Education

• Ph.D. in Physics from Tata Institute of Fundamental Research, Mumbai, India,
• M.Sc. in Physics from Hyderabad Central University, Hyderabad, India

Experience

• Post-doctoral fellow at INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy (2006-2008)
• Principle Investigator of a DST project at Indian Institute of Technology Madras, Chennai, India (2009-2010)

Research Work / Area

Early phases in Massive Star Formation, Embedded Galactic clusters, Globular clusters, Galactic structure, Laboratory experiments with Polycyclic Aromatic Hydrocarbons (PAHs).

International Refereed Publications

2010 - Astronomical Techniques, Introduction to Astronomy and Astrophysics, Astrophysical Concepts, Modern Physics Laboratory

2011 - Diffuse Matter in Space, Astronomical Techniques, Introduction to Astronomy and Astrophysics, Planetary Explorations, Astronomy Lab

2012 - Astronomical Techniques

2013 - Introduction to Astronomy and Astrophysics, Astronomical Techniques, Introduction to Space science and Applications

2014 - Structure and Evolution of Stars, Radiative Processes in Astrophysics, Introduction to Space science and Applications, Observational Astronomy Lab

2015 - Radiative Processes in Astrophysics, Introduction to Astronomy and Astrophysics, Planetary Science, Observational Astronomy Lab

2016 - Structure and Evolution of Stars, Planetary Science, Observational Astronomy Lab

2017 - Astrophysical Concepts, Introduction to Space science and Applications, Observational Astronomy Lab

2018 - Structure and Evolution of Stars, Computational Astrophysics, Observational Astronomy Lab

2019 - Astrophysical Concepts, Introduction to Astronomy and Astrophysics, Observational Astronomy Lab

2020 - Galaxies (Structure, Dynamics and Evolution), Astronomical Techniques, Observational Astronomy Lab

2021 - Galaxies (Structure, Dynamics and Evolution), Astronomical Techniques, Observational Astronomy Lab

2022 - Structure and Evolution of Stars, Observational Astronomy Lab, Introduction to Astronomy and Astrophysics, Introduction to Space science and Applications

2023 - Structure and Evolution of Stars, Astronomical Techniques, Electrodynamics and Special Relativity, Observational Astronomy Lab

2024 - Structure and Evolution of Stars, Observational Astronomy Lab

 - Represented India as a Team Leader at the XV International Olympiad on Astronomy and Astrophysics (IOAA) at Kutaisi, Georgia in 2022

 - Secretary and member of Executive Council, Astronomical Society of India (ASI) - Term 2022-2025

 - Represented India as a Team Observer at the XIV International Olympiad on Astronomy and Astrophysics (IOAA) at Bogota, Columbia in 2021 (Online)

 - National Astronomy Education Co-ordinator (NAEC), India to liase with the International Astronomical Union (IAU) Office of Astronomy Education (OAE).

 -  Member of Public Outreach and Education Committee of Astronomical Society of India (2019-2021)

 - Gave a series of online lectures (15 hrs) on Introduction to Stars (available here) in association with Breakthrough Science Society and Astronomical Society of India

 -  Represented India as a Team Leader at the XII International Olympiad on Astronomy and Astrophysics (IOAA) at Beijing, China in 2018

 -  Taken a module of lectures for the course Stars and Stellar systems for Swayam-MHRD under the Annual Refresher Programme in Teaching (ARPIT) category

 -  Resource person at International Astronomy Olympiad camps held at Homi Bhabha Centre for Science Education (HBCSE-TIFR)

 -  Past member of AstroSat Training and Outreach Team (TOT)

 -  Author of articles in India Science Wire by Vigyan Prasar and for AstroSat Picture of the Month (APOM)

 -  Given numerous talks and demonstration workshops at various levels (high-school students, college students, teachers)

 -  Organised night-sky sessions in colleges

Doctoral Theses

1. Amal G. Cherian (Ongoing)

2. Arun Seshadri (Ongoing)

3. Sreelekshmi Mohan (Completed in July 2023) - Protostellar Jets: Numerical Modeling and Observational Studies, 

4. Dr. Veena V. S. (Completed June 2018) - IRDCs to Star clusters: In-Depth study of the Structure, Evolution and Kinematics of few Southern star-forming regions,; Awarded the Abhayankar Best Thesis award by the Astronomical Society of India in 2019

Masters Theses

1. Viswas Patel (Ongoing) - Revealing the Cosmic Cradle: Analyzing Galactic Young Stellar Clusters

2. Nishant Patel (Ongoing) - Structure and Kinematics of Infrared Dark Rings

3. Kiran L. (Completed 2022)- Probabilisitic classification of infrared sources in the Galactic Plane

          a. Probabilistic classification of infrared-selected targets for SPHEREx mission: in search of young stellar objects

          b. The SPHEREx Target List of Ice Sources (SPLICES)

4. Amit M. (Completed 2022) - Galactic star forming regions from balloon borne imaging observations

5. Nikitha Jithendran (Completed 2021) - Investigation of globular cluster NGC5053 with AstroSat-UVIT

6. Shashank Mamgain (Completed 2021) - Searching for brown dwarfs towards star-forming regions

7. D. Bhavana (Completed 2020) - A Study of Red Horizontal Branch Stars in the Globular Cluster NGC 2808

8. Vipin Kumar (Completed 2020) - A Multiwavelength investigation of the southern star-forming region RCW 42

9. Swapnil Singh (Completed 2019) - Low frequency radio observations of star-forming dusty galaxies

10. Chithra Raghavan (Completed 2019) - Star-formation using UVIT of the ring galaxy NGC1433

11. Ayisha Ashraf (Completed 2019) - [CII] mapping observations of massive star-forming regions

12. Rashi Jain (Completed 2018) - ASTROSAT-UVIT investigation of the globular cluster NGC2808.

13. Ashish Devaraj (Completed 2017) – Star-formation in ring galaxies

14. Govind Nandakumar (Completed 2015) – Star-forming activity towards HII region complex in IRAS 17160-3707

BTech Project Theses 

1. Prateeksha Naik - OI lines in Herbig Ae/Be stars

2. Srirag Nambiar - Embedded star cluster detection using Advanced Pattern Recognition Algorithms

3. Tanul Gupta - Simulations of Young Embedded Clusters

4. Saurabh Bansal - Radio Signatures of Galactic Infrared Bubbles

Massive star formation in the hub-filament system of RCW 117

We present a multiwavelength investigation of the optical nebula RCW 117, housing the IRAS object 17059-4132, in infrared (Spitzer GLIMPSE in midinfrared and Herschel Hi-Gal in far infrared) and radio (GMRT) wavelengths. We also study the gas kinematics towards the region using molecular line emission from ¹³CO (ThRUMMS survey) and 6 other molecules from the MALT90 survey. The cold dust component mapped using Hi-Gal data reveals an intricate hub-filamentary structure, with the hub located towards the IRAS object, and filaments extending outwards in all directions. We use the Hi-Gal maps for generating the high-resolution hydrogen column density map for the region using the getsf software, and find that the column density is highest towards the hub (~10²³ cm^-2), and decreases towards the filaments (~10²² cm^-2). A total of 88 cores and 12 filaments are detected towards the region, with 14 massive cores, including the most massive one, and 6 filaments being associated with the hub. We also find ~39% of the cores to be located along the filaments. Warm dust emission, mapped using the GLIMPSE data shows peak emission towards the hub. The radio emission, mapped using GMRT at 610 and 1280 MHz, also peaks towards the hub, suggesting the presence of ionised gas within the hub. These observations strongly suggest that RCW 117 may plausibly be undergoing massive star- formation. The Lyman continuum photon rate calculated from the 1280 MHz flux, suggests the presence of a single main sequence star of spectral type O6. We also detect 34 Class 0/I young stellar objects (YSOs) using the GLIMPSE catalog, with 9 of them located towards the hub, and the rest of them towards cores located along the filaments. The ¹³CO spectrum towards the hub generated using ThRUMMS, shows peak emission towards the LSR velocity of ~21 km/s. The hub-filamentary morphology is visible in the ¹³CO integrated intensity map. We construct the velocity, velocity dispersion and column density profiles along the filaments. We observe clear velocity gradients of 0.3 - 1 km/s along the filaments, while the velocity dispersion and column density is seen to be higher towards the ends closer to the hub. The presence of multiple cores along the filaments is suggestive of cores accreting from the filaments, resulting in filament fragmentation, while velocity gradients along the filaments suggest longitudinal flow of matter along filaments and into the hub. Increased velocity dispersion towards the hub may point to turbulence generated due to massive star-formation within the hub. Based on the above evidences, we suggest that the star-formation towards the hub and the region in general may be explained using the Global Hierarchical Collapse (GHC) model.

Caption: (a) Herschel colour-composite image of RCW 117 comprising of emission at 350 μm (red), 160 μm (green), and 70 μm (blue), showing the hub-filamentary structure. The IRAS object 17059–4132 is marked as a black cross. (Inset) Rectangular region shown in the colour-composite image, showing the optical nebula associated with RCW 117 from the Digitized Sky Survey (DSS). The contours represent the 70 μm emission, with levels 0.25, 0.75, 2.5, 7.5, 20, 75 Jy pixel⁻¹. (b) The column density map for RCW 117 is shown. The central hub is marked as a black circle. (c) Cores and filament skeletons extracted using getsf. The white solid circle encloses the hub. The most massive core C1, is marked using a white solid ellipse within the hub.

Caption: (a) Variation of velocity (relative to the LSR velocity), calculated using the ¹³CO (J = 1–0) line, along the filament for Fil-1 to Fil-5, which represent filaments converging to the hub. The origin corresponds to the end of the filament located nearest to the hub. (b) Variation in the velocity dispersion along the filaments. (c) Variation of mean column densities along the filaments. (d) Greyscale image is the column density in units of 10²⁰ cm⁻², with the velocities of filaments marked as coloured circles, in units of km/s.

Ref: Arun Seshadri, S. Vig, S. K. Ghosh, D. K. Ojha, Massive star formation in the hub–filament system of RCW 117, Monthly Notices of the Royal Astronomical Society, Volume 527, Issue 2, January 2024, Pages 4244–4259, DOI: https://doi.org/10.1093/mnras/stad3385

Radio lobes at Parsec Scale Discovered towards East-West jet of RAFGL2591 using the GMRT

High mass stars play a significant role in the evolution of galaxies and deposit angular momentum, kinetic energy and turbulence into the surrounding interstellar medium. The initial stages of stellar birth are generally accompanied by collimated jets or wide angle outflows which are indications of on-going star formation activity. Jets are generally supersonic and generate shocks upon their impact with the surrounding medium. These shocked regions from ionized jets, although weak, are generally detected as radio continuum sources. In search of jets and shocked regions, we have observed the massive star forming region RAFGL2591 in Cygnus X region at a distance of 3.3 kpc with the Giant Metrewave Radio Telescope (GMRT) at 325, 610 and 1280 MHz. For the first time, we have detected radio jet lobes in the E-W direction, labelled as GMRT-1 and GMRT-2 driven by the protostar VLA 3 which are shown in the Figure. In contrast to GMRT-1, which exhibits a flat radio spectral index, GMRT-2 exhibits a steeply negative value which is suggestive of non-thermal emission. H₂ emission maps from the United Kingdom Infrared Telescope (UKIRT) show the presence of numerous knots, arcs and extended emission towards the East-West jet, excited by the protostar VLA 3. In addition, we found a few H₂ knots in the North-East and South-West for the first time. Understanding the radio lobes (GMRT-1, GMRT-2) and H₂ emission towards this region requires knowledge of both the well-known East-West jet and its less well-known North-East and South-West sibling jet. We used a numerical model that included thermal and non-thermal emission to simulate the radio emission from the lobes, and we discovered number densities pointing in the direction of these lobes in the range of 100 to 1000 per cc. We have noticed that the East-West jet lobe has a misalignment exhibiting reflection symmetry with a 20 degrees bending. We propose that this misalignment may be due to the precession brought on by a binary partner and/or a supersonic side wind from a source(s) nearby.

Caption: Three colour composite image of the RAFGL2591 region encompassing the E-W jet is shown in the top panel, with UKIDSS J band (blue), UWISH2 2.12 micron (green), and GMRT 1280 MHz radio image (red). The 1280 MHz radio contours are shown in white, while the magenta contours depict the 250 micron emission from Herschel. The white dotted lines (top panel) point to the radio lobes from VLA 3, highlighting the misalignment between them. The central region is enlarged in the bottom panel. Here, the CO outflow is shown as cyan and red contours, while the cyan and orange dashed arrows indicate the directions of the blue and red lobes of the NE-SW jet. The inset shown on the top left of this panel zooms close to VLA 3. The violet contours represent VLA 8.4 GHz emission overlaid over the UKDISS J band image, with the emission in the latter also highlighted through the green contours.

Ref: New radio lobes at parsec scale from the East-West protostellar jet RAFGL2591, A. G. Cheriyan, S. Vig, Sreelekshmi Mohan, 2023, Monthly Notices of Royal Astronomical Society, 525,2172, DOI: https://doi.org/10.1093/mnras/stad2407

Probabilistic Classification of Infrared-selected targets for SPHEREx mission: In search of YSOs

 The sources seen in the Infrared (IR) bands are diverse, and include objects such as the Young stellar objects (YSOs), reddened main sequence (MS) stars, Asymptotic Giant Branch (AGB) stars, and Active Galactic Nuclei (AGN). Amongst these classes, YSOs represent the earliest phases of star formation embedded in their natal clouds, whilst the others represent mostly more evolved phases of stars (MS and AGB) or bright compact central regions of galaxies (AGN). SPHEREx is a NASA’s upcoming mission, one of whose primary aims is to detect biogenic ices such as H₂O, CO₂, etc., along the lines-of-sight toward YSOs and protoplanetary disks, from a target list. In this work, we have probabilistically classified the SPHEREx targets as YSOs, (reddened) MS stars, AGB stars and AGNs, with machine and deep learning algorithms using 2MASS and AllWISE photometry. Further, we sub-classified the YSOs as Class I, II, III and flat spectrum YSOs based on spectral index and AGB stars into carbon-rich (C AGB) and oxygen-rich (O AGB) stars using machine learning models. Unlike previous approaches, we have adopted an ensemble approach and incorporated the uncertainty in photometry during training and classification through uncertainty-based resampling method. After classification we found that out of 8,308,384 SPHEREx targets, 1,966,340 have class prediction with probability exceeding 90%, amongst which ~1.7% are YSOs, ~58.2% are AGB stars, ~40% are (reddened) MS stars, and ~0.1% are AGN whose red broadband colors mimic YSOs. We validated our classification using the spatial distributions of predicted YSOs towards the Cygnus-X star-forming complex, as well as AGB stars across the Galactic plane. We estimated the distance to the Cygnus-X region as 1.76 +/- 0.56 kpc, which is in line with the value in literature estimated using parallax and proper motions of water masers towards this complex.

Caption: (a) Visual depiction of the two-stage classifier. An ensemble of 100 RF, FNN and CNNs each are built for stage-1 classification as well as for AGB sub-classification (marked by blue arrows). YSOs are sub-classified based on spectral index (marked by red arrows). The black arrows indicate the flow of input data in the classifier. (b) Plot of spatial distribution of different classes of YSOs in the target list on the Mollweide projection of the sky plane. These objects are identified close to the Galactic mid-plane and some higher latitude molecular clouds. Regions occupied by SPHEREx targets are colorized using the coloring scheme displayed at the top of the plot and those not occupied by SPHEREx targets are left blank.

Ref: Probabilistic Classification of Infrared-selected targets for SPHEREx mission: In search of YSOs, K. Lakshmipathaiah, S. Vig, Matthew L. N. Ashby, Joseph L. Hora, Miju Kang, and Rama Krishna Sai S. Gorthi, 2023, Monthly Notices of the Royal Astronomical Society, 526, p1923, DOI:10.1093/mnras/stad2782

Understanding massive protostellar jets through shocked emission in multiple knots: A case study of HH80-81 jet

The HH80-81 system is known to be the largest and most collimated Herbig-Haro system in the Galaxy and is driven by the massive protostar IRAS 18162-2048. We have explored the partially ionized and molecular regions of the jet in the near-infrared wavelength for understanding the jet properties and estimation of its physical parameters. For this, we have utilized the emission from shocks generated by the jet. The widely used shock tracers in jets are the 2.122 µm molecular H₂ and 1.644 µm [Fe II] emission lines. We have, for the first time, carried out a combined 2.122 µm H₂ and 1.644 µm [Fe II] imaging using the UKIRT, followed by a detailed qualitative and quantitative analysis of the HH80-81 jet. In addition to this, we have also imaged the region in near-and mid-infrared broadband emission. In the narrow-band emission, we have detected nine groups of knot-like structures in the jet including HH80 and HH81 spaced 0.2 − 0.9 pc apart. We have identified the nature of shocks associated with the jet knots and inferred a dominance of dissociative J-type shocks in the overall jet. The mass-loss rates of the knots determined from [Fe II] luminosities are in the range ∼3.0 × 10⁻⁷ − 5.2 × 10⁻⁵ M_⊙ yr⁻¹, consistent with those from massive protostars. Towards the central region of the jet, we have observed various arcs in H₂ (white arcs) emission which resemble bow shocks, and strings of H₂ knots (yellow diamonds) which reveal traces of multiple outflows in addition to the HH80-81 main jet, which are marked in the figure shown below.

Caption: 2MASS-JHK bands color-composite image of the central region of HH80-81 jet (K: red, H: green, J: blue). The NIR [Fe II] emission is overlaid as green contours, the arrows depict outflows detected in this region. The cyan crosses indicate driving sources of the detected jet/outflows, the magenta crosses indicate two YSOs of interest in the region, the white arcs represent the bow shocks identified in the H2 emission and the yellow diamonds show H2 knots.

Ref: Imaging of HH80-81 jet in the NIR shock tracers H₂ and [Fe II], Sreelekshmi Mohan, S. Vig, W. P. Varricatt, A. Tej, 2023, The Astrophysical Journal, Volume 942, Issue 2, 76 (14 pages), DOI 10.3847/1538-4357/aca413

Investigating star-formation activity towards the southern HII region RCW 42

Massive stars (M ≳ 8 Msun) play an important role in the evolution of the interstellar medium due to their high energy output, supernovae explosions, and enrichment of the surrounding medium by heavy elements. The formation of these stars can be studied through the HII regions formed due to the increased output of UV photons from them. Moreover, a multiwavelength study of the molecular clouds associated with these HII regions gives important clues about the evolutionary stages of star-formation. We have studied the southern HII region RCW 42 and its associated molecular cloud at radio, near, mid, far infrared and millimeter wavelengths to estimate its properties (column density, temperature, electron density, ionization fraction, bolometric luminosity) and study the evolutionary stages of various clumps present in the region. The HII region has been investigated by studying the ionized gas emission, emission from cold and warm dust and identifying its ionizing candidates. An extended green object EGO G274.0649-01.1460 has also been identified in the region. We have constructed column density and temperature maps and have identified five dust clumps from the former. We have also identified two mm emission cores towards the radio emission peak. All the five dust clumps are found to be in the active/evolved phase based on various star-formation tracers.

Caption: (a) Optical and radio continuum emission contours towards RCW 42 (b) Color-composite image of RCW 42 depicting the ionized gas emission at 1280 MHz (red), cold dust emission at 250 μm (green) and mid-infrared emission at 8 μm (blue). Ionizing candidates are shown as x and + signs. (c) . Maps of column density overlaid with clump apertures (left), and (b) dust temperature overlaid with contours of radio emission (right).

Ref: Investigating star-formation activity towards the southern HII region RCW 42, Vipin Kumar, Sarita Vig, V.S. Veena, Sreelakshmi Mohan, S.K. Ghosh, Anandmayee Tej and D.K. Ojha, 2022, Monthly Notices of the Royal Astronomical  Society,  Volume  515,  Issue  4,  October 2022, Pages  5730–5742, DOI: https://doi.org/10.1093/mnras/stac2124

Discovery of UV bright stellar population candidates in a metal-poor Globular Cluster NGC 5053 using AstroSat-UVIT

Globular clusters are known to serve as fundamental test beds for stellar evolution theories. NGC 5053, a metal-poor and a rather dispersed globular cluster, was studied in the ultraviolet regime with AstroSat's Ultra Violet Imaging Telescope (UVIT). The images of the cluster were analyzed in various filters across the FUV and NUV bands by a team led by IIST researchers. The team discovered eight blue straggler candidates, six evolved blue straggler candidates, and an extreme horizontal branch candidate among the cluster's new probable UV bright population. Using GAIA EDR3 data, a proper motion analysis was used to validate their association with the cluster, and spectral energy distribution (SED) studies were used to corroborate the nature of these candidates. Furthermore, the radial distribution analysis of the blue straggler population shed some light on the potential formation mechanism of these stars in NGC 5053.

Caption: (Left) UVIT-AstroSat image of the globular cluster NGC 5050 with the far-ultraviolet emission displayed in blue and near-ultraviolet emission in yellow. The image also shows the location of a few discovered candidates of the cluster. (Right) The UVIT color-magnitude diagram showing the cluster's various populations.

Ref: Stellar populations of the globular cluster NGC 5053 investigated using AstroSat - Ultra Violet Imaging Telescope, K. J. Nikitha, S. Vigand S. K. Ghosh, 2022, Monthly Notices of Royal Astronomical Society, Volume 514, Issue 4, August 2022, Pages 5570–5582, DOI: https://doi.org/10.1093/mnras/stac1444

Modeling radio spectra of Protostellar Jets: Thermal and Non-thermal emission

Protostellar jets serve as the principal signature of ongoing star formation activity. Observations have revealed that the radio emission from protostellar jets arise from a combination of thermal free-free and non-thermal synchrotron emission mechanisms. The observed radio spectra of protostellar jets can be explained with the help of emission models and we have developed, for the first time, a simplistic numerical model that is applicable for narrow as well as wide-angle protostellar jets, and could explain the signatures of synchrotron emission in their radio spectra. In addition, we introduce a lateral variation in the ionization fraction within the jet such that the jet is highly ionized along its axis and the ionization fraction decreases as a power-law with distance from the axis. The model geometry is such that the highly ionized regions close to the jet axis contribute to the majority of free-free emission and the outer edges that impact on the ambient medium result in the formation of astrophysical shocks where the conditions are suitable for the generation of synchrotron radiation along with free-free emission. We have studied the influence of each parameter on the characteristics of the model spectra and this enables us in estimating the parameters associated with the jets for which non-thermal emission was detected. The figure shown below represents the model jet geometry and illustrates the variation in flux densities across the length of the protostellar jet.

Caption: [Left] Schematic diagram of the jet representing the different layers of particle distribution along a specific line-of-sight at an arbitrary jet length projected on the sky plane (y). Regions 1 and 3 give rise to a combination of thermal and non-thermal emission, while Region 2 solely contributes to thermal emission. [Center] The flux density distribution (combined free-free and synchrotron) as a function of frequency (ν) and projected length (y) plotted in logarithmic space. The black curve represents the variation of the turnover frequency where emission is maximum. l₁, l₂ and l₂ marked in white are three different positions along y, whose spectra are shown in [right].

Ref: Radio spectra of protostellar jets: Thermal and non-thermal emission, Sreelekshmi Mohan, S. Vig, S. Mandal, Monthly Notices of Royal Astronomical Society (MNRAS), 2022, 514, p3709–3724, DOI: 10.1093/mnras/stac1159

Cold Dust content of Nearby galaxies

Star-formation takes place in the cold dense molecular clouds, which also harbour the coldest dust grains present in star-forming galaxies. The emission from these very cold dust grains is challenging to detect alongside the overpowering emission from the warmer dust grains and the contamination from thermal and non-thermal radio emission at millimeter/sub-millimeter wavelengths. In this work, we looked at the multi-wavelength emission from four nearby star-forming spiral galaxies to search for signatures of these very cold dust grains and also quantify the very cold dust content. We do this by constructing their Spectral Energy Distributions (SEDs) across a vast wavelength range, extending from ultraviolet to radio frequencies, by combining observations from 12 different instruments/telescopes. These SEDs have information about various physical processes taking place in the galaxy embedded in them. We modelled the SEDs using a tool called CIGALE (Code Investigating GALaxy Emission) to extract various physical parameters of the galaxy and estimate the total and very cold dust components of the galaxies in our sample. We found hints of very cold dust in two of the targets, NGC 7496 and NGC 7590, where the very cold dust accounts for nearly half of the total dust content. The results for one of the galaxies in the sample, NGC 7590, are shown in the figure below.

Ref: The cold dust content of the nearby galaxies IC 5325, NGC 7496, NGC 7590, and NGC 7599, Swapnil Singh, M. L. N. Ashby, Sarita Vig, S. K. Ghosh, T. Jarrett, T. M. Crawford, Matthew A. Malkan, M. Archipley and J. D. Vieira, 2021, MNRAS, 504, p4143-4159, DOI: 10.1093/mnras/stab1048

Discovery of a UV bright star population in the Globular Cluster NGC 2808

Globular clusters are the best laboratories to study the evolution of stars. The globular cluster NGC 2808 was studied in ultraviolet using the Ultraviolet Imaging Telescope (UVIT) on-board AstroSat by a team led by IIST researchers. Using different wavebands (filters), the team discovered the presence of a distinct group of red horizontal branch stars in the cluster, which sheds light on the understanding of multiple populations within the cluster.
 
Caption: UVIT-AstroSat image of the globular cluster NGC 2808, with far-ultraviolet shown in blue and near- ultraviolet in yellow. The red and light-blue circles show the locations of two populations of faint red-horizontal branch stars identified using UVIT-AstroSat. (Right) Four populations of ultraviolet stars identified in the cluster using the UVIT colour-magnitude diagram.

Ref: Investigation of the globular cluster NGC 2808 with the Ultra-Violet Imaging Telescope, Rashi Jain, S. Vig, S. K. Ghosh, S. K. 2019, MNRAS, 485, p2877

HI Jet towards a Supernova Remnant

A supernova explosion heralds the death of a massive star and a supernova remnant represents the heated leftover gaseous matter of this event in the neighbourhood. The supernova remnant G351.7, was discovered using GMRT by a team led by IIST. In addition, a jet of atomic hydrogen has been found emanating from a region in the supernova remnant G351.7 in a follow-up study. This is the first time that such a highly collimated HI jet from a SNR has been detected.

Caption: Image shows radio continuum emission from supernova remnant G351.6 at 325 MHz. The blue colour on the right enlarged picture depicts the atomic hydrogen. The arrows indicate direction of the jet lobes and cross shows the location of high energy gamma-ray source.

Ref:(i) Non-thermal emission from massive star-forming regions: a possible SNR candidate G351.7-1.2, V.S. Veena, S. Vig, B. Sebastian, D.V. Lal, A. Tej, S. K. Ghosh, MNRAS, 2019, 482, 4630, (ii) High-velocity H I jet- like feature towards the SNR candidate G351.7-1.2, V.S. Veena, S. Vig, N. Roy, J. Roy, 2019, MNRAS Letters, 488, L59