Research Projects

The study of Be stars can provide insight into the dynamic processes related to star - disc interaction. Be stars belong to the broad category of emission line stars (ELS), which are characterized by H-alpha emission lines in the spectra. This is indicative of the presence of a circumstellar medium, mostly in the form of a disc, where the emission lines of hydrogen and other metals form. Among the category of Be stars, the formation of a decretion disc in a Classical Be star is a mystery. It has been identified that H-alpha emission can be transient in nature, suggesting that the disc forms and dissipates in certain classical Be stars. The formation and evolution of disc in Be stars can be understood from the analysis of a population of Be stars in diverse metallicity environments. The availability of spectra of millions of stars from the LAMOST survey program opened up the field of emission-line star research. The survey collected data for stars belonging to different regions of the Galaxy, particularly those belonging to the anti-center direction. As part of the concluded SERB CRG program, we compiled a sample of 3339 early-type ELS in the Galaxy, and classified them to various evolutionary phases (Shridharan et al. 2021). We found that the disc of Be stars behave distinctly towards late spectral type and found a new population of classical Ae stars (Anusha et al. 2020). We plan to explore this further by analyzing the light curves of these stars from missions such as TESS. This will reveal whether the changes in the disc are connected to the asteroseismic activity of the host star. It has been proposed that the formation of disc in Be stars is mediated by the presence of a companion. In some cases, the presence of a companion is evident in the form of X-ray emission, and these systems are known as Be/X-ray binaries. We studied an interesting system named LY CMa recently where we found a correlation between the H-alpha and X-ray emission, suggestive of the interaction the degenerate companion is making with the disc (Bhattacharyya et al. 2022). This was made possible due to the optical/IR follow-up of Be/X-ray binaries, which is a clever approach to understand the changes in the disc. We plan to analyze the role of binaries in a broader context by studying more such samples of Be/X-ray binaries and to develop population models which explain the possible combination of companions to Be stars. As a final point we would like to understand the formation of organic molecules in the protoplanetary disc of Herbig Ae/Be (HAeBe) stars. From Spitzer infrared spectra we found the presence of organic molecules such as Polycyclic Aromatic hydrocarbons and fullerenes in the circumstellar environment of HAeBe stars. The mechanisms for the formation and destruction of these molecules in the disc of these stars is not explored properly, and we plan to take this up with further observations using JWST space telescope.