IIA VIVEK, MFLAME: Fitting Lyα absorption lines using machine learning
We introduce FLAME, a machine-learning algorithm designed to fit Voigt profiles to H I Lyman-alpha (Lyα) absorption lines using deep convolutional neural networks. FLAME integrates two algorithms: the first determines the number of components required to fit Lyα absorption lines, and the second calculates the Doppler parameter b, the H I column density NHI, and the velocity separation of individual components. For the current version of FLAME, we trained it on low-redshift Lyα forests observed with the far-ultraviolet gratings of the Cosmic Origin Spectrograph (COS) on board the Hubble Space Telescope (HST). Using these data, we trained FLAME on ∼106 simulated Voigt profiles – which we forward-modeled to mimic Lyα absorption lines observed with HST-COS – in order to classify lines as either single or double components and then determine Voigt profile-fitting parameters. FLAME shows impressive accuracy on the simulated data, identifying more than 98% (90%) of single (double) component lines. It determines b values within ≈ ± 8 (15) km s−1 and log NHI/cm2 values within ≈ ± 0.3 (0.8) for 90% of the single (double) component lines. However, when applied to real data, FLAME’s component classification accuracy drops by ∼10%. Nevertheless, there is reasonable agreement between the b and NHI distributions obtained from traditional Voigt profile-fitting methods and FLAME’s predictions. Our mock HST-COS data analysis, designed to emulate real data parameters, demonstrates that FLAME is able to achieve consistent accuracy comparable to its performance with simulated data. This finding suggests that the drop in FLAME’s accuracy when used on real data primarily arises from the difficulty in replicating the full complexity of real data in the training sample. In any case, FLAME’s performance validates the use of machine learning for Voigt profile fitting, underscoring the significant potential of machine learning for detailed analysis of absorption lines.
IIA MANJUNATH HEGDEThermal and magnetic field structure of near-equatorial coronal holes
Coronal holes are low-density and unipolar magnetic field structures in the solar corona that trigger geomagnetic disturbances on the Earth. Hence, it is important to understand the genesis and evolutionary behavior of these coronal activity features during their passage across the solar disk. Aims. We study the day-to-day latitudinal variations of thermal and magnetic field structures of near-equatorial coronal holes. For this purpose, eight years of full-disk SOHO/EIT 195 Å calibrated images were used. Methods. Using the response curves of the SOHO/EIT channels and assuming thermodynamic equilibrium, we estimated the temperature structure of coronal holes. From the latitudinal variation in the magnetic pressure, we inferred the magnitude of the magnetic field structure of coronal holes. Results. Except for the temperature T, we find that the variations in the average photon flux F, in the radiative energy E, in the area A, and in the magnitude of the magnetic field structure |B| of coronal holes depend on latitude. The typical average values of the estimated physical parameters are A ∼ 3.8(±0.5)×1020 cm2, F ∼ 2.3(±0.2)×1013 photons cm−2 s−1, E ∼ 2.32(±0.5)×103 ergs cm−2 s−1, T ∼ 0.94(±0.1)×106 K and |B|∼0.01(±0.001) G. Conclusions. When coronal holes are anchored in the convection zone, these activity features would be expected to rotate differentially. The thermal wind balance and isorotation of coronal holes with the solar plasma therefore implies a measurable temperature difference between the equator and the two poles. Contrary to this fact, the variation in the thermal structure of near-equatorial coronal holes is independent of latitude, which leads to the conclusion that coronal holes must rotate rigidly and are likely to be initially anchored below the tachocline. This confirms our previous study.
IIA ADITYA, KHow does dark matter stabilize disc galaxies?
The study presents a theoretical framework for understanding the role of dark matter on the stability of the galactic disc. We model the galaxy as a two-component system consisting of stars and gas in equilibrium with an external dark matter halo. We derive the equations governing the growth of perturbations and obtain a stability criterion that connects the potential of the dark matter halo and the gas fraction with the stability levels of the galaxy. We find that a two-component disc is more susceptible to the growth of gravitational instabilities than individual components, particularly as gas fractions increase. However, the external field, due to the dark matter halo, acts as a stabilizing agent and increases the net stability levels even in the presence of a cold gas component. We apply the stability criterion to models of the Milky Way, low surface brightness galaxies, and baryon-dominated cold rotating disc galaxies observed in the early universe. Our results show that the potential due to the dark matter halo plays a significant role in stabilizing nearby galaxies, such as the Milky Way, and low surface brightness galaxies, which would otherwise be prone to local gravitational instabilities. However, we find that the baryon-dominated cold disc galaxies observed in the early universe remain susceptible to the growth of local gravitational instabilities despite the stabilizing effect of the dark matter halo.
IIA ANNAPURNI SUBRAMANIAMDiscovery of a Barium Blue Straggler Star in M67 and “Sighting” of Its White Dwarf Companion
We report the discovery of a barium blue straggler star (BSS) in M67, exhibiting enhancements in slow neutron-capture (s-)process elements. Spectroscopic analysis of two BSSs (WOCS 9005 & WOCS 1020) and four stars located near the main-sequence turn-off using GALAH spectra, showed that WOCS 9005 has a significantly high abundance of the s-process elements ([Ba/Fe] = 0.75 ± 0.08, [Y/Fe] = 1.09 ± 0.07, and [La/Fe] = 0.65 ± 0.06). The BSS (WOCS 9005) is a spectroscopic binary with a known period, eccentricity, and a suspected white dwarf (WD) companion with a kinematic mass of 0.5 M⊙. The first "sighting" of the WD in this barium BSS is achieved through multiwavelength spectral energy distribution (SED) with the crucial far-UV data from the UVIT/AstroSat. The parameters of the hot and cool companions are derived using binary fits of the SED using two combinations of models, yielding a WD with Teff in the range 9750–15,250 K. Considering the kinematic mass limit, the cooling age of the WD is estimated as ∼60 Myr. The observed enhancements are attributed to a mass transfer (MT) from a companion asymptotic giant branch star, now a WD. We estimate the accreted mass to be 0.15 M⊙, through wind accretion, which increased the envelope mass from 0.45 M⊙. The detection of chemical enhancement, as well as the sighting of WD in this system, have been possible due to the recent MT in this binary, as suggested by the young WD.
IIA STALIN, C. SSpectropolarimetric view of the gamma-ray emitting NLS1 1H0323 + 342
The gamma-ray emitting narrow-line Seyfert 1 galaxies are a unique class of objects that launch powerful jets from relatively lower-mass black hole systems compared to the Blazars. However, the black hole masses estimated from the total flux spectrum suffer from the projection effect, making the mass measurement highly uncertain. The polarized spectrum provides a unique view of the central engine through scattered light. We performed spectropolarimetric observations of the gamma-ray emitting narrow-line Seyfert 1 galaxy 1H0323 + 342 using SPOL/MMT. The degree of polarization and polarization angle are 0.122 ± 0.040 per cent and 142 ± 9 degrees, while the H α line is polarized at 0.265 ± 0.280 per cent. We decomposed the total flux spectrum and estimated broad H α full width at half maximum of 1015 km s−1. The polarized flux spectrum shows a broadening similar to the total flux spectrum, with a broadening ratio of 1.22. The Monte Carlo radiative transfer code ‘STOKES’ applied to the data provides the best fit for a small viewing angle of 9–24 deg and a small optical depth ratio between the polar and the equatorial scatters. A thick broad-line region with significant scale height can explain a similar broadening of the polarized spectrum compared to the total flux spectrum with a small viewing angle.
IIA SMITHA SUBRAMANIANA Partial Near-infrared Guide Star Catalog for Thirty Meter Telescope Operations
At first light, the Thirty Meter Telescope (TMT) near-infrared (NIR) instruments will be fed by a multiconjugate adaptive optics instrument known as the Narrow Field Infrared Adaptive Optics System (NFIRAOS). NFIRAOS will use six laser guide stars to sense atmospheric turbulence in a volume corresponding to a field of view of 2', but natural guide stars (NGSs) will be required to sense tip/tilt and focus. To achieve high sky coverage (50% at the north Galactic pole), the NFIRAOS client instruments use NIR on-instrument wave front sensors that take advantage of the sharpening of the stars by NFIRAOS. A catalog of guide stars with NIR magnitudes as faint as 22 mag in the J band (Vega system), covering the TMT-observable sky, will be a critical resource for the efficient operation of NFIRAOS, and no such catalog currently exists. Hence, it is essential to develop such a catalog by computing the expected NIR magnitudes of stellar sources identified in deep optical sky surveys using their optical magnitudes. This paper discusses the generation of a partial NIR Guide Star Catalog (IRGSC), similar to the final IRGSC for TMT operations. The partial catalog is generated by applying stellar atmospheric models to the optical data of stellar sources from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) optical data and then computing their expected NIR magnitudes. We validated the computed NIR magnitudes of the sources in some fields by using the available NIR data for those fields. We identified the remaining challenges of this approach. We outlined the path for producing the final IRGSC using the Pan-STARRS data. We have named the Python code to generate the IRGSC as irgsctool, which generates a list of NGS for a field using optical data from the Pan-STARRS 3pi survey and also a list of NGSs having observed NIR data from the UKIRT Infrared Deep Sky Survey if they are available. irgsctool is available in the public domain on this GitHub public repository (https://github.com/sshah1502/irgsc), while the generated and validated IRGSC for the 20 test fields and additional Pan-STARRS Medium Deep Survey fields can be found on Zenodo.
IIA KSHAMA, S. KA comparative analysis of the active galactic nucleus and star formation characteristics of broad- and narrow-line Seyfert 1 galaxies
We report here our comparative analysis of the active galactic nucleus (AGN) and star formation (SF) characteristics of a sample of narrow-line Seyfert 1 (NLS1) and broad-line Seyfert 1 (BLS1) galaxies. Our sample consisted of 373 BLS1 and 240 NLS1 galaxies and spanned the redshift 0.02 < z < 0.8. The broad-band spectral energy distribution, constructed using data from the ultra-violet to the far-infrared, was modelled using CIGALE to derive the basic properties of our sample. We searched for differences in stellar mass (M*), star formation rate (SFR), and AGN luminosity (LAGN) in the two populations. We also estimated new radiation-pressure-corrected black hole masses for our sample of BLS1 and NLS1 galaxies. While the virial black hole mass (MBH) of BLS1 galaxies is similar to their radiation-pressure-corrected MBH values, the virial MBH values of NLS1 galaxies are underestimated. We found that NLS1 galaxies have a lower MBH of log (MBH [M⊙]) = 7.45 ± 0.27 and a higher Eddington ratio of log (λEdd) = −0.72 ± 0.22 than BLS1 galaxies, which have log (MBH [M⊙]) and λEdd values of 8.04 ± 0.26 and −1.08 ± 0.24, respectively. The distributions of M*, SFR, and specific star formation (sSFR = SFR/M*) for the two populations are indistinguishable. This analysis is based on an independent approach and contradicts reports in the literature that NLS1 galaxies have a higher SF than BLS1 galaxies. While we found that LAGN increases with M*, LSF flattens at high M* for both BLS1 and NLS1 galaxies. The reason may be that SF is suppressed by AGN feedback at M* higher than ∼1011 M⊙ or that the AGN fuelling mechanism is decoupled from SF. Separating the sample into radio-detected and radio-undetected subsamples, we found no difference in their SF properties suggesting that the effect of AGN jets on SF is negligible.
IIA KHUSHBU, KPhoto-ionization structures of Planetary Nebula IC 2003 with [WR] central star
We present ionization structures of IC 2003, a planetary nebula with [WR] central star, using a 1-D dusty photo-ionization code: ”CLOUDY 17.03”. The photo-ionization model is constrained by archival UV emission line fluxes, medium-resolution optical spectroscopy, IRAS 25 µm flux, absolute Hβ flux, and the mean angular size of the nearly spherical optical nebula. To constrain the carbon abundance and the effect of photo-electric heating in the ionized gas, we used UV emission lines. We considered an amorphous carbon dust grain with MRN and KMH size distributions to address the importance of photo-electric heating in the ionized nebula. We show that KMH grain size distribution with quantum dust heating reproduces the observations quite well. We construct the ionization structures of different elements at their different ionization stages in the nebula. We derive the physical properties of the planetary nebula and its chemical composition, as well as the parameters of its central star. The estimated nebular dust-to-gas mass ratio is 2:37 x 103 , and the enhanced photo-electric heating yielded by small dust grains is 9:4% of the total heating. We considered the H-poor model atmosphere for the central star; the effective temperature of the central star is 177 kK, the specific gravity log(g) is 6, and its luminosity (L*) is 6425 Lʘ. The derived central star parameters plotted on stellar evolutionary tracks correspond to a central star mass of 0.636 Mʘ and to a progenitor mass of 3.26 Mʘ.
IIA DIPANKAR BANERJEEProbing Velocity Dispersion Inside Coronal Mass Ejections: New Insights on Their Initiation
This work studies the kinematics of the leading edge and the core of six coronal mass ejections (CMEs) in the combined field of view of Sun Watcher using Active Pixel System detector and Image Processing (SWAP) on board PRoject for On-Board Autonomy (PROBA-2) and the ground-based K-Cor coronagraph of the Mauna Loa Solar Observatory. We report, for the first time, on the existence of a critical height hc, which marks the onset of velocity dispersion inside the CME. This height for the studied events lies between 1.4 and 1.8 R⊙, in the inner corona. We find the critical heights to be relatively higher for gradual CMEs, as compared to impulsive ones, indicating that the early initiation of these two classes might be different physically. We find several interesting imprints of the velocity dispersion on CME kinematics. The critical height is strongly correlated with the flux-rope minor radius and the mass of the CME. Also, the magnitude of the velocity dispersion shows a reasonable positive correlation with the above two parameters. We believe these results will advance our understanding of CME initiation mechanisms and will help provide improved constraints on CME initiation models.
IIA ARCHANA SOAMGas Kinematics and Dynamics of Carina Pillars: A Case Study of G287.76-0.87
We study the kinematics of a pillar, namely G287.76-0.87, using three rotational lines of 12CO(5-4), 12CO(8-7), 12CO(11-10), and a fine structure line of [O i] 63 μm in southern Carina observed by SOFIA/GREAT. This pillar is irradiated by the associated massive star cluster Trumpler 16, which includes η Carina. Our analysis shows that the relative velocity of the pillar with respect to this ionization source is small, ∼1 km s−1, and the gas motion in the tail is more turbulent than in the head. We also performed analytical calculations to estimate the gas column density in local thermal equilibrium (LTE) conditions, which yields NCO as (∼0.2–5) × 1017 cm−2. We further constrain the gas's physical properties in non-LTE conditions using RADEX. The non-LTE estimations result in nH2 ≃ 10 5 cm-3 and NCO ≃ 1016 cm−2. We found that the thermal pressure within the G287.76-0.87 pillar is sufficiently high to make it stable for the surrounding hot gas and radiation feedback if the winds are not active. While they are active, stellar winds from the clustered stars sculpt the surrounding molecular cloud into pillars within the giant bubble around η Carina