We present results of a search for variable stars in a region of the globular cluster NGC 4147 based on photometric observations with 4K×4K CCD imager mounted at the axial port of the recently installed 3.6 m Devasthal optical telescope at Aryabhatta Research Institute of Observational Sciences, Nainital, India. We performed time series photometry of NGC 4147 in V and R bands, and identified 42 periodic variables in the region of NGC 4147, 28 of which have been detected for the first time. Seventeen variable stars are located within the half light radius 0.48 arcmin, of which 10 stars are newly identified variables. Two of 10 variables are located within the core radius 0.09 arcmin. Based on the location in the V /(V − R) colour magnitude diagram and variability characteristics, 7, 8, 5 and 1 newly identified probable member variables are classified as RRc, EA/E, EW and SX Phe, respectively. The metallicity of NGC 4147 estimated from light curves of RRab and RRc stars with the help of Fourier decomposition is found to be characteristics of Oosterhoff II. The distance derived using light curves of RRab stars is consistent with that obtained from the observed V /(V − R) colour-magnitude diagram.
We present the design and performance of the TANSPEC, a medium-resolution 0.55–2.5 μm cryogenic spectrometer and imager, now in operation at the 3.6 m Devasthal Optical Telescope (DOT), Nainital, India. The TANSPEC provides three modes of operation, which include photometry with broad- and narrowband filters, spectroscopy with short slits of 20″ length and different widths (from 0.″5 to 4.″0) in cross-dispersed mode at a resolving power R of ∼2750, and spectroscopy with long slits of 60″ length and different widths (from 0.″5 to 4.″0) in prism mode at a resolving power R of ∼100–350. TANSPEC’s imager mode provides a field of view of 60″ × 60″ with a plate scale of 0.″245 pixel−1 on the 3.6 m DOT. The TANSPEC was successfully commissioned during 2019 April–May, and the subsequent characterization and astronomical observations are presented here. The TANSPEC was made available to the worldwide astronomical community for science observations from 2020 October.
We present a recent upgradation of the ARIES IMaging POLarimeter (AIMPOL) mounted on the 104[Formula: see text]cm Sampurnanand telescope of ARIES, Nainital since 2004. AIMPOL is upgraded by replacing the older detector with a new CCD, Pylon 1300B and the older sliding filter assembly with an automatic wheel filter assembly. A characterization of this CCD is performed and several CCD parameters like gain, read-out noise, dark current, and linearity are verified. The average value of the bias offset is measured to be ∼600 ADU whereas the dark current is measured to be 0.2[Formula: see text]e−/pixel/h at [Formula: see text]C. The CCD can be operated safely between [Formula: see text] C to [Formula: see text]C due to the almost constant dark current in this temperature range. The nonlinearity of the CCD is measured to be ∼2%, which is suitable for scientific observations. A few polarimetric observations are also taken using the upgraded AIMPOL. The degree of polarization and position angle of a few standard polarized stars are found to be similar to their standard and previously observed values.
We present the design and performance of the TANSPEC, a mediumresolution 0.55 − 2.5 µm cryogenic spectrometer and imager, now in operation at the 3.6-m Devasthal Optical Telescope (DOT), Nainital, India. The TANSPEC provides three modes of operation which include, photometry with broad-and narrow-band filters, spectroscopy with short slits of 20 length and different widths (from 0.5 to 4.0 ) in cross-dispersed mode at a resolving power R of ∼2750, and spectroscopy with long slits of 60 length and different widths (from 0.5 to 4.0 ) in prism mode at a resolving power R of ∼100-350. TANSPEC's imager mode provides a field of view of 60 × 60 with a plate scale of 0.245 /pixel on the 3.6-m DOT. The TANSPEC was successfully commissioned during April-May 2019 and the subsequent characterization and astronomical observations are presented here. The TANSPEC has been made available to the worldwide astronomical community for science observations from October 2020.
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