Observation and characterization of extra-solar planets using Indian facilities

Abstract

Detection and characterization of extra-solar planets (also known as exoplanets) is an emerging field that has been constantly evolving with the advent of new cutting-edge observational techniques and the development of state-ofthe-art models to interpret the observational results. Since the discovery of the first confirmed planet orbiting around a Solar type star, 51 Pegasi, in 1995, the astronomers have engaged in a global and systematic quest for understanding the origin and evolution of the exoplanets. Till date over 4200 exoplanetary detections have been confirmed and a few of those planets have been studied extensively using different photometric and spectroscopic techniques. Transit photometry and transit spectroscopy are the two essential tools, in this regard, for the detection and characterization of the exoplanets. We have used the 2m Himalayan Chandra Telescope (HCT) and the 1.3m Jagadish Chandra Bhattacharyya Telescope (JCBT) for the photometric follow-up observations of the transit events of some confirmed Jupiter-sized close-in planets (hot Jupiters) such as WASP-33b, WASP-50b, WASP-12b, HATS-18b, HAT-P-36b, etc. This exercise is a part of the capability testing of the two telescopes and their backend instruments in the field of transit photometry. Leveraging the large aperture of both the telescopes used, the images acquired during several nights were used to produce the transit light curves with high photometric signal-tonoise ratio (SNR > 200) by performing differential photometry. In order to reduce the fluctuations in the transit light curves due to various sources such as stellar activity, varying sky transparency etc. we preprocessed them using wavelet denoising and applied the Gaussian process correlated noise modeling technique while modeling the transit light curves. A state-of-the-art algorithm used for modeling the transit light curves provided the physical parameters of the planets with more precise values than reported earlier. Also, we present the results obtained from the high-resolution transit spectroscopic observations of some bright stars (Vmag < 12) from the 2.34 m Vainu Bappu Telescope (VBT) which are aimed at the characterization of the atmospheres of the exoplanets. The results show that the spectral SNR achieved with these observations are not enough to draw any inference on the atmospheric contents of the exoplanets and instead, we need repeated observations to improve the SNR, preferably a telescope with an even larger aperture (> 4m). Besides, another important aspect of the project is the theoretical modeling of the atmospheres of the hot Jupiters to predict the nature of their transmission, reflection and emission spectra for different values of the physical parameters such as size, surface gravity, irradiation temperature, internal temperature, etc. We have used external databases for the abundance and opacity of the atoms and molecules in the planetary atmospheres, considering solar metallicity and solar Carbon-to-Oxygen (C/O) ratio. We have developed a complete pipeline that calculates all the physical and chemical properties of the atmospheres of the hot Jupiters and computes the effect of the interaction between the light and the atmospheric contents by either using the Beer-BouguerLambert law or solving the 1-D multiple scattering radiative transfer equations using discrete space theory. We have extensively studied the effect of scattering albedo and the planetary emission on the transmission spectra of the hot Jupiters. These studies are aimed at a more accurate and consistent representation of all the physical and chemical processes occurring in the atmospheres of the exoplanets to precisely model the bulk amount of observational data to be obtained from the upcoming missions such as James Webb Space Telescope (JWST), Atmospheric Remote-sensing Exoplanet Large-survey (ARIEL) and so forth.