学术文献库

Measurement of internal structures in the prestellar core is essential for understanding the initial conditions prior to star formation. In this work,, we study the ammonia lines (NH3 ) (J,K=1,1 and 2,2) in the central region of the prestellar core L1517B with the Karl G. Jansky Very Large Array Radio Telescope (VLA, spatial resolution ~ 3.7"). Our analysis indicates that the central region of the core is close-to-round in shape obtained both from NH3 (1,1) and (2,2) emissions. Radially averaged kinetic temperature (T_k ) is almost constant with a mean value of ~9 K. A radially sharp decrease in kinetic temperature (T_k ) has not been observed inside the central dense nucleus of this prestellar core. In addition, we also notice that there is an overall velocity gradient from north-east to south-west direction in this region, which may be indicative of the rotational motion of the core. We then calculate the parameter beta, which is defined as the ratio of rotational energy to gravitational potential energy and find that beta equals to ~ 5 x 10^-03 ; which indicates that rotation has no effect at least inside the central region of the core. We also perform the viral analysis and observe that the central region may be in a stage of contraction. From this study, we also show that turbulence inside the central region is subsonic in nature (sonic Mach number, M_s< 1) and has no prominent length-scale dependence. Furthermore, we notice that the decrement of excitation temperature (T_ex ) and column density of NH3 from the centre of the core to the outer side with the peak values of 5.6 K and ~ 10^15 cm-2 respectively. In conclusion, this work examines different physical and kinematical properties of the central region of the L1517B prestellar core.