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Over time, pre-main-sequence (PMS) stars evolve into main-sequence (MS) stars. Stars evolving from PMS to MS phase is a significant subject of research that aims to better understand stellar phases and their properties. Existing literature shows a lack of study of stars in between PMS and MS phase. 'We focused on what belongs in the midst of these two phases. Classical Be (CBe) and Herbig Ae/Be (HAeBe) stars, corresponding to MS and PMS phases, are two well known categories of emission-line stars. Through optical and infrared photometric analysis of a sample of 2167 CBe and 225 HAeBe stars, we identified 98 such rare stars which are in transition between PMS and MS phase. Those rare stars are termed as 'Transition Phase' (TP) candidates in our study. Using the machine learning approach, the potential of the identified TP candidates was verified. 'This article provides a brief overview of the research contributions made by the CHRIST (Deemed to be University) team in this field. [ABSTRACT FROM AUTHOR]

Mechanisms of the disk formation in Be stars may differ from one star to another and cause variations in the circumstellar disk’s spectral characters. δ-Scorpii is one of the bright Be binary stars that has been classified as a Be star since the 1990s when the star showed a weak Balmer emission line. In this work we study the characteristics of the Be disk of this star in the optical region during close encounters with its companion in order to investigate the appearance of the Be phenomenon. This work presents a monitoring and analysis of δ-Scorpii’s spectral character in the optical region during the 2011 periastron passage. The line profiles and strength (EW), relative intensity (I/Ic) and V/R ratio of the circumstellar regions Hα, Hβ, Hγ and HeI 6678 are used in the investigation of the Be disk characters of δ-Scorpii. We found that all physical characteristics of the line profiles such as equivalent width (EW), full width at half maximum (FWHM), etc. were enhanced during the time of the periastron. We suggest that the effects are owed to the tidal interaction of the companion in close encounters which might have a strong influence on the appearance and survival of the Be phenomenon of δ-Scorpii. [ABSTRACT FROM AUTHOR]

Advances in the technology of astronomical spectra acquisition have resulted in an enormous amount of data available in world-wide telescope archives. It is no longer feasible to analyze them using classical approaches, so a new astronomical discipline, astroinformatics, has emerged. We describe the initial experiments in the investigation of spectral line profiles of emission line stars using machine learning with attempt to automatically identify Be and B[e] stars spectra in large archives and classify their types in an automatic manner. Due to the size of spectra collections, the dimension reduction techniques based on wavelet transformation are studied as well. The result clearly justifies that machine learning is able to distinguish different shapes of line profiles even after drastic dimension reduction. [ABSTRACT FROM AUTHOR]