Optical spectroscopy of exoplanets and hosts stars

Abstract

The thesis work ’Spectroscopic Characterization of Exoplanets and Host Stars,’ tries a tiny step towards understanding the connection between the exoplanet and the host star. We study the observational perspective of exoplanets and host stars using optical spectroscopy. Our analysis of host star carbon abundances as a function of planet occurrence rate in the LAMOST-Kepler field shows giant planets are preferentially found around iron-rich and carbon-rich host stars. However, the sub-solar [C/Fe] value of giant planet host stars indicates that carbon may not be as important as iron or that the overall metallicity is crucial rather than a single element like carbon or iron for planet formation. Differential abundance analysis of planet hosts in visual binary twin systems shows that planet-induced pollution in the host star chemical abundance is less than 0.01 dex. It is well within the typical error in abundance estimates, which indicates that occurrence rate calculations are not influenced by planet pollution in the host star photosphere. The accuracy of differential abundances needs to be better than 0.01dex to infer any trend in the abundances due to planet formation. The low-resolution transmission spectroscopy from the 2 m Himalayan Chandra Telescope using long-slit multi-object observations successfully detected several atmospheric features in the atmosphere of three exoplanets HAT-P-1 b, KELT-18 b, and WASP-127 b. The advantage of having a bluer part of the spectra, we were able to detect CaI (4227 ˚A) in the atmosphere of HAT-P-1 b and Rayleigh scattering slope in the atmosphere of WASP-127 b. We observed flat, featureless transmission spectra of KELT-18 b for the first time at low resolution. Simultaneous observation of reference stars helped to avoid the systematic errors introduced during the observations. We perform transmission spectroscopy with Keck-HIRES for the first time. We achieved a wavelength calibration accuracy of 60 m/s for HIRES, using a wavelength recalibration method. We detect residual sodium signals at a blue-shifted stellar rest frame location. Occulted and unocculted stellar inhomogeneity can change the observed transit signal or can add extra noise to the observed data. Here we studied three years of disk-integrated solar spectra from HARPS to quantify the inhomogeneity using the spectral indices. From the preliminary analysis, we found that the faculae fraction than the spot fraction influences the line indices. Ca II H & K linearly correlated with faculae fraction, and all the Balmer lines are sensitive to faculae fraction but have a complex trend compared to CaII H & K lines.