arXiv subjects

Neelam Panwar

Publications and source records attributed to Neelam Panwar.

At least 19 recordsLinked to original sources

arXiv2026

Observations of Binary Stars with the 1.3-m Devasthal Fast Optical Telescope Using Speckle Interferometry: An Attempt

We present a feasibility study exploring the implementation of optical interferometry and speckle techniques with the 1.3-m Devasthal Fast Optical Telescope (DFOT) at ARIES, which is currently dedicated to photometric observations. Using the sCMOS camera as the DFOT backend, we perform interferometric speckle observations of several binary stars. Standard Speckle Interferometry (SI) algorithms are applied to analyze the recorded data. While this study does not aim to achieve the diffraction limit of DFOT or address a full science-driven resolution case, it serves as a crucial testbed for instrumentation, data acquisition, and analysis of Speckles with DFOT. Notably, we successfully identify and correct tracking-related positional errors in the observed binary systems, demonstrating the viability of the approach. These results provide strong motivation for more systematic observations and future implementation of optical interferometry techniques at meter-class telescopes.

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arXiv2025

Unveiling the Dual Nature of V1180 Cas: UXor-like Dips and EXor-like Bursts Across a Decade

We present a detailed analysis of the long-term photometric and spectroscopic evolution of V1180 Cas over a decade, aiming to identify the dominant mechanisms behind its variability. We combine multi-band light curves from 1999 to 2025 with over 30 epochs of optical to near-infrared spectroscopy (0.5-2.5 $\mu$m), analyzing variability patterns, color behavior, and emission line diagnostics. We investigate the temporal evolution of accretion and outflow indicators and their correlation with photometric states. The light curve reveals a transition from sporadic early dimming events to a quasi-periodic pattern since 2018, with eleven major dips showing asymmetry and stochastic sub-structure. Color-magnitude diagrams show classic UXor-like blueing during deep minima, while near-infrared and mid-infrared color changes indicate thermal evolution of disk. Spectroscopic analysis reveals persistent hydrogen, Ca II, He I, and forbidden line emission. Accretion diagnostics track photometric variability, and forbidden lines often intensify during dips, implying a physical link between extinction and outflows. Estimated accretion rates range from $\sim10^{-8}-10^{-7}$ $M_\odot$yr$^{-1}$; the outflow rate and density diagnostics are consistent with disk winds and shock-excited jets. V1180 Cas demonstrates dual-mode variability driven by both variable circumstellar extinction and episodic accretion events. The hybrid UXor/EXor behavior, combined with evolving disk signatures and persistent outflows, suggests a young stellar object undergoing coupled accretion-extinction-outflow evolution. Continued monitoring will be essential to fully resolve the physical processes shaping its variability.

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arXiv2025

Stellar Multiplicity via Speckle Interferometry with the 3.6 m Devasthal Optical Telescope

Conventional ground-based optical telescopes, even those with large apertures, primarily observe stars, close binaries, and multiple systems as unresolved point sources through photometric measurements. Spectroscopy can identify multiple stellar components within a system, but both techniques are fundamentally limited in resolving stellar surfaces and providing direct angular separations. Although photometric and spectroscopic observations yield critical information on magnitudes/flux, metallicities, and orbital properties, complementary high-angular-resolution methods are required to constrain additional system characteristics, including angular orbital parameters, model-independent distances, radii, and stellar masses. The limitations of these two methods arise due to the Diffraction Limit of the telescopes and atmospheric turbulence. Speckle Interferometry (SI) is a clever and affordable method for ground-based telescopes to work around atmospheric turbulence. In this work, we utilize the speckle images obtained by the 3.6 m DOT and demonstrate the capability of SI to resolve binary systems, measure their orbital separations, and determine their position angles. For systems with faint companions where conventional analysis fails, we employ Bayesian inference to model speckle patterns and estimate orbital parameters with high precision. These results establish the effective methodology for using a medium-sized, 4-m class telescope like the DOT as a high-resolution stellar interferometer and demonstrate the potential of speckle interferometry as a powerful technique to advance optical interferometric studies within Indian astronomy.

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arXiv2025

Investigating the Influence of Radiative Feedback in Bright-Rimmed Cloud 44

Radiative feedback from massive stars plays a central role in the evolution of molecular clouds and the interstellar medium. This paper presents a multi-wavelength analysis of the bright-rimmed cloud, BRC 44, which is located at the periphery of the Hii region Sh2-145 and is excited by the massive stars in the region. We use a combination of archival and newly obtained infrared data, along with new optical observations, to provide a census of young stellar objects (YSOs) in the region and to estimate stellar parameters such as age, mass etc. The spatial distribution of YSOs visible in the optical wavelength suggests that they are distributed in separate clumps compared to the embedded YSOs and are relatively older. Near-Infrared (NIR) spectroscopy of four YSOs in this region using the TANSPEC mounted on the 3.6m Devasthal Optical Telescope (DOT) confirms their youth. From Spectral Energy Distribution (SED) fitting, most of the embedded YSO candidates are in their early stage of evolution, with the majority of them in their Class II and some in Class I stage. The relative proper motions of the YSOs with respect to the ionizing source are indicative of the rocket effect in the BRC. The 12CO, 13CO, and C18O observations with the Purple Mountain Observatory are used to trace the distribution of molecular gas in the region. A comparison of the cold molecular gas distribution with simple analytical model calculations shows that the cloud is in the compression stage, and massive stars may be influencing the formation of young embedded stars in the BRC region due to radiative feedback.

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arXiv2025

Investigating Pulsating Variables and Eclipsing Binaries in NGC 2126 using Ground and Space-based Photometry, Astrometry, Spectroscopy and Modeling

Pulsating variables are prevalent in the classical {\delta} Scuti instability strip of intermediate-age open star clusters. The cluster membership of these stars facilitates a comparative analysis of their evolution in analogous environments. In this study, we integrate ground-based observations, TESS Full Frame Images (FFIs), and Gaia DR3 data to investigate variable stars in the intermediate-age open star cluster NGC 2126. We performed ground-based time-series observations of NGC 2126 to identify variable stars within its vicinity. Next, we determined the membership of these stars using parallax and the proper motions from Gaia DR3 archive. Then, we searched the TESS Full Frame Images (FFIs) for counterparts to the variables identified above and performed their frequency analysis and classification. Finally, we modeled the light curves (LCs) of detected eclipsing binaries (EBs), including V551 Aur, which has a pulsating component. We found 25 members and 85 field variable stars. In TESS FFIs, we found LCs for 11 known variables and a new rotational variable. We determined that the pulsating EB V551 Aur is a member of the cluster. The low- and medium-resolution spectra revealed the line profile variation and the basic parameters for the star, respectively. Simultaneous modeling of the eclipses and the embedded pulsations resulted in improved orbital parameters for the binary system. We also report the determination of orbital parameters for the previously uncharacterized EB system UCAC4 700-043174.

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arXiv2025

Research on the Interstellar Medium and Star Formation in the Galaxy: An Indian Perspective

Although the star formation process has been studied for decades, many important aspects of the physics involved remain unsolved. Recent advancement of instrumentation in the infrared, far-infrared and sub-millimetre wavelength regimes have contributed to a significantly improved understanding of processes in the interstellar medium (ISM) leading to star formation. The future of research on the ISM and star formation looks exciting with instruments like the JWST, ALMA, etc., already contributing to the topic by gathering high-resolution high-sensitivity data and with several larger ground- and space-bound facilities either being planned or constructed. India has a sizable number of astronomers engaged in research on topics related to the ISM and star formation. In this white paper invited by the Astronomical Society of India to prepare a vision document for Indian astronomy, we review the Indian contributions to the global understanding of the star formation process and suggest areas that require focused efforts both in creating observing facilities and in theoretical front in India, in order to improve the impact of our research in the coming decades.

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arXiv2024

Twins in Diversity: Understanding circumstellar disk evolution in the twin clusters of W5 complex

Young star-forming regions in massive environments are ideal test beds to study the influence of surroundings on the evolution of disks around low-mass stars. We explore two distant young clusters, IC 1848-East and West located in the massive W5 complex. These clusters are unique due to their similar (distance, age, and extinction) yet distinct (stellar density and FUV radiation fields) physical properties. We use deep multi-band photometry in optical, near-IR, and mid-IR wavelengths complete down to the substellar limit in at least five bands. We trace the spectral energy distribution of the sources to identify the young pre-main sequence members in the region and derive their physical parameters. The disk fraction for the East and West clusters down to 0.1 M$_\odot$ was found to be $\sim$27$\pm$2% (N$_{disk}$=184, N$_{diskless}$=492) and $\sim$17$\pm$1% (N$_{disk}$=173, N$_{diskless}$=814), respectively. While no spatial variation in the disk fraction is observed, these values are lower than those in other nearby young clusters. Investigating the cause of this decrease, we find a correlation with the intense feedback from massive stars throughout the cluster area. We also identified the disk sources undergoing accretion and observed the mass accretion rates to exhibit a positive linear relationship with the stellar host mass and an inverse relationship with stellar age. Our findings suggest that the environment significantly influences the dissipation of disks in both clusters. These distant clusters, characterized by their unique attributes, can serve as templates for future studies in outer galaxy regions, offering insights into the influence of feedback mechanisms on star and planetary formation.

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arXiv2024

Low-mass stellar and substellar content of the young cluster Berkeley 59

We present a multi-wavelength analysis of the young star cluster Berkeley 59 (Be 59) based on the $Gaia$ data and deep infrared (IR) observations with the 3.58-m Telescopio Nazionale Galileo and $Spitzer$ space telescope. The mean proper motion of the cluster is found to be $\mu$$_\alpha$cos$\delta$ $\sim$ -0.63 mas yr$^{-1}$ and $\mu$$_\delta$ $\sim$ -1.83 mas yr$^{-1}$ and the kinematic distance of the cluster, $\sim$ 1 kpc, is in agreement with previous photometric studies. Present data is the deepest available near-IR observations for the cluster so far and reached below 0.03 M$_\odot$. The mass function of the cluster region is calculated using the statistically cleaned color-magnitude diagram and is similar to the Salpeter value for the member stars above 0.4 M$_\odot$. In contrast, the slope becomes shallower ($\Gamma$ $\sim$ 0.01 $\pm$ 0.18) in the mass range 0.04 - 0.4 M$_\odot$, comparable to other nearby clusters. The spatial distribution of young brown dwarfs (BDs) and stellar candidates shows a non-homogeneous distribution. This suggests that the radiation feedback from massive stars may be a prominent factor contributing to the BD population in the cluster Be 59. We also estimated the star-to-BD ratio for the cluster, which is found to be $\sim$ 3.6. The Kolomogorov-Smirnov test shows that stellar and BD populations significantly differ, and stellar candidates are near the cluster center compared to the BDs, suggesting mass segregation in the cluster toward the substellar mass regime.

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arXiv2024

Foreground Dust Properties towards the Cluster NGC 7380

Using starlight polarization, we present the properties of foreground dust towards cluster NGC 7380 embedded in H{\sc ii} region Sh 2-142. Observations of starlight polarization are carried out in four filters using an imaging polarimeter equipped with a 104-cm ARIES telescope. Polarization vectors of stars are aligned along the Galactic magnetic field. Towards the east and southeast regions, the dust structure appears much denser than in other regions (inferred from extinction contours and colour composite image) and is also reflected in polarization distribution. We find that the polarization degree and extinction tend to increase with distance and indication for the presence of a dust layer at a distance of around 1.2 $kpc$. We have identified eight potential candidates exhibiting intrinsic polarization by employing three distinct criteria to distinguish between stars of intrinsic polarization and interstellar polarized stars. For interstellar polarized stars, we find that the maximum polarization degree increases with the color excess and has a strong scatter, with the mean value of 1.71$\pm$0.57$\%$. The peak wavelength spans $0.40-0.88\mu$m with the mean value of 0.56$\pm$0.07 $\mu m$, suggesting similar grain sizes in the region as the average diffuse interstellar medium. The polarization efficiency is also found to decrease with visual extinction as $P_{max}/A_{V}\propto A_{V}^{-0.61}$. Our observational results are found to be consistent with the predictions by the radiative torque alignment theory.

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arXiv2023

Cluster Formation in a Filamentary Cloud: The Case of the Stellar Cluster NGC 2316

We present a multi-wavelength analysis of the star cluster NGC 2316 and its surroundings. We estimated the physical parameters of the NGC 2316 cluster, including its shape (elongated), size (Rcluster = 0.4 pc), distance (1.3 +/- 0.3 kpc), and minimum reddening (AV = 1.55 mag). We discovered two massive stars (B2.0V-B1.5V, age ~12 Myr) embedded (AV = 4 mag) within this cluster. The cluster region still forms young stars even though the most massive star was born ~12 Myr ago. We also found evidence of positive feedback from these massive stars. We identified a cold gas/dust lane extending westward from the cluster. The western end of the dust lane seems to favor low-mass star formation, whereas the cluster's end favors bit massive star formation, which seems to have started earlier than the western end. We found an elongated molecular cloud in this region, characterized by numerous filamentary structures. The morphology of the filaments, along with position-velocity (pv) maps, velocity dispersion maps, channel maps, etc., indicate a coalescence of filaments and a potential longitudinal flow of matter toward the cluster through the western end of the gas/dust lane. This entire region seems to be a Hub-filamentary system (HFS), in which the NGC 2316 cluster is probably the hub and the dark lane is the main filamentary structure. Being the gravity well of this HFS, star formation started first in the NGC 2316 region and went on to the other filamentary nodes.

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arXiv2023

4K$\times$4K CCD Imager for the 3.6m DOT: Recent up-gradations and results

The 4K$\times$4K CCD Imager is the first light instrument for the 3.6m 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 article, 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.

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arXiv2023

Exploring Stellar Cluster and Feedback-driven Star Formation in Galactic Mid-infrared Bubble [HKS2019] E70

We present a comprehensive analysis of the Galactic mid-infrared (MIR) bubble [HKS2019] E70 (E70) by adopting a multi-wavelength approach to understand the physical environment and star formation scenario around it. We identified a small (radius ~1.7 pc) stellar clustering inside the E70 bubble and its distance is estimated as 3.26 +/- 0.45 kpc. This cluster is embedded in the molecular cloud and hosts massive stars as well as young stellar objects (YSOs), suggesting active star formation in the region. The spectral type of the brightest star 'M1' of the E70 cluster is estimated as O9V and a circular ring/shell of gas and dust is found around it. The diffuse radio emission inside this ring/shell, the excess pressure exerted by the massive star 'M1' at the YSOs core, and the distribution of photo-dissociation regions (PDRs), a Class I YSO, and two ultra-compact (UC) H II regions on the rim of this ring/shell, clearly suggest positive feedback of the massive star 'M1' in the region. We also found a low-density shell-like structure in 12 CO(J=1-0) molecular emission along the perimeter of the E70 bubble. The velocity structure of the 12 CO emission suggests that the feedback from the massive star appears to have expelled the molecular material and subsequent swept-up material is what appears as the E70 bubble.

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arXiv2023

Post-outburst evolution of bonafide FUor V2493 Cyg: A Spectro-photometric monitoring

We present here the results of eight years of our near-simultaneous optical/near-infrared spectro-photometric monitoring of bonafide FUor candidate `V2493 Cyg' starting from 2013 September to 2021 June. During our optical monitoring period (between October 16, 2015 and December 30, 2019), the V2493 Cyg is slowly dimming with an average dimming rate of $\sim$26.6 $\pm$ 5.6 mmag/yr in V band. Our optical photometric colors show a significant reddening of the source post the second outburst pointing towards a gradual expansion of the emitting region post the second outburst. The mid infra-red colors, on the contrary, exhibits a blueing trend which can be attributed to the brightening of the disc due to the outburst. Our spectroscopic monitoring shows a dramatic variation of the H$\alpha$ line as it transitioned from absorption feature to the emission feature and back. Such transition can possibly be explained by the variation in the wind structure in combination with accretion. Combining our time evolution spectra of the Ca II infra-red triplet lines with the previously published spectra of V2493 Cyg, we find that the accretion region has stabilised compared to the early days of the outburst. The evolution of the O I $\lambda$7773 \AA~ line also points towards the stabilization of the circumstellar disc post the second outburst.

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arXiv2023

Structural Analysis of Open Cluster Bochum 2

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 $3.8\pm0.4$ kpc. We have found that this cluster holds young ($\sim5$ Myr) and massive (O$7-$O$9$) stars as well as an older population of low mass stars. We found that the massive stars have 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 $-2.42\pm0.13$ in the mass range $\sim0.72<$M/M$_{\odot}<2.8$. The tidal radius of the Boc2 cluster ($\sim7-9$) is much more than its observed radius ($\sim1.1$ 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.

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arXiv2023

Photometric and Kinematic study of the open cluster NGC 1027

We present photometric and kinematic analysis 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 found about 2 arcmin away from the center reported earlier. Radius has been estimated to be about 8.00 arcmin(2.65pc). Using proper motion Gaia EDR3 data, membership probabilities has been derived for the stars in the region of cluster radius. We find mean proper motion of the cluster to be $\sim$(-0.84, 2.04) mas yr$^{-1}$ in (RA, DEC). We find 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 out of 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 cluster suggesting that mass segregation may be imprint of its dynamical relaxation.

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arXiv2023

Survey of H{\alpha} emission-line stars in the star-forming region IC 5070

Actively accreting young stellar objects show H$\alpha$ emission line in their spectra. We present the results of survey for H$\alpha$ emission-line stars in the star-forming region IC~5070 taken with 2-m Himalyan {\it Chandra} Telescope. Based on the H$\alpha$ slitless spectroscopy data, we identified 131 emission-line stars in $\sim$ 0.29 square degrees area of the IC~5070 region. Using Gaia Early Data Release 3, we estimated the mean proper motion and parallax of the emission-line stars. We also estimated the mean distance and reddening toward the region using the emission-line stars, that are $\sim$ 833 pc and $\sim$2 mag, respectively. By examining the locations of these stars in the color-magnitude diagrams constructed using Gaia and PanSTARRS1 data, we found that a majority of the H$\alpha$ emitters are young low-mass ($<$ 1.5 $M\odot$) stars. We also compared our catalog of emission-line stars with the available young stellar catalogs and found that most of them are Class~{II}/ flat spectrum sources with the spectral type ranging from K to M. Based on the proper motion/ parallax values and locations on the color-magnitude diagrams, about 20 emission-line stars are flagged as non-members. The relative proper motion of the emission-line stars with respect to the ionizing source suggest the possibility of the `rocket effect' scenario in the remnant cloud (BRC~31).

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arXiv2023

Teutsch 76: a Deep Near-Infrared Study

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 (DOT) along with the recently available high quality proper motion data from the {\it Gaia} data release 3 and deep photometric data from Pan-STARRS1 survey. We have found that the T76 cluster is having a central density concentration with circular morphology, probably due to the star formation processes. The radius of the T76 cluster is found to be 45$^{\prime}{^\prime}$ (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 $5.7\pm1.0$ kpc and is having an age of $50\pm10$ Myr. The mass function slope ($\Gamma$) in the cluster region in the mass range $\sim$0.75$<$M/M$_\odot$$<$5.8 is estimated as $-1.3\pm0.2$, which is similar to the value `-1.35' given by \citet{1955ApJ...121..161S}. The cluster is not showing any signatures of mass-segregation and is currently undergoing dynamical relaxation.

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arXiv2023

Photometric variable stars in the young open cluster NGC 6823

We present stellar variability towards the young open cluster NGC\,6823. Time series $V$- and $I$-band CCD photometry led to identification and characterization of 88 variable stars, of which only 14 have been previously recognized. We ascertain the membership of each variable with optical $UBVI$ and infrared photometry, and with Gaia EDR3 parallax and proper motion data. Seventy two variable stars are found to be cluster members, of which 25 are main sequence stars and 48 are pre-main-sequence stars. The probable cluster members collectively suggest an isochrone age of the cluster to be about 2~Myrs based on the GAIA photometry. With the color and magnitude, as well as the shape of the light curve, we have classified the main sequence variables into $\beta$~Cep, $\delta$~Scuti, slowly pulsating B type, and new class variables. Among the pre-main-sequence variables, eight are classical T Tauri variables, and four are Herbig Ae/Be objects, whereas the remaining belong to the weak-lined T Tauri population. The variable nature of 32 stars is validated with TESS light curves. Our work provides refined classification of variability of pre-main-sequence and main-sequence cluster members of the active star-forming complex, Sharpless\,86. Despite no strong evidence of the disk-locking mechanism in the present sample of TTSs, one TTS with larger $\Delta(I-K)$ is found to be slow rotator.

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