Photometric and Spectroscopic studies of low mass eclipsing binary and exoplanet candidates

Abstract

Eclipsing binary (EB) is a class of binary systems in which the total brightness of the system changes with time as seen by the observer due to speci c orbital geometry. On the basis of the Roche lobe geometry or morphologically, EBs are divided into detached, semi-detached, and contact binaries. EBs hold an important role in modernday astronomy and astrophysics as they allow astronomers to accurately determine stellar parameters. EBs are also considered as one of the most promising distance indicators. Although EBs are being studied for nearly two decades, the number of wellcharacterized EBs is still small compared to the huge number of known EBs. The same situation is happening in the case of detected exoplanets. The eld of exoplanets is newer than EBs but due to multiple exoplanet search missions, their number is tremendously increasing with time. A large fraction of known and candidate exoplanets require followup observations. In this thesis, we analyzed a sample of contact and detached EBs. We also performed follow-up observations for two exoplanet candidates to understand their nature. In the rst part of the thesis, we studied 9 W Uma systems. We collected multiband photometric and low-resolution spectroscopic data for each system. Besides our photometric data, we also collected photometric data from other surveys e.g. Super- WASP, PTF, ZTF, ASAS-SN, Kepler/K2, TESS, etc. for the studied sample. On the basis of performed period analysis, period change was detected in four systems. The observed period change rates were high enough to be explained completely by gravitational radiation or magnetic braking. Therefore, mass transfer between components was considered the major reason for observed period change rates. Fundamental parameters such as mass, radii, luminosity, inclination, and temperature ratio of the components were determined from photometric data. In the studied sample, 4 systems were found with inclination angle > 75 and 3 with inclination angle < 65 . The reliability of determined parameters decreases with decreasing inclination angle, so, determined parameters for low inclination systems might not be completely trustworthy. The asymmetry of LCs is quite common in such type of systems and six systems in the current sample showed LC asymmetry. It is impossible to clearly understand the main reason for such asymmetry on the basis of photometric data alone but spot formation is among one of the main reasons. On the basis of derived parameters, ve systems were categorized as A-subtype W UMa systems and others as W-subtype W UMa systems. The primary components of studied systems were found close to the ZAMS in the mass-luminosity and mass-radius diagram. The secondary components were found to be more evolved and away from ZAMS. The low-resolution LAMOST spectra for each system were compared with known inactive stars of same spectral type to get clues about the magnetic activity. The subtracted spectra show small excess emission in some systems but due to the low-resolution of used spectra and the contact nature of systems it was hard to calculate individual component contribution. In the second part of the thesis, we studied 2 EB candidates and derived their accurate parameters. For this purpose, we used Kepler/K2, ASAS-SN and our observations along with high-resolution spectroscopic data. Following the period investigation procedure, the period of both the systems were found constant over the last 3 years. The radial velocities (RVs) from spectra were derived using the cross-correlation function (CCF) technique. The LCs and RV data were analyzed with PHOEBE software package to derive orbital solutions. Both the systems were found to have high massratio > 0.85. The masses and radii for each components were between 1-2 M and 1-2 R , respectively. We investigated their evolution using di erent evolutionary tracks and isochrones. The nal part is about follow-up spectroscopic observations of 2 exoplanet candidates. Due to the absence of photometric data for BD+27 62, the period was investigated for EPIC 201270464 only. No period change in EPIC 201270464 was detected in the analysis. For each source, we collected 17 high-resolution spectra. The RVs were determined using the CCF technique with the help of appropriate synthetic template spectra. Phase-folded RV curves were also not showing any detectable variation. For BD+27 62, we need more photometric observations to reach any solid conclusion. In the case of EPIC 201270464, we concluded that the detected transit signal was due to another nearby system EPIC 201270176. Therefore, the reported transit in EPIC 201270464 was a false signal due to another closeby faint EB.