AR_final file_2018-19

silicates. The dust grains accountable for the crys- talline silicate features in absorption seem to origi- nate in outer regions which are cold. Since MWC 1080A is a very young but massive star with a small disk size, most of the observed polarization is caused due to the envelope which consists of ma- terial flowing in from the ISM. We have also checked the validity of the compos- ite dust models with the polarization data of SVS13 (V*V512 Per) presented in Figure 19. SVS13 po- larimetry data is from UKIRT 3.8m telescope with IRPOL on CGS4 (Cooled Grating Spectrometer). The DDA based calculations give a model with SiCSi, having 0.3 volume fraction of inclusions, for oblate spheroidal dust grains (AR = 1.5) of effec- tive radius 0.5 µm to best fit the SVS13 polariza- tion data. The EMA T-Matrix based calculations are in agreement with the type of inclusion, i.e., SiC, but vary in the degree of oblateness (AR = 2.0), and volume fraction of inclusions (0.2). Solar Astrophysics Observations and modelling of chro- mospheric evaporation in coronal loops The problem of solar coronal heating has been one of the most stubborn in the field of astrophysics. One of the essential pieces of observations that has been missing is chromospheric evaporation in quiescent coronal loops. Note that such evapora- tion flows have been observed in large flares. So, the question remains that if the physics of solar flares is similar to that which is involved in small scale events such as small transient brightenings and even the coronal loops. Girjesh Gupta, Aveek Sarkar and Durgesh Tripathi have for the first time shown the presence of chromospheric evapo- ration related to small transient brightenings that leads to the formation of coronal loops (see Figure 20). For this purpose, they have used the obser- vations from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) and the Interface Region Imaging Spectro- graph (IRIS) and the Extreme-ultraviolet Imaging Spectrometer and X-Ray Telescope, both onboard Hinode. They have also aided the data with the magnetic field measurements in the photospheric from the Helioseismic and Magnetic Imager (HMI), also onboard SDO. The observations from these instruments are complemented with 1D hydrody- namic simulations and forward modelling. They have found evidence of chromospheric evaporation at the two footpoints of a coronal loop after the occurrence of two transient brightenings. In hotter channels of AIA, such as 131, 94, and 335Angstrom appeared nearly simultaneously, and that the evap- oration flows were the fastest in these channels. The temperature attained a maximum of 10 MK during the evaporation. At the footpoints, they have also observed redshifts in transition that were co-temporal and co-spatial with the observation of the evaporation. The simulated results were quali- tatively in agreement with those observed. Energetics of tiniest EUV brighten- ings ever observed in solar atmo- sphere using Hi-C The first Hi-C rocket experiment of NASA has pro- vided the highest spatial and temporal resolution observations of the solar corona. However, Hi-C carried only one science filter onboard. Therefore, it was essential to combine the Hi-C observations with those taken using AIA on board SDO that pro- vides views using 6 EUV channels, albeit with lesser spatial and temporal resolution. Srividya Subra- manian, Vinay L. Kashyap, Durgesh Tripathi , Maria S. Madjarska, and John G. Doyle have made use of Hi-C and AIA observations to study the thermal structure and energetics of the point-like extreme ultraviolet (EUV) brightenings, which oc- curred within a system of fan loops. By using an automatic procedure, they identified 27 brighten- ings in Hi-C and also in AIA. Though AIA’s res- olution is much poorer in comparison with Hi-C, the code could still identify those brightenings in 193 Angstrom images. They have employed the Differential Emission Measure (DEM) techniques to study the energetics of these brightenings. These are the smallest brightenings in EUV ever detected and for the first time they provide such a compre- ( 85 )