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.

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.

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.

To investigate the star-formation process, we present a multi-wavelength study of a massive star-forming site RAFGL 5085, which has been associated with the molecular outflow, Hii region and near-infrared cluster. The continuum images at 12, 250, 350 and 500 μm show a central region (having $M_{\rm clump}\sim 225$ $M_{\odot}$) surrounded by five parsec-scale filaments, revealing a hub-filament system (HFS). In the Herschel column density ($N$(H$_2$)) map, filaments are identified with higher aspect ratios (length/diameter) and lower $N$(H$_2$) values ($\sim$0.1–$2.4 \times 10^{21}$ cm$^{−2}$), while the central hub is found with a lower aspect ratio and higher $N$(H$_2$) values ($\sim$3.5–$7.0 \times 10^{21}$ cm$^{−2}$). The central hub displays a temperature range of [19, 22.5] K in the Herschel temperature map, and is observed with signatures of star formation (including radio continuum emission). The JCMT ${}^{13}$CO($J = 3$–2) line data confirm the presence of HFS and its hub is traced with supersonic and non-thermal motions having higher Mach number and lower thermal to non-thermal pressure ratio. In the ${}^{13}$CO position–velocity diagrams, velocity gradients along the filaments towards the HFS appear to be observed, suggesting the gas flow in the RAFGL 5085 HFS and the applicability of the clump-fed scenario.

TIFR-ARIES Near Infrared Spectrometer (TANSPEC) instrument provides simultaneous wavelength coverage from 0.55 to 2.5 $\mu$m, mounted on India’s largest ground-based telescope, 3.6-m Devasthal Optical Telescope at Nainital, India. The TANSPEC offers three modes of observations, imaging with various filters, spectroscopy in the low-resolution prism mode with derived $R \sim 100$–400 and the high-resolution cross-dispersed mode (XD-mode) with derived median $R \sim 2750$ for a slit of width 0.5 arcsec. In the XD-mode, 10cross-dispersed orders are packed in the $2048 \times 2048$ pixels detector to cover the full wavelength regime. As the XD-mode is most utilized as well as for consistent data reduction for all orders and to reduce data reductiontime, a dedicated pipeline is essential. In this paper, we present the code for the TANSPEC XD-mode data reduction, its workflow, input/output files and a showcase of its implementation on a particular dataset. This publicly available pipeline pyTANSPEC is fully developed in Python and includes nominal human intervention only for the quality assurance of the reduced data. Two customized configuration files are used to guide the data reduction. The pipeline creates a log file for all the fit files in a given data directory from its header, identifies correct frames (science, continuum and calibration lamps) based up on the user input, offers an option to the user for eyeballing and accepting/removing of the frames, does the cleaning of raw science frames and yields final wavelength calibrated spectra of all orders simultaneously.

We present a study of the molecular cloud in Sh2-112 massive star forming region using the 3-2 transition of CO isotopologues: CO, ${}^{13}$CO and C ${}^{18}$O; supplemented in part by CGPS Hi line emission and MSX data. Sh2-112 is an optically visible region powered by an O8V type massive star BD$+$45 3216, and hosts two Red MSX Survey sources: G083.7962$+$03.3058 and G083.7071$+$03.2817, classified as Hii region and young stellar object, respectively. Reduced spectral data products from the James Clerk Maxwell Telescope archive, centered on the two RMS objects with $\sim$$7' \times 7'$ field-of-view each, were utilized for the purpose. The ${}^{13}$CO(3-2) channel map of the region shows the molecular cloud to have filamentary extensions directed away from the massive star, which also seems to be at the edge of a cavity like structure. Multiple molecular cloud protrusions into this cavity structure, host local peaks of emission. The integrated emission map of the region constructed from only those emission clumps, detected above 5$\sigma$ level in the position–position–velocity space affirms the same. MSX sources were found distributed along the cavity boundary, where the gas has been compressed. Spectral extraction at these positions yielded high Mach numbers and low ratios of thermal to non-thermal pressures, suggesting a dominance of supersonic and non-thermal motion in the cloud.

We have performed a detailed analysis on the Teutsch 76 (T76) open cluster using the deep near infrared (NIR) observations taken with the TANSPEC instrument mounted on the 3.6m Devasthal optical telescope along with the recently available high quality proper motion data from the Gaia data release 3 and deep photometric data from Pan-STARRS1 survey. We have found that the T76 cluster is having a centraldensity concentration with circular morphology, probably due to the star-formation processes. The radius of the T76 cluster is found to be 45$''$ (1.24 pc) and 28 stars within this radius were marked as highly probable cluster members. We have found that the cluster is located at a distance of $5.7 \pm 1.0$ kpc and is having an ageof $50\pm 10$ Myr. The mass function slope ($\Gamma$) in the cluster region in the mass range of $\sim$0.75 < $M/M_{\odot}$ < 5.8 is estimated as $−1.3 \pm 0.2$, which is similar to the value of $−$1.35 given by Salpeter (1955). The cluster is notshowing any signatures of mass-segregation and is currently undergoing dynamical relaxation.

In recent times, 3.6m Devasthal Optical Telescope (DOT) has been installed with an optical to near infra-red spectrograph, TANSPEC, which provides spectral coverage from 0.55 to 2.5 microns. Using TANSPEC, we have obtained a single epoch spectrum of a set, containing nine FUors and EXors. We have analysed line profiles of the sources and compared them with the previously published spectra of these objects. Comparing the line profile shapes with the existing theoretical predictions, we have tried to interpret the physical processes that are responsible for the current disc evolution and the present accretion dynamics. Our study has shown the importance of time-evolved spectroscopic studies for a better understanding of the evolution of the accretion a mechanisms. This in turn can help in the better characterization of the young stars displaying episodic accretion behavior.

TIFR Near Infrared Imaging Camera-II (TIRCAM2) is being used at the Devasthal Optical Telescope (DOT) operated by Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, Uttarakhand, India. In addition to the normal full frame observations, there has been a requirement for high speed sub-array observations for applications, such as lunar occultation and star speckle observations. Fastsub-array modes have been implemented in TIRCAM2 with suitable changes in the camera software at the computer and controller DSP code level. Successful observations have been carried out with the fast sub-array mode of observation.

Using optical photometric observations from 1.3-mDevasthal Fast OpticalTelescope and deep nearinfrared (NIR) photometric observations from TANSPEC mounted on 3.6-mDevasthal Optical Telescope, along with the multi-wavelength archival data, we present our study of open cluster Kronberger 55 to understand the star-formation scenario in the region. The distance, extinction and age of the cluster Kronberger 55 are estimated as $\sim$3.5 kpc, $E(B − V) \sim 1.0$ mag and $\lesssim$5 Myr, respectively. We identified Young Stellar Objects (YSOs)based on their excess infrared (IR) emission using the two-color diagrams (TCDs). The mid-infrared (MIR) images reveal the presence of extended structure of dust and gas emission along with the outflow activities in the region with two peaks, one at the location of cluster Kronberger 55 and another at 5$'$.35 southwards to it. Theassociation of radio continuum emission with the southern peak, hints towards the formation of massive star/s. The Herschel sub-millimeter maps reveal the presence of two clumps connected with a filamentary structure in this region, and such configuration is also evident in the ${}^{12}$CO(1–0) emission map. Our study suggests that this region might be a hub-filament system undergoing star formation due to the `end-dominated collapse scenario’.

LDN1415-IRS, a low-mass young stellar object (YSO), went into an outburst between 2001 and 2006, illuminating a surrounding nebula, LDN1415-Neb. LDN1415-Neb was found to have brightened by $I = 3.77$ mag by April 2006. The optical light curve covering $\sim$15.5 years, starting from October 2006 to January 2022, is presented in this study. The initial optical spectrum indicated the presence of winds in the system, but the subsequent spectra have no wind indicators. The declining light curve and the absence of the P-Cygni profile in later epoch spectra indicate that the star and nebula system is retrieving back from its outburst state. Two Herbig–Haro objects (HHOs) are positioned linearly with respect to the optical brightness peak of the nebula, probably indicating the circumstellar disk being viewed edge-on. Our recent deep near-infrared (NIR) imaging using TANSPEC has revealed the presence of a nearby star-like source, south of the LDN1415-IRS, at an angular distance of $\sim$5.4$''$.

We present photometric and kinematic analyses of an intermediate-age open cluster NGC 1027 using $UBV(RI)_c$ and Gaia Early Data Release 3 (EDR3) data. Structural and fundamental parameters, such as cluster center, cluster extent, reddening, age and distance are estimated in this study. Cluster center is foundabout 4 arcmin away from the center reported earlier. Radius has been estimated to be about 8.00 arcmin (2.65 pc). Using proper motion Gaia EDR3 data, membership probabilities have been derived for the stars in the region of cluster radius. We found mean proper motion of the cluster to be $\sim$($−$0.84, 2.04) mas yr$^{−1}$ in (RA,DEC). We found 217 most probable ($P_{\mu}$ > 70%) cluster members with mean parallax $0.892\pm 0.088$ mas. Out of these, 160 members have counterparts in our optical observations. Few stars having $P_{\mu}$ > 70%, are found outof the cluster radius showing imprints of dynamical evolution. The color–color and color–magnitude diagrams for the cluster members found within 8.00 arcmin have been constructed using $UBV(RI)_c$ photometry and Gaia EDR3 data. This yields a reddening $E(B − V) \sim 0.36$ mag, age $\sim$130 Myr and distance $\sim$1.14 kpc The mass function slope in the cluster region is $\Gamma \sim −1.46 \pm 0.15$, which is similar to other Galactic open clusters. The dynamical study shows lack of faint stars in its inner region leading to mass segregation effect. A comparison of dynamical age with cluster age indicates that NGC 1027 is a dynamically relaxed clustersuggesting that mass segregation may be imprint of its dynamical relaxation.

TIFR Near Infrared Imaging Camera-II (TIRCAM2) is being used at the 3.6-m Devasthal Optical Telescope (DOT) operated by Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, Uttarakhand, India. Earlier, the TIRCAM2 was used at the main port of the DOT on time-shared basis. It has now been installed at the side port of the telescope. Side port installation allows near simultaneous observations with the main port instrument as well as longer operating periods. Thus, the TIRCAM2 serves the astronomical community for a variety of observations ranging from lunar occultations, transient events and normal scheduledobservations.

We present the results from our deep optical photometric observations of Bochum 2 (Boc2) star cluster obtained using the 1.3-m Devasthal Fast Optical Telescope along with archival photometric data from Pan-STARRS2/2MASS/UKIDSS surveys. We also used high-quality parallax and proper motion data from the Gaia Data Release 3. We found that the Boc2 cluster has a small size ($\sim$1.1 pc) and circular morphology. Using Gaia parallax of member stars and isochrone fitting method, the distance of this cluster is estimated as $3.8 \pm 0.4$ kpc. We have found that this cluster holds young ($\sim$5 Myr) and massive (O7–O9) stars as well asan older population of low mass stars. We found that the massive stars were formed in the inner region of the Boc2 cluster in a recent epoch of star formation. We have derived mass function slope ($\Gamma$) in the cluster region as $−2.42 \pm 0.13$ in the mass range of ${\sim}0.72$ < $M/M_{\odot}$ < 2.8. The tidal radius of the Boc2 cluster ($\sim$7–9) is much more than its observed radius ($\sim$1.1 pc). This suggests that most of the low-mass stars in this cluster are the remains of an older population of stars formed via an earlier epoch of star formation.

Using multi-wavelength data sets, we studied the star-formation activity in H ii region Sh 2-61 (hereafter S61). We identified a clustering in the region and estimated the membership using the Gaia proper motion data. The physical environment of S61 is inspected using infrared to radio wavelength images. We alsodetermined the Lyman continuum flux associated with the H ii region and found that the H ii region is formed by at least two massive stars (S1 and S2). We also analyzed the ${}^{12}$CO ($J = 3$–2) JCMT data of S61, and a shellstructure accompanying three molecular clumps are observed towards S61. We found that the ionized gas in S61 is surrounded by dust and a molecular shell. Many young stellar objects and three molecular clumps are observed at the interface of the ionized gas and surrounding gas. The pressure at the interface is higher than in a typical cool molecular cloud.