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In the current work we present the first investigations of 14 neglected, late-type, short period contact binaries using period variation, photometric and spectroscopic analysis performed on long term space and ground based observations. The binaries in study belong to spectral classes F to K. In this study the two contact binaries TIC 242100930 and TIC 332918217 are suggestive to be precursors to merger candidates since they showed highest period decreasing rates ∼ 10−6 day/yr. Preliminary photometric analysis using PHOEBE revealed 9 of them to be in marginal, 4 in over and 1 in deep contact configuration. The evidence of magnetic activity is observed in 6 of the contact binaries either by presence of spots in their photometric solution or photospheric and chromospheric lines in their spectra from LAMOST/VBT/HCT, suggesting such activity to be an inherent feature in these binaries, irrespective of their evolutionary stages. The equivalent widths of Na and Hα lines, in the spectra taken from VBT and HCT for TIC 7022755 and TIC 20572196, show strong phase dependent variability. Additionally a strong correlation is found between equivalent widths of Na and Hα lines through out the observed phases, for the high mass ratio contact binary TIC 7022755. TIC 50717816 is found to be a deep overcontact binary (f ≥ 50%) with extreme low mass ratio (q ∼ 0.22), showing a long term period decrease, which may further evolve into a progenitor to blue straggler, due to merger of its components. Using the collective results from current study, an attempt is made to explain the evolution of the 14 contact binaries via AML and TRO models.

We present the first pulsation analysis of four totally eclipsing Algol systems S Cnc, SS Cet, TW And, and VW Cyg using the latest data available from Kepler (K2), and TESS databases. Based on the characteristics observed they are classified to be oscillating eclipsing Algol binaries with primary components having γ Dor type pulsations. The photometric solutions were derived for five Algols including TT Hya using Wilson-Devinney code (v2015), and the absolute parameters of all Algols in study were computed. The period variation study was also conducted using the O-C diagram and the variation is correlated either to mass loss or mass transfer or presence of third body in these systems. All the available IUE high and low resolution spectra for S Cnc, TT Hya as well as VBT and LAMOST spectra for SS Cet were used to measure the equivalent widths of prominent lines, and their significance is presented. Based on the photometric, spectroscopic, period variation, and pulsation studies the evolutionary scenario of all the five Algols is discussed using Teff - Luminosity, q-r and q-p diagrams.

This paper reports the first spectroscopic observations in the H α region at different orbital phases and the revised photometric solutions, for the contact binary KP101231 (V1) in the direction of the open cluster Praesepe. The photometric solutions obtained for the data in V and R passbands using the Wilson–Devinney (WD) method suggest that both components were in good thermal contact. The equivalent widths (EW) of H α and Na lines were studied at various phases and a filled-in absorption profile around phase 0.58–0.68 was observed and compared with other phases. A correlation was observed between the profiles of H α and Na lines at various phases.

This paper reports the first spectroscopic observations in the H[alpha] region at different orbital phases and the revised photometric solutions, for the contact binary KP101231 (V1) in the direction of the open cluster Praesepe. The photometric solutions obtained for the data in V and R passbands using the Wilson-Devinney (WD) method suggest that both components were in good thermal contact. The equivalent widths (EW) of H[alpha] and Na lines were studied at various phases and a filled-in absorption profile around phase 0.58-0.68 was observed and compared with other phases. A correlation was observed between the profiles of H[alpha] and Na lines at various phases.

The analysis of spectroscopic data for 30 Algol-type binaries is presented. All these systems are short period Algols having primaries with spectral types B and A. Dominant spectral lines were identified for the spectra collected and their equivalent widths were calculated. All the spectra were examined to understand presence of mass transfer, a disk or circumstellar matter and chromospheric emission. We also present first spectroscopic and period study for few Algols and conclude that high resolution spectra within and outside the primary minimum are needed for better understanding of these Algol type close binaries.

The first photometric, spectroscopic, and period variation studies of neglected short-period eclipsing binary V2840 Cygni are presented. High Mass Ratio Contact Binaries, especially those in the weak-contact configuration are vital while probing into the evolutionary models of CBs using stellar parameters. The photometric solutions reveal the weak-contact nature of V2840 Cygni with a high mass ratio (\\(\\sim1.36\\)), motivating us to investigate the nature of such binaries. The period variation study of V2840 Cygni spanning for 15 years shows a secular period decrease at a rate of \\(\\sim5.5\\times10^{-7}\\)d/yr indicating mass transfer between the components. The superimposed cyclic variation provides a basic understanding of the possible third body (P\\(_3\\) \\(\\sim8\\) yr, m\\(_3\\) \\(\\sim0.51\\)M\\(_\\odot\\)). Following the derived parameters, the evolution of the system is discussed based on Thermal Relaxation Oscillation (TRO) model. It is found that V2840 Cygni falls in a special category of HMRCBs, that validates TRO. To characterise the nature of HMRCBs, a catalog of 59 CBs with high mass ratios has been compiled along with their derived parameters from the literature. For all the HMRCBs in the study, a possible correlation between their contact configuration and observed period variations for relative log\\emph{J\\(_{rel}\\)} is discussed. The spectroscopic study of V2840 Cygni provides evidence of the presence of magnetic activity in the system and the existence of ongoing mass transfer which is additionally deduced from the period variation study. The LAMOST spectra of 17 HMRCBs are collected to interpret the stellar magnetic activity in such systems.

Binary stars are believed to be key determinants in understanding globular cluster evolution. In this paper, we present the Multi-band photometric analyses of five variables in the nearest galactic globular cluster M4, from the observations of CASE, M4 Core Project with HST for four variables (V48, V49, V51, and V55) and the data collected from T40 and C18 Telescopes of Wise Observatory for one variable (NV4). The light curves of five binaries are analyzed using the Wilson-Devinney method (WD) and their fundamental parameters have been derived. A period variation study was carried out using times of minima obtained from the literature for four binaries and the nature of the variation observed is discussed. The evolutionary state of systems is evaluated using M-R diagram, correlating with that of a few well-studied close binaries in other globular clusters. Based on the data obtained from the Gaia DR3 database, a three-dimensional Vector-Point Diagrams (VPD) was built to evaluate the cluster membership of the variables, and two out of them (V49 and NV4) were found to be not cluster members.