Abstract Details

Name: K. Sankarasubramanian
Affiliation: ISRO Satellite Centre
Conference ID: ASI2017_694
Title : A Novel Spectroscopic Concept for High Time Cadence Velocity Measurements
Authors and Co-Authors : Mohana Krishna (ISAC), Raja Bayanna (USO/PRL), and Shibu Mathew (USO/PRL)
Abstract Type : Oral
Abstract Category : Instrumentation and Techniques
Abstract : High time cadence is one of the requirement for the study of flows in the solar atmosphere e.g., Evershed flows, Inverse Evershed flows, down flows around pores and active regions etc. High cadence flow measurements is also required for local helioseismology with a large enough FOV. At present, the cadence of spectroscopic measurements are limited to the scanning capability (with a good SNR) of a spectrograph or Fabry-Perot based system and is limited to about a minute for a FOV of an arcminute. The scanning mode of operation would also introduce spurious signals in the velocity measurements especially if the observing conditions are not stable. In order to improve on the cadence and minimize the spurious signals, a novel solar spectroscopic concept is developed for the Multi Application Solar Telescope (MAST). The concept combines the advantages of a Fabry-perot system with that of the lenslet arrays to obtain single shot spectroscopy by producing images of the same FOV but with different wavelength tuning. Since it is a single shot spectroscopy, all the information required to form a 3D data cube (x,y,lambda) of a FOV of interest is obtained simultaneously minimizing spurious signals produced by other methods. An optical setup was developed, installed and demonstrated at the back end of the MAST telescope. Preliminary observations of a sunspot (NOAA 12526) at the position angle of S05W23 was observed on Mar 31st 2016. Evershed flow velocity was obtained from this instrument and compared with the regular scanned spectroscopy (using FP with MAST and spectrograph based instrument using Hinode's SOT-SP). The high degree of comparison between them provides confidence that the method works. While the other two measurements are done at a low cadence, this novel method can reach a cadence as high as one 3D data cube in few seconds. The merits and demerits of this method and its potential use for future solar telescopes will be briefed in this paper.