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.
In this paper, we present the instrumental characterization and performance of the 4[Formula: see text]k CCD detector mounted on a 104-cm Sampurnanand telescope located at ARIES, Manora Peak Nainital, India. A detailed description of the filter wheel and its motion is presented. We measured the gain and read-out noise along with the linearity of the detector. Gain estimates are 5–10% higher than manufacturer values. The estimated read-out noise values do not fall within the manufacturer’s range. It is expected that experimentally derived values will be more precise than designed values. It is suggested that the current derived values will be used rather than the designed values. The response to the incident light on the detector is linear to 99% level. To study the performance of a 4[Formula: see text]k CCD camera, we observe an open cluster Czernik 43. The fundamental parameters, i.e. log(age), distance and reddening [Formula: see text] are estimated as 7.9, 2.5[Formula: see text]kpc and 0.65[Formula: see text]mag, respectively. The estimated parameters of the cluster are comparable to the values derived in the literature within the error. Our detailed analysis illustrates that the detector is precise enough to carry out routine astronomical observations.
The 4K × 4K CCD Imager is the first light instrument for the 3.6[Formula: see text]m Devasthal Optical Telescope and is producing broad-band imaging observations of many Galactic and extra-galactic sources since 2015–2016. Capabilities of the CCD Imager are demonstrated recently through several publications using the well-calibrated multi-band deep photometric results as expected from other similar facilities globally. In this paper, we summarize some of the recent up-gradations made to improve the Imager, i.e. mounting the new filter wheel casing, replacing stray light baffles and discussing the fringe pattern corrections in redder filters. Some of the new science initiatives like galaxy-embedded faint point sources including WR stars and the observations of low surface brightness galaxy clusters are also discussed.
As a part of in-house instrument developmental activity at ARIES, the 4Kx4K CCD Imager is designed and developed as a first-light instrument for the axial port of the 3.6-m Devasthal Optical Telescope (DOT). The f/9 beam of the telescope having a plate-scale of ~6.4”/mm is utilized to conduct deeper photom-etry within the central 10' field of view. The pixel size of the blue-enhanced liquid nitrogen cooled STA4150 4Kx4K CCD chip is 15 µm, with options to select gain and speed values to utilize the dynamic range. Using the Imager, it is planned to image the central ~ 6.5’ x6.5’ field of view of the telescope for various science goals by getting deeper images in several broad-band filters for point sources and objects with low surface brightness. The fully assembled Imager along with automated filter wheels having Bessel UBV RI and SDSS ugriz filters was tested in late 2015 at the axial port of the 3.6-m DOT. This instrument was finally mounted at the axial port of the 3.6-m DOT on 30 March 2016 when the telescope was technically activated jointly by the Prime Ministers of India and Belgium. It is expected to serve as a general purpose multi-band deep imaging instrument for a variety of science goals including studies of cosmic transients, active galaxies, star clusters and optical monitoring of X-ray sources discovered by the newly launched Indian space-mission called ASTROSAT, and follow-up of radio bright objects discovered by the Giant Meterwave Radio Telescope.
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