AR_final file_2018-19

0.06 M ⊙ . The mass function of the cluster peaks around 0.3 M ⊙ , and in the sense of dN / dm = m − α , where N is the number of members and m is stel- lar mass, with a slope α = 0.49 ± 0.03 in the mass range 0.3-2.3 M ⊙ . This is much shallower than that of the field population in the solar neighborhood. The slope α = -1.69 ± 0.14 from 0.3 M ⊙ to 0.06 M ⊙ , the lowest mass in our sample. The cluster is mass-segregated and has a shape elongated toward the Galactic plane. Our list contains nine substellar members, including three new discoveries of an M8, an L1, and an L4 brown dwarfs, extending from the previously known coolest members of late-M types to even cooler types. This work has been done in collaboration with Shih-Yun Tang, W. P. Chen, P. S. Chiang, Gregory J. Herczeg, and Bertrand Gold- man. Kanti Jotania Study of coronal mass ejection(CME) and associ- ated geomagnetic storm relation Coronal mass ejections (CMEs) are the outburst of solar wind plasma from the Sun. If this plasma happens to travel in th Sun Earth line and collide with the Earths magnetosphere, the disturbance can lead to geomagnetic storms (GMS). It is now well understood that most of the GMS are asso- ciated with CMEs, and therefore, much attention is paid to studying the relationship between the CMEs and the GMS. In order to establish the re- lation between the solar origin, and the GMS, it is important to study the initial CME parameters and how it affects the strength of the GMS. We have used SOHO data with a few criteria. Main concern is to understand on what parameters CME and GMS are related. It is believed that GMS arises due to interaction of plasma with Earth’s magneto- sphere, various parameters like disturbance storm time, and Kp index, etc. In this work, we use the SOHO-LOCO CME catalogue, and lists all the CMEs that have occurred since 1996 and also gives its various parameters like initial speed, location, etc. The events are selected based on initial speed of CME and source location. Minu Joy Constraints on tensor to scalar ratio using WKB approximation Scalar and tensor power spectra are studied using Wenzel-Kramers-Brillouin (WKB) approximation. The spectral indices and spectra generated with WKB approximation are compared with the obser- vational data, and we see that the WKB approxi- mated power spectra could become a viable alter- native for slow-roll spectra. The advantage of this method is that it gives the higher order corrections and the precise details of power law model. Run- ning Monte-Carlo chains with CosmoMC and gen- erating the plots with Getdist, the tensor to scalar ratio ( r ) is also analysed. Constraining the cosmo- logical parameters with WKB approximation, an upper limit at r < 0 . 1109 is obtained. Here r is de- fined at the pivot scale k ∗ = 0 . 05 Mpc − 1 . We also report the bounds on r 0 . 002 , the tensor to scalar ratio at k ∗ = 0 . 002 Mpc − 1 as r 0 . 002 < 0 . 1055 which is consistent with the Planck results within 1 σ lim- its. This work has been done in collaboration with Aiswarya A. Md. Mehedi Kalam Analytical model of compact star in low-mass X-ray binary with de Sitter spacetime Actually, we are trying to give a generalized metric solution (Heintzmann H., 1969, Z. Phys., 228 , 489) for compact stars. In this work, we have studied the inner structure of compact stars in low-mass X-ray binary by using Heintzmann metric with desitter spacetime, and the outcome results were compared with observed data. We have proposed a stiff equa- tion of state relating pressure with matter density. From our study we have calculated probable radii, compactness (u) and surface red-shift (Zs) of six compact stars in low-mass X-ray binaries namely, Cyg X-2, V395 Carinae/2S 0921-630, XTE J2123- 058, X1822-371 (V691 CrA), 4U 1820-30, and GR Mus (XB 1254-690) and the estimated results were compared with the recent observational data. This work has been done in collaboration with Sajahan Moll, Rabiul Islam, amd Md. A. K. Jafry. ( 195 )