K. T. PAUL
Articles written in Journal of Astrophysics and Astronomy
Volume 38 Issue 1 March 2017 Article ID 0006 Research Article
We present the optical spectroscopic study of two classical Be stars, 59 Cyg and OT Gem obtained over a period of few months in 2009. We detected a rare triple-peak H$\alpha$ emission phase in 59 Cyg and a rapid decrease in the emission strength of H$\alpha$ in OT Gem, which are used to understand their circumstellar disks. We find that 59 Cyg is likely to be rapid rotator, rotating at a fractional critical rotation of $\sim$ 0.80. The radius of the H$\alpha$ emission region for 59 Cyg is estimated to be \( R_d/R_*\) $\sim$, assuming a Keplerian disk, suggesting that it has a large disk. We classify stars which have shown triple-peaks into two groups and find that the triple-peak emission in 59 Cyg is similar to $\zeta$ Tau. OT Gem is found to have a fractional critical rotation of $\sim$0.30, suggesting that it is either a slow rotator or viewed in low inclination. In OT Gem, we observed a large reduction in the radius of the H$\alpha$ emission region from $\sim$6.9 to $\sim$1.7 in a period of three months, along with the reduction in the emission strength. Our observations suggest that the disk is lost from outside to inside during this disk loss phase in OT Gem.
Volume 42 All articles Published: 13 November 2021 Article ID 0109
We performed the slitless spectroscopic survey to identify classical Be (CBe) stars in openclusters older than 100 Myr. Observing a sample of 71 open clusters, we identified 13 CBe stars in 11 open clusters, one of, which (TYC 2679-432-1) is a new detection. The 13 CBe stars show both H$\alpha$ in emission and IR excess, which confirm that they possess gaseous circumstellar discs. Two more CBe stars are found toexhibit H$\alpha$ in absorption for the first time, indicating that might be passing through disc-less episode presently. The spectral-type estimation is done for all these 15 stars and it is noticed that they belong to B0.5–B8 type. Moreover, we found that the distribution of our sample is peaking near late B-types as expected.
Volume 43 All articles Published: 19 December 2022 Article ID 0102
Variability is a commonly observed property of classical Be (CBe) stars. 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. In this paper, we present the study of a set of selected nine bright CBe stars, in the wavelength range of 6200–6700 Å, to better understand their disc transient nature through continuous monitoring of their Hα line profile variations for five consecutive years (2015–2019). Based on our observations, we suggest that four of the program stars (HD 4180, HD 142926, 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 remaining four stars (HD 237056, HD 33357, HD 38708 and HD 60855) have shown signs of hosting a stable disc in recent epochs. Through visual inspection of the overall variation observed in the Hα EW for these stars, we classified theminto groups of growing, stable and dissipating discs, respectively. Moreover, our comparative analysis using the BeSS database points out that the star HD 60855 has passed through a disc-less episode in 2008, with its disc formation happening probably over a timescale of only two months, between January and March 2008
Volume 44, 2023
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