AR-2019-2020

HCOOH may not be detected. To our knowledge, no transitions of cis-HCOOH are yet detected in the interstellar medium, though a and b components of its electric dipole moment are quite large. Using spectroscopic data of trans-HCOOH and cis-HCOOH, we have calculated energies of 100 ro- tational levels for each of the 8 groups, and the ra- diative transition probabilities (Einstein A and B coefficients) for radiative transitions between the levels. Since the rate coefficients for collisional transitions between the levels are not available, by using the scaled values for them along with the ra- diative transition probabilities, we have solved a set of 100 statistical equilibrium equations coupled with the equations of radiative transfer for each group. We have investigated intensities of 16 ob- served a -type transitions and 12 b -type transitions of trans-HCOOH. We have also found six transi- tions, 1 10 − 1 11 (1.405 GHz), 2 12 − 3 03 (7.545 GHz), 3 12 − 3 03 (79.744 GHz), 3 21 − 3 12 (222.287 GHz), 1 11 − 2 02 (30.843 GHz) and 4 13 − 4 04 (82.740 GHz) of cis-HCOOH showing anomalous absorption and nine transitions 4 14 − 3 13 (85.042 GHz), 5 15 − 4 14 (106.266 GHz), 3 03 − 2 02 (65.840 GHz), 4 04 − 3 03 (87.694 GHz), 5 05 − 4 04 (109.470 GHz), 5 05 − 4 14 (40.778 GHz), 7 07 − 6 16 (90.910 GHz), 4 04 − 3 13 (16.350 GHz) and 6 06 − 5 15 (65.661 GHz) of cis- HCOOH showing emission feature. These transi- tions of cis-HCOOH in addition to those of trans- HCOOH may help in the identification of HCOOH in a cosmic object. LVG analysis of amidogen radical (NH 2 ) found in interstellar medium and in cometary material Amidogen (NH 2 ), a b -type asymmetric top molecule with electric dipole moment 1.82 ± 0.05 Debye, is detected in Sgr B2, in high-mass star- forming regions W31C (G10.6-0.4), W49N (G43.2- 0.1), W51 (G49.5-0.4), G34.3+0.1, and in several comets. Because of two hydrogen atoms, each with nuclear spin 1/2, its rotational energy levels can be classified into ortho and para groups. We have not considered for fine structure splitting and hyper- fine structure splitting of rotational levels. For 15 rotational levels in the ground vibrational state, having energy up to 400 cm − 1 , for each specie, the energies of rotational levels, and Einstein A and B coefficients for radiative transitions between the levels are calculated, using accurate values of spec- troscopic data. These radiative transition probabil- ities along with the collisional rate coefficients (ob- tained from a scaling law) are employed as input parameters for solving a set of statistical equilib- rium equations coupled with the equations of ra- diative transfer for each group. Several emission lines produced by amidogen are found. For each specie of NH 2 , we have considered some strongest emission lines along with the observed one, which may help for identification of NH 2 in the interstel- lar medium (ISM) and in the cometary material. Ranjan Sharma Revisiting Vaidya-Tikekar stellar model in the lin- ear regime In this work, we have developed a new class of solutions describing the interior of a spherically symmetric static star composed of an anisotropic matter distribution by revisiting the Vaidya and Tikekar stellar model in the linear regime. The Vaidya and Tikekar ansatz is characterized by a geometric feature that time t = constant hypersur- face of the associated spacetime when embedded in a 4-Euclidean space becomes spheroidal. Physical viability of the subsequent stellar model has been analyzed. Impact of the curvature parameter K of the Vaidya and Tikekar ansatz, which charac- terizes the departure from spherical geometry, on the mass-radius relationship of the star has been probed. In the context of density dependent bag model for strange stars, a corelation between the curvature parameter K , the bag constant B , the mass M and the radius R of some of the well known strange star candidates like Her X-1, RX J1856- 37 and SAX J1808.4 have been investigated. The possibility of fine-tuning these parameter based on observational data has been outlined. This work is done in collaboration with Shyam Das, Megan Govender, and Dishant M. Pandya. Anisotropic generalization of Vaidya-Tikekar su- perdense stars Exact solutions to Einstein field equations corre- sponding to various astrophysical systems and their physical interpretation are of prime significance for our understanding of gross physical features of rel- ativistic compact objects. In this work, the authors have developed a new class of solutions describing the interior of a superdense relativistic star com- posed of an anisotropic matter distribution with spheroidal spatial hypersurface. Thus, the new class of solutions may be treated as an anisotropic