About my Research Work

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 analysed 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.

Read the complete article at: https://www.sciencedirect.com/science/article/abs/pii/S1384107623001513?via%3Dihub

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In the current study, we present the first photometric, period variation, and flaring activity investigations of TIC 24233294. Additionally, we also review and report the flaring activity of five well-studied eclipsing binaries BX Tri, V405 And, GJ 3236, Thor 42, and GU Boo. Using the Transiting Exoplanet Survey Satellite (TESS) data, continuous variations in the light curves of binaries TIC 24233294, and BX Tri are analysed and presented. The primary and secondary components of all the six binaries in the study are M-type dwarfs. All these binaries are observed to be in detached/semi-detached configuration. Photometric analysis on TIC 24233294 and BX Tri was carried out using the Wilson–Devinney program. The long-term orbital period changes are analyzed and presented, on the basis of photometric solutions and the evolutionary status of the binary systems in the study. Flares are observed to be common in stars with outer convection zones. We identified flares on all binaries in the study and calculated their characteristic parameters like amplitudes, frequency, duration, and energies. Many superflares and few hyperflares were identified in the list of flares detected within the energy range of 10^33-10^37 erg. The flare events in the binaries could be related to the strong tidal interactions between the components of the binaries and fully/deeper convective interiors.

Read the complete article at: https://www.sciencedirect.com/science/article/abs/pii/S0273117723004416 73117723004416

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RAVI RAJA POTHUNENI, Shanti Priya Devarapalli and Rukmini Jagirdar

The first photometric, spectroscopic and period variation studies of neglected short-period eclipsing binary V2840 Cygni are presented. High mass ratio contact binaries (HMRCBs), especially those in the weak-contact configuration, are vital when probing the evolutionary models of contact binaries (CBs) using stellar parameters. The photometric solutions reveal the weak-contact nature of V2840 Cygni with a high mass ratio (∼1.36), motivating us to investigate the nature of such binaries. The period variation study of V2840 Cygni spanning 15 yr shows a secular period decrease at a rate of ∼5.5 × 10−7 day yr−1, indicating mass transfer between the components. The superimposed cyclic variation provides a basic understanding of the possible third body (P3 ∼ 8 yr, m3 ∼ 0.51 M⊙). Following the derived parameters, the evolution of the system is discussed based on the thermal relaxation oscillation (TRO) model. It is found that V2840 Cygni falls in a special category of HMRCBs, which validates TRO. To characterize 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 Jrel 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.

Read the complete research article at: https://iopscience.iop.org/article/10.1088/1674-4527/acae6e

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Photometric investigation of eight ultra-short period eclipsing binaries from OGLE

Shanti Priya D., Ravi Raja P., Rukmini J., Raghu Prasad M. and Vineet S. Thomas

Short period eclipsing binaries are known to be key gauges to investigate and understand fundamental stellar properties. Studies of these binaries (also known as W UMa systems) to date have indicated a well-defined short period limit of about 0.22 d. These binaries whose orbital periods are shorter than 0.22 d are considered scarce systems and termed as ultra-short period eclipsing binaries (USPEBs) (Rucinski 1992, 2007). Examining these binaries will help in understanding the mechanism involved in the formation of such tight systems, which is different from the formation of early-type main sequence stars.

For our investigation, we collected data from the OGLE-III survey that conducted long-term observations of fields towards the Galactic bulge during its tenure in 2001–2009. Soszyński et al. (2015) created model light curves using a script developed by Pilecki & Stepien (2012) to classify binary systems that were observed in OGLE. However, the details of photometric parameters were neither reported nor discussed previously in the literature. Therefore, we performed a detailed photometric analysis of the eight USPEBs chosen and obtained the photometric elements. 

We obtained the photometric solutions for the selected eight USPEBs using the WD method, v.2003. We found that all eight systems were high mass ratio, late-type binaries and categorized as W-subtype systems (Binnendijk 1970; Rucinski 1974). However, none of them showed any spot activity or evidence of third light. The components have almost equal surface temperatures, and the temperature difference between them (∆T ) is <∼ 106 K. Such temperature difference indicates that system components are in thermal contact, and large amounts of energy transfer from the more massive to the less massive component take place. All of them show shallow fill-out factors (f <20%), suggesting that these system components are in a broken contact phase, which is a typical property observed in USPEBs (Hilditch 1989).

Read the complete research article at: https://iopscience.iop.org/article/10.1088/1674-4527/20/8/113

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Photometric study of 61 totally eclipsingcontact binaries from the ASAS, OGLE,HATNet, AST3 and TESS databases

J. Rukmini, D. Shanti Priya, M. Raghu Prasad and P. Ravi Raja

Eclipsing binaries in pre-contact and marginal contact phases are important systems to help understand close binary evolution from detached to contact stages. The contact binary systems with mass ratios < 0.25 and fillout factors > 50% are prominent sources of interest, as they are progenitors of some fascinating objects and related to several key astrophysical processes (Liao et al., 2017).

Photometric data of contact binaries with totality were collected from various archival databases like the All Sky Automated Sky Survey-3 (ASAS, Pojmanski, 2004), the Optical Gravitational Lensing Experiment-3 (OGLE, Udalski et al., 2008), the Hungarian Automated Telescope Network (HATNet, Hartman et al., 2004), the Antarctic Survey Telescope at Dome A (AST3, Wang et al., 2017), and the Transiting Exoplanet Survey Satellite (TESS,Stassun et al., 2018).  Phased light curves were then analysed using the software package PHysics Of Eclipsing BinariEs (PHOEBE) (Prsa 2006).

The variables were classified on the basis of fillout factors as shallow/marginal, over-contact and deep-contact binaries. The absolute parameters were derived using the Gazeas (2009). Most of the binaries in this study are found to be low mass ratio systems with primaries the more massive of the two stars.

Read the complete research article at: https://ui.adsabs.harvard.edu/abs/2020CoSka..50..436R/abstract

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Characteristic Study of Red Dwarfs using Hertzsprung-Russell and Infrared Color-Color Diagrams (on-going)

Ravi Raja P, Ojjas Sharma, Anuvab Rudra, Baibav Sarkar, Bhagyavasu Sharma, Saihajleen Kaur, Shubhranshu

Red Dwarfs being the majority of the stars in the galaxy are very enthralling astronomical objects to observe and study in order to get an insight about the origin, structure and evolution of star and in order to explore the formation and existence of exoplanets, especially habitability around them. In this project, we have collected a sample of 58 red dwarfs from various catalogs and presented them on H-R and Infrared color-color diagrams with calculated distances, absolute magnitudes using GAIA parallaxes and obtained infrared colors. The results obtained are helpful to understand about red dwarfs, especially their location on HRD and identification of cooler or redder dwarfs on Color-Color Diagram.

The selection criteria set up for the data mining is based on sub-spectral types of K and M. We have chosen sub-spectral types from K5-M5.

Based on the selection criteria as specified above, we have planned to data mine the red dwarfs. We have used the following databases to collect their samples and necessary information such as Infrared colors of the stars, effective temperature from GAIA etc. These databases include SIMBAD, VizieR and GAIA-dr2.

For the collected samples and obtained information, we have determined distances using Parallax angle and Absolute Magnitudes for each of the objects under study.

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