in most instruments. The transit method allows us to separate the planet from its star by observing the planet-star system in and out of a transit event. During transit, the planet passes in front of its star and obstructs some of its light. Comparing the flux before and during the transit, we see a small dip when the planet is in transit. During transit, the stellar light passes through the terminator, the transition zone between the day and the night side. Superimposed on the stellar spectrum, we see the spectral features of the molecules present in the upper part of the planetary atmosphere. During secondary eclipse, the planet is passing behind its star, looking at the star with its dayside. The dip is observed when the planet is hidden by the star. Comparing the flux in and out of eclipse, we obtain information about the planetary dayside thermal emission.
  
  Planetary spectra can be observed using either spectroscopy or photometry. In spectroscopy, we measure many spectral channels at ones. In photometry, we measure the flux only in certain wavelengths. However, we choose wavelength regions where we know that certain molecular species have spectral features. Thus, combining photometry measurements in multiple broad wavelength regions (bandpasses), we get useful information about the species present in the planetary atmosphere. The majority of the most abundant molecular species have spectral features in the infrared.
  
  Two techniques have been proposed to date to characterize exoplanetary atmospheres. One employs the direct method, where the theoretical spectra are generated based on several physical parameters and comparisons with the observations are done by eye [e.g., @FortneyEtal2005apjlhjmodels]. The other is called the inverse approach, where the properties of the planetary atmosphere are determined based on the available observations. This approach uses a statistical exploration algorithm that seeks the best combination of physical parameters that matches the data [@MadhusudhanSeager2010; @BennekeSeager2012-Retrieval; @LineEtal2014-Retrieval-I; @Waldmann2015-TAU]. Both approaches provide information about the atmospheric temperature and pressure profile, chemical composition, and energy redistribution. However, the inverse approach allows for better exploration of plausible ranges for physical parameters and a more accurate match to the data.
  
  Interested in characterizing planetary atmospheres, for my dissertation I have focused on transiting hot Jupiters. I chose to observe hot Jupiters during secondary eclipse, as this geometric configuration provides the best way to study the temperature and pressure structures and chemical compositions of planetary dayside atmospheres.
  
  I have used the [*Spitzer Space Telescope*]{} to observe and analyze their atmospheres, employing broadband photometry in multiple bandpasses. Although not designed for exoplanetary observations, [*Spitzer*]{} enabled some revolutionary achievements in the exoplanetary field. It was the first telescope that detected the emission from a planetary atmosphere [@CharbonneauEtal2005apjTrES1; @DemingEtal2005natHD209458b] and the first that found a carbon-rich planet [@MadhusudhanEtal2011natWASP12batm]. A large number of characterized exoplanetary atmospheres followed [e.g., @TodorovEtal2010ApJ-HAT-P-1b; @ChristiansenEtal2010ApJ-HAT-P-7b; @O'DonovanEtal2010ApJ-Tres-2; @MachalekEtal2010-XO-3b; @DemingEtal2011ApJ-CoRoT-1-2; @KnutsonEtal2011ApJ-GJ436b; @CrossfieldEtal2012ApJ-HD209458b; @StevensonEtal2010Natur; @CubillosEtal2013apjWASP8b; @BlecicEtal2013ApJ-WASP-14b; @BlecicEtal2014ApJ-WASP-43b]. Trained to target and observe exoplanets with [*Spitzer*]{}, among dozens of planets, I have selected WASP-14b and WASP-43b as the main objects of my study. Both planets, having unusually high signal-to-noise ratios, provided excellent opportunities to study their gaseous envelopes in more detail.
  
  In the beginning of my Ph.D. studies, our research group did not have an atmospheric modeling tool. Thus, we had to call on an external theorist to help us characterize planetary atmospheres. In 2011, I proposed to my committee to develop modeling methods that would allow us to do the atmospheric characterization within our research group. At the time, only one theorist employed the aforementioned inverse technique to infer exoplanetary thermal structures and chemical compositions [@MadhusudhanSeager2009ApJ-AbundanceMethod; @MadhusudhanSeager2010]. Wishing to provide others with the tools to do the atmospheric analysis themselves, our research group decided to make an open-source code that incorporates thermochemical, radiative, and statistical algorithms within the inverse approach. This tool allows us to calculate thermochemical states in planetary atmospheres, and put constraints on the atmospheric chemical composition, temperature profile, energy redistribution, equilibrium and non-equilibrium processes, and the presence or absence of thermal inversion using either transit or eclipse geometry. We call this project BART, Bayesian Atmospheric Radiative Transfer. To develop the thermochemical algorithm, (TEA, Thermochemical Equilibrium Abundances) and parts of BART, I received a NASA Earth and Space Science Fellowship in 2012 and continued to be funded through the end of my Ph.D. studies.
  
  In this dissertation, through observations, thermochemical calculations, and atmospheric modeling, we have gained new insights into the equilibrium chemistry, thermal structure, and composition of several hot Jupiters. During this process, chemical and modeling tools have been developed that our research group is sharing with the community.
  
  Chapter \[chap:WASP14b\] presents the [*Spitzer*]{} observations, secondary eclipse analysis, and atmospheric characterization of WASP-14b. Chapter \[chap:WASP43b\] describes the secondary eclipse observations and atmospheric analysis of WASP-43b. Chapter \[chap:TEA\] presents the open-source Thermochemical Equilibrium Abundances (TEA) code that calculates equilibrium abundances of gaseous molecular species and its application to several hot Jupiters, and Chapter \[chap:BART\] describes my contributions to the open-source Bayesian Atmospheric Radiative Transfer (BART) code and its application to WASP-43b.
  
  The legacy of this dissertation are the two [*Spitzer*]{} secondary eclipse analyses of WASP-14b and WASP-43b, a comprehensive atmospheric analysis of WASP-43b, and two open-source codes, TEA and BART, that we hope will provide useful contributions to the field and grow as the science progresses.
  
  THERMAL EMISSION OF WASP-14b REVEALED WITH THREE SPITZER ECLIPSES {#chap:WASP14b}
  =================================================================
  
  [**Jasmina Blecic, Joseph Harrington, Nikku Madhusudhan, Kevin B. Stevenson, Ryan A. Hardy, Patricio E. Cubillos, Matthew Hardin, Christopher J. Campo, William C. Bowman, Sarah Nymeyer, Tomas J. Loredo, David R. Anderson, and Pierre F. L. Maxted** ]{}
  
  [ *Planetary Sciences Group, Department of Physics, University of Central Florida, Orlando, FL 32816-2385, USA\
  Max-Planck-Institut für Astronomie, D-69117 Heidelberg, Germany\
  Department of Physics and Department of Astronomy, Yale University, New Haven, CT 06511, USA\
  Center for Radiophysics and Space Research, Space Sciences Building, Cornell University Ithaca, NY 14853-6801, USA\
  Astrophysics Group, Keele University, Keele, Staffordshire ST5 5BG, UK* ]{}
  
  Received 6 November 2011.
  
  Accepted 25 September 2013.
  
  Published in [*The Astrophysical Journal*]{} 15 November 2013.
  
  ©AAS. Reproduced with permission.
  
  [y]{}y
  
  SPITZER OBSERVATIONS OF THE THERMAL EMISSION FROM WASP-43b {#chap:WASP43b}
  ==========================================================
  
  [**Jasmina Blecic, Joseph Harrington, Nikku Madhusudhan, Kevin B. Stevenson, Ryan A. Hardy, Patricio E. Cubillos, Matthew Hardin, M. Oliver Bowman, Sarah Nymeyer, David R. Anderson, Coel Hellier, Alexis M.S. Smith and Andrew Collier Cameron** ]{}
  
  [ *Planetary Sciences Group, Department of Physics, University of Central Florida, Orlando, FL 32816-2385, USA\
  Max-Planck-Institut für Astronomie, D-69117 Heidelberg, Germany\
  Department of Physics and Department of Astronomy, Yale University, New Haven, CT 06511, USA\
  Astrophysics Group, Keele University, Keele, Staffordshire ST5 5BG, UK\
  SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, UK* ]{}
  
  Received 26 February 2013.
  
  Accepted 7 December 2013.
  
  Published in [*The Astrophysical Journal*]{} 16 January 2014.
  
  ©AAS. Reproduced with permission.
  
  [y]{}y
  
  TEA: A CODE FOR CALCULATING THERMOCHEMICAL\
  EQUILIBRIUM ABUNDANCES {#chap:TEA}
  ===========================================
  
  [**Jasmina Blecic, Joseph Harrington, M. Oliver Bowman**]{}
  
  [*Planetary Sciences Group, Department of Physics, University of Central Florida, Orlando, FL 32816-2385, USA*]{}
  
  Submitted to [*The Astrophysical Journal Supplement Series*]{}
  
  18 May 2015
  
  Publication reference:
  
  Blecic, J., Harrington, J., & Bowman, M. O. 2015, ArXiv e-prints
  
  [y]{}y
  
  THE BAYESIAN ATMOSPHERIC RADIATIVE TRANSFER CODE AND APPLICATION TO WASP-43b  {#chap:BART}
  =============================================================================
  
  [**Jasmina Blecic, Joseph Harrington, P. Cubillos, M. Oliver Bowman, Patricio Rojo, M. Stemm , Nathaniel B. Lust, Ryan C. Challener, Austin J. Foster, Andrew S. D. Foster, Sarah D. Blumenthal, Dylan Bruce, Thomas J. Loredo**]{}
  
  [*Planetary Sciences Group, Department of Physics, University of Central Florida, Orlando, FL 32816-2385, USA\
  Department of Astronomy, Universidad de Chile, Santiago de Chile, Chile\
  Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853-6801* ]{}
  
  [y]{}y
  