| Authors : | Gourav Banerjee (1) (lead author who will present the paper),
Blesson Mathew (1), K. T. Paul (1), Annapurni Subramaniam (2), Anjusha Balan (1), Suman Bhattacharyya (1), R. Anusha (3), Deeja Moosa (1), C S Dheeraj (1), Aleeda Charly (1) and Megha Raghu (1)
(1) Department of Physics and Electronics, CHRIST (Deemed to be University), Bangalore
(2) Indian Institute of Astrophysics, Bangalore,
(3) Department of Physics and Astronomy, University of Western Ontario, Canada |
| Abstract : | A classical Be (CBe) star is a special class of massive B-type main sequence star surrounded by a geometrically thin, equatorial, gaseous, decretion disc orbiting the star in Keplerian rotation. Spectra of CBe stars show emission lines of different elements such as hydrogen, iron, oxygen, helium, calcium, etc. CBe stars usually exhibit either short-term or long-term variability in spectral line profiles. In extreme cases, complete disappearance of the Hα emission line occurs, indicating a disc-less state in CBe stars. The disc-loss and reappearing phases can be identified by studying the Hα line profiles of CBe stars on a regular basis. Noticing a scarcity in literature about any such work, we performed the first study of a set of selected 9 bright CBe stars, in the wavelength range of 6200 - 6700 Å, to understand their disc transient nature through continuous monitoring of their Hα line profile variations for 5 consecutive years (2015 -- 2019). Our results suggest that 4 of the program stars (HD 4180, BD+42 2652, HD 164447 and HD 171780) are possibly undergoing disc-loss episodes, whereas one other star (HD 23302) might be passing through disc formation phase. The rest 4 stars (HD 237056, HD 33357, HD 38708 and HD 60855) have shown signs of hosting a stable disc in recent epochs. We also found that 2 among these 9 stars (HD 33357 and HD 38708) might be weak Hα emitters in nature (exhibiting Hα EW < -5 Å). Moreover, our comparative analysis using the BeSS database indicates that the star HD 60855 has passed through a disc-less episode, with its disc formation happening over a timescale of 2 months, between January and March 2008. Our study will help in modeling of CBe stars discs, thus providing a better understanding about the ‘Be phenomenon' in CBe stars. |
