Svensk Sammanfattning Vetenskap om exoplaneter är väldig kompetitiv. Teleskopobservationer är svåra och dyra. Korrekt selektion av objekt och observationsschema är viktiga för att detektera biomarkörer utan att missa dem. Att planera och schemalägga är där- för lika viktiga som observationerna. För att kunna detektera biomarkörer i en exoplanets atmosfär observeras planeten när den passerar framför stjärnan den cirkulerar runt om. Teleskopen och dess placering ger riktlinjer till observation- sprocessen, så väl som planetens och stjärnans egenskaper. I den första delen har vi diskuterat litteratur om exoplanetvetenskap, speciellt om hur man kan bestämma atmosfärens sammansättning och modellering av planeternas atmosfärer. I den an- dra delen presenterar vi en sådan programvara, utvecklad för CRIRES+. Vi visar några användningsexempel och presenterar förslag av planeter som kan observeras över året. Vi jämför resultaten med ett annat liknande verktyg och diskuterar skillnaderna. 1 Abstract In recent decades, thousands of exoplanets have been discovered. The next step is to characterize the observed planets in terms of their radii, masses, density, physical conditions and composition of their atmospheres. Several space-based observatories such as TESS and CHEOPS have started determining the first three observables but characterization of exoplanetary atmospheres is waiting for observation campaigns with instruments like CRIRES+ at the VLT and NIRSpec on the JWST. To ensure the ef- ficiency of data acquisition, careful planning of observations is necessary. In this project we developed a software tool to select and rank candidates based on the feasibility of observations of atmospheric features during transits with CRIRES+. We also review different techniques to retrieve transmission spectra from transit observations and modeling of exoplanet atmospheres in order to clarify the re- quirements for the data. Our CRIRES-planning-tool is built on astronomical observation planning methods from astropy and astroplan and the exposure time calculator designed for CRIRES+ by ESO and UU. We conclude that observations for atmospheric characterization with CRIRES+ are fea- sible. However, we observed that for a robust candidate selection, careful iterative tuning of proposed constraints is required. 2 Contents 1 Introduction 4 2 Theory and literature review5 2.1 Exoplanet transit........................................5 2.1.1 Photometric lightcurve and transmission spectroscopy............... 10 2.2 Atmospheric retrieval methods for transmission spectroscopy............... 13 2.2.1 A novel planetary model-independent transmission spectrum recovery method.. 13 2.2.2 Cross correlation methods to retrieve the transmission spectrum of an exoplane- tary atmosphere.................................... 16 2.2.3 Optimal estimation and bayesian inference...................... 17 2.3 Planetary atmospheric models................................. 20 2.3.1 Parametric forward models.............................. 23 2.3.2 Scattering, albedos and the two-stream approximation............... 28 2.3.3 Self-consistent one-dimensional planetary models.................. 36 2.3.4 General circulation models and three dimensional radiative hydrodynamics mod- els, detailed cloud and dust physics.......................... 44 3 Summary and conclusion of the literature review 51 4 Description and results of the CRIRES-planning-tool 54 4.1 Functionalities and methods of CRIRES-planning-tool................... 55 4.2 Constraints for candidates................................... 59 4.3 Signal-to-noise ratio and the exposure time calculator.................... 61 4.4 Input parameters to the ETC, restrictions and future improvements............ 62 4.5 Test and comparison of results................................ 63 4.6 Results of detectable transits for one year.......................... 64 5 Discussion 69 6 Conclusion 70 3 1 Introduction Today, the atmospheric composition of the planets in our Solar System has been roughly determined (de Pater and Lissauer, 2010). Besides, discoveries of exoplanets have revealed that the architecture of our Solar System is not typical at all (Wright et al., 2011). Therefore, we may expect very different planetary compositions, and atmospheric properties than can be found in our Solar System. On the other side, investigating their compositions will bring us closer to answer one of the most interesting questions about our own existence. Are we alone in the universe? However, we shall see, before we are able to answer this question we still have a long way to go. The next step will be to characterize planetary atmospheres and learn about the habitability of these remote and different worlds. To shed light onto the question of atmospheric composition of exoplanets, the CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES)(Kaeufl et al., 2004) was developed. An upgraded version of CRIRES, now called CRIRES+, is mounted at Paranal observatory on the very large telescope, (VLT), unit telescope 3 (UT3). To plan observations with CRIRES+ we developed a software tool called (CRIRES-planning-tool). Although it was developed to plan transit observations, it may easily be extended to other kinds of observations with CRIRES+. With the upgrade CRIRES+ has now enhanced observation efficiency, increased wavelength coverage, an upgrade of the focal plane detector array to increase the number of accessible diffraction orders, new wavelength calibration methods to reach wavelength precision of 5 m/s and a new spectropolarimetric unit (Follert et al., 2014). Previous scientific highlights with CRIRES were measuring the length of an exoplanet day for the first time (Snellen et al., 2014), creating the first weather map for the nearest brown dwarf to Earth (Crossfield et al., 2014) or finding the first superstorm on an exoplanet, HD209458 b and measuring its mass (Snellen et al., 2010a) to name but a few. To plan transit observations of exoplanets we used the python libraries astropy,(Price-Whelan et al., 2018) and astroplan,(Morris et al., 2018), which provide useful methods to assess times and coordi- nates for observability at observatories all over the world. To calculate the signal-to-noise ratio (SNR) for an observation we use the Exposure Time Calculator (ETC), developed by the European Southern Observatory (ESO) in Garching, Munich, Germany together with Uppsala University (UU)1. CRIRES-planning-tool is written in python and selects candidates from the NASA Exoplanet Archive (Akeson et al., 2013) to assess which candidates can be observed when, what signal-to-noise ratio can be reached for CRIRES+, and ranks the planets after criteria deduced from these properties. The output of the software tool is used for decision making, which targets should be observed and when, and provides an important basis to plan for best efficiency in time and data quality. This manuscript provides an overview of the structure of the software tool and describes and discusses some of the used methods. The software comes with an extensive documentation. The README file provides information about the different functionalities, accessibility, structure, installation, and further development possibilities of the CRIRES-planning-tool. The tool is available on GitHub2. The thesis contains two major parts. The first part (chapter2) gives an overview of the present state of exoplanetary astrophysical techniques, both in observation and theory. In section 2.1 we introduce the reader to the technique of transit photometry, highlighting its strengths and limitations, and derive the basic equations for transmission spectroscopy. In section 2.2 we present two important methods for transmission spectra retrieval, and two techniques to compare retrieved spectra with synthesized spectra 1https://etctestpub.eso.org/observing/etc/crires 2https://github.com/jonaszubindu/CRIRES-planning-tool 4 from planetary models. In section 2.3 we provide an extensive overview about the different physics treated by a planetary model, such as radiative transfer, thermodynamics, convection, chemistry, clouds, and hydrodynamics and present examples to the different kinds of planetary models developed to study exoplanetary atmospheres. At the end of this part we will give a short summary and conclusion of the reviewed topics. In the second part (chapter4), we shall provide the reader with a brief introduction to the CRIRES-planning-tool. In sections 4.1, and 4.2, we explain the functionalities and used methods to select candidates for obser- vations and assess their observability from the Paranal observatory, in section 4.3 we give an overview about the ETC and the computation of signal-to-noise ratio, and in section 4.4 explain each parameter used for the ETC. In section 4.5 we compare our tool with two other transit observation planning tools, highlighting differences between these tools and verifying our own findings. Finally in 4.6 we present preliminary results of possible transit observations over the course of one year. A discussion of the CRIRES-planning-tool can be found in chapter5, and a short conclusion of the findings is given in6. 2 Theory and literature review One idea to determine the composition of an exoplanet’s atmosphere is to retrieve the transmission spectrum of the star light passing through the atmosphere and investigate the spectrum for known molecular transitions. Since planetary atmospheres consist of molecules, and in case of hot Jupiters, atoms, one aims at observing only molecular bands. Subtracting