• SAURABH SHARMA

      Articles written in Journal of Astrophysics and Astronomy

    • Detection of PAH and nbL features in planetary nebulae NGC 7027 and BD $+$30$^{\circ}$ 3639 with TIRCAM2 instrument on 3.6 m DOT

      RAHUL KUMAR ANAND SHANTANU RASTOGI BRIJESH KUMAR ARPAN GHOSH SAURABH SHARMA D. K. OJHA S. K. GHOSH

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      High resolution infrared imaging observations of the young planetary nebulae (PNe) NGC 7027 and BD $+$30$^{\circ}$ 3639, taken with the newly installed TIFR near infrared camera-II (TIRCAM2) on 3.6 m Devasthal optical telescope (DOT), ARIES, Nainital, are being reported. The images are acquired in J, H, K,polycyclic aromatic hydrocarbon (PAH) and narrow-band L (nbL) filters. The observations show emission from warm dust and PAHs in the circumstellar shells. The imaging of the two objects are among the first observations in PAH and nbL bands using TIRCAM2 on DOT. The NGC 7027 images in all bands showsimilar elliptical morphology with $\sim$6$^{\prime\prime}$.7 and $\sim$4$^{\prime\prime}$.5 semi-major and semi-minor axes. Considering size up to 10% of peak value the nebula extends upto 800 from the central star revealing a multipolar evolution. The relatively cooler BD $+$30$^{\circ}$ 3639 shows a rectangular-ring shaped nebula. In J and H bands it shows an angular diameter of $\sim$8$^{\prime\prime}$, while a smaller $\sim$6$^{\prime\prime}$.9 size is observed in K, PAH and nbL bands. The 3.28 $\mu$m emission indicates presence of PAHs at about 6000 and 5000 AU from the central stars in NGC 7027 and BD $+$30$^{\circ}$ 3639 respectively. Analysis suggests domination of neutral PAHs in BD $+$30$^{\circ}$ 3639, while in NGC 7027 there is higher ionization and more processed PAH population.

    • Observations with the 3.6-meter Devasthal optical telescope

      RAM SAGAR BRIJESH KUMAR SAURABH SHARMA

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      The 3.6-meter Indo–Belgian Devasthal optical telescope (DOT) has been used for optical and nearinfrared (NIR) observations of celestial objects. The telescope has detected stars of $B=24.5 \pm 0.2$, $R = 24.6 \pm 0.12$ and $g= 25.2 \pm 0.2$ mag in exposure times of 1200, 4320 and 3600 s respectively. In one hour of exposure time, a distant galaxy of $24.3 \pm 0.2$ mag and point sources of $\sim$25 mag have been detected in the SDSS $i$ band. The NIR observations show that stars up to $J = 20\pm 0.1$, $H = 18.8 \pm 0.1$ and $K = 18.2 \pm 0.1$ mag can be detected in effective exposure times of 500, 550 and 1000 s respectively. The $nbL$ band sources brighter than $\sim$9.2 mag and strong ($\geq$0.4 Jy) $PAH$ emitting sources like Sh 2-61 can also be observed with the 3.6-meter DOT. A binary star with angular separation of 0:$''$4 has been resolved by the telescope. Sky images with sub-arcsec angular resolutions are observed with the telescope at wavelengths ranging from optical to NIR for a good fraction of observing time. The on-site performance of the telescope is found to be at par with the performance of other, similar telescopes located elsewhere in the world. Owing to the advantage of its geographicallocation, the 3.6-meter DOT can provide optical and NIR observations for a number of frontline galactic and extra-galactic astrophysical research problems, including optical follow-up of GMRT and AstroSat sources and optical transient objects.

    • TIFR treasures for astronomy from ground to space

      SUPRIYO GHOSH DEVENDRA K. OJHA SAURABH SHARMA MILIND B. NAIK

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      The infrared astronomy group of the Department of Astronomy and Astrophysics at Tata Institute of Fundamental Research has been pursuing astronomical instrumentation activities since its inception. The group has been routinely involved in a balloon-borne astronomy program from field station atHyderabad with indigenously developed payloads. Ground-based astronomical activities began with a single element infrared detector. Later, over time, larger format array detectors are being used in the cameras. These astronomy cameras have been routinely used at observatories across India. Recently, the group has also developed a laboratory model of the infrared spectroscopic imaging survey payload, targeted for the small satellite mission of the Indian Space Research Organisation, which will carry out spectroscopic measurements in the wavelength range 1.7–6.4 $\mu$m seamlessly.

    • Optical observations of star clusters NGC 1513 and NGC 4147; white dwarf WD 1145$+$017 and K band imaging of star-forming region Sh 2-61 with the 3.6-m Devasthal optical telescope

      RAM SAGAR R. K. S. YADAV S. B. PANDEY SAURABH SHARMA SNEH LATA SANTOSH JOSHI

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      The UBVRI CCD photometric data of open star cluster NGC 1513 are obtained with the 3.6-m Indo-Belgian Devasthal optical telescope (DOT). Analyses of the GAIA EDR3 astrometric data have identified 106 possible cluster members. The mean proper motion of the cluster is estimated as $\mu_{\alpha}\cos\delta=1.29\pm 0.02$ and $\mu_{\delta}=-3.74\pm0.02$ mas yr$^{-1}$. Estimated values of reddening $E(B-V)$ and distance to the NGC 1513 are $0.65 \pm 0.03$ mag and $1.33 \pm 0.1$ kpc, respectively. Age of $225 \pm 25$ Myr is assigned to the cluster by comparing theoretical isochrones with deeply observed cluster sequences. Using observations taken with the 3.6-m DOT, values of distance and age of the galactic globular cluster NGC 4147 areestimated as $18.2 \pm 0.2$ Kpc and $14 \pm 2$ Gyr, respectively. The optical observations of planetary transit around white dwarf WD $1145\pm 017$ and $K$-band imaging of star-forming region Sharpless Sh 2-61 demonstrate observing capability of 3.6-m DOT. Optical and near-infrared observations of celestial objects and events are being carried out routinely with the 3.6-m DOT. They indicate that the performance of the telescope is at par with those of other similar telescopes located elsewhere in the world. We, therefore, statethat this observing facility augurs well for multi-wavelength astronomy including the study of astrophysical jets.

    • Photometric studies on the host galaxies of gamma-ray bursts using 3.6m Devasthal optical telescope

      RAHUL GUPTA SHASHI BHUSHAN PANDEY AMIT KUMAR AMAR ARYAN AMIT KUMAR ROR SAURABH SHARMA KUNTAL MISRA A. J. CASTRO-TIRADO SUGRIVA NATH TIWARI

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      In this paper, we present multi-band photometric observations and analysis of the host galaxies for a sample of five interesting gamma-ray bursts (GRBs) observed using the 3.6mDevasthal optical telescope (DOT) and the back-end instruments. The host galaxy observations of GRBs provide unique opportunities to estimatethe stellar mass, ages, star-formation rates and other vital properties of the burst environments and hence, progenitors. We performed a detailed spectral energy distribution (SED) modeling of the five host galaxies using an advanced tool called $\mathtt{Prospector}$, a stellar population synthesis model. Furthermore, we comparedthe results with a larger sample of well-studied host galaxies of GRBs, supernovae and normal star-forming galaxies. Our SED modeling suggests that GRB 130603B, GRB 140102A, GRB 190829A and GRB 200826A have massive host galaxies with high star-formation rates (SFRs). On the other hand, a supernovae-connectedGRB 030329 has a rare low-mass galaxy with a low star-formation rate.We also find that GRB 190829A has the highest (in our sample) amount of visual dust extinction and gas in its local environment of the host, suggesting that the observed very high-energy emission from this burst might have a unique local environment. Broadly,the five GRBs in our sample satisfy the typical correlations between host galaxies parameters and these physical parameters are more common to normal star-forming galaxies at the high-redshift Universe. Our results also demonstrate the capabilities of 3.6m DOT and the back-end instruments for the deeper photometric studies ofthe host galaxies of energetic transients, such as GRBs, supernovae and other transients in the long run.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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