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Harmeen Kaur

Publications and source records attributed to Harmeen Kaur.

16 recordsLinked to original sources

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.

astro-ph.SR

Unraveling the Feedback-Regulated Star Formation Activities around the Expanding Galactic MIR Bubble [HKS2019] E71

We explore the physical environment of the Galactic mid-infrared (MIR) bubble [HKS2019] E71 (hereafter E71) through a multi-wavelength approach. E71 is located at the edge of a filamentary structure, as traced in Herschel images (250-500 $\mu$m), Herschel column density map, and molecular maps in the velocity range [-20,-14] km/s. It hosts a stellar cluster (radius~1.26 pc, distance~1.81+/-0.15 kpc) associated with radio continuum emission, including a centrally positioned B1.5-type massive star (hereafter 'm2'), along with an enhanced population of evolved low-mass stars and young stellar objects. MIR images and molecular line maps reveal a PDR surrounding 'm2', exhibiting an arc-like structure along the edges of E71. Regularly spaced molecular and dust condensations are identified along this structure. The position-velocity map of 12CO emission suggests an expansion of molecular gas concentrated at the periphery of E71. Near-infrared spectroscopic observations with TANSPEC confirm the presence of the accretion process in a massive young stellar object (MYSO) located near the edge of the bubble. High-resolution uGMRT radio continuum maps uncover substructures in the ionized emission, both toward the MYSO and the center of E71. These findings support that 'm2' has shaped an arc-like morphology through its feedback processes. The pressure exerted by 'm2' and the velocity structure of the 12/13CO(1-0) emission suggest that the stellar feedback has likely driven out molecular material, leading to the formation of the expanding E71 bubble. Our overall investigation infers that the "collect and collapse" process might be a possible mechanism that can describe the ongoing star formation activities around the E71 bubble.

astro-ph.GA

Long-term investigation of an open cluster Berkeley 65

We present a decade-long investigation of a poorly studied cluster, Berkeley 65 (Be 65), using deep optical data from the telescopes of ARIES, Nainital Observatory. We estimate its radius ($R_{cluster}$ = 1.6$^{'}$, aspect ratio of $\sim$1.1), distance (2.0 $\pm$ 0.1 kpc) and age ($\sim$160 Myrs). A clear turn-off point at $\sim$1.7 M$_\odot$ in the mass function suggests the escape of low-mass stars, and the lower photometric mass compared to the dynamical mass indicates ongoing disruption due to external forces. Our long-baseline optical photometric data also identifies 64 periodic and 16 non-periodic stars in this region. We have presented the light curves and the classification of those variables. The periodic stars have periods ranging from $\sim$0.05 days to $\sim$3.00 days and amplitude ranges from $\sim$8 mmag to $\sim$700 mmag. The nonperiodic stars show variation from $\sim$30 mmag to $\sim$500 mmag. The periodic stars include main-sequence pulsating variables such as Slow Pulsating B-type, $\delta$ Scuti, RR Lyrae, and $\gamma$ Doradus. We report a detached binary system and rotating variables similar to BY Draconis-type stars exhibiting variable brightness caused by starspots, chromospheric activity, and magnetic field-related phenomena.

astro-ph.SR

Investigating the Star-forming Sites in the Outer Galactic Arm

We aim to investigate the global star formation scenario in star-forming sites AFGL 5157, [FSR2007] 0807 (hereafter FSR0807), [HKS2019] E70 (hereafter E70), [KPS2012] MWSC 0620 (hereafter KPS0620), and IRAS 05331+3115 in the outer galactic arm. The distribution of young stellar objects in these sites coincides with a higher extinction and H2 column density, which agrees with the notion that star formation occurs inside the dense molecular cloud cores. We have found two molecular structures at different velocities in this direction; one contains AFGL 5157 and FSR0807, and the other contains E70, [KPS2012] MWSC 0620, and IRAS 05331+3115. All these clusters in our target region are in different evolutionary stages and might form stars through different mechanisms. The E70 cluster seems to be the oldest in our sample; AFGL 5157 and FSR0807 formed later, and KPS0620 and IRAS 05331+3115 are the youngest sites. AFGL 5157 and FSR0807 are physically connected and have cold filamentary structures and dense hub regions. Additionally, the near-infrared photometric analysis shows signatures of massive star formation in these sites. KPS0620 also seems to have cold filamentary structures with the central hub but lacks signatures of massive stars. Our analysis suggests molecular gas flow and the hub filamentary star formation scenario in these regions. IRAS 05331+3115 is a single clump of molecular gas favoring low-mass star formation. Our study suggests that the selected area is a menagerie of star-forming sites where the formation of the stars happens through different processes.

astro-ph.GA

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.

astro-ph.GA

Dissecting the morphology of star forming complex S193

We have studied a star-forming complex S193 using near-infrared (NIR) observations and other archival data covering optical to radio wavelengths. We identified stellar clusters in the complex using the NIR photometric data and estimated the membership and distance of the clusters. Using the mid-infrared (MIR) and far-infrared (FIR) images, the distribution of the dust emission around H\,{\sc ii} regions is traced in the complex. The $Herschel$ column density and temperature maps analysis reveal 16 cold dust clumps in the complex. The H$α$ image and 1.4 GHz radio continuum emission map are employed to study the ionised gas distribution and infer the spectral type and the dynamical age of each H\,{\sc ii} region/ionised clump in the complex. The $^{12}$CO(J =3$-$2) and $^{13}$CO(J =1$-$0) molecular line data hint at the presence of two velocity components around [-43,-46] and [-47,-50] km/s, and their spatial distribution reveals two overlapping zones toward the complex. By investigating the immediate surroundings of the central cluster [BDS2003]57 and the pressure calculations, we suggest that the feedback from the massive stars seems responsible for the observed velocity gradient and might have triggered the formation of the central cluster [BDS2003]57.}

astro-ph.GA

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.

astro-ph.GA

Investigating star formation activity in the Sh 2-61 H II region

Using the multiwavelength 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 also determined 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 12CO (J =3-2) JCMT data of S61, and a shell structure 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 the surrounding gas. The pressure at the interface is higher than in a typical cool molecular cloud.

astro-ph.GA

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 ($Γ$) 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.

astro-ph.SR

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 ($Γ$) 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.

astro-ph.SR

Spectroscopy of 9 eruptive young variables using TANSPEC

In recent times, 3.6m Devasthal Optical Telescope (DOT) has installed an optical to near infra-red spectrograph, TANSPEC, which provides spectral coverage from 0.55-2.5 microns. Using TANSPEC, we have obtained a single epoch spectrum of a set 9 FUors and EXors. We have analysed line profiles of the sources and compared 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 for time evolved spectroscopic studies for better understanding the evolution of the accretion mechanisms. This in turn can help in better categorisation of the young stars displaying episodic accretion behaviour.

astro-ph.SR

Kronberger 55: A Candidate for End-dominated Collapse Scenario

Using optical photometric observations from 1.3m Devasthal Fast Optical Telescope and deep near-infrared (NIR) photometric observations from TANSPEC mounted on 3.6m Devasthal 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 ~3.5 kpc, E(B-V)~1.0 mag and $\lesssim$55 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. The association 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 strcuture in this region, and such configuration is also evident in the 12CO(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'.

astro-ph.GA

TANSPEC: TIFR-ARIES Near Infrared Spectrometer

We present the design and performance of the TANSPEC, a medium-resolution $0.55-2.5~μ$m cryogenic spectrometer and imager, now in operation at the 3.6-m Devasthal Optical Telescope (DOT), Nainital, India. The TANSPEC provides three modes of operation which include, photometry with broad- and narrow-band filters, spectroscopy with short slits of 20$^{\prime \prime}$ length and different widths (from 0.5$^{\prime \prime}$ to 4.0$^{\prime \prime}$) in cross-dispersed mode at a resolving power R of $\sim$2750, and spectroscopy with long slits of 60$^{\prime \prime}$ length and different widths (from 0.5$^{\prime \prime}$ to 4.0$^{\prime \prime}$) in prism mode at a resolving power R of $\sim$100-350. TANSPEC's imager mode provides a field of view of 60$^{\prime \prime} \times 60^{\prime \prime}$ with a plate scale of 0.245$^{\prime \prime}$/pixel on the 3.6-m DOT. The TANSPEC was successfully commissioned during April-May 2019 and the subsequent characterization and astronomical observations are presented here. The TANSPEC has been made available to the worldwide astronomical community for science observations from October 2020.

astro-ph.IM

Unveiling the physical conditions in NGC 6910

Deep and wide-field optical photometric observations along with multiwavelength archival datasets have been employed to study the physical properties of the cluster NGC 6910. The study also examines the impact of massive stars to their environment. The age, distance and reddening of the cluster are estimated to be $\sim$4.5 Myr, $1.72\pm0.08$ kpc, and $ E(B-V)_{min}= 0.95$ mag, respectively. The mass function slope ($Γ= -0.74\pm0.15$ in the cluster region is found to be flatter than the Salpeter value (-1.35), indicating the presence of excess number of massive stars. The cluster also shows mass segregation towards the central region due to their formation processes. The distribution of warm dust emission is investigated towards the central region of the cluster, showing the signature of the impact of massive stars within the cluster region. Radio continuum clumps powered by massive B-type stars (age range $\sim$ 0.07-0.12 Myr) are traced, which are located away from the center of the stellar cluster NGC 6910 (age $\sim$ 4.5 Myr). Based on the values of different pressure components exerted by massive stars, the photoionized gas associated with the cluster is found to be the dominant feedback mechanism in the cluster. Overall, the massive stars in the cluster might have triggered the birth of young massive B-type stars in the cluster. This argument is supported with evidence of the observed age gradient between the cluster and the powering sources of the radio clumps.

astro-ph.SR

A Search for variable stars in the four open star clusters

We present a CCD photometric survey for the search of variable stars in four open clusters namely Berkeley 69, King 5, King 7, and Berkeley 20. The time series observations were carried out for 1 and/or 2 nights for each of the clusters in the year 1998, which have led to identify nineteen variable stars in these clusters. Out of these 19 variable stars, five stars show delta Scuti like variability and two stars show W UMa type variability. In other stars, we could not find the periods and hence the type of variability due to the lack of sufficient data. The periods of delta Scuti type stars are found to be in the range of 0.13 to 0.21 days, whereas the two stars in the cluster Berkeley 20, which showed W UMa type variability have orbital periods of 0.396 and 0.418 days, respectively. Using the Gaia data, the basic parameters of the clusters Berkeley 69, King 7 and King 5 are also revised. The age and reddening are estimated to be 0.79 \pm 0.09 Gyr and 0.68 \pm 0.03 mag for Berkeley 69, 0.79 \pm 0.09 Gyr and 1.22 \pm 0.03mag for the cluster King 7 and 1.59 \pm 0.19 Gyr and 0.63 \pm 0.02 mag for the cluster King 5, respectively. Signature of mass segregation is found in the clusters King 7 and King 5.

astro-ph.SR

Study of open cluster King 13 using CCD VI, 2MASS and Gaia DR2 Astrometry

In this paper, we present astrophysical parameters of the open cluster King 13 based on the VI CCD and 2MASS JHKs photometric data. This is a poorly studied cluster, for which new results have been found in the present work. To identify probable members, we use proper motion data from Gaia DR2 catalogue. The mean proper motion of the cluster is determined as -2.8 \pm 0.2 and -0.88 \pm 0.14 mas yr{-1} and cluster extent is derived as 3'.2. Using color-magnitude diagrams, we estimate the age and distance of the cluster as 510 \pm 60 Myr and 3.84 \pm 0.15 kpc respectively. Interstellar reddening E(B-V) in the direction of the cluster is determined as 0.80 \pm 0.2 mag using color-color diagram. Mass function slope of the cluster is found to be comparable with the Salpeter value. The total mass of this cluster is derived as 270 M_{\odot}. The present analysis shows that King 13 is a dynamically relaxed cluster.

astro-ph.GA