Optical and infrared studies of herbig Ae/Be stars
The work makes use of the unprecedented capability of the Gaia mission to study various properties of Herbig Ae/Be stars. We placed the Herbig Ae/Be stars in the Gaia color-magnitude diagram and accurately estimated their age and mass. The mass accretion rate is calculated from Hα line flux measurements of 106 HAeBe stars. The mass accretion rate is found to decay exponentially with the age of Herbig Ae/Be stars. Further, the immediate neighborhood of two Herbig Ae/Be stars, V1787 Ori and IL Cep, are studied using the astrometric and photometric data from the Gaia mission. We discovered a low mass binary companion to V1787 Ori using the analysis of distance and proper motion values from Gaia DR2. The mass ratio of the coeval binary system is found to be 0.23. Such a skewed mass ratio system is rarely identified in Herbig Ae/Be binary systems. The method of identification and characterization of the V1787 Ori wide binary system opens up the possibility of identifying more such systems. The HBe star IL Cep tells a much more complex story. The star is identified with a cluster of low mass stars associated with it. We identified 79 co-moving stars that are coeval to IL Cep, within 2 pc radius, from the analysis of Gaia EDR3 astrometry. The triggered star formation process called the "Rocket effect" caused by a massive star HD 216658 is identified to be the cause of the clustered star formation near IL Cep. The effect of this process is demonstrated for the first time using the proper motion data from Gaia. The immediate neighborhood of Herbig Ae/Be stars is identified as the formation region of long-chain carbon molecules such as Fullerenes and Polycyclic Aromatic Hydrocarbons.