IIA VIVEK, MTransient LoBALs at high velocities: A case of extreme broad absorption line variability in J115636.82+085628.9
We present a multiepoch spectroscopic study of the broad absorption line (BAL) quasar J115636.82+085628.9 (zem = 2.1077), based on five spectra spanning nearly two decades in the observer’s frame. This source exhibits remarkable variability in both low-ionization (LoBAL: Al III and Mg II) and high-ionization (HiBAL: C IV and Si IV) absorption features. For the first time, we detect the emergence and subsequent disappearance of LoBAL troughs at high velocities (∼20,000 km s −1), coinciding with the strengthening and weakening of the corresponding HiBAL absorption. The C IV BAL profile extends from ∼6700 km s−1 to a conservative upper limit of 30,000 km s−1 and is composed of narrow, variable absorption features embedded within a broad, smoothenvelope. Both C IV and Si IV BAL troughs exhibit dramatic equivalent width (EW) changes—among the most extreme reported to date. Notably, these EW variations are strongly anticorrelated with continuum flux changes inferred from optical photometric light curves. We interpret this variability as the result of a new absorbing flow transiting into our line of sight, increasing the shielding of a more distant, preexisting outflow and giving rise to transient LoBAL absorption. This scenario supports a unified picture in which LoBAL and HiBAL features arise from similar outflow structures, with observed differences governed primarily by line-of-sight column densities consistent with previous findings.
IIA PRAJWEL JOSEPHEuclid: Early Release Observations of ram-pressure stripping in the Perseus cluster Detection of parsec-scale star formation within the low surface brightness stripped tails of UGC 2665 and MCG +07-07-070⋆
Euclid is delivering optical and near-infrared imaging data over 14 000 deg2 on the sky at spatial resolution and surface brightness levels that can be used to understand the morphological transformation of galaxies within groups and clusters. Using the Early Release Observations (ERO) of the Perseus cluster, we demonstrate the capability offered by Euclid in studying the nature of perturbations for galaxies in clusters. Filamentary structures are observed along the discs of two spiral galaxies, UGC 2665 and MCG +07-07-070, with no extended diffuse emission expected from tidal interactions at surface brightness levels of ∼30 mag arcsec‑2. The detected features exhibit a good correspondence in morphology between optical and near-infrared wavelengths, with a surface brightness of ∼25 mag arcsec‑2, and the knots within the features have sizes of ∼ 100 pc, as observed through IE imaging. Using the Euclid, CFHT, UVIT, and LOFAR 144 MHz radio continuum observations, we conducted a detailed analysis to understand the origin of the detected features. We constructed the Euclid IE‑YE, YE‑HE, and CFHT u ‑ r, g ‑ i colour-colour plane and show that these features contain recent star formation events, which are also indicated by their Hα and NUV emissions. Euclid colours alone are insufficient for studying stellar population ages in unresolved star-forming regions, which require multi-wavelength optical imaging data. There are features with red colours that can be explained by dust being stripped along with the gas in these regions. The morphological shape, orientation, and mean age of the stellar population, combined with the presence of extended radio continuum cometary tails can be consistently explained if these features formed during a recent ram-pressure stripping event. This result further confirms the exceptional qualities of Euclid in the study of galaxy evolution in dense environments.
IIA ARUN ROYPolycyclic Aromatic Hydrocarbons in the circumstellar medium of Herbig Ae/Be stars
We present a comprehensive mid-infrared spectroscopic survey of 124 Herbig Ae/Be stars using newly processed Spitzer/IRS spectra from the newly released CASSISjuice database. Based on prominent dust and molecular signatures (polycyclic aromatic hydrocarbons (PAHs), silicates, and hydrogenated amorphous carbons), we classify the stars into five groups. Our analysis reveals that 64% of the spectra show PAH emission, with detections peaking in the stellar effective temperature range 7000–11,000 K (B9–A5). Silicate features appear in 50% of the sample and likewise diminish at higher temperatures. Additionally, we find that future PAH studies can focus on Herbig Ae/Be stars with a spectral index n2−24 > −1 and flared morphologies to maximize PAH detections. The 6.2 μm PAH band is the most frequently observed in our sample, shifting blueward with increasing stellar temperature, and this is the largest sample yet used to test that peak shift. The weaker 6.0 μm feature does not shift with 6.2 μm, implying a distinct origin of C=O (carbonyl) or olefinic C=C stretching relative to C–C vibrations. We examined the 11.0/11.2 μm PAH ratio using high-resolution Spitzer spectra for the first time in a sample of Herbig Ae/Be stars, finding a range of ionization conditions. This study provides a strong foundation for future JWST observations of intermediate-mass pre-main-sequence stars.
IIA HEGDE, MPredicting CME speed at 20R⊙ using machine learning approaches
Coronal mass ejections (CMEs) are significant drivers of space weather, and accurately predicting their propagation speed is crucial for mitigating their impact on Earth’s environment. In this study, we leverage machine learning techniques to model and predict CME speed at 20R⊙ utilizing data from the Coordinated Data Analysis Workshop catalog. We considered data from Solar Cycles 23 and 24, divided into their rising, maxima, decline, and minima phases, to train multivariate linear regression, Random Forest, and XGBoost machine learning models aimed at predicting CME speeds at 20R⊙. The machine learning models use linear speed, acceleration, width, and kinetic energy as input features to estimate CME speeds at 20R⊙. Our results indicate that Random Forest and XGBoost models significantly outperform linear regression model across all datasets, achieving high R2 values (≈0.97) and low relative errors (6%) for most phases, especially during high solar activity. Feature importance analysis identifies CME linear speed and acceleration as the dominant predictors of CME speed at 20R⊙. This result is consistent with physical models, which describe CME propagation as being influenced primarily by initial speed and the drag force acting through acceleration or deceleration in the interplanetary medium. The trained models were applied to available events from Solar Cycle 25, to predict CME speeds at 20R⊙. The predicted values showed very good agreement with the actual speeds reported in the CDAW catalog. This successful application demonstrates the models’ generalizability and potential for forecasting future CME dynamics. Furthermore, such data-driven predictions can complement physicsbased models—such as the Drag-Based Model—by providing reliable speed estimates at specific heliocentric distances, thereby enhancing the accuracy of space weather forecasts.
IIA ARCHANA SOAMB-fields and dust in interstellar filaments using dust polarization (BALLAD-POL). IV.Grain alignment mechanisms in the cocoon nebula (IC 5146) using polarization observations from JCMT/POL-2
The polarization of starlight and thermal dust emission from aligned nonspherical grains provides a powerful tool for tracing magnetic field morphologies and strengths in the diffuse interstellar medium to star-forming regions, and constraining the properties of dust grains and their alignment mechanisms. However, the physics of grain alignment is not yet fully understood. The alignment based on radiative torques (RATs), known as RAT alignment or the RAT-A mechanism, is the most acceptable mechanism. In this work, we investigate the grain alignment mechanisms in the F13 (F13N and F13C) and F13S filamentary regions of the Cocoon Nebula (IC 5146) using observations of polarized thermal dust emission from James Clerk Maxwell Telescope/POL-2 at 850 μm. We find that the polarization fraction decreases with increasing total intensity and gas column density in each region, termed a polarization hole. We investigate any role of magnetic field tangling in the observed polarization hole by estimating the polarization angle dispersion function. Our study finds that the polarization hole is not significantly influenced by magnetic field tangling, but is mainly due to the decrease in RAT alignment efficiency of grains in denser regions. To test whether the RAT-A mechanism can reproduce the observed results, we estimate the minimum alignment size of grains using RAT theory. Our study finds strong evidence for the RAT-A mechanism that can explain the polarization hole. We also find potential hints that the observed higher polarization fractions in some regions of the F13 filament can be due to the combined effects of both suprathermal rotation by RATs and enhanced magnetic relaxation, supporting the magnetically enhanced RAT mechanism.
IIA BACHAM E. REDDYLi enrichment in Red Clump Giants: Clues for past binary interaction or merger events
To understand the underlying mechanisms of high Li abundances among core He-burning or red clump (RC) giants, we analyzed a sample of 5227 RC giants of mass M < 2 M⊙ using spectra and asteroseismic data. We found 120 RC giants (∼2%) with a lower limit of A(Li) = 0.7 dex, a factor of 40 more than their predecessors close to the red giant branch tip. Of the 120 RC giants, we could measure actual rotations for 16 RC giants using stellar spots from the Kepler light-curve analysis. We found that most of the high-rotation RC giants are also very high Li-rich RC giants, and the rotation seems to decline rapidly with Li abundance depletion, suggesting that both the high rotation and high Li abundance are transient phenomena and associated with a single source. Further, we found a significantly high occurrence of 15% and 12% of Li-rich RC giants among extremely low-mass RC giants and RC giants with anomalous [C/N] ratios, respectively. The extremely low mass, fast rotation, and anomalous [C/N] values of RC giants are attributed to their past binary interaction/merger history. The results pose the question of whether the binary interaction/merger is a prerequisite, along with the He flash, for Li enhancement among RC giants.
IIA MUTHU PRIYAL, VShort and intermediate periodicities in Ca II K plage areas as seen in Kodaikanal images for individual cycles from 14 to 22
We analyze historical Ca II K images from the Kodaikanal Observatory (KO) spanning 1907 to 1996, encompassing Solar Cycles 14 through 22. These digitized images were processed using the Equal Contrast Technique (ECT) to ensure uniform data quality for studying long and short-term variations. From these standardized images, we identify and compute the areas of both plages and network regions in both solar hemispheres in every image. We then utilizy this revised, uniform Ca II K plage area time series for Solar Cycles 14 to 22. Our primary objective is to investigate the presence of short, Rieger-type periods and quasi-biennial oscillations (QBOs), specifically those near ≈ 1.3 years. To achieve this, we employ both Lomb-Scargle periodograms and Morlet wavelet maps. Our power spectrum analysis consistently shows that Rieger-type periods are significant across all solar cycles, in both the northern and southern hemispheres and in the whole disk data. However, the wavelet analysis reveals that both Rieger-type and QBO periodicities are intermittent, exhibiting varying periods in different cycles and hemispheres. This indicates that plages and network areas demonstrate asymmetric behavior between the two hemispheres. We have also discussed the potential reasons behind these observed periodicities.
IIA VIVEK, MX-ray selected broad absorption line quasars in SDSS-V: BALs and non-BALs span the same range of X-ray properties
Broad absorption line (BAL) quasars are often considered X-ray weak relative to their optical/UV luminosity, whether intrinsically (i.e. the coronal emission is fainter) or due to large column densities of absorbing material. The SDSS-V is providing optical spectroscopy for samples of quasar candidates identified by eROSITA as well as Chandra, XMM, or Swift, making the resulting data sets ideal for characterizing the BAL quasar population within an X-ray selected sample. We use the Balnicity Index (BI) to identify the BAL quasars based on absorption of the C IV λ1549 emission line in the optical spectra, finding 143 BAL quasars in our sample of 2317 X-ray selected quasars within 1.5≤z≤3.5. This observed BAL fraction of ≈ 6 per cent is comparable to that found in optically selected samples. We also identify absorption systems via the Absorption Index (AI) which includes mini-BALs and NALs, finding 954 quasars with AI >0 . We consider the C IV emission space (equivalent width versus blueshift) to study the BAL outflows within the context of the radiatively driven accretion disc–wind model. X-ray selection excludes the highest outflow velocities in emission but includes the full range of absorption velocities which we suggest is consistent with the BAL gas being located further from the X-ray corona than the emitting gas. We observe both X-ray weak and X-ray strong BALs (via the optical-to-X-ray spectral slope, αox) and detect little evidence for differing column densities between the BAL and non-BAL quasars, suggesting the BALs and non-BALs have the same shielding gas and intrinsic X-ray emission.
IIA HEMA, B. PPhotospheric Helium Abundance in Cool Giants: A Comprehensive Study
High-resolution optical spectra of 16 red giants, two early asymptotic giant branch (AGB) stars, and two supergiants, having no/minimal - to super-lithium (Li)-rich abundances, are analyzed to investigate the helium (He)-enhancement. The spectra of eight giants were obtained from the Himalayan Chandra Telescope, and for the rest of the program stars the spectral data were collected from various public archives. Our detailed abundance analyses of the program stars involve the determination of stellar parameters and abundances for about 20 elements among the key abundances of He, Li, C, N, O, and the 12C/13C ratios. The difference in the Mg abundance derived from Mg I lines and the MgH band, and the difference in carbon abundance from C I and the CH band, are used as a clue to the mild hydrogen-deficiency/ helium-enhancement. From this analysis, four red giants, an early-AGB star, and a supergiant star were found to be enhanced in helium. All these He-enhanced stars are also found to be super-Li rich except for the supergiant. Since the He-rich red giants are Li rich as well, this implies that He enrichment is accompanied by Li enrichment, but not vice versa. This is the first spectroscopic measurement of photospheric He abundance in normal and Li-rich field giants. The Li enrichment is observed across the giant branch from red giant branch (RGB)-bump (KIC 9821622) to AGB phase, unlike that expected from the RGB-tip to red clump phase. A plausible scenario for the enrichment of He as well as Li in giants is the fresh synthesis of Li in the interiors of giants and dredging-up along with He to the surface from deeper layers. However, there could be multiple scenarios operating in tandem. This analysis of He and Li enrichment along with other key elements provides more insights to decipher the mystery of Li enrichment in giants.
IIA SIPRA HOTAUVIT Study of the Magellanic Clouds (U-SMAC). III. hierarchical star formation in the small magellanic cloud regulated by turbulence
The Small Magellanic Cloud (SMC), a satellite galaxy of the Milky Way, is an irregular dwarf galaxy exhibiting evidence of recent and ongoing star formation. We performed a spatial clustering analysis of far-ultraviolet stars in the SMC younger than 150 Myr using data from the Ultra Violet Imaging Telescope on board AstroSat. We identified 236 young stellar structures as surface overdensities at different significance levels. The sizes of these structures range from a few parsecs to several hundred parsecs. Their irregular morphologies are characterized by a perimeter–area dimension, derived from the projected boundaries of the young stellar structures, of Dp = 1.46 ± 0.4. The 2D fractal dimensions obtained from, respectively, the number–size relation and the size distribution are D2 = 1.64 ± 0.03 and D2 = 1.31 ± 0.16. These values indicate significant lumpiness among the young stellar structures. In addition, the surface density distribution of the identified structures follows a log-normal distribution. These features are strikingly similar to those of the turbulent interstellar medium, thus supporting the scenario of hierarchical star formation regulated by supersonic turbulence.