AR-2019-2020

Figure 20: (Left): The profiles of CaII in HD 72350 obtained during 1996 (black line) by Cha and Sembach are superposed with the profile obtained on 2018 February 3 with the SALT (blue line). (Right): Profile of NaI D2 in HD 72350 obtained by Cha and Sembach (black line) is shown superposed on the profile of NaI D2 observed on 2018 February 3 with the SALT (red line). Note the strengthening of the +39 kms − 1 component in both CaII and NaI momentum due to loss of energy by GW emission and collapses to a black hole before the Alfven timescale, i.e., before the differential rotation is damped by magnetic dissipation. This scenario is currently favoured by the combined multi-messenger astrophysical observations. They estimated the collapse time and threshold mass for prompt collapse for the EoSs with and without strangeness, using recently proposed fit formulas obtained using observations of short gamma ray bursts and hydrodynamical simulations. Solar Astrophysics Doppler shift and its centre-to-limb variation in active regions in the tran- sition region This work is based on combined observations of the Interface Region Imaging Spectrograph (IRIS) and the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI), both on-board the Solar Dynamic Observatory (SDO). It is aimed at understanding the role of Doppler motions in transferring mass and energy in an active region in the lower transition region of the solar atmosphere. This incorporates a detailed study of the role of line-of-sight (LOS) magnetic fields in this dynamic coupling, with observations of the same bipolar active region 12641 as it moved across the disk from east to west. (See Fig.21). Using the LoS magnetic field observations from HMI and Siiv 1394 Angstrom line emission recorded by IRIS, Durgesh Tripathi and collaborators infer that the two opposite polarity strong field regions, separated by a narrow weak field corridor, are predominantly redshifted to 5-10 km/s. On the contrary, the weak field corridor has redshifts ranging between 3-9 km/s. Both velocity estimates depend on the disk position. However, a common feature for all disk positions is a narrow lane within the corridor region with near-zero velocities. Therefore, the Doppler velocities in the corridor has two components- a low velocity component centered near 0 km/s and a comparatively higher velocity component at around 10 km/s. This component and the velocities in the strong fields show a small CLV within an error margin of ± 0.23-2.00 km/s. Moreover, these are independent of the systematic errors (0.87 km/s) incurred in the measurements. To explain the observations, we suggest that the emission in the lower transition region comes from “Type II spicules”. They, further, invoke the idea of a “chromospheric wall”, associated with classical cold spicules, so as to explain the small CLVs of flows.