AR_final file_2018-19

QPOs in 15 different observation IDs with fre- quency around 67Hz, although quality factor nearly 20 but in two IDs frequency is found just dou- ble. Typical fractional rms for GRS 1915+105 is dominating the hard band increasing steeply with energy more than 13% at 20-40 keV band. This work has been done in collaboration with Umang Pandya, and Rajmal Jain. Deepak Jain Bounds on graviton mass using weak lensing and SZ effect in galaxy clusters In General Relativity (GR), the graviton is mass- less. However, a common feature in several the- oretical alternatives of GR is a non-zero mass for the graviton. These theories can be described as massive gravity theories. Despite many theoretical complexities in these theories, on phenomenolog- ical grounds, the implications of massive gravity have been widely used to put bounds on graviton mass. One of the generic implications of giving a mass to the graviton is that the gravitational po- tential will follow a Yukawa-like fall off. We use this feature of massive gravity theories to probe the mass of graviton by using the largest gravi- tationally bound objects, namely galaxy clusters. In this work, we use the mass estimates of galaxy clusters measured at various cosmologically defined radial distances measured via weak lensing (WL) and Sunyaev-Zel’dovich (SZ) effect. We also use the model independent values of Hubble parameter H(z) smoothed by a non-parametric method, Gaus- sian process. Within 1 σ confidence region, we ob- tain the mass of graviton m g < 5 . 9 × 10 − 30 eV with the corresponding Compton length scale λ g > 6 . 82 Mpc from weak lensing and m g < 8 . 31 × 10 − 30 eV with λ g > 5 . 012 Mpc from SZ effect. This anal- ysis improves the upper bound on graviton mass obtained earlier from galaxy clusters. This work has been done in collaboration with Akshay Rana, Shobhit Mahajan, and Amitabha Mukherjee. Jessy Jose The Planck Cold Clump G108.37-01.06: A site of complex interplay between H II Regions, young clusters, and filaments The Planck Galactic Cold Clumps (PGCCs) are possible representations of the initial conditions and very early stages of star formation. With the objective of understanding better the star and star cluster formation, we probe the molecular cloud associated with PGCC G108.37-01.06 (hereafter PG108.3), which can be traced in a velocity range of -57 to -51 km s − 1 . The INT Photometric Hα Survey images reveal Hα emission at various lo- cations around PG108.3, and optical spectroscopy of the bright sources in those zones of Hα emission discloses two massive ionizing sources with spectral type O8-O9V and B1V. Using the radio continuum, we estimate ionizing gas parameters and find the dynamical ages of H II regions associated with the massive stars in the range of 0.5-0.75 Myr. Based on the stellar surface density map constructed from the deep near-infrared Canada-France-Hawaii Tele- scope observations, we find two prominent star clusters in PG108.3; of these, the cluster associ- ated with H II region S148 is moderately massive ( ∼ 240 M ⊙ ). A careful inspection of James Clerk Maxwell telescope, 13 CO (3-2) molecular data ex- hibits that the massive cluster is associated with a number of filamentary structures. Several embed- ded young stellar objects (YSOs) are also identi- fied in PG108.3 along the length and junction of filaments. We find evidence of a velocity gradi- ent along the length of the filaments. Along with kinematics of the filaments and the distribution of ionized, molecular gas and YSOs, we suggest that the cluster formation is most likely due to the lon- gitudinal collapse of the most massive filament in PG108.3. This work has been done in collabora- tion with Somnath Dutta, Soumen Mondal, and Manash R. Samal. Characterization of stellar and substellar members in the Coma Berenices Star Cluster We have identified stellar and substellar members in the nearby star cluster Coma Berenices, us- ing photometry, proper motions, and distances of a combination of 2MASS, UKIDSS, URAT1, and Gaia/DR2 data. Those with Gaia/DR2, parallax measurements provide the most reliable sample to constrain the distance, averaging 86.7 pc with a dispersion of 7.1 pc, and age of ∼ 800 Myr, of the cluster. This age is older than the 400-600 Myr commonly adopted in the literature. Our analysis, complete within 5 ◦ of the cluster radius, leads to identification of 192 candidates, among which, af- ter field contamination is considered, about 148 are true members. The members have J ∼ 3 mag to ∼ 17.5 mag, corresponding to stellar masses 2.3- ( 194 )