AR-2019-2020

and the embedding dimension used for the con- struction of the network, and clearly distinguishes between the recurrence network from chaotic time series and white noise. Since the measure is char- acteristic to the network topology, it can be used to quantify the information loss associated with the structural change of a chaotic attractor in terms of the difference in the link density of the correspond- ing recurrence networks. We also indicate some practical applications of the proposed measure in the recurrence analysis of chaotic attractors as well as the relevance of the proposed measure in the context of the general theory of complex networks. This work has been done in collaboration with Ran- jeev Misra, and G. Ambika Jessy Jose A novel survey for young substellar objects with the W-band filter: The coolest and lowest mass mem- bers of the Serpens-South Star-forming region Given its relative proximity ( ∼ 430 pc), compact size ( < 20 ), young age ( ∼ 0.5 Myr), and rich number of young stellar objects, the Serpens-South star-forming region is a promising site for studying young substellar objects, yet the low-mass mem- bers of this region remain largely undiscovered. In our deep photometric survey using a custom 1.45 μ m filter (W-band), as well as standard J and H near-IR filters using 3.6m Canada-France-Hawaii Telescope (CFHT), we identify candidate low-mass young brown dwarfs in the Serpens-South region. We constructed a reddening-insensitive index (Q) by combining J, H and W-band photometry for survey objects, in order to identify candidate low- mass members of Serpens based on the strength of the water-absorption feature at 1.45 μ m in the at- mospheres of mid-M and later objects. We then conducted spectroscopic follow-up using ArCoIRIS spectrograph of 4m Blanco Telescope to confirm youth and spectral type for our candidates. This is the first survey to identify the very low-mass and coolest members of Serpens-South. We identify four low-mass candidate Serpens members, which all display IR excess emission, indicating the likely presence of circumstellar disks around them. One of the four candidate low-mass members in our list, SERP182918-020245, exhibits Pa β and Br γ emission features, confirming its youth and on- going magnetospheric accretion. Our new candi- date members have spectral types > M4 and are the coolest and lowest mass candidate members yet identified in Serpens-South. This survey has been done in collaboration with Beth A. Biller, Loic Albert, Sophie Dubber, Katelyn Allers, Gregory J Herezeg, et al. Md. Mehedi Kalam Analytical model of strange star in Durgapal space- time. we have presented a new strange star model based on Durgapal IV metric. Here, we have applied a specific method to study the inner physical proper- ties of the compact objects 4U 1702-429, 2A 1822- 371, PSR J1756-2251, PSR J1802-2124 and PSR J1713+0747, and calculated central density ( ρ 0 ), surface density ( ρ b ), central pressure ( p 0 ), surface red-shift ( Z s ), compactness and probable radius of the above mentioned star. Further, we perform different tests to study the stability of our model and finally we are able to give an equation based on pressure and density, i.e., probable equation of state (EoS) which has an important significances in the field of astrophysics. This work has been done in collaboration with Rabiul Islam, and Sajahan Molla. Nishikanta Khandai The population of galaxies that contribute to the HI mass function We look at the contribution of different galaxy pop- ulations to the atomic hydrogen (HI) mass func- tion (HIMF) and the HI density parameter, Ω HI , in the local universe. Our analysis is based on a sample of 7857 HI-selected galaxies from a volume common to the SDSS and ALFALFA (40% cata- logue – α. 40) surveys. We define different pop- ulations of galaxies in the colour( u-r )-magnitude ( M r ) plane and compute the HIMF for each of them. Additionally, we compute the HIMF for dark galaxies; these are undetected in SDSS and represent ∼ 2% of the total sample. We find that the luminous red population dominates the total HIMF for log 10 ( M HI h 2 70 / M ) ≥ 10 . 4. The full red population – luminous and faint – represents about ∼ 17% of the Ω HI budget, while that of the dark population is ∼ 3%. The HIMF about the knee, log 10 ( M HI h 2 70 / M ) ∈ [8 , 10 . 4], is dominated by the faint and luminous blue populations, the latter dominating at larger masses in this interval.