| Abstract : | 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, with a mass ratio of 0.23, using the analysis of distance and proper motion values from Gaia DR2. The HBe star IL Cep is identified with a cluster of low mass stars associated with it. The triggered star formation process called the "Rocket effect" is demonstrated for the first time using the proper motion data from Gaia near IL Cep.
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. We discovered six HAeBe star spectra with Fullerene emission. Fullerene features are arise from the extended circumstellar environments such as reflection nebulae in the case of four Herbig Ae/Be stars. For the remaining two Herbig Ae/Be stars, we report first detection of Fullerene originating from the circumstellar disk of young stars. Finally, the Spitzer spectra of 93 Herbig Ae/Be stars are used to study the PAH emission, which is the largest sample to date. We found 58% of the Herbig Ae/Be star spectra have PAH features. The stars with higher effective temperatures (> 20,000 K) are devoid of PAH features in their spectra. |
