भारतीय खगोलभौतिकी संस्थान
Indian Institute of Astrophysics
Exploring the Universe since 1786

We present measurements of seeing-induced crosstalk using spectropolarimetric observations of sunspots recorded simultaneously in the H𝛼 and Ca ii 8662 Å lines with the Kodaikanal Tower Tunnel (KTT) telescope. The Kodaikanal Tower Tunnel telescope is integrated and installed with an image stabilization system consisting of a tip–tilt and an autoguider system. Additionally, the spectropolarimeter at KTT is upgraded to allow for the simultaneous recording of spectropolarimetric observations in three spectral lines. The tip–tilt system is shown to have a cutoff frequency of 80 Hz, effectively reducing the seeing induced crosstalk in the measured Stokes parameters by at least a factor of 2.

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First-time airglow observations of the nighttime thermospheric wind from an in-house developed ground-based Fabry–Perot Interferometer are recorded from the Kolhapur location of India. This was the first attempt to build such an instrument, and thus the quality of the data recorded in the field is satisfactory. The instrument has been thoroughly calibrated in the laboratory, and the accuracy of the important parameter finesse of the etalon is found to be ≈94% in agreement with the value supplied by the manufacturer. The airglow observations from the field indicate that the vertical wind observed looking toward Zenith over the course of the night is zero, ensuring a 100% accuracy. However, the temperature measurements were found to be approximately 30% in agreement with the measurements repoted in literature. To improve this measurement, improvements in the optical design need to be made. The paper concludes with conclusions and a brief idea of the proposed improvisations in the design.

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Recently we had reported commissioning of a prototype for pulsar observations at low radio frequencies (<100 MHz) using log-periodic dipole antennas in the Gauribidanur Radio Observatory (≈77°E, 14°N) near Bangalore in India (https://www.iiap.res.in/?q=centers/radio). The aforementioned system (the Gauribidanur Pulsar System) is currently being augmented to directly digitize the radio-frequency signals from the individual antennas in the array. Our initial results using a 1 bit raw voltage-recording system indicate that such a back-end receiver offers distinct advantages like (i) simultaneous observations of any set of desired directions in the sky with multiple offline beams and smaller data rate/volume, and (ii) archival of the observed data with minimal resources for reanalysis in the future, either in the same or a different set of directions in the sky.

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