arXiv subjects

Susmita Das

Publications and source records attributed to Susmita Das.

At least 19 recordsLinked to original sources

arXiv2026

Large Magellanic Cloud Globular Clusters in the Near-infrared. I. RR Lyrae in Reticulum

Reticulum is an old, metal-poor, and sparsely populated globular cluster in the outer regions of the Large Magellanic Cloud (LMC) and hosts a rich population of RR Lyrae stars. Being as close as possible to a single stellar population with negligible metallicity spread and low reddening, Reticulum is an ideal laboratory for testing stellar pulsation models and calibrating population II distance indicators. We present homogeneous multi-epoch near-infrared (NIR, JHKs) observations of RR Lyrae variables in Reticulum obtained with the Flamingos-2 imager on the 8.1-m Gemini South Telescope. Using NIR light-curve templates, we derive accurate intensity-averaged magnitudes and peak-to-peak amplitudes for 32 RR Lyrae stars, including 22 fundamental-mode (RRab), 4 first-overtone (RRc), and 6 mixed-mode (RRd) pulsators. The empirical JHKs period-luminosity (PL) relations of Reticulum RR Lyrae are very tight, exhibiting dispersions (~0.05 mag) comparable to those observed in Galactic globular clusters. The derived PL slopes are shallower than those reported for Galactic cluster variables. Adopting recent empirical and theoretical period-luminosity-metallicity (PLZ) calibrations based on Galactic globular clusters and pulsation models, we derive a true distance modulus of $\mu_0 = 18.472 \pm 0.035$ mag to Reticulum. This cluster distance is in excellent agreement with the precise geometric distance to the LMC and places Reticulum close to the LMC barycentric distance. The well-characterized RR Lyrae population and a precise distance make Reticulum a potential anchor for calibrating Population II distance ladder.

astro-ph.SR↗

arXiv2026

The simulation on neutron background reduction for InDEx at JUSL

Dark matter experiments are rare event search experiments that require zero background environment over very long exposures. To achieve this condition, a detailed simulation of detector geometry and experimental setup is required before the experiment is executed. Simulation plays a significant role in detector design and also provides a cost-effective and risk-free approach for predicting outcomes before real world experimentation. The present simulation work is focused on neutron background reduction for a dark matter direct detection experiment in India, the Indian Dark matter search Experiment (InDEx). The FLUKA and FLAIR simulation tools have been used throughout the simulation process. The experimental and simulation results available in the literature are being reproduced using FLUKA for validation purposes. The calibration and InDEx experiment are simulated, and the results are compared against the experimental results. For neutron background reduction in future experiments, the use of high density polyethylene (HDPE) is suggested and a shielding design using HDPE is presented. The results show that shielding reduces detector event rates by two orders of magnitude compared to the prior InDEx experiment without shielding.

hep-ex↗

arXiv2026

Photometric metallicity of Galactic RR Lyrae stars in the Gaia DR3 era

We present a new, calibrated $G$-band relationship between pulsation period $P$, Fourier parameter $\phi_{31}$, and metallicity [Fe/H] for galactic RR Lyrae stars from the Gaia survey. A set of 72 fundamental mode RR Lyrae stars were identified for deriving the relation in the $G$-band, after visual examination of their light curves. Unlike recent large-scale calibrations, our relation prioritizes calibration purity by anchoring exclusively to a homogeneously analyzed sample of high-resolution spectroscopic metallicities from the literature. Our best fit relation is $\text{[Fe/H]} = (-6.93 \pm 0.58) - (6.04 \pm 0.37)P + (1.65 \pm 0.11)\phi_{31}$. We compare the [Fe/H] predicted by our relation for the stars in our calibration sample with that obtained from previously established relations in the $G$-band using different approaches. Our calibrated $G$-band $P$-$\phi_{31}$-[Fe/H] relationship demonstrates high reliability when validated against spectroscopic data, achieving a negligible bias of $0.00$ dex and an empirical RMS scatter of 0.26 dex. Furthermore, by applying an Orthogonal Distance Regression (ODR) routine that fully propagates parameter covariance, we establish a mathematically strict empirical baseline whose theoretical uncertainties perfectly align with this observed dispersion. We find that the inclusion of the $R_{21}$ Fourier parameter offers no significant improvement in metallicity estimation. Comparisons with literature confirm that our linear relation aligns closely with other Gaia DR3-based studies, while offering improved precision over older DR2-based relations.

astro-ph.SR↗

arXiv2025

On Quasinormality of compact perturbations of the isometries

We study the compact perturbations of an isometry on a separable Hilbert space and provide a complete characterization of when they are quasinormal. Based on that, we present a complete classification for a rank-one perturbation of a unilateral shift of finite multiplicity to be quasinormal in the setting of the Hardy space. The result can also be generalized for a separable Hilbert space. As an application, we provide a complete characterization for quasinormality of a rank-one perturbation of the Hardy shift.

math.FA↗

arXiv2025

Type II Cepheids: Period-Luminosity-Metallicity relations for the Population II distance scale

Type II Cepheids are a class of pulsating variable stars that play a critical role in our understanding of stellar evolution, distance measurement and tracing the structure and kinematics of old stars in nearby galaxies. This review provides a comprehensive summary of the current state of research on Type II Cepheids, including their observed properties, pulsation mechanisms and their distinction from other variable stars. These pulsating variable stars, found primarily in older stellar populations, exhibit well-defined period-luminosity relations but with an added advantage that they exhibit weak or negligible dependence on metallicity. We explore their relevance in the context of their role as distance indicators and potential calibrators of the first rung of the extragalactic distance ladder. Finally, the review highlights recent advancements in theoretical models, observations across different wavelengths and ongoing debates concerning their classification.

astro-ph.SR↗

arXiv2025

Dark matter direct search result from InDEx run2 at JUSL

The Indian Dark matter search Experiment (InDEx) has been initiated at Jaduguda Underground Science Laboratory (JUSL) to explore the low mass region of dark matter. The detectors used by InDEx are superheated droplet detectors with active liquid C2H2F4. The run1 of InDEx was with 2.47 kg-days of exposure at a threshold of 5.87 keV. In the present work, the run2 of InDEx, the detectors were set at 1.95 keV thresholds with an active liquid mass of 70.4 g. For a runtime of 102.48 days, the experimental results set constraint on spin-independent at 20.4 GeV/c2 and on spin-dependent at 21.0 GeV/c2 WIMP mass respectively. There is a shift of the most sensitive WIMP mass towards the lower region and an improvement of the sensitivity limit over the InDEx run1.

hep-ex↗

arXiv2025

The Dark Matter Search at Jaduguda Underground Science Laboratory

The first run for the dark matter direct search experiment at Jaduguda Underground Science Laboratory is presented in this article. The experiment named InDEx; the Indian Dark matter search Experiment has been initiated with superheated emulsion detector consisting of the droplets of tetrafluoroethane ($C_2H_2F_4$). The detector ran for an effective period of 48.6 days at a threshold of 5.87 keV with an exposure of 2.47 kg-days. It is observed that the minimum sensitivity for the SI cross-section of $[7.939\pm(0.375)_{statistical}(^{+1.386}_{-0.909})_{systematic}]\times 10^{-39}$ $cm^2$ for fluorine appears at WIMP mass of 30.67 $GeV/c^2$. The InDEx with larger exposures is under development and yet to come in near future.

hep-ex↗

arXiv2025

In-Context Learning as an Effective Estimator of Functional Correctness of LLM-Generated Code

When applying LLM-based code generation to software development projects that follow a feature-driven or rapid application development approach, it becomes necessary to estimate the functional correctness of the generated code in the absence of test cases. Just as a user selects a relevant document from a ranked list of retrieved ones, a software generation workflow requires a developer to choose (and potentially refine) a generated solution from a ranked list of alternative solutions, ordered by their posterior likelihoods. This implies that estimating the quality of a ranked list -- akin to estimating "relevance" for query performance prediction (QPP) in IR -- is also crucial for generative software development, where quality is defined in terms of "functional correctness". In this paper, we propose an in-context learning (ICL) based approach for code quality estimation. Our findings demonstrate that providing few-shot examples of functionally correct code from a training set enhances the performance of existing QPP approaches as well as a zero-shot-based approach for code quality estimation.

cs.SE↗

arXiv2025

Multiwavelength study of observed and predicted pulsation properties of First overtone Cepheids in the Magellanic Clouds

We present a detailed analysis of the light curves and pulsation properties of First Overtone (FO) Cepheids in the Magellanic Clouds (MCs) obtained using observations and predictions from stellar pulsation models. Multiwavelength observational light curves were compiled from the literature (OGLE-IV, Gaia and VMC). We investigate the period-amplitude (PA), period-colour (PC), period-luminosity (PL), and amplitude-colour (AC) relations for FO Cepheids at multiwavelengths. We find that the PA distribution of FO Cepheids in the MCs modelled using a Gaussian Mixture Model shows that the SMC consists of higher amplitude stars than the LMC. We find multiple break-points in the PC/PL/AC relations for FO/FU Cepheids in the optical and near-infrared bands including the one near to P = 2.5 d in the MCs using piecewise regression analysis and F- test statistics. Similarly, for the LMC FO Cepheids, we find a break-point in the PC/PL/AC relations near P = 0.58 d. The slopes of the PC relations for LMC FO Cepheids are found to be shallow for 0.58 < P(d) < 2.5 but steeper for P < 0.58 d and P > 2.5 d. We complemented the observed relations using theoretical models for FO Cepheids with chemical compositions Z = 0.008 and Z = 0.004, appropriate for the LMC and SMC, respectively computed with MESA-RSP. Our results show that the pulsation properties of FO Cepheids in PC/PL/AC relations and colour-magnitude diagram are strongly correlated and their connections can provide stringent constraints for the theoretical pulsation models.

astro-ph.GA↗

arXiv2025

Sub-Day Timescale X-ray Spectral Variability of the TeV Blazars Mrk 421 and 1ES 1959+650

We present X-ray spectra ($0.7-20$ keV) of two high synchrotron-peaked blazars Mrk 421 and 1ES 1959+650 from simultaneous observations by the SXT and LAXPC instruments onboard \textit{AstroSat} and the \textit{Swift}-XRT during multiple intervals in 2016-19. The spectra of individual epochs are satisfactorily fitted by the log-parabola model. We carry out time-resolved X-ray spectroscopy using the \textit{AstroSat} data with a time resolution of $\sim$10 ks at all epochs, and study the temporal evolution of the best-fit spectral parameters of the log-parabola model. The energy light curves, with duration ranging from $0.5-5$ days, show intra-day variability and change in brightness states from one epoch to another. We find that the variation of the spectral index ($\alpha$) at hours to days timescale has an inverse relation with the energy flux and the peak energy of the spectrum, which indicates a harder-when-brighter trend in the blazars. The variation of curvature ($\beta$) does not follows a clear trend with the flux and has an anti-correlation with $\alpha$. Comparison with spectral variation simulated using a theoretical model of time variable nonthermal emission from blazar jets shows that radiative cooling and gradual acceleration of emitting particles belonging to an initial simple power-law energy distribution can reproduce most of the variability patterns of the spectral parameters at sub-day timescales.

astro-ph.HE↗

arXiv2025

Zero Products of Toeplitz operators on the Hardy and Bergman spaces over an annulus

We study the zero product problem of Toeplitz operators on the Hardy space and Bergman space over an annulus. Assuming a condition on the Fourier expansion of the symbols, we show that there are no zero divisors in the class of Toeplitz operators on the Hardy space of the annulus. Using the reduction theorem due to Abrahamse, we characterize compact Hankel operators on the Hardy space of the annulus, which also leads to a zero product result. Similar results are proved for the Bergman space over the annulus.

math.FA↗

arXiv2025

Variable stars in Galactic globular clusters II. Population II Cepheids

We identified a sample of 88 bona fide Population II Cepheids (henceforth referred to as Cepheids) and 44 candidates in Galactic globular clusters (GCs). Seventy-eight of the Cepheids in the sample align within $2\,\sigma$ of the period-luminosity relation for Milky Way Type II Cepheids (T2CEPs). Nine align with the period-luminosity relation for fundamental-mode anomalous Cepheids (ACEPs), and only one (BL Bo\"otis) follows the relation for first-overtone ACEPs, as determined from observations of ACEPs in the Large Magellanic Cloud. For sources in common between our catalog and the OGLE catalog, the classification agrees in 94% of cases. In comparison, for sources shared between the Gaia Specific Object Study (SOS) and OGLE, the agreement is 74%. In the dense environments of GCs, our analysis shows that the completeness of the Gaia catalogs for Cepheids is 64% for the SOS and 74% for the classifier of variable stars. We determined the red and blue edges of the instability strip for T2CEPs using linear MESA-RSP models. We find that the best-fit models, with $M = 0.6\,{\rm M}_\odot$ and Z = 0.0003, are able to fit $90%$ of the stars in our sample. This percentage is the same for helium abundances $Y = 0.220$ and $0.245$. Higher values of $Y$ lower this percentage, and the same effect is observed with lower values of $Z$. In the future, combining the sample of T2CEPs with the precise parallaxes obtained from GCs will strengthen the geometric calibration of a distance ladder based on Population II stars. This will be useful for determining distances within the Milky Way and for cross-checking distances to Local Group galaxies determined through other methods.

astro-ph.SR↗

arXiv2025

A theoretical framework for BL Her stars IV. New period-luminosity relations in the Rubin-LSST filters

We present new theoretical light curves in the Rubin-LSST filters for a fine grid of BL Her models computed using MESA-RSP. We also derive new theoretical period-luminosity (PL) and period-Wesenheit (PW) relations in the Rubin-LSST filters with the goal to study the effect of convection parameters and metallicity on these relations. The grid of BL Her models was computed with the input stellar parameters: metallicity ($-2.0\; \mathrm{dex} \leq \mathrm{[Fe/H]} \leq 0.0\; \mathrm{dex}$), stellar mass ($0.5M_{\odot}-0.8M_{\odot}$), stellar luminosity ($50L_{\odot}-300L_{\odot}$), and effective temperature (across the full extent of the instability strip; in steps of 50K) and using four sets of convection parameters. Bolometric correction tables from MIST were used to transform the theoretical bolometric light curves of the BL Her models into the Rubin-LSST ugrizy filters. The PL relations of the BL Her models exhibit steeper slopes but smaller dispersion with increasing wavelengths in the Rubin-LSST filters. The PL and PW slopes for the complete set of BL Her models computed with radiative cooling (sets B and D) are statistically similar across the grizy filters. The BL Her models exhibit weak or negligible effect of metallicity on the PL relations for wavelengths longer than the g filter for both the cases of the complete set of models as well as the low-mass models. However, we find significant effect of metallicity on the PL relation in the u filter. Strong metallicity effects are observed in the PWZ relations involving the u filter and are found to have significant contribution from the high-metallicity BL Her models. Due to negligible metallicity effect for relations involving the Wesenheit indices $W(i,g-i)$, $W(z,i-z)$ and $W(y,g-y)$, we recommend these filter combinations for BL Her stars when observed with the Rubin-LSST to be used as reliable standard candles.

astro-ph.SR↗

arXiv2024

A theoretical framework for BL Her stars III. A case study: Robust light curve optimisation in the LMC

We carry out an extensive light curve comparison of BL Her stars using observations from Gaia DR3 and stellar pulsation models computed using MESA-RSP with the goal to obtain the best-matched modeled-observed pairs for BL Her stars in the LMC. We use the Fourier decomposition technique to analyse the light curves in the G band obtained from Gaia DR3 and from MESA-RSP and use a robust light curve fitting approach to score the modeled-observed pairs with respect to their pulsation periods and over their Fourier parameter space. We obtain the best-fit models for 48 BL Her stars in the LMC and thereby provide the stellar parameter estimates of these stars, 30 of which are labelled as the gold sample with superior light curve fits. We find a relatively flat distribution of stellar masses between 0.5-0.65 Msolar for the gold sample of modeled-observed pairs. An interesting result is that the majority of the best-matched models in the gold sample are computed using the convection parameter sets without radiative cooling. The period-Wesenheit relation for the best-matched gold sample of 30 BL Her models exhibits a slope of $-2.805 \pm 0.164$ while the corresponding period-radius relation exhibits a slope of $0.565 \pm 0.035$, both in good agreement with the empirical PW and PR slopes from BL Her stars in the LMC, respectively. We also used the Wesenheit magnitudes of the 30 best-matched modeled-observed pairs to estimate a distance modulus of $\mu_{\rm LMC} = 18.582 \pm 0.067$ to the LMC, which lies within the bounds of previous literature values. We also discuss the degeneracy in the stellar parameters of the BL Her models that result in similar pulsation periods and light curve structure, and highlight that caution must be exercised while using the stellar parameter estimates.

astro-ph.SR↗

arXiv2024

A Survey on Automatic Online Hate Speech Detection in Low-Resource Languages

The expanding influence of social media platforms over the past decade has impacted the way people communicate. The level of obscurity provided by social media and easy accessibility of the internet has facilitated the spread of hate speech. The terms and expressions related to hate speech gets updated with changing times which poses an obstacle to policy-makers and researchers in case of hate speech identification. With growing number of individuals using their native languages to communicate with each other, hate speech in these low-resource languages are also growing. Although, there is awareness about the English-related approaches, much attention have not been provided to these low-resource languages due to lack of datasets and online available data. This article provides a detailed survey of hate speech detection in low-resource languages around the world with details of available datasets, features utilized and techniques used. This survey further discusses the prevailing surveys, overlapping concepts related to hate speech, research challenges and opportunities.

cs.CL↗

arXiv2024

New theoretical instability regions, period-luminosity relations and masses for blue large-amplitude pulsators

Blue large-amplitude pulsators (BLAPs) are a recently discovered group of hot pulsating stars whose evolutionary status remains uncertain. Their supposed progenitors are either $\simeq 0.3M_{\odot}$ shell H-burning stars or $\simeq 1.0M_{\odot}$ core He-burning stars, both relying on mass loss or a merger event in a (rarely observed) close interacting binary system. With the goal to understand the stellar masses of BLAPs, we therefore carried out a linear non-adiabatic analysis of a grid of models computed using mesa-rsp, with appropriate input stellar parameters $ZXMLT_{\rm eff}$ and convection parameter sets. We discuss the impact of stellar mass, metallicity, helium abundance and convection parameters on the theoretical instability regions of BLAPs. We also derive new theoretical period relations; our theoretical period relations using low stellar masses seem to be in better agreement with the observed period relations. Although only two BLAPS have been observed to be multi-periodic oscillator so far, we analyse theoretical $P_{1O}/P_F$ ratios and compare these values with other classical pulsators. Furthermore, we provide the first asteroseismic mass estimate for the triple-mode pulsator, OGLE-BLAP-030 which seems to be well-constrained in the range of $0.62-0.64 M_{\odot}$ with a high metallicity of $Z=0.07$, albeit with a few sources of uncertainty involved. This would place the BLAP star intermediate to the two proposed mass scenarios so far.

astro-ph.SR↗

arXiv2024

Invariant subspaces of compressions of the Hardy shift on some parametric spaces

We study the class of operators $S_{\alpha,\beta}$ obtained by compressing the Hardy shift on the parametric spaces $H^2_{\alpha, \beta}$ corresponding to the pair $\{\alpha,\beta\}$ satisfying $|\alpha|^2+|\beta|^2=1$. We show, for nonzero $\alpha,\beta$, each $S_{\alpha,\beta}$ is indeed a shift $M_z$ on some analytic reproducing kernel Hilbert space and present a complete classification of their invariant subspaces. While all such invariant subspaces $\clm$ are cyclic, we show, unlike other classical shifts, they may not be generated by their corresponding wandering subspaces $(\clm\ominus S_{\alpha,\beta}\clm)$. We provide a necessary and sufficient condition along this line and show, for a certain class of $\alpha, \beta$, there exist $S_{\alpha,\beta}$-invariant subspaces $\clm$ such that $\clm\neq [\clm\ominus S_{\alpha,\beta}\clm]_{S_{\alpha,\beta}}$.

math.FA↗

arXiv2024

Bridging theory and observations in stellar pulsations: The impact of convection and metallicity on the instability strips of Classical and Type-II Cepheids

The effect of metallicity on the theoretical and empirical period-luminosity (PL) relations of Cepheid variables is not well understood and remains a highly debated issue. Here, we examine empirical colour-magnitude diagrams (CMDs) of Classical and Type-II Cepheids in the Magellanic Clouds and compare those with the theoretically predicted instability strip (IS) edges. We explore the effects of incorporating turbulent flux, turbulent pressure, and radiative cooling into the convection theory on the predicted IS at various metallicities using MESA-RSP. We find that the edges become redder with the increasing complexity of convection physics incorporated in the fiducial convection sets, and are similarly shifted to the red with increasing metallicity. The inclusion of turbulent flux and pressure improves the agreement of the red edge of the IS, while their exclusion leads to better agreement with observations of the blue edge. About 90% of observed stars are found to fall within the predicted bluest and reddest edges across the considered variations of turbulent convection parameters. Furthermore, we identify and discuss discrepancies between theoretical and observed CMDs in the low effective temperature and high luminosity regions for stars with periods greater than ~ 20 days. These findings highlight the potential for calibrating the turbulent convection parameters in stellar pulsation models or the prediction of a new class of rare, long-period, 'red Cepheids', thereby improving our understanding of Cepheids and their role in cosmological studies.

astro-ph.SR↗