An Infrared Stellar Thermometer

Abstract: Infrared (IR) spectroscopy has many advantages over optical, one of which is allowing us to see through intergalactic dust, letting us probe deeper into space and dust-dense regions such as galactic centers. However the investigating the IR spectral range is a relatively new field, owing to recent developments in detector technology, and stellar parameter determination in IR is not well researched. This thesis aims to explore stellar temperature determination in this spectral range. Temperature can be considered as one of the most important stellar parameters, as it is crucial to know when determining chemical abundances, and it allows us to classify stars from which we may then analyse individual bodies and stellar populations. A variety of methods exist for determination, however in this thesis we use spectral synthesis. We determine the effective temperature through spectral synthesis done with high resolution and high signal-to-noise ratio H-band (1.5{1.8 microns) spectra taken by the IGRINS spectrometer of 12 K-giants, with a range of temperatures between 4100{5200 K and metallicites between -0.80{0.30 dex. We use stellar parameters from J¨onnson et. al. (in prep) determined in the optical range for modelling stellar atmospheres, and as a benchmark for stellar temperatures. We find that only using Fe I absorption lines for spectral synthesis produces poor results in comparison, and choose to additionally look at CO molecular lines, using carbon and oxygen abundances found in J¨onnson et. al. (in prep.). While these produce temperatures closer to the benchmark, the best results are found from a combination of Fe I and CO lines which give temperatures on average 40 K higher with σ = 24 K.