IIA VIPIN KUMAR SHARMADoes DESI DR2 Challenge ΛCDM Paradigm?
Although the debate about the systematic errors of DESI DR1 is still open, recent DESI DR2 is consistent with DESI DR1 and further strengthens the results of DESI DR1. In our analysis, both the LRG1 point at zeff = 0.510 and the LRG3+ELG1 point at zeff = 0.934 are in tension with the ΛCDM-anchored value of Ωm inferred from Planck and the Type Ia supernovae compilations Pantheon+, Union3, and DES-SN5YR. For luminous red galaxy 1 (LRG1) the tensions are 2.42σ, 1.91σ, 2.19σ, and 2.99σ, respectively; for LRG3+emission line galaxy 1 (ELG1) they are 2.60σ, 2.24σ, 2.51σ, and 2.96σ, respectively. From low to high redshift bins, DESI DR2 shows improved consistency relative to DESI DR1: the Ωm tension decreases from 2.20σ to 1.84σ. However, DESI DR2 alone does not provide decisive evidence against the ΛCDM model, and the apparent signal is largely driven by specific tracers, LRG1 and LRG2. In the ω0ωaCDM analysis, including all tracers yields a posterior mean with ω0 > −1, which aligns with scenarios of dynamical dark energy as a potential explanation and suggests that the DESI DR2 challenges the ΛCDM paradigm. While removing LRG1 and/or LRG2 fully restores ΛCDM concordance (i.e., ω0 → −1), we also find ω0(LRG1)>ω0(LRG2) , indicating LRG1 drives the apparent dynamical dark energy trend more strongly. Model selection using the natural log Bayes factor lnBF≡ln(ZΛCDM/Zω0ωaCDM) shows weak evidence for ΛCDM when LRG1, LRG2, or both are removed, and it is inconclusive for the full sample; thus, the data do not require the extra ωa freedom, and the apparent ω0 > −1 preference should be interpreted cautiously as a manifestation of the ω0─ωa degeneracy under limited per tracer information.
IIA ADITYA, KEvolution of Low Surface Brightness Ultrathin Galaxies: The Role of Dark Matter Halo and Bar Formation on Disk Thickness
We investigate how stellar disks sustain their ultrathin structure throughout their evolution. We follow the evolution of ultrathin stellar disks with varying dark matter (DM) halo concentration (c) using collisionless N-body simulations with AREPO. We test models embedded in steep (c = 12), shallow (c = 2), and intermediate (c = 6) DM concentrations. Our models match the observed structural properties of the stellar disk in the low surface brightness (LSB) ultrathin galaxy FGC 2366, specifically its surface brightness, disk scalelength, and vertical thinness (hz/RD = 0.1), while excluding gas, allowing us to isolate the effects of DM. The internal disk heating mechanism driven by bars is suppressed in the LSB ultrathin stellar disks regardless of the DM concentration. The ratio of disk thickness (hz) to scalelength (RD) remains constant at ≤0.1 throughout their evolution. To clearly establish that the LSB nature of stellar disks is the key to preventing disk thickening, we construct the initial conditions by increasing the stellar mass fraction from fs ∼ 0.01 to 0.02 and 0.04, respectively, while keeping the total mass equal to 1011M⊙ and hz/RD ≤ 0.1 unchanged. We find that models with a higher stellar mass fraction embedded in a shallow DM potential (c = 2) form bars and undergo significant disk thickening (hz/RD ≫ 0.1) concurrent with the bar growth. We conclude that if the LSB disks are thin to begin with, they remain so throughout their evolution in isolation, regardless of the concentration of the DM halo.
IIA NITESH K. DUBEYIsentropic processes for axisymmetric black holes
We demonstrate that the isentropic absorption of a classical charged test particle is classically forbidden for all (3 þ 1)-dimensional stationary, nonextremal, axisymmetric black holes in any diffeomorphism invariant theory of gravity. This result is derived purely from the near-horizon geometry and thermodynamic properties of the black hole spacetime, independent of the specific gravitational theory. We further consider the Kerr-Newman black hole in general relativity and analyse, using the quantum tunneling approach, the conditions under which isentropic absorption may be allowed. Broader implications for the second law and extremality bounds are discussed.
IIA DIPANKAR BANERJEEThe Effect of Poloidal Magnetic Field and Helicity Injection in a Breakout Coronal Mass Ejection
Coronal mass ejections (CMEs), as crucial drivers of space weather, necessitate a comprehensive understanding of their initiation and evolution in the solar corona in order to better predict their propagation. Solar Cycle 24 exhibited lower sunspot numbers compared to Solar Cycle 23, along with a decrease in the heliospheric magnetic pressure. Consequently, a higher frequency of weak CMEs was observed during Solar Cycle 24. Forecasting CMEs is vital, and various methods, primarily involving the study of the global magnetic parameters using data sets like Space-weather Helioseismic and Magnetic Imager Active Region Patches, have been employed in earlier works. In this study, we perform numerical simulations of CMEs within a magnetohydrodynamics framework using Message Passing Interface–Adaptive Mesh Refinement Versatile Advection Code in 2.5D. By employing the breakout model for CME initiation, we introduce a multipolar magnetic field configuration within a background bipolar magnetic field, inducing shear to trigger the CME eruption. Our investigation focuses on understanding the impact of the background global magnetic field on CME eruptions. Furthermore, we analyze the evolution of various global magnetic parameters in distinct scenarios (failed eruption, single eruption, and multiple eruptions) resulting from varying amounts of helicity injection in the form of shear at the base of the magnetic arcade system. Our findings reveal that an increase in the strength of the background poloidal magnetic field constrains CME eruptions. Furthermore, we establish that the growth rate of absolute net current helicity is the crucial factor that determines the likelihood of CME eruptions.
IIA SRIRAM, SDMD-based Multi-Object Spectrograph (D-MOS): AIV and first light results
A Digital Micromirror Device (DMD)-based Multi-Object Spectrograph (D-MOS) with an integrated imager has been developed. The optical performance of the MOS is evaluated through comprehensive laboratory calibration and on-sky observations using the 1.3-meter J.C. Bhattacharya (JCB) Telescope at the Vainu Bappu Observatory (VBO). The system is designed to assess the viability of using a DMD as a programmable slit mechanism for future ultraviolet-optical space missions. A complete imager-cum-spectrograph assembly was constructed using off-the-shelf optical components and configured for operation in the optical band, employing a DLP9500 DMD with a 1920×1080 micromirror array. Calibration experiments established the DMD-to-detector coordinate mapping and validated the strategies for object selection and slit placement. On-sky tests in crowded stellar fields confirmed successful slit targeting, precise object alignment, and multiplexed spectral acquisition. The spectrograph achieved a peak efficiency of 32%, a spectral resolving power of R∼1000 at 6000Å, a multiplexing capability of up to 46 slits (extendable to 85), and a contrast ratio of ∼ 6000. These results demonstrate the robustness and effectiveness of the DMD MOS system under real observational conditions and raise its TRL level for use in next-generation spectroscopic space missions.
IIA MRIDWEEKA SINGHA tale of three cataclysmic variables with distinct superhumps
Superhumps are among the most commonly observed variable features in the light curves of cataclysmic variables (CVs). To study the superhump behaviour of CVs, we present Transiting Exoplanet Survey Satellite (TESS) observations of three CVs: CRTS J110014.7+131552, SDSS J093537.46+161950.8, and [PK2008] HalphaJ130559. Among them, a super-outburst has been observed in CRTS J110014.7+131552, which is associated with the precursor outburst, where prominent superhumps have been observed during maximum of the outburst with a mean period of 0.06786(1) d. We observed variations in the superhump period, along with changes in the shape of the light curve profile and the amplitude of the superhumps during different phases of the outburst, indicating disc-radius variation as well as periodically variable dissipation at the accretion stream’s bright spot. The data on SDSS J093537.46+161950.8 reveal previously unknown variations modulated with periods of 0.06584(2) d and 2.36(2) d, related to the positive superhump and the disc-precession periods, respectively, which can reasonably be interpreted as a result of the prograde precession of an eccentric accretion disc. Despite its short orbital period, the lack of outburst activity, its stable long-term brightness, discovery spectrum, and absolute magnitude suggest that the object might not be an SU UMa type dwarf nova. Instead, it could belong to the group of highmass-transfer CVs below the period gap: either a rare class of nova-like variables or a high-luminosity intermediate polar, a subclass of magnetic CVs. For [PK2008] HalphaJ130559, a new average orbital period of 0.15092(1) d has been identified. Additionally, this system displays previously undetected average periods of 0.14517(3) d and 3.83(1) d, which could be provisionally identified as negative superhump and disc-precession periods, respectively. If the identified simultaneous signals do indeed reflect negative superhump and disc-precession period variations, then their origin might be associated with the retrograde precession of a tilted disc and its interaction with the secondary stream.
IIA SRIRAM, SDigital micromirror device characterization in optical band for astronomical multi-object spectrograph
The Digital Micromirror Device (DMD), a micro-electro-mechanical system (MEMS) consisting of individually controllable micromirrors, has emerged as a versatile tool for astronomical instrumentation, particularly in multi-object spectroscopy (MOS). Unlike traditional slit masks or fiber-based systems, DMDs offer dynamic reconfigurability, enabling efficient light modulation and enhanced spectral acquisition. Their adaptability has led to widespread adoption in ground-based spectrographs (e.g., RITMOS, BATMAN, SAMOS, IRMOS) and feasibility studies for space missions (e.g., EUCLID, CASTOR, SUMO, SIRMOS). DMDs have demonstrated robustness in space qualification tests, including radiation exposure, thermal cycling, and mechanical stress, making them viable for space-based applications. Recent advancements, such as UV-transparent windows and enhanced coatings, further expand their potential for ultraviolet astronomy. In India, the success of AstroSat’s Ultra Violet Imaging Telescope (UVIT) has motivated the development of the next-generation INdian Spectroscopic and Imaging Space Telescope (INSIST), which includes a DMD-based MOS for UV/optical observations. To advance its Technology Readiness Level (TRL), we evaluated the Texas Instruments DLP9500 DMD (1920 × 1080 micromirrors, 10 µm pitch) in the optical band, assessing key parameters such as diffraction efficiency, reflectivity, contrast, micromirror repeatability, and Point Spread Function (PSF) alignment. This study establishes a foundation for future UV-optimized DMD applications in INSIST and other astronomical missions.
IIA SIVARANI, TNon-linear solar EUV-driven sodium release from the lunar surface: a contrast to the linear PSD model
The correlation between solar Extreme Ultra-Violet (EUV) radiation above 8.8 eV and the release of sodium from the lunar surface via photon-stimulated desorption (PSD) is investigated. We use simultaneous measurements of EUV photon flux and Na optical spectral line flux (FNa) from the lunar exosphere. Data were acquired with the high-resolution (R∼72 000) Echelle Spectrograph on the 2.34-m Vainu Bappu Telescope during the lunar first quarter (2024 January–March), observing Na I D2 and D1 flux at altitudes below ∼590 km from the surface. Simultaneous EUV and FUV measurements were acquired from the GOES-R Series Extreme Ultraviolet Sensor (EUVS), while NUV data were obtained from the Total and Spectral Solar Irradiance Sensor-1 (TSIS-1) aboard the ISS. We correlated FNa with EUV photon flux from EUVS across six bands spanning 256–1405 Å (48.5–8.8 eV) and NUV (2000–4000 Å) from TSIS-1. A non-linear rise in lunar exospheric sodium with increasing EUV and FUV fluxes was observed, contrasting with previous linear PSD models. The EUV radiation above 10 eV drives sodium release, with 256-304 Å wavelengths as dominant contributors. Additionally, the NUV flux and FNa are positively correlated, indicating the role of sodium release. The zenith column density averages 3.3 × 109 atoms cm−2, with Characteristic temperatures averaging at ∼6700 K and scale heights of ∼1500 km. Elevated temperatures and sodium densities during solar activity suggest enhanced Na release during flares. These results emphasize the need for a revised PSD model above 8.8 eV and improved constraints on the PSD cross-section
IIA PRAMOD KUMAR SAsteroseismology of HD 23734, HD 68703, and HD 73345 using K2–TESS space-based photometry and high-resolution spectroscopy
In this paper, we present a comprehensive study of three stars, HD 23734, HD 68703, and HD 73345, which were previously observed as chemically peculiar candidates within the Nainital-Cape survey and reported as null results for the pulsational variability. Frequency analyses of K2 and TESS time-series photometric data reveal the co-existence of rotational modulation and pulsation. We use the spectrum synthesis technique to determine fundamental parameters and chemical composition, which shows that all the three stars are likely to be chemically normal. The evolutionary status of the target stars corresponds to the main-sequence phases and places them within the δ Scuti instability strip of the Hertzsprung–Russell diagram. The line profile variability is observed in all three stars, especially intriguing in HD 68703 and a typical signature of the non-radial pulsation, demands further detailed examination. Using TESS photometry, we identified the radial modes of orders n = 3 and 4 for HD 23734, n = 1, 3, and 4 for HD 68703, and n = 3, 4, and 5 for HD 73345. In addition to the presence of pulsation and rotation, HD 73345 exhibits a steady increase in radial velocity that we interpret as the star being likely to be part of a long-period binary system. Finally, we propose an extended campaign aimed for the in-depth spectroscopic and spectropolarimetric study of selected pulsating stars monitored under the Nainital-Cape survey project.
IIA PUJA PORELInvestigating the kinematics of molecular gas in cometary globule L1616
LDN 1616 is a cometary globule located approximately 8◦ west of the Orion OB1 associations. The massive OB stars in the Orion belt region act as catalysts, triggering the star formation activity observed in the L1616 region which is a photodissociation region (PDR). This paper provides an in-depth analysis of gas kinematics within the L1616 PDR, leveraging the Heterodyne Array Receiver Programme on the James Clerk Maxwell Telescope to observe 13CO and C18O J = 3 → 2 emissions. Employing the Clumpfind algorithm on the C18O emission data, we identify three distinct clumps within this PDR. For each of these clumps, we derive key physical parameters, including the mean kinetic temperature, optical depth, and velocity dispersion. In addition, we compute the non-thermal velocity dispersion and Mach number, providing critical insights into the turbulent dynamics of the gas. Comprehensive evaluation of mass, including virial and energy budget evaluations, are conducted to assess the gravitational stability and star-forming potential of the identified clumps. While previousstudies have proposed that radiation-driven implosion (RDI) is the dominant mechanism initiating star formation in LDN 1616, our results suggest that the clumps may represent pre-existing substructures within the PDR. This interpretation is supported by our estimation of a relatively low interstellar radiation field (G0), which, although insufficient to form clumps independently, may enhance gravitational instability through additional compression. Thus, our findings offer a more nuanced perspective on the role of RDI, highlighting its capacity to trigger star formation by amplifying the instability of pre-existing clumpy structures in PDRs like LDN 1616.