Spectroscopic Studies of Galactic Field Be Stars
Title
Spectroscopic Studies of Galactic Field Be Stars
Description
Be stars provide excellent opportunity to study circumstellar disks. But the disc formation
mechanism of classical Be (CBe) stars- the Be phenomenon- is still poorly understood. This
can be understood by studying CBe stars in various locations like clusters and fields. Spectra
of Be stars show interesting emission lines of different elements like hydrogen, helium, iron,
oxygen calcium, etc. These emission lines are valuable indicators in providing information
about the circumstellar disks of Be stars. In the past several decades various aspects of Be
stars have been studied. But literature review clearly indicates the need of further studies to
frame a consolidated picture about Be phenomenon in CBe stars.
It is found that especially, the region ?????? 7500 - 8800 ??? is a less studied, and thus
poorly understood area in Be star research. But this area shows some interesting features
like emission lines calcium, iron, oxygen and Paschen series. So, here we have studied a
sample of 118 field CBe stars taken from the catalogue of Jaschek & Egret (1982) and whose
medium resolution spectra were obtained in ?????? 3800 ?? 9000 ??? region during December,
2007 to January, 2009 with the 2.1-m Himalayan Chandra Telescope (HCT), located at Hanle,
Ladakh, India and operated by the Indian Institute of Astrophysics (IIA), Bangalore.
In this thesis, we present three works which investigate the disc properties of our 118
program Be stars by studying their spectral line features, focussing primarily on the less
explored ?????? 7500 - 8800 ??? region. Firstly, we have analyzed the less studied Fe II 7712
??? emission line for our stars to understand the possible Fe II line excitation mechanism
in CBe stars. Our work predicts that Ly???fluorescence may be the possible Fe II line
excitation mechanism in CBe stars. Secondly, we have studied the Ca II triplet emission lines
for our stars and have developed a new technique for deblending Ca II components from
their counterpart Paschen lines, thus providing a more efficient way to analyze Ca II lines.
Analyzing Ca II lines through this technique, we suggest that the gas producing these lines
is optically thick. This leads us to predict that Ca II lines may be an indicator of binarity
in Be stars. Lastly, we have estimated the Balmer decrement values, D34 and D54 for 81 of
our sample stars to shed light on opacity effects in Be star disks. Our work confirms the
disc transient nature of Be stars through epoch-wise D34 and D54 variation study and also
suggests that Be star disks are optically thick.
Creator
Gourav Banerjee
Source
Physics
Date
Collection
Citation
Gourav Banerjee, “Spectroscopic Studies of Galactic Field Be Stars,” CHRIST (Deemed To Be University) Institutional Repository, accessed October 5, 2024, https://archives.christuniversity.in/items/show/1572.