Browsing by Author "Tandon, S. N."

Now showing 1 - 6 of 6

Evalution of a CMDS imager as readout for imaging photon counters
(2011-07-06) Tandon, S. N.
This work is motivated by a desire to check if CMOS detectors, which are somewhat inferior to CCDs in terms of noise and dark current, but are much simpler to use, could be used as readout in imaging photon counters. Tests have been made on the performance of a CMOS detector used as readout of an image intensifier. The main conclusions are that: a) the detector has adequate dynamic range as well as sensitivity for photon counting, b) with an optics for reduction by a factor about three between the intensifier and the readout, it is found that 10-20 micron wide slits are recorded with an rms width of - 0.14 pixels, i.e. - 11 microns on the slit-plane - this includes effects due to finite resolution of the intensifier, and c) the detector is capable of giving a rms precision of - 0.03 pixels ( - 0.7 microns) on centroids of images similar to those of intensified photon events.
Exposure time calculator for IFOSC and sky background estimation
(Bull. Astr. Soc. India, 2005-06-22) Chakraborty, Pavan; Das, H.K.; Tandon, S. N.
This paper describes a spectroscopy exposure time calculator for the faint object spectrograph, the \IUCAA Faint Object Spectrograph" (IFOSC). It is intended to provide reasonable estimates of exposure times for observations. The background sky brightness is modeled for different phases and angular distance from the Moon. The code automatically calculates the Lunar Ephemerides from the date and time of observations and uses it for sky brightness computations. We adopt a new technique of scaling the Rayleigh and the Mie scattering functions, according to the corresponding extinction terms. This estimation of the sky brightness with moonlight ¯ts reasonably well with the observed sky brightness measured at the IUCAA telescope site. A simple component model is used for the optical elements. Each compo- nent is described by simple wavelength dependent extinction tables. At present, a blackbody/power-law spectrum is chosen as the input spectrum. Model or actual spectrum can also be used. The input blackbody spectrum is computed using the stellar \Spectral type" and scaled by the apparent V magnitude of the star. The programme is easily con¯gurable for di®erent sites and instruments. The code is written in ANSI C and thus portable to any system. A graphically interactive interface using HTML-cgi script has also been developed.
Imaging polarimetry of some selected dark clouds
(2015-03-01) Sen, A.K.; Gupta, Ranjan; Ramprakash, A. N.; Tandon, S. N.
Implementation of transfer-pupil in a spectrograph on optical telescopes
(2011-07-06) Das, H.K.; Kohok, Abhay; Tandon, S. N.
Based on the transfer pupil technique we develop a method to measure the lower order aberration coe±cients for optical telescopes; the method makes use of a Hartmann mask in a spectrograph for sampling the wavefront at di®erent locations.
IUCAA 2 meter telescope and its first light instrument IFOSC
(Bull. Astr. Soc. India, 2002-06-05) Gupta, Ranjan; Burse, Mahesh P.; Das, H.K.; Kohok, A.; Ramaprakash, A.N; Engineer, S.; Tandon, S. N.
The various features of the IUCAA 2-meter telescope, its site parameters and considerations made for preserving the local seeing in terms of ventilation, thermal emissivity of the dome etc are described. The first light back-end instrument for this telescope, i.e. Iucaa Faint Object Spectrometer and Camera (IFOSC), too is described in some detai
Studying the Imaging Characteristics of Ultra Violet Imaging Telescope (UVIT) through Numerical Simulations
(2009-03-01) Srivastava, Mudit K.; Prabhudesai, Swapnil M.; Tandon, S. N.
Ultra-Violet Imaging Telescope (UVIT) is one of the ﬁve payloads aboard the Indian Space Research Organization (ISRO)’s ASTROSAT space mission. The science objectives of UVIT are broad, extending from individual hot stars, star-forming regions to active galactic nuclei. Imaging performance of UVIT would depend on several factors in addition to the optics, e.g. resolution of the detectors, Satellite Drift and Jitter, image frame acquisition rate, sky background, source intensity etc. The use of intensiﬁed CMOS-imager based photon counting detectors in UVIT put their own complexity over reconstruction of the images. All these factors could lead to several systematic eﬀects in the reconstructed images.