IIA SONITH, L. SThe 2021 hot-type symbiotic outburst of YY herculis: An optical follow-up study
We have followed up on the hot-type classical symbiotic outburst reported in YY Her using the Himalayan Chandra Telescope. The outburst coincides with the secondary minima of the system. Approximately 12 similar brightening events have been reported between 1890 and 2020, with only the 1993 outburst being studied spectroscopically. In our study, we monitored the system from 2021 to 2023, covering ∼1.5 orbital cycles, providing an opportunity to understand the spectral evolution of the outburst over a complete orbital period of YY Her. We found that the temperature and luminosity estimations based on emission line fluxes exhibit orbital phase dependence. The values estimated at phase 0.5, corresponding to the secondary minimum, were the most reliable. The temperature of the hot component is ≈1.41 × 105 K, and the luminosity is ≈1020 L⊙ during the outburst, reduced to ≈1.3 × 105 K and ≈830 L⊙ after one orbital cycle at phase 0.5. Temperature estimations during the outbursts suggest that YY Her exhibits both hot-type (2021) and cool-type (1993) behavior, similar to another symbiotic star, AG Dra. Using variations of the Ca II absorption lines, we confirmed the contribution of the ellipsoidal effect in secondary minima in the YY Her light curve.
IIA JUDHAJEET BASUChallenging classical paradigms: Recurrent nova M31N 2017-01e, a BeWD system in M31?
M31N 2017-01e is the second-fastest recurrent nova known, with a recurrence period of 2.5 yr in the Andromeda galaxy (M31). This system exhibits a unique combination of properties: a low outburst amplitude (∼3 mag), starkly contrasting with known recurrent novae (typically ≥6 mag), and a very fast evolution (t2 ∼ 5 days). Its position coincides with a bright variable source (MV ∼ ‑4.2, B ‑ V = 0.042) displaying a 14.3 day photometric modulation, which has been suggested as the likely progenitor. We present a multiwavelength analysis of optical and UV data spanning quiescence and the 2019 and 2024 outbursts. Archival high-resolution imaging reveals two nearby faint sources within 5″ of the proposed nova system, which we identified as unrelated field stars. Color analysis and spectral energy distribution fitting suggest the progenitor is likely an early-type star. Combined with archival spectra consistent with a B-type star with Hα in emission, this points to the quiescent counterpart being a Be star with a circumstellar disk. We propose that M31N 2017-01e arises from a rare BeWD binary, where the white dwarf (WD) accretes from the decretion disk of its companion, explaining its rapid recurrence, low-amplitude outbursts, and unusual quiescent luminosity and color. This analysis highlights M31N 2017-01e as a compelling outlier among recurrent novae, suggesting a distinct accretion mechanism and evolutionary path that challenges the prevailing paradigm.
IIA ARUN, RWhen the Wall Fell: Study of Polycyclic Aromatic Hydrocarbons in T Chamaeleontis Using JWST
We investigate the polycyclic aromatic hydrocarbon (PAH) emission features of T Cha, a G8-type T Tauri star that has exhibited “seesaw”-type mid-infrared continuum variability over nearly two decades due to the destruction of the disk’s inner wall, using JWST/Mid-Infrared Instrument and Spitzer observations. We report the first detection of weak PAH emission at 6.2, 7.7, and 8.6 μm in the Spitzer/Infrared Spectrograph spectrum from 2005. The destruction of the inner wall in the 2022 JWST epoch allowed more ultraviolet photons to reach the outer disk, increasing the flux levels of PAH bands and allowing their detection well above the continuum. The 11.2 μm PAH flux increases by a factor of 3, yet its profile shape remains remarkably stable, and the 6.2/11.2 μm flux ratio has increased, but the charge state of the PAH population remains 75% neutral. The PAH features exhibit a “class C” spectral profile, with redshifted peaks and broadened wings consistent with emission from lowmass T Tauri disks, while the weak 12.7/11.2 ratio points to a lower abundance of duo and trio hydrogen modes, implying a predominantly zigzag carbon structure. A faint “class A” subcomponent in the 6.2 and 7.7 μm bands may indicate additional PAH processing by ultraviolet radiation from accretion hotspots. Placement on PAH charge–size grids locates T Cha in the low-ionization, small-size regime (NC ≤ 30), signifying a largely neutral PAH population in multiple epochs spanning 18 yr. Through multiepoch, high-resolution data from JWST and Spitzer, we identify T Cha as a benchmark source for probing disk evolution and PAH processing, emphasizing the potential of temporal monitoring with JWST
IIA SAHU, D. KLong-term monitoring of a dynamically new comet C/2020 V2 (ZTF)
Comet C/2020 V2 (ZTF, Zwicky Transient Facility) is categorized as a dynamically new long-period comet, making its first approach to the inner Solar system. We have observed this comet for around 32 months (from 2022 January to 2024 July) at heliocentric distances from 5.41 au (pre-perihelion) to 5.26 au (post-perihelion) through various telescopes, employing photometric (60 epochs) and spectroscopic techniques (5 epochs). Using these observations, we derived the production rates of different molecules such as CN(0 − 0), C2(ν = 0), and C3 and calculated the production rate ratios. The values of the ratios closest to the perihelion are found to be log (C2/CN) = −0.04 ± 0.03 and log (C3/CN) = −0.70 ± 0.04, which implies a typical carbon composition. The mean photometric broad-band colours are found to be B − V = 0.77 ± 0.04, V − R = 0.43 ± 0.04, R − I = 0.42 ± 0.06, and B − R = 1.19 ± 0.04. The stability of the molecular production rate ratios and mean photometric broad-band colours, pre- and post-perihelion, implies a homogeneous composition. The mean reflectivity gradient for B − V colour is 10.90 ± 3.62 per cent/1000 Å; V − R colour is 6.15 ± 3.51 per cent/1000 Å; and for R − I colour is 4.94 ± 3.56 per cent/1000 Å which issimilarto the mean value ofthe dynamically new comets. Additionally, using an asymmetric non-gravitational force model, we report the comet’s nuclear radius to be 1.1 ± 0.1 km. Our results are expected to provide inputs to the selection of a potential dynamically new comet as a target for the Comet Interceptor mission.
IIA RAJU, K. PWhich solar latitude follows the sunspot cycle exactly?
The large-scale convection in the Sun known as supergranulation is manifested as a network structure on the solar surface. The network cells have an average lifetime of 24 hr, a size of about 30 Mm, and a lane width of about 6 Mm. We have obtained the lane widths and intensities at different latitudes from the Ca II K spectroheliograms from the 100 yr Kodaikanal archival data. We have then calculated the cross-correlation function of lane widths and intensities with sunspot number at every latitude from 60°N to 60°S. The correlation coefficients of the quantities show an approximate north–south symmetry with broad peaks around ±(11–22)° latitude with values of about 0.8. The results imply that these latitudes follow the sunspot cycle strongly. The maximum correlation for the lane widths occurs (18 ± 2)°N and (20 ± 2)°S with no phase difference. For intensities, this happens at (13 ± 2)°N and (14 ± 2)°S with a phase difference of 1.25–1.5 yr. It is interesting to note that the lane width correlations peak during the solar maximum, whereas the intensity correlations peak 1.25–1.5 yr after the solar maximum. The results generally show that no unique latitude exactly follows the solar cycle for all quantities. The results are important in flux transport on the solar surface and have implications for the quiet Sun UV irradiance variations.
IIA STALIN, C. SThe detection of teraelectronvolt radiation from a flat-spectrum radio quasar
The very high-energy (VHE; >100 GeV) radiation carries the signatures of the matter–energy interaction in some of the most extreme astrophysical environments. Considering broad emission line blazars, i.e., flat-spectrum radio quasars (FSRQs), the dense photon fields surrounding the relativistic jet can prohibit the particle population from accelerating to very high energies and producing VHE radiation. They can also possibly make the environment opaque for the VHE γ rays due to γγ pair production, thus explaining the paucity of VHE-detected FSRQs and nondetection of TeV radiation (>1 TeV) from them. Here we report, for the first time, a >7σ detection of an FSRQ, S5 1027+74 (z = 0.123), in the VHE band, including the first ever detection of TeV emission from an object of this class, using the Fermi Large Area Telescope observations. Its γ-ray spectrum covering the 100 MeV–2 TeV band revealed a prominent spectral break with a flat, rising shape above ∼10 GeV, a feature never detected from other VHE-detected FSRQs. The radio-to-γ-ray spectral energy distribution of S5 1027+74 provides strong evidence of a third bump peaking at multi-TeV energies. These enigmatic findings imply that FSRQ jets can accelerate particles to extremely high energies and provide tantalizing clues about the complex radiative environment of relativistic jets.
IIA PRAJWEL JOSEPHRedshift ∼2.7 is not special comment on the Kolmogorov analysis of JWST deep survey galaxies
Galikyan et al. (2025, A&A, 696, L21) reported a statistically significant change in galaxy spectral properties at redshift z ' 2.7 based on a Kolmogorov Stochasticity Parameter analysis of JWST spectroscopic data of galaxies. In this comment, we demonstrate that this result is critically driven by a single outlier in the dataset that was employed. This outlier arises from the use of a questionable redshift estimate for one spectrum. When the outlier is removed or the redshift is corrected, the claimed transition at z ' 2.7 disappears entirely. By independently reproducing the previous analysis, we demonstrate that the claimed feature is not a robust statistical signal, but an artefact of this anomalous data point.
IIA DEBIKA CHOWDHURYInflationary magnetogenesis beyond slow-roll and its induced gravitational waves
The origin of magnetic fields observed on both astrophysical and cosmological scales is a compelling problem that has the potential to shed light on the early Universe. We analytically investigate inflationary magnetogenesis in scenarios where a brief departure from slow-roll inflation—akin to mechanisms proposed for primordial black hole formation—leads to enhanced magnetic field generation with a growing power spectrum. Focusing on the Ratra model, we derive an analytic bound on the growth of the magnetic field power spectrum in this context, showing that the spectral index can reach 𝑑ln𝒫𝐵/𝑑ln𝑘 =4.75 during the growth phase. This growth enables amplification from cosmic-microwave-background-safe large-scale amplitudes to values of astrophysical relevance. We further compute the stochastic gravitational wave background sourced by the resulting magnetic fields, incorporating their rich spectral features. Under suitable conditions, the induced signal exhibits a characteristic frequency dependence and amplitude within reach of future gravitational wave observatories, providing a distinctive signature of this mechanism and a specific class of templates for upcoming gravitational wave searches.
IIA ANNAPURNI SUBRAMANIAMDetection of young massive white dwarfs in core-collapsed globular cluster NGC 362
Core-collapsed globular clusters are ideal targets to explore the presence of stellar collision products. Here, we have studied 17 far-UV bright white dwarf (WD) members in the globular cluster NGC 362 using data obtained from the Ultra Violet Imaging Telescope (UVIT) mounted on AstroSat and from the Hubble Space Telescope. Multiwavelength spectral energy distributions (SEDs) are analyzed using UV and optical data sets to characterize and determine the parameters of WDs. Fourteen of the WDs fit single-component SEDs well, while three showed a good fit with a two-component SED model, indicating a binary system comprising a WD and a low-mass main-sequence (MS) star. The effective temperatures, radii, luminosities, and masses of WDs are in the ranges 22,000–70,000 K, 0.008–0.028 R⊙, 0.09–3.0 L⊙, and 0.30–1.13 M⊙, respectively. The effective temperatures, radii, luminosities, and masses of the companions (low-mass MS stars) are 3500–3750 K, 0.150–0.234 R⊙, 0.003–0.01 L⊙, and 0.14–0.24 M⊙, respectively. The three binary systems (WD-MS), along with the massive WDs, may have formed through dynamical processes that occurred during the core collapse of the cluster. This is the first evidence of a massive WD formation in a core-collapsed cluster, which is the missing link in the formation of a fast radio burst (FRB) progenitor in a globular cluster. This study provides evidence that NGC 362 hosts stellar systems that may evolve into exotic stars such as Type Ia supernovae and/or FRBs in the future. This Letter is paper VI of the Globular Cluster UVIT Legacy Survey.
IIA SAHU, D. KSN 2023vbg: a type IIn supernova resembling sn 2009ip, with a long-duration precursor and early-time bump
Type IIn supernovae (SNe) resembling SN 2009ip (09ip-like SNe) originate from the interaction between circumstellar material (CSM) and the ejecta. This subclass not only shares similar observational properties around the maximum but is also commonly characterized by a long-duration precursor before its maximum. Investigating the observed properties of the precursor provides constraints on the mass-loss history of the progenitor. We present observational data of SN 2023vbg, an 09ip-like type IIn SN that displayed unique observational properties compared to other 09ip-like SNe. SN 2023vbg showed a long-duration precursor at Mg ∼ ‑14 mag lasting for ∼100 days, followed by a bright bump at Mg ∼ ‑17 mag at 12–25 days before the maximum. The luminosity of the precursor is similar to those of other 09ip-like SNe, but the bright bump has not been observed in other cases. After reaching the peak luminosity, the light curve exhibited a relative smooth decline. While the Hα profile displays two velocity components (∼500 and 3000 km s‑1), a broad component observed in other 09ip-like SNe was not seen, but it may emerge later. We suggest that these properties are explained by the difference in the CSM structure as compared to other 09ip-like SNe; SN 2023vbg had an inner denser CSM component, as well as generally smooth CSM density distribution in a more extended scale than in the others. Such diversity of CSM likely reflects the diversity of pre-SN outbursts, which in turn may mirror the range of evolutionary pathways in the final stages of the progenitors.