arXiv subjects

Shraddha Biswas

Publications and source records attributed to Shraddha Biswas.

8 recordsLinked to original sources

arXiv2026

Blue Straggler Stars in Berkeley 18: A Multiwavelength Study of Their Physical Properties and Dynamical Evolution

Berkeley~18 is an old open cluster in the outer Galactic disk that hosts a population of blue straggler stars (BSSs). We present a comprehensive multiwavelength analysis of its BSS population using \textit{Gaia} DR3 astrometry, optical--infrared photometry, and time-domain TESS observations. Using a Gaussian Mixture Model (GMM) in astrometric space, we identify 798 high-probability cluster members ($p > 0.7$). Isochrone fitting yields an age of $3.2 \pm 0.2$ Gyr and a heliocentric distance of $5.01^{+0.75}_{-0.55}$ kpc. We identify 24 BSS candidates above the main-sequence turn-off. Spectral energy distribution (SED) modelling reveals effective temperatures of $6000$--$8500$ K, radii of $1.4$--$5.7\,R_\odot$, and luminosities of $3.3$--$38\,L_\odot$, indicating a heterogeneous population spanning multiple evolutionary stages. The BSS population exhibits only a mild central concentration, with a low $A^{+}$ parameter and an extremely low stellar collision-rate proxy, implying weak mass segregation and an inefficient collisional channel. We find no significant photometric variability among the BSS candidates within TESS's sensitivity limits. Although WISE W3/W4 data initially suggested possible mid-infrared excesses, detailed image inspection and SPHEREx spectrophotometry indicate that these are caused by background contamination and blending, with no clear evidence of circumstellar dust. The structural parameters derived from King-profile fitting ($r_c = 6.91^{+0.91}_{-0.73}$ arcmin, $r_t = 13.23^{+0.44}_{-0.43}$ arcmin) indicate a dynamically evolved, low-density system. Together, these results suggest that dynamical interactions are inefficient in Berkeley~18 and that binary evolution is likely the dominant formation channel of BSSs.

astro-ph.SR↗

arXiv2026

Multiwavelength Study of Blue Straggler Stars in Tombaugh 2: Evidence for Binary Mass Transfer and Constraints on Cluster Dynamical State

We present a focused multiwavelength study of blue straggler stars (BSSs) in the intermediate-age open cluster Tombaugh 2, located in the outer Galactic disk, to constrain the dominant formation pathways of BSSs in a low-density environment. Cluster members are identified using Gaia DR3 astrometry through a Gaussian Mixture Model, yielding a clean sample of high-probability members. Color-magnitude diagram analysis indicates an age of 1.74 Gyr. The radial surface density profile is well described by a King model, indicating a centrally concentrated overall structure, while the cluster exhibits only weak or no clear evidence of mass segregation among its stellar populations. We identify 26 BSS candidates and 2 YSS candidates. Spectral energy distributions constructed from ultraviolet, optical, and infrared photometry reveal that 9 BSSs (32%) exhibit significant ultraviolet excess, indicating an additional hot component. Binary SED decomposition identifies stripped companions with effective temperatures Teff $\sim$ (1.5-8) $\times$ 10$^4$ K and radii R $\sim$ 0.04-0.28 R_$\odot$, consistent with proto-white dwarfs, extremely low-mass pre-helium white dwarfs, and young hot remnants formed through recent mass transfer. A slight central concentration of BSSs, together with stripped companions, suggests that binary mass transfer is an important formation channel, with no evidence for merger-driven formation. Multi-epoch VLT/FLAMES spectroscopy reveals radial-velocity variability in several systems, providing independent evidence for binarity. Our results highlight that optical-infrared photometric analyses alone may fail to detect hot compact companions, while spectroscopy and ultraviolet observations provide complementary constraints, with ultraviolet data offering a direct probe of such companions in intermediate-age open clusters.

astro-ph.SR↗

arXiv2026

Revisiting the Orbital Dynamics of the Hot Jupiter WASP-12 b with New Transit Times

In this study, we examine the transit timing deviations of the extensively studied hot Jupiter WASP-12 b using a comprehensive dataset of 391 transit light curves. The dataset includes 7 new photometric observations obtained with the 1.3 m Devasthal Fast Optical Telescope, the 0.61 m VASISTHA telescope, and the 0.3 m AG Optical IDK telescope, along with 119 light curves from the Transiting Exoplanet Survey Satellite (TESS), 97 from the Exoplanet Transit Database (ETD), 34 from the ExoClock Project, and 134 from previously published sources. To ensure homogeneity and precision, we modeled all 391 light curves and determined their mid-transit times. A detailed transit timing analysis revealed a significant orbital decay rate of $-31.97 \pm 0.80~\mathrm{ms~yr^{-1}}$, corresponding to a stellar tidal quality factor of $Q'_\star = (1.52 \pm 0.038) \times 10^{5}$, thereby confirming that the orbit of WASP-12 b is indeed decaying rapidly. Furthermore, the computation of model selection metrics ($χ^2_r$, BIC, AIC) favors orbital decay as the most likely explanation. However, the presence of an eccentricity above the threshold value allows apsidal precession to remain a viable alternative. We also derived a planetary Love number of $k_p = 0.63 \pm 0.089$, consistent with Jupiter's value, suggesting a similar internal density distribution. In this study, orbital decay is strongly supported, as a plausible cause of the timing deviations observed in WASP-12 system. Continued high-precision monitoring will be essential to further constrain the system's orbital evolution.

astro-ph.EP↗

arXiv2025

Dynamical and Photometric Analysis of NGC 146 and King 14: Evidence for a Co-Moving, Unbound Cluster Pair

To understand the nature of the NGC 146-King 14 cluster pair, we conducted a detailed photometric, astrometric, and dynamical study using multiwavelength data from Gaia DR3, Pan-STARRS1, WISE, and TESS. Using a probabilistic approach, we identified 770 and 690 high-probability members of NGC 146 and King 14, respectively. Both clusters exhibit well-defined radial density profiles consistent with King models. We estimate the cluster ages as 20 $\pm$ 5 Myr and 50 $\pm$ 10 Myr from isochrone fitting, and distances of 2.98 $\pm$ 0.33 kpc and 2.51 $\pm$ 0.23 kpc from parallaxes after applying the Bailer-Jones criteria. The clusters show consistent mean proper motions. The mass function slopes (1.51 $\pm$ 0.18 and 1.50 $\pm$ 0.15) are close to the Salpeter value, and the extinction follows a normal Galactic reddening law (RV ~ 3.1). Three-dimensional mapping gives a projected separation of ~ 9 pc. Orbit integration using the galpy MWPotential2014 model shows that NGC 146 and King 14 move in nearly circular, disk-like orbits with similar mean orbital radii (Rm ~ 9 kpc) and orbital periods of roughly 255 Myr. A dynamical separation of ~ 32 pc indicates that both clusters share a common spatial and kinematic association, consistent with a co-moving pair. However, their relative velocity exceeds the escape velocity set by their combined mass, indicating they are not gravitationally bound. TESS light curves reveal seven variable stars, including $γ$ Doradus, SPB stars, and eclipsing binaries, though only one is a likely member. Overall, the clusters likely formed within the same giant molecular cloud and now exist as an unbound co-moving pair.

astro-ph.GA↗

arXiv2025

The Unexplored Dusty Nova LMCN 2009-05a in the Large Magellanic Cloud

We present a detailed spectrophotometric study of nova LMCN 2009-05a, located in the Large Magellanic Cloud (LMC). Photometric observations reveal a dust dip in the optical light curve, classifying it as a D-class nova. Light curve analysis yields t2 and t3 decline times of approximately 46 and 80 days, respectively, placing the nova in the category of moderately fast novae. Spectroscopic observations cover multiple phases, including pre-maximum, early decline, and nebular. The spectra are initially dominated by hydrogen Balmer and Fe II lines with P-Cygni profiles, which later transition into pure emission. During the optical minimum, a discrete absorption feature was observed in the Hα and [O I] line profiles. The physical and chemical properties during the early decline and nebular phases were analyzed using the photoionization code CLOUDY. Dust temperature, mass, and grain size were estimated through spectral energy distribution (SED) fitting to the WISE data. On day 395 post-outburst, we estimate the dust temperature to be approximately 700 K. Additionally, we examined the correlation between dust condensation time (tcond ) and t2 for LMC novae, finding a trend consistent with previous studies of Galactic novae.

astro-ph.SR↗

arXiv2025

Investigating Transit Timing Variations in the Ultra-short Period Exoplanet WASP-19b

In this study, we present a comprehensive analysis of transit timing variations (TTVs) in the ultra-short-period gas giant WASP-19b, which orbits a G-type main-sequence star. Our analysis is based on a dataset comprising 204 transit light curves obtained from the Transiting Exoplanet Survey Satellite (TESS), the Exoplanet Transit Database (ETD), and the ExoClock project, supplemented by 18 publicly available light curves. Mid-transit times were extracted from these data, and an additional 98 mid-transit times compiled from the literature were incorporated, resulting in a combined dataset spanning approximately 14 years. After excluding light curves significantly impacted by stellar activity, such as starspot anomalies, the final dataset consisted of 252 high-quality mid-transit times. Initial inspection of the transit timing residuals using an apsidal precession model suggested the possible presence of an additional planetary companion. However, subsequent frequency analysis and sinusoidal model fitting indicate that the observed TTVs are more consistently explained by apsidal precession of WASP-19b's orbit. We also considered alternative mechanisms, including the Applegate mechanism and the Shklovskii effect. Our findings suggest that stellar magnetic activity, potentially linked to the Applegate mechanism, may also contribute to the observed timing variations. To further constrain the origin of the TTVs and assess the contributions of these mechanisms, continued high-precision photometric monitoring of the WASP-19 system is strongly recommended.

astro-ph.EP↗

arXiv2025

Transit Timing Variations of the Sub-Saturn Exoplanet HAT-P-12b

We present Transit Timing Variations (TTVs) of HAT-P-12b, a low-density sub-Saturn mass planet orbiting a metal-poor K4 dwarf star. Using 14 years of observational data (2009-2022), our study incorporates 7 new ground-based photometric transit observations, three sectors of Transiting Exoplanet Survey Satellite (TESS) data, and 23 previously published light curves. A total of 46 light curves were analyzed using various analytical models, such as linear, orbital decay, apsidal precession, and sinusoidal models to investigate the presence of additional planets. The stellar tidal quality factor ($Q_\star' \sim$ 28.4) is lower than the theoretical predictions, making the orbital decay model an unlikely explanation. The apsidal precession model with a $χ_r^2$ of 4.2 revealed a slight orbital eccentricity (e = 0.0013) and a precession rate of 0.0045 rad/epoch. Frequency analysis using the Generalized Lomb-Scargle (GLS) periodogram identified a significant periodic signal at 0.00415 cycles/day (FAP = 5.1$\times$10$^{-6}$ %), suggesting the influence of an additional planetary companion. The sinusoidal model provides the lowest reduced chi-squared value ($χ_r^2$) of 3.2. Sinusoidal fitting of the timing residuals estimated this companion to have a mass of approximately 0.02 $M_J$ , assuming it is in a 2:1 Mean-Motion Resonance (MMR) with HAT-P-12b. Additionally, the Applegate mechanism, with an amplitude much smaller than the observed TTV amplitude of 156 s, confirms that stellar activity is not responsible for the observed variations.

astro-ph.EP↗

arXiv2024

Probing the Possible Causes of the Transit Timing Variation for TrES-2b in TESS Era

Nowadays, transit timing variations (TTVs) are proving to be a very valuable tool in exoplanetary science to detect exoplanets by observing variations in transit times. To study the transit timing variation of the hot Jupiter, TrES-2b, we have combined 64 high-quality transit light curves from all seven sectors of NASA's Transiting Exoplanet Survey Satellite (TESS) along with 60 best-quality light curves from the ground-based facility Exoplanet Transit Database (ETD) and 106 mid-transit times from the previous works. From the precise transit timing analysis, we have observed a significant improvement in the orbital ephemerides, but we did not detect any short period TTVs that might result from an additional body. The inability to detect short-term TTVs further motivates us to investigate long-term TTVs, which might be caused by orbital decay, apsidal precession, Applegate mechanism, and $Rϕ$mer effect and the orbital decay appeared to be a better explanation for the observed TTV with $ΔBIC$ = 4.32. The orbital period of the hot Jupiter TrES-2b appears to be shrinking at a rate of $-5.58 \pm 1.81$ ms/yr. Assuming this decay is primarily caused by tidal dissipation within the host star, we have subsequently calculated the stellar tidal quality factor value to be 9900, which is 2 to 3 orders of magnitude smaller than the theoretically predicted values for other hot-Jupiter systems and its low value indicates more efficient tidal dissipation within the host star. Additional precise photometric and radial velocity observations are required to pinpoint the cause of the change in the orbital period.

astro-ph.EP↗