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Large language models (LLMs) encode vast amounts of world knowledge acquired via training on large web-scale datasets crawled from the internet. However, these datasets typically exhibit a geographical bias towards English-speaking Western countries. This results in LLMs producing biased or hallucinated responses to queries that require answers localized to other geographical regions. In this work, we introduce a new benchmark named LoFTI (Localization and Factuality Transfer to Indian Locales) that can be used to evaluate an LLM's localization and factual text transfer capabilities. LoFTI consists of factual statements about entities in source and target locations; the source locations are spread across the globe and the target locations are all within India with varying degrees of hyperlocality (country, states, cities). The entities span a wide variety of categories. We use LoFTI to evaluate Mixtral, GPT-4 and two other Mixtral-based approaches well-suited to the task of localized factual transfer. We demonstrate that LoFTI is a high-quality evaluation benchmark and all the models, including GPT-4, produce skewed results across varying levels of hyperlocality., Comment: 21 pages

We studied the influence of a massive star on a mid-infrared bubble and its surrounding gas in the IRAS\,16489-4431 star-forming region using multi-wavelength data. The {\it Spitzer} mid-infrared band images revealed the shocked nature of the bubble. Analyses showed that the bubble is developed by a massive star owing to its strong radiation pressure. Evidence of collected material along the edge of the bubble was noted by the cold gas tracer line observed using Atacama Millimeter/submillimeter Array (ALMA). The presence of dense dust cores with bi-polar outflows and young stellar objects toward the collected material is suggestive of active star formation possibly influenced by the expansion of the radiation driven bubble., Comment: 12 pages, 6 figures, accepted for publication in Bulletin de la Soci\'et\'e Royale des Sciences de Li\`ege (BSRSL)

We uncover a hub-filament system associated with massive star formation in the G083.097$+$03.270. Diagnosed with simultaneous $^{12}$CO, $^{13}$CO, and C$^{18}$O line observations, the region is found to host two distinct and elongated filaments having separate velocity components, interacting spatially and kinematically, that appear to have seeded the formation of a dense hub at the intersection. A large velocity spread at the hub in addition to clear bridging feature connecting the filaments in velocity are indicating merging of filaments. Along the filaments axis, the velocity gradient reveals a global gas motion with an increasing velocity dispersion inward to the hub signifying turbulence. Altogether, the clustering of Class I sources, a high excitation temperature, a high column density, and presence of a massive outflow at the central hub suggest enhanced star formation. We propose that merging of large-scale filaments and velocity gradients along filaments are the driving factors in the mass accumulation process at the hub that have sequentially led to the massive star formation. With two giant filaments merging to coincide with a hub therein with ongoing star formation, this site serves as a benchmark for the `filaments to clusters' star-forming paradigm., Comment: 12 pages, 7 figures, 1 table, accepted for publication in ApJ

We present a comprehensive analysis of a Transiting Exoplanet Survey Satellite (TESS) high-quality light curve for a young brown dwarf, MHO~4 having spectral type M7.0, in the Taurus star-forming region. We investigate the rotation periods and characterize the BD's dynamic atmosphere and surface features. We present light curve analysis of MHO~4, and estimate the rotation period to be around 2.224~d. Remarkably, MHO~4 exhibits two significant flaring events. Furthermore, we also estimated bolometric flare energies to be within the energy range of $10^{34}$ to $10^{35}$ erg, which sits in the superflare category., Comment: 10 pages, 5 figures

Real extreme/intermediate mass ratio inspiral(E/IMRI) systems are likely to contain large accretion disks which could be as massive as the central supermassive black hole. Therefore, contrary to its ideal model, a real E/IMRI system contains a third important component: the accretion disk. We study the influence of these disks on the emitted GW profile and its detectability through proposed LISA observation. We use a semi-relativistic formalism in the Kerr background (Gair & Glampedakis 2006; Barausse & Rezzolla 2008) for the case of transonic accretion flow which is a potential candidate to describe the accretion flows around AGN. The hydrodynamic drag of the disks modified the motion of the companion as a result the emitted wave changes in amplitude and phase. We found that these changes are detectable through the last few years of observation by LISA (in some cases as small as six months) for EMRIs residing within 3 GPc from the detector and for the accretion rate of the primary black hole of the order of $\dot{M}=1 \dot{M}_{Edd}$. These choices of parameter values are consistent with real systems. The drag effect and hence the detectability of the emitted GW is sensitive to the hydrodynamical model of the disk. Therefore such observations will help one to identify the nature of the accretion flow and verify various paradigms of accretion physics., Comment: 17 pages, 17 figures

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., Comment: 19 pages, 19 figures, accepted for publication in MNRAS

We present the star formation activity around the emission nebula Sh2-112. At a distance of $\sim2.1$~kpc, this \ion{H}{2} complex, itself 3~pc in radius, is illuminated by the massive star (O8\,V) BD$+$45\,3216. The associated molecular cloud extends in angular scales of $2\fdg0\times0\fdg83$, corresponding to linear sizes of 73~pc by 30~pc, along the Galactic longitude. The high-resolution ($30\arcsec$) extinction map reveals a chain of dust clumps aligned with the filament-like structure with an average extinction of $A_{V} \sim 2.78$~mag, varying up to a maximum of $\sim17$~mag. Our analysis led to identification of a rich population ($\sim 500$) of young (average age of $\sim 1$~Myr) stars, plus a numerous number ($\sim 350$) of H$\alpha$ emitters, spatially correlated with the filamentary clouds. Located near the edge of the cloud, the luminous star BD$+$45\,3216 has created an arc-like pattern as the ionizing radiation encounters the dense gas, forming a blister-shaped morphology. We found three distinct young stellar groups, all coincident with relatively dense parts of the cloud complex, signifying ongoing star formation. Moreover, the cloud filament (excitation temperature $\sim 10$~K) traced by the CO isotopologues and extending nearly $\sim 80$~pc is devoid of ionized gas except at the dense cores (excitation temperature $\sim$ 28--32~K) wherein significant ionized emission excited by OB stars (dynamical age $\sim$ 0.18--1.0~Myr) pertains. The radial velocity is dynamic (median $\sim -3.65$~km~s$^{-1}$) along the main filament, increasing from Galactic east to west, features mass flow to form the massive stars/clusters at the central hubs., Comment: 29 pages, 16 figures, 5 tables, accepted for publication in ApJ

In this paper, we have defined bicomplex valued functions of bounded variations and rectifiable hyperbolic path. We have studied the integration of product-type bicomplex functions over rectifiable hyperbolic path. Also we have established bicomplex analogue of the Fundamental Theorem of Calculus for line integral.

Contrary to orthogonal multiple-access (OMA), non-orthogonal multiple-access (NOMA) schemes can serve a pool of users without exploiting the scarce frequency or time domain resources. This is useful in meeting the sixth generation (6G) network requirements, such as, low latency, massive connectivity, users fairness, and high spectral efficiency. On the other hand, content caching restricts duplicate data transmission by storing popular contents in advance at the network edge which reduces 6G data traffic. In this survey, we focus on cache-aided NOMA-based wireless networks which can reap the benefits of both cache and NOMA; switching to NOMA from OMA enables cache-aided networks to push additional files to content servers in parallel and improve the cache hit probability. Beginning with fundamentals of cache-aided NOMA technology, we summarize the performance goals of cache-aided NOMA systems, present the associated design challenges, and categorize related recent literature based on their application verticals. Concomitant standardization activities and open research challenges are highlighted as well.

LDN 1615/1616 and CB 28 (hereafter, L1616) together form a cometary globule located at an angular distance of about 8 degrees west of the Orion OB1 association, aligned roughly along the east-west direction, and showing a distinct head-tail structure. The presence of massive stars in the Orion belt has been considered to be responsible for the radiation driven implosion mode of star formation in L1616. Based on the latest Gaia EDR3 measurements of the previously known young stellar objects (YSOs) associated with L1616, we find the distance to this cloud of 384$\pm$5 pc. We present optical polarimetry towards L1616 that maps the plane-of-sky component of the ambient magnetic field (B$_{POS}$) geometry. Based on the proper motion of the YSOs associated with L1616, we investigate their plane-of-sky motion relative to the exciting star $\epsilon$ Ori. Using the Gaia EDR3 measurements of the distances and proper motions of the YSOs, we find two additional sources comoving with the known YSOs. One comoving source is HD33056, a B9 star and the other might be a young pre-main sequence star not reported in previous studies. The mean direction of B$_{POS}$ is found to follow the cloud structure. This could be the effect of dragging of the magnetic field lines by the impact of the ionizing radiation from $\epsilon$ Ori. Based on the pressure exerted on L1616, and the ages of the associated YSOs, we show that it could possibly be the main source of ionization in L1616, and thus the star formation in it.

We study the characteristics of planetary nebulae (PNe), MaC 2-1 and Sp 4-1. We use our optical spectra taken at 2 m Himalayan Chandra Telescope, Spitzer mid-infrared (mid-IR) spectra, HST images, and IR photometric data. These PNe have not been individually studied in details earlier. Both the PNe are in the low- to moderate-excitation class. MaC 2-1 shows the presence of silicon carbide (SiC) and magnesium sulphide (MgS) dust. Sp 4-1 hosts polycyclic aromatic hydrocarbon (PAH) molecules. We obtain plasma properties of the PNe from the optical and mid-IR emission line fluxes. We compute photoionization models of the PNe for self-consistent estimation of physical parameters associated with the central star and the nebula, including nebular abundances. From the modelling of the IR data, we obtain the characteristics of dust and molecules formed in the nebulae. From our study, we estimate that the progenitors of MaC 2-1 and Sp 4-1 had masses of 1.2 and 1.55 $M_{\sun}$, respectively, and both of them seem to have born in metal poor environment. Both are distant PNe, with the estimated distances of 16 and 18 kpc for MaC 2-1 and Sp 4-1, respectively., Comment: 15 pages, 13 figures, 9 tables

We perform photoionization modeling of the dusty nova V1280 Scorpii (V1280 Sco) with an aim to study the changes in the physical and chemical parameters. We model pre and post dust phase, optical and near-Infrared (NIR), spectra using the photoionization code \textsc{cloudy}, v.17.02, considering a two-component (low density and high density region) model. From the best-fit model, we find that the temperature and luminosity of the central ionizing source in the pre-dust phase are in the range 1.32 - 1.50 $\times 10^4$ K and 2.95 - 3.16 $\times 10^{36}$ ergs$^{-1}$, respectively, which increase to 1.58 - 1.62 $\times 10^4$ K and 3.23 - 3.31 $\times 10^{36}$ ergs$^{-1}$, respectively, in the post-dust phase. It is found that a very high hydrogen density ($\sim 10^{13} - 10^{14}$ cm$^{-3}$) is required for the generation of spectra properly. Dust condensation conditions are achieved at high ejecta density ($\sim 3.16 \times 10^{8}$cm$^{-3}$) and low temperature ($\sim$2000 K) in the outer region of the ejecta. It is found that a mixture of small (0.005 - 0.25$\mu$m) amorphous carbon dust grains and large (0.03 - 3.0$\mu$m) astrophysical silicate dust grains iis present n the ejecta in the post-dust phase. Our model yields very high elemental abundance values as C/H = 13.5 - 20, N/H = 250, O/H = 27 - 35, by number, relative to solar in the ejecta, during the pre-dust phase, which decrease in the post-dust phase., Comment: Accepted on 02 November 2021, for publication in The Astrophysical Journal (ApJ)

In this paper we introduce topological modules over the ring of bihyperbolic numbers. We discuss bihyperbolic convexity, bihyperbolic-valued seminorms and bihyperbolic-valued Minkowski functionals in topological bihyperbolic modules. Finally we introduce locally bihyperbolic convex modules., Comment: arXiv admin note: text overlap with arXiv:1507.05816 by other authors

In this paper our main aim is to develop some basic properties of hyperbolic valued metric spaces. We also establish the hyperbolic version of Banach contraction principle. Further we construct a hyperbolic valued metric on the space of all hyperbolic valued continuous functions and prove some results.

We estimate effective temperature ($T_{\rm eff}$), stellar radius, and luminosity for a sample of 271 M-dwarf stars (M0V-M7V) observed as a part of CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) radial-velocity planet survey. For the first time, using the simultaneously observed high resolution (R$\sim90000$) spectra in the optical (0.52 - 0.96 $\mu$m) and near-infrared (0.96 - 1.71 $\mu$m) bands, we derive empirical calibration relationships to estimate the fundamental parameters of these low-mass stars. We select a sample of nearby and bright M-dwarfs as our calibrators for which the physical parameters are acquired from high-precision interferometric measurements. To identify the most suitable indicators of $T_{\rm eff}$, radius, and luminosity (log $L/L_{\odot}$), we inspect a range of spectral features and assess them for reliable correlations. We perform multivariate linear regression and find that the combination of pseudo equivalent widths and equivalent width ratios of the Ca II at 0.854 $\mu$m and Ca II at 0.866 $\mu$m lines in the optical and the Mg I line at 1.57 $\mu$m in the NIR give the best fitting linear functional relations for the stellar parameters with root mean square errors (RMSE) of 99K, 0.06 $R_{\odot}$ and 0.22 dex respectively. We also explore and compare our results with literature values obtained using other different methods for the same sample of M dwarfs., Comment: 12 pages, 7 figures and 7 tables; accepted on July 24, 2021 for publication in MNRAS

In this article we have studied bicomplex valued measurable functions on an arbitrary measurable space. We have established the bicomplex version of Lebesgue's dominated convergence theorem and some other results related to this theorem. Also we have proved the bicomplex version of Lebesgue-Radon-Nikodym theorem. Finally we have introduced the idea of hyperbolic version of invariant measure.

We present the time-dependent properties of a poorly known OH/IR star $-$ IRAS 18278+0931 (hereafter, IRAS 18+09) towards the Ophiuchus constellation. We have carried out long-term optical/near-infrared (NIR) photometric and spectroscopic observations to study the object. From optical $R$- and $I$-band light curves, the period of IRAS 18+09 is estimated to be 575 $\pm$ 30 days and the variability amplitudes range from $\Delta$R $\sim$ 4.0 mag to $\Delta$I $\sim$ 3.5 mag. From the standard Period-Luminosity (PL) relations, the distance ($D$) to the object, 4.0 $\pm$ 1.3 kpc, is estimated. Applying this distance in the radiative transfer model, the spectral energy distribution (SED) are constructed from multi-wavelength photometric and IRAS-LRS spectral data which provides the luminosity, optical depth, and gas mass-loss rate (MLR) of the object to be 9600 $\pm$ 500 $L_{\odot}$, 9.1 $\pm$ 0.6 at 0.55 $\mu$m and 1.0$\times$10$^{-6}$ M$_\odot$ yr$^{-1}$, respectively. The current mass of the object infers in the range 1.0 $-$ 1.5 $M_\odot$ assuming solar metallicity. Notably, the temporal variation of atomic and molecular features (e.g., TiO, Na I, Ca I, CO, H$_2$O) over the pulsation cycle of the OH/IR star illustrates the sensitivity of the spectral features to the dynamical atmosphere as observed in pulsating AGB stars., Comment: 14 pages, 7 figures, 5 tables. Accepted for publication in AJ

We present comprehensive characterization of the Galactic open cluster M 36. Some two hundred member candidates, with an estimated contamination rate of $\sim$8%, have been identified on the basis of proper motion and parallax measured by the $Gaia$ DR2. The cluster has a proper motion grouping around ($\mu_{\alpha} \cos\delta = -$0.15 $\pm$ 0.01 mas yr$^{-1}$, and $\mu_{\delta} = -$3.35 $\pm$ 0.02 mas yr$^{-1}$), distinctly separated from the field population. Most member candidates have parallax values 0.7$-$0.9 mas, with a median value of 0.82 $\pm$ 0.07 mas (distance $\sim$1.20 $\pm$ 0.13 kpc). The angular diameter of 27$'$ $\pm$ $0\farcm4$ determined from the radial density profile then corresponds to a linear extent of 9.42 $\pm$ 0.14 pc. With an estimated age of $\sim$15 Myr, M 36 is free of nebulosity. To the south-west of the cluster, we discover a highly obscured ($A_{V}$ up to $\sim$23 mag), compact ($\sim$ $1\farcm9 \times 1\farcm2$) dense cloud, within which three young stellar objects in their infancy (ages $\lesssim$ 0.2 Myr) are identified. The molecular gas, 3.6 pc in extent, contains a total mass of (2$-$3)$\times$10$^{2}$ M$_{\odot}$, and has a uniform velocity continuity across the cloud, with a velocity range of $-$20 to $-$22 km s$^{-1}$, consistent with the radial velocities of known star members. In addition, the cloud has a derived kinematic distance marginally in agreement with that of the star cluster. If physical association between M 36 and the young stellar population can be unambiguously established, this manifests a convincing example of prolonged star formation activity spanning up to tens of Myrs in molecular clouds., Comment: 24 pages, 14 figures, 4 tables

We present here optical I-band photometric variability study down to $\simeq$ 19 mag of a young ($\sim$2-3 Myr) star-forming region IC 348 in the Perseus molecular cloud. We aim to explore the fast rotation (in the time-scales of hours) in Very Low Mass stars (VLMs) including Brown Dwarfs (BDs). From a sample of 177 light-curves using our new I-band observations, we detect new photometric variability in 22 young M-dwarfs including 6 BDs, which are bonafide members in IC 348 and well-characterized in the spectral type of M-dwarfs. Out of 22 variables, 11 M dwarfs including one BD show hour-scale periodic variability in the period range 3.5 - 11 hours and rest are aperiodic in nature. Interestingly, an optical flare is detected in a young M2.75 dwarf in one night data on 20 December 2016. From the flare light curve, we estimate the emitted flared energy of 1.48 $\times$ 10$^{35}$ ergs. The observed flared energy with an uncertainty of tens of per cent is close to the super-flare range ($\sim$ 10$^{34}$ ergs), which is rarely observed in active M dwarfs., Comment: 12 pages, 5 figures

X-shaped radio galaxies are a subclass of radio sources that exhibit a pair of secondary low surface brightness radio lobes oriented at an angle to the primary high surface brightness lobes. Sometimes, the secondary low brightened lobes emerge from the edges of the primary high brightened lobes and form a Z-symmetric morphology. We present a systematical search result for X-shaped radio galaxies (XRGs) and Z-shaped radio galaxies (ZRGs) from the VLA Faint Images of the Radio Sky at Twenty-Centimeters (VLA FIRST) Survey at 1.4 GHz. Our search yields a total of 296 number of radio sources, out of which 161 are XRGs and 135 are ZRGs. We have also made optical identification of these sources from the different available literature. J1124+4325 and J1319+0502 are the farthest known XRG and ZRG, respectively. We have estimated spectral index and radio luminosity of these radio sources and made a comparative study with previously detected XRGs and ZRGs. The average value of luminosities for XRGs is higher than that of ZRGs. With the help of a large sample size of the newly discovered XRGs and ZRGs, various statistical properties of these sources are studied. Out of 161 XRGs presented in the current paper, 70% (113) are FR II radio galaxies and 13% (20) are FR I radio galaxies. For 28 XRGs, the morphology is complex and could not be classified. For XRGs, the statistical studies are done on the angle between the major axis and minor axis and the relative size of the major and minor axes. For the ZRGs a statistical study is done on the angular size., Comment: Published in ApJSS

We present results of study, using observed and published spectra in optical region, of few novae (T CrB, GK Per, RS Oph, V3890 Sgr and V745 Sco) in their quiescence phase and a symbiotic star (BX Mon). Observations were made using the facilities available at 2m Himalayan Chandra Telescope (HCT). Generally, the spectra show prominent low ionization emission features of hydrogen, helium, iron and oxygen and TiO absorption features due to the cool secondary component; T CrB and GK Per show higher ionization lines. We used photoionization code CLOUDY to model these spectra. From the best-fit models, we have estimated the physical parameters, e.g., temperature, luminosity & hydrogen density; estimated elemental abundances and other parameters related to the system. By matching the spectra of various giants with the absorption features and from the best-fit, we determined the type of secondaries and also their contribution to the spectra.

We present results of our study of two planetary nebulae (PNe), PB1 and PC 19. We use the optical spectra of these two PNe observed at 2 m Himalayan Chandra Telescope and also archival and literature data for the study. We use the morphokinematic code SHAPE to construct 3D morphologies of the PNe and the photoionization code CLOUDY to model the observed spectra. The 3D model of PB 1 consists of an elongated shell surrounded by a bipolar halo and that of PC 19 consists of an open lobed bipolar structure and a spiral filamentary pair. We analyze the ionization structure of the PNe by deriving several plasma parameters and by photoionization modelling. We estimate the elemental abundances of the the elements, He, C, N, O, Ne, S, Ar, and Cl, from our analysis. We find He, C and N abundances to be significantly higher in case of PB 1. We estimate different physical parameters of the central stars, namely effective temperature, luminosity and gravity, and of the nebula, namely hydrogen density profiles, radii, etc., from photoionization modelling. We estimate distances to the PNe as $\sim$4.3 kpc for PB 1 and as $\sim$5.6 kpc for PC 19 by fitting the photoionization models to absolute observed fluxes. Progenitor masses are estimated from theoretical evolutionary trajectories and are found to be $\sim$1.67 and $\sim$2.38 $M_{\odot}$ for PB 1 and PC 19, respectively., Comment: 20 pages, 14 figures, 9 tables

We present here identification and characterization of the young stellar population associated with an active star-forming site Sh2-242. We used our own new optical imaging and spectroscopic observational data, as well as several archival catalogs, e.g., Pan-STARRS 1, $Gaia$ DR2, IPHAS, WIRCam, 2MASS, and $Spitzer$. Slit spectroscopic results confirm the classification of the main ionizing source BD+26 980 as an early-type star of spectral type B0.5 V. The spectrophotometric distance of the star is estimated as 2.08 $\pm$ 0.24 kpc, which confirms the source as a member of the cluster. An extinction map covering a large area (diameter $\sim$ 50') is generated with $H$ and $K$ photometry toward the region. From the map, three distinct locations of peak extinction complexes ($A_{V}$ $\simeq$ 7$-$17 mag) are identified for the very first time. Using the infrared color excess, a total of 33 Class I and 137 Class II young objects are classified within the region. The IPHAS photometry reveals classification of 36 H$\alpha$ emitting sources, which might be class II objects. Among 36 H$\alpha$ emitting sources, 5 are already identified using infrared excess emission. In total, 201 young objects are classified toward S242 from this study. The membership status of the young sources is further windowed with the inclusion of parallax from the $Gaia$ DR2 catalog. Using the optical and infrared color-magnitude diagrams, the young stellar objects are characterized with an average age of $\sim$ 1 Myr and the masses in the range 0.1$-$3.0 $M_\odot$. The census of the stellar content within the region is discussed using combined photometric and spectroscopic data., Comment: 17 pages, 12 figures, Published in the Astronomical Journal

We present here medium resolution (\lambda /\Delta\lambda\sim1200) H- and K-band spectra of M type dwarf stars covering the wavelength range 1.50 - 1.80 {\mu}m and 1.95 - 2.45 {\mu}m. The sample includes 53 dwarf stars (M0V-M7V) from new observations using the TIFR Near-Infrared Spectrometer and Imager (TIRSPEC) instrument on the 2-m Himalayan Chandra Telescope (HCT). Using interferometrically-measured effective temperature (T_{eff}), radius and luminosity of nearby bright calibrator stars, we have created new empirical relationships among those fundamental parameters and spectral indices. The equivalent widths of H-band spectral features like Mg (1.57 {\mu}m), Al (1.67 {\mu}m) and Mg (1.71 {\mu}m), and the H_{2}O-H index are found to be good indicators of T_{eff}, radius and luminosity and we establish the linear functions using these features relating to those stellar parameters. The root mean squared error (RMSE) of our best fits are 102K, 0.027R_{\sun} and 0.12dex respectively. Using spectral type standards along with known parallaxes, we calibrate both H and K-band H_{2}O indices as a tracer of spectral type and absolute K_{s} magnitude. Metallicities of M-dwarf samples are estimated using the K-band calibration relationships. The mass of M-dwarfs could be determined using the luminosity (L/L_{\sun}) and we establish a new empirical relation for this. We also compare and contrast our results with other similar work from the literature., Comment: 19 pages, 12 figures, accepted on February 08, 2020 for publication in Monthly Notices of the Royal Astronomical Society (MNRAS)

We present optical $I$-band light curves of the stars towards a star-forming region Cygnus OB7 from 17 nights photometric observations. The light curves are generated from a total of 381 image frames with very good photometric precision. From the light curves of 1900 stars and their periodogram analyses, we detect 31 candidate variables including five previously identified. 14 out of 31 objects are periodic and exhibit the rotation rates in the range of 0.15 to 11.60 days. We characterize those candidate variables using optical/infrared colour-colour and colour-magnitude diagrams. From spectral indices of the candidate variables, it turns out that four are probably Classical T-Tauri stars (CTTSs), rest remain unclassified from present data, they are possibly field stars or diskless pre-main sequence stars towards the region. Based on their location on the various colour-magnitude diagrams, the ages of two T Tauri Stars were estimated to be $\sim$ 5 Myr. The light curves indicate at least five of the periodic variables are eclipsing systems. The spatial distribution of young variable candidates on Planck 857 GHz (350 $\mu$m) and 2MASS $K_s$ images suggest that at least two of the CTTSs are part of the active star-forming cloud Lynds 1003., Comment: 14 pages, 12 figures

We present here new medium resolution spectra ($\lambda/\Delta\lambda$ $\sim$ 1200) of K$-$M giants covering wavelength range 1.50$-$1.80 and 1.95$-$2.45 $\mu$m. The sample includes 72 K0$-$M8 giants from our TIRSPEC observations and all available 35 giants in that spectral range from archival IRTF spectral library. We have calibrated here the empirical relations between fundamental parameters (e.g., effective temperature, surface gravity) and equivalent widths of some important spectral features like Si I, Na I, Ca I, $^{12}$CO. We find that the $^{12}$CO first overtone band at 2.29 $\mu$m and second overtone band at 1.62 $\mu$m are a reasonably good indicator of temperature above 3400 K and surface gravity. We show that the dispersion of empirical relations between $^{12}$CO and $T_{eff}$ significantly improve considering the effect of surface gravity., Comment: 17 pages, 10 figures, Accepted for publication in MNRAS

We present here a method to estimate physical parameters of novae systems using an extensive grid of photoionization models for novae. We use the photoionization code CLOUDY to construct grid of models covering a wide range of different parameters, e.g. total hydrogen density ($n_H$), source temperature ($T_{BB}$) and luminosity ($L$), inner radius ($R_{in}$) and thickness of ejecta ($\Delta R$), keeping other elements at solar metallicity. In this way, a total of 1792 models have been generated. From the model generated spectra which cover a wide wavelength region from ultra-violet to infrared, we calculate ratios of hydrogen and helium emission lines fluxes which are generally strong in novae spectra. We show that physical parameters associated with novae system could be estimated by comparing these line ratios with those obtained from observed spectra. We elaborate the idea with examples and estimate the parameter values in case of few other novae. The results of the grid model are available online., Comment: Accepted for publication in MNRAS. 10 pages, 10 figures

The {\it Planck} Galactic Cold Clumps (PGCCs) are the possible representations of the initial conditions and the very early stages of star formation. With an objective to understand better the star and star cluster formation, we probe the molecular cloud associated with PGCC G108.37-01.06 (hereafter, PG108.3), which can be traced in a velocity range $-$57 to $-$51 km s$^{-1}$. The IPHAS images reveal H$\alpha$ emission at various locations around PG108.3, and optical spectroscopy of the bright sources in those zones of H$\alpha$ emission disclose two massive ionizing sources with spectral type O8-O9V and B1V. Using the radio continuum, we estimate ionizing gas parameters and find the dynamical ages of \hii regions associated with the massive stars in the range 0.5$-$0.75 Myr. Based on the stellar surface density map constructed from the deep near-infrared CHFT observations, we find two prominent star clusters in PG108.3; of which, the cluster associated with \hii region S148 is moderately massive ($\sim$ 240 M$\sun$). A careful inspection of JCMT $^{13}$CO(3$-$2) molecular data exhibits that the massive cluster is associated with a number of filamentary structures. Several embedded young stellar objects (YSOs) are also identified in the PG108.3 along the length and junction of filaments. We find the evidence of velocity gradient along the length of the filaments. Along with kinematics of the filaments and the distribution of ionized, molecular gas and YSOs, we suggest that the cluster formation is most likely due to the longitudinal collapse of the most massive filament in PG108.3., Comment: 22 pages, 17 figures, Accepted for publication in Astrophysical Journal

We present here the recent results on two distant Galactic H II regions, namely NGC~2282 and Sh2-149, obtained with multiwavelength observations. Our optical spectroscopic analysis of the bright sources have been used to identify the massive members, and to derive the fundamental parameters such as age and distance of these regions. Using IR colour-colour criteria and H$_\alpha$-emission properties, we have identified and classified the candidate young stellar objects (YSOs) in these regions. The $^{12}$CO(1-0) continuum maps along with the {\it K}-band extinction maps, and spatial distribution of YSOs are used to investigate the structure and morphology of the molecular cloud associated with these H II regions. Overall analysis of these regions suggests that the star formation occurs at the locations of the denser gas, and we also find possible evidence of the induced star formation due to the feedback from massive stars to its surrounding molecular medium., Comment: 4 pages, 2 figures

We describe the time-dependent properties of a new spectroscopically confirmed Mira variable, which was discovered in 2013 as MASTER-Net Optical Transient (OT) J212444.87+321738.3 towards the Cygnus constellation. We have performed long-term optical/near-infrared (NIR) photometric and spectroscopic observations to characterize the object. From the optical/NIR light curves, we estimate a variability period of 465 $\pm$ 30 days. The wavelength-dependent amplitudes of the observed light-curves range from $\Delta$I$\sim$4 mag to $\Delta$K$\sim$1.5 mag. The (J-K) color-index varies from 1.78 to 2.62 mag over phases. Interestingly, a phase lag of $\sim$60 days between optical and NIR light curves is also seen, as in other Miras. Our optical/NIR spectra show molecular features of TiO, VO, CO, and strong water bands which are a typical signature of oxygen-rich Mira. We rule out S- or C-type as ZrO bands at 1.03 and 1.06 $\mu$m and $C_2$ band at 1.77 $\mu$m are absent. We estimate the effective temperature of the object from the SED, and distance and luminosity from standard Period-Luminosity relations. The optical/NIR spectra display time-dependent atomic and molecular features (e.g. TiO, NaI, CaI, H$_2$O,CO), as commonly observed in Miras. Such spectroscopic observations are useful for studying pulsation variability in Miras., Comment: 17 pages, 6 figures, accepted for publication in The Astronomical Journal

We report here CCD $I$-band time-series photometry of a young (2$-$5 Myr) cluster NGC 2282 to identify and understand the variability of pre-main-sequence (PMS) stars. The $I$-band photometry, down to $\sim$ 20.5 mag, enables us to probe the variability towards the lower mass end ($\sim$ 0.1 M$_\odot$) of the PMS stars. From the light curves of 1627 stars, we identified 62 new photometric variable candidates. Their association with the region was established from H$\alpha$ emission and infrared (IR) excess. Among 62 variables, 30 young variables exhibit H$\alpha$ emission, near-IR (NIR)/mid-IR (MIR) excess or both, and they are candidate members of the cluster. Out of 62 variables, 41 are periodic variables with the rotation rate ranging from 0.2 to 7 days. The period distribution exhibits a median period at $\sim$ 1-day as in many young clusters (e.g., NGC~2264, ONC, etc.), but it follows a uni-modal distribution unlike others having bimodality with the slow rotators peaking at $\sim$ 6$-$8 days. To investigate the rotation-disk and variability-disk connection, we derived NIR excess from $\Delta$(I$-$K) and MIR excess from $Spitzer$ [3.6]$-$[4.5] $\mu$m data. No conclusive evidence of slow rotation with the presence of disks around stars and fast rotation for diskless stars is obtained from our periodic variables. A clear increasing trend of the variability amplitude with the IR excess is found for all variables.

Optical spectra of the 2006 outburst of RS Ophiuchi beginning one day after discovery to over a year after the outburst are presented here. The spectral evolution is found to be similar to that in previous outbursts. The early phase spectra are dominated by hydrogen and helium (I & II) lines. Coronal and nebular lines appear in the later phases. Emission line widths are found to narrow with time, which is interpreted as a shock expanding into the red giant wind. Using the photoionisation code CLOUDY, spectra at nine epochs spanning 14 months after the outburst peak, thus covering a broad range of ionisation and excitation levels in the ejecta, are modelled. The best-fit model parameters indicate the presence of a hot white dwarf source with a roughly constant luminosity of 1.26 x 10^{37} erg/s. During first three months, the abundances (by number) of He, N, O, Ne, Ar, Fe, Ca, S and Ni are found above solar abundances; abundances of these elements decreased in the later phase. Also presented are spectra obtained during quiescence. Photoionisation model of the quiescence spectrum indicates the presence of a low luminosity accretion disk. The helium abundance is found to be subsolar at quiescence., Comment: Accepted for publication in MNRAS. 15 pages, 26 figures and 6 tables