IIA DIPANKAR BANERJEEAnalysis of BMR Tilt from AutoTAB Catalog: Hinting toward the Thin Flux Tube Model?
One of the intriguing mechanisms of the Sun is the formation of bipolar magnetic regions (BMRs) in the solar convection zone (CZ), which are observed as regions of concentrated magnetic fields of opposite polarity on the photosphere. These BMRs are tilted with respect to the equatorial line, which statistically increases with latitude. The thin flux tube model, employing the rise of magnetically buoyant flux loops and their twist by Coriolis force, is a popular paradigm for explaining the formation of tilted BMRs. In this study, we assess the validity of the thin flux tube model by analyzing the tracked BMR data obtained through the Automatic Tracking Algorithm for BMRs. Our observations reveal that the tracked BMRs exhibit the expected collective behaviors. We find that the polarity separation of BMRs increases over their normalized lifetime, supporting the assumption of a rising flux tube from the CZ. Moreover, we observe an increasing trend of the tilt with the flux of the BMR, suggesting that rising flux tubes associated with lower flux regions are primarily influenced by drag force and Coriolis force, while in higher flux regions, magnetic buoyancy dominates. Furthermore, we observe Joy's law dependence for emerging BMRs from their first detection, indicating that at least a portion of the tilt observed in BMRs can be attributed to the Coriolis force. Notably, lower flux regions exhibit a higher amount of fluctuations associated with their tilt measurement compared to stronger flux regions, suggesting that lower flux regions are more susceptible to turbulent convection.
IIA SUSMITHA, AMining the GALAH Data. I. Study of Five Super Lithium-rich Metal-poor Giants
The presence of a large amount of Li in giants is still a mystery. Most of the super Li-rich (SLR) giants reported in recent studies are in the solar metallicity regime. Here, we study the five metal-poor SLRs from the Galactic Archeology with HERMES Data Release 3, with their [Fe/H] ranging from −1.35 to −2.38 with lithium abundance of A(Li) 3.4 dex. The asteroseismic analysis reveals that none are on the red giant branch. The average period spacing (ΔP ) values indicate giants are in the core He-burning phase. All of them are low-mass giants (M < 1.5 Me). Their location in the Hertzsprung–Russell diagram suggests one of them is in the red clump (RC) phase, and interestingly, the other four are much brighter and coincide with the early asymptotic giant branch phase. The analysis of the abundance reveals that C, O, Na, Ba, and Eu are normal in giants of respective metallicities and evolutionary phases. Further, we did not find any strong evidence of the presence of dust in the form of infrared excess or binarity from the available radial velocity data. We discuss a few scenarios for the existence of SLRs at higher luminosity, including past merger events. Our findings will help in understanding the production and evolution of Li among giants, in particular, during the RC phase and the post-RC phase.
IIA MRIDWEEKA SINGHSN 2019nyk: A rapidly declining Type II supernova with early interaction signatures
We present an optical photometric and spectroscopic analysis of the fast-declining hydrogen-rich Type II supernova (SN) 2019nyk. The light curve properties of SN 2019nyk align well with those of other fast-declining Type II SNe, such as SNe 2013by and 2014G. SN 2019nyk exhibits a peak absolute magnitude of −18.09 ± 0.17 mag in the V band, followed by a rapid decline at 2.84 ± 0.03 mag (100 d)−1 during the recombination phase. The early spectra of SN 2019nyk exhibit high-ionisation emission features as well as narrow H Balmer lines, persisting until 4.1 d since explosion, indicating the presence of circumstellar material (CSM) in close proximity. A comparison of these features with other Type II SNe displaying an early interaction reveals similarities between these features and those observed in SNe 2014G and 2023ixf. We also compared the early spectra to literature models, estimating a mass-loss rate of the order of 10−3 M⊙ yr−1. Radiation hydrodynamical modelling of the light curve also suggests the mass loss from the progenitor within a short period prior to explosion, totalling 0.16 M⊙ of material within 2900 R⊙ of the progenitor. Furthermore, light curve modelling infers a zero-age main sequence mass of 15 M⊙ for the progenitor, a progenitor radius of 1031 R⊙, and an explosion energy of 1.1 × 1051 erg.
IIA ARUN SURYAOptical spectroscopy of comets using Hanle Echelle Spectrograph (HESP)
Observing the vibrational/rotational lines in a comet’s optical spectrum requires high-resolution spectroscopy, as they are otherwise seen as a blended feature. To achieve this, we have obtained medium and high-resolution (R (λ/Δλ) = 30 000 and 60 000) spectra of several comets, including C/2015 V2 (Johnson), 46P/Wirtanen, 41P/Tuttle–Giacobini–Kresák, and 38P/Stephan–Oterma, using the Hanle Echelle Spectrograph (HESP) mounted on the 2-m Himalayan Chandra Telescope (HCT) in India. The spectra effectively cover the wavelength range 3700–10 000 Å, allowing us to probe the various vibrational bands and band sequences to identify the rotational lines in the cometary molecular emission. We were also able to separate the cometary Oxygen lines from the telluric lines and analyse the green-to-red (G/R) forbidden oxygen [O i] ratios in a few comets. For comets C/2015 V2, 46P, and 41P, the computed G/R ratios, 0.04 ± 0.01, 0.04 ± 0.01, and 0.08 ± 0.02, respectively, point to H2O being a major source of Oxygen emissions. Notably, in the second fibre pointing at a location 1000 km away from the photocentre of comet 46P, the G/R ratio reduced by more than half the value observed in the first fibre, indicating the effects of quenching within the inner coma. We also measured the NH2 ortho-to-para ratio of comet 46P to be about 3.41 ± 0.05 and derived an ammonia ratio of 1.21 ± 0.03 corresponding to a spin temperature of ∼26 K. With these, we present the results of the study of four comets from different cometary reservoirs using medium and high-resolution optical spectroscopy, emphasizing the capabilities of the instrument for future cometary studies.
IIA AMRUTHA, SA comparative study of star-forming dwarf galaxies using the UVIT
We present a far-ultraviolet (FUV) study of 16 star-forming dwarf galaxies (SFDGs) using the Ultra Violet Imaging Telescope. Morphologically, SFDGs are classified as dwarf spirals, dwarf irregulars, and blue compact dwarfs (BCDs). We extracted the star-forming complexes (SFCs) from the sample galaxies, derived their sizes, and estimated the FUV + 24 μm star-formation rates (SFRs). We also determined the approximate stellar disc mass associated with the SFCs using Infrared Array Camera 3.6 micron images. We derived the specific SFRs (sSFRs), as well as the SFR densities [Σ(SFR)] for the SFCs. We find that the lower Σ(SFR) for each type is different, with the dwarf irregulars having the lowest Σ(SFR) compared with others. However, the median size of the SFCs in the dwarf irregulars is the largest compared with the other two types when compared at roughly the same distance. We have derived the star-forming main sequence (SFMS) on the scale of SFCs for all three classes of SFDGs. We find that although all SFDGs approximately follow the global SFMS relation, i.e. SFR ∝ M*α (where globally α ≈ 1 for low-surface brightness galaxies and 0.9 for SFDGs), on the scale of SFCs the α value for each type is different. The α values for dwarf spirals, dwarf irregulars, and BCDs are found to be 0.74 ± 0.13, 0.87 ± 0.16, and 0.80 ± 0.19, respectively. However, the age of all SFCs approximately corresponds to 1 Gyr. Finally, we find that the outer SFCs in most galaxies except BCDs have a high sSFR, supporting the inside-out model of galaxy growth.
IIA WAGEESH MISHRADistribution and recovery phase of geomagnetic storms during solar cycles 23 and 24
Coronal mass ejections (CMEs) and Stream Interaction Regions (SIRs) are the main drivers of intense geomagnetic storms. We study the distribution of geomagnetic storms associated with different drivers during solar cycles 23 and 24 (1996–2019). Although the annual occurrence rate of geomagnetic storms in both cycles tracks the sunspot cycle, the second peak in storm activity lags the second sunspot peak. SIRs contribute significantly to the second peak in storm numbers in both cycles, particularly for moderate to stronger-than-moderate storms. We note semiannual peaks in storm numbers much closer to equinoxes for moderate storms, and slightly shifted from equinoxes for intense and stronger-than-intense storms. We note a significant fraction of multiple-peak storms in both cycles due to isolated ICMEs/SIRs, while single-peak storms from multiple interacting drivers, suggesting a complex relationship between storm steps and their drivers. Our study focuses on investigating the recovery phases of geomagnetic storms and examining their dependencies on variousstorm parameters. Multiple-peak storms in both cycles have recovery phase duration strongly influenced by slow and fast decay phases with no correlation with the main phase build-up rate and Dst peak. However, the recovery phase in single-peak storms for both cycles depends to some extent on the main phase build-up rate and Dst peak, in addition to slow and fast decay phases. Future research should explore recovery phases of single and multiple-peak storms incorporating in situ solar wind observations for a deeper understanding of storm evolution and decay processes.
IIA RAVINDRA, BComparison between variations in solar UV radiation and sunspot parameters with Mg II daily index as a proxy
Solar UV radiation influence the Earth’s climate and upper atmosphere. The UV emission from the Sun modulates with the sunspot cycle with an 11-year periodicity. The variations in UV, EUV, and X-rays emission are significant during the solar cycle evolution compared to the visible part of the spectrum. The h & k lines of the Mg II spectra emitted from the chromosphere represent the solar UV variability. The sunspot’s magnetic fields and dynamics are responsible for the UV and EUV emissions from the solar chromosphere and corona. This paper compares the Mg II core-to-wing ratio of the h & k lines observed at 278 nm wavelength (obtained from Solar Backscattered Ultraviolet Spectrograph (SBUV) instrument onboard the NOAA satellite) with the sunspot area parameter obtained from Royal Greenwich Observatory. When the sunspot group area is small, there is a linear relationship between the sunspot group area and the Mg II index. But a non-linear relationship between the two is observed for the large sunspot group area. There is no phase delay between the appearance of sunspot groups on the solar photosphere and the emission from the Mg II doublet. Apart from 11-year periodicity, we observed common 4.7, 3.2, and 2.2-year periodicity in both the data sets, suggesting the Mg II index is related to the sunspot parameters
IIA VEMAREDDY, PFilament Eruption from Active Region 13283 Leading to a Fast Halo-CME and an Intense Geomagnetic Storm on 2023 April 23
Using multi-instrument and multiwavelength observations, we studied a coronal mass ejection (CME) that led to an intense geomagnetic storm on 2023 April 23. The eruption occurred on April 21 in solar active region (AR) 13283 near the disk center. The AR was in its decay stage, with fragmented polarities and a preexisting long filament channel a few days before the eruption. The study of the magnetic field evolution suggests that the flux rope (filament) was built up by monotonous helicity accumulation over several days, and furthermore, converging and canceling fluxes led to a change in helicity injection, resulting in an unstable nature of the magnetic flux rope (MFR) and its further eruption. Importantly, the CME morphology revealed that the MFR apex underwent a rotation of up to 56°in clockwise direction owing to its positive helicity. The CME decelerates in the field of view (FOV) of the Large Angle Spectrometric Coronagraph and has a plane-of-sky velocity of 1226 km s−1 at 20 Re. In the FOV of the Heliospheric Imager, the lateral expansion of the CME is tracked better than the earthward motion. This implies that the arrival time is difficult to assess. The in situ arrival of the interplanetary CME shock was at 07:30 UT on April 23, and a geomagnetic storm commenced at 08:30 UT. The flux rope fitting to the in situ magnetic field observations reveals that the magnetic cloud flux rope orientation is consistent with its near-Sun orientation, which has a strong negative Bz-component. The analysis of this study indicates that the near-Sun rotation of the filament during its eruption to the CME is the key to the negative Bz-component and consequently the intense geomagnetic storm.
IIA REKHESH MOHANIndia's low-cost star tracker is up and running in space
A new low-cost star sensor developed by astronomers from off-the-shelf components was recently launched by ISRO on board PSLV C-55. In its first-ever space test, the sensor, which is mounted on the PSLV Orbital Experimental Module (POEM), is performing well, and the initial data has now validated its design as well as its function.
The StarBerrySense payload developed by the Indian Institute of Astrophysics (IIA), an autonomous institute of the Department of Science and Technology (DST), was launched on 22 April. This novel low-cost sensor designed to quickly calculate where the satellite is pointing is being tested in space for the very first time. The astronomers from the Space Payloads Group at the institute have announced that not only has StarBerrySense withstood the harsh conditions in space and is functioning as expected, the initial data shows that it is able to calculate the pointing direction.
For any space mission, it is crucial to know where the satellite is being pointed to at any given time. While there are several ways to do this, a star sensor provides the most accurate information about a spacecraft’s orientation. The start sensor designed by the Space Payloads Group at IIA is capable of finding its pointing direction in space by identifying the stars in its field of view. “This payload is built around the well-known minicomputer RaspberryPi, and the electronics and software were designed in-house,” said Bharat Chandra, the technical lead of the project and a Ph.D. student at the Indian Institute of Astrophysics. “The advantage of this payload is that it is cost-effective, simple to build, and can be deployed on a wide variety of satellites,” he added.
“StarBerrySense was mounted on ISRO's PSLV Orbital Experimental Module (POEM), which provides a stable platform for our payload to operate from. POEM is a unique initiative by ISRO that utilises the spent 4th stage of the PSLV as an orbital platform for carrying out scientific experiments. It is an excellent opportunity to conduct short-term scientific experiments in space,” said Rekhesh Mohan, the Principal Investigator of the StarBerrySense project.
The primary objective was to assess its survivability and performance in space. “The flight qualification tests were done at the MGK Menon Laboratory for Space Sciences, located in the CREST campus of the Indian Institute of Astrophysics at Hosakote. Sky imaging tests were conducted at our Vainu Bappu Observatory”, said Binukumar, former visiting scientist at IIA and a member of the StarBerrySense team. “During the days following the launch, we have verified that StarBerrySense is performing as expected in space,” said Shubham Ghatul, a Ph.D. student in the team.
The main function of StarBerrySense is to image the field of view, correctly identify the stars it sees, and calculate the pointing direction. Shubhangi Jain, a Ph.D. student in the team, said, “Analysis of the preliminary data has confirmed that the imaging equipment works as expected, and the onboard software is able to calculate the pointing direction.” “Using the images received from the payload, we are verifying its accuracy by comparing with data from international databases,” Mahesh Babu, an electronics engineer with the team, added.
“Working with the PSLV team was a great learning experience for the whole team. Guidance and support from IN-SPACe was also invaluable in this successful venture,” added Rekhesh Mohan. The team also consisted of Margarita Safonova (DST Woman-Scientist) and Jayant Murthy (Visiting Professor).
DOI: https://doi.org/10.1117/1.JATIS.8.3.036002
HDSR GAJENDRA PANDEYHelium Enhancement in the Metal-rich Red Giants of Omega Centauri
Unlike the typical globular clusters, the stars of Omega Centauri do not show the same metal content, a parameter that indicates its age, but a large range in it. A team of scientists from the Indian Institute of Astrophysics (IIA) studied numerous stars of this cluster and discovered Helium (He) enhanced cool bright stars among the metal-rich sample of Omega Centauri. This result, based on a spectroscopic survey of the cluster, determines the He-abundance of these stars for the first time. The study provides a very important clue for the origin of the He-enhanced population establishing that these are the second generation of stars formed from the metal-rich and He-enhanced material from the first generation of stars. And, also that the He-enhanced main-sequence stars evolve to the metal-rich He-enhanced cool bright stars.