AR_final file_2018-19

Transport of energy to the solar chromosphere through low-frequency acoustic waves The problem of the heating of the solar chro- mosphere remains to be solved. Several studies have shown that magnetic fiels, especially the in- clined ones, play an essential role in transporting waves from the photosphere to the chromosphere, where they are expected to steepen in shocks and contribute to the coronal heating. S. Paul Ra- jaguru, C. R. Sangeetha and Durgesh Tripathi have revisited some of those works and used the state-of-the-art observations from AIA (1600 and 1700 Angstrom , and HMI to study the relationships between magnetic field properties (inclination and strength) and the propagation of acoustic waves (phase travel time). The obtained energy estimates in waves with frequencies 2–5 mHz frequency range are about a factor of two higher than those reported earlier. These new observations also reveal that a significant amount of waves with frequencies lower than the cut-off frequency gets channelled through the inclined field lines. Note that, in the presence of the inclined field, the cut-off frequency reduces. Instrumentation Wide Area Optical Linear Polarime- ter Wide Area Linear Optical Polarimeter (WALOP) instruments are being developed to survey the po- larization of around a million stars in the Galac- tic polar regions. This instrument will combine a wide field of view capability(35 arcminutes × 35 arcminutes ) with high polarimetry accuracy of 0.1% to enable a fast and accurate survey. Two such polarimeters are currently being designed and developed at IUCAA, by A. N. Ramaprakash , Siddharth Maharana and Ioannis Kypriotakis one each for the 1 m SAAO Telescope, South Africa and the 1.3 m Skinakas Observatory Telescope, Greece. Wollaston prisms are the most common polar- ization analyzer optics used in optical polarime- ters due to their high polarization efficiency. The biggest challenge in building polarimeters with a field of view as large as WALOP is the chromatic aberrations caused by Wollaston prisms: a small dispersion is introduced in the outgoing beams from the Wollaston prisms. Siddharth Maha- rana has obtained a solution to this problem and has made an optical design that can achieve an ap- proximately seeing limited PSF (point spread func- tion), which will enable high accuracy imaging po- larimetry. The simulated PSF for a star corrected for the dispersion in WALOP design is shown in Figure 23. The PSF is small, giving a crisp im- age spread over a very few pixels. For comparison, Figure 24 shows a simulated spot digram without correction for chromatic aberrations introduced by the Wollaston prisms. ( 90 )