Research Highlights
ARTICLES | IIA

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

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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.

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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

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.

Astronomers have discovered a new active galaxy identified as the farthest gamma-ray emitting galaxy that has so far been stumbled upon. This active galaxy called the Narrow-Line Seyfert 1 (NLS1) galaxy, which is about 31 billion light-years away, opens up avenues to explore more such gamma-ray emitting galaxies that wait to meet us.

Ever since 1929, when Edwin Hubble discovered that the Universe is expanding, it has been known that most other galaxies are moving away from us. Light from these galaxies is shifted to longer (and this means redder) wavelengths - in other words, it is red-shifted. Scientists have been trying to trace such red-shifted galaxies to understand the early Universe.

Scientists from ARIES, an autonomous institute of the Department of Science & Technology (DST), Government of India, in collaboration with researchers from other institutions, studied around 25,000 luminous Active galactic nuclei (AGN) from the Sloan Digital Sky Survey (SDSS), a major optical imaging and spectroscopic survey of astronomical objects in-operation for the last 20 years and found a unique object that emits high-energy gamma rays located at a high redshift (more than 1). They identified it as a gamma-ray emitting NLS1 galaxy, which is a rare entity in space.

Powerful relativistic jets, or sources of particles in the Universe traveling nearly at speed to light, are usually produced by AGN powered by large black holes and hosted in a giant elliptical galaxy. However, detection of gamma-ray emission from NLS1 challenges the idea of how relativistic jets are formed because NLS1s are a unique class of AGN that are powered by black hole of low mass and hosted in spiral galaxy. As of today, gamma-ray emission has been detected in about a dozen NLS1 galaxies, which are a separate class of AGN identified four decades ago. All of them are at redshifts lesser than one, and no method was present till date to find NLS1 at redshifts larger than one. This discovery opens up a new way to find gamma-ray emitting NLS1 galaxies in the early Universe.

For the research, the scientists used one of the largest ground-based telescopes in the world, the 8.2 m Subaru Telescope located at Hawaii, USA. They helped establish a new method to find high redshift NLS1 galaxies that were not known previously by comparing different emission lines in their spectra. The new gamma-ray emitting NLS1 was formed when the Universe was only about 4.7 billion years old as compared to its current age of about 13.8 billion years.

The research led by Dr. Suvendu Rakshit, Scientist, ARIES, in collaboration with various scientists Malte Schramm (Japan), C. S. Stalin (IIA, India), I. Tanaka (USA), Vaidehi S. Paliya (ARIES), Indrani Pal (IIA, India), Jari Kotilainen (Finland) and Jaejin Shin (South Korea) has recently been accepted for publication in the journal Monthly Notices of Royal Astronomical Society. Motivated by this finding, Dr. Rakshit and his collaborators are keen to exploit the capabilities offered by the TIFR-ARIES Near-Infrared Spectrometer on the recently commissioned 3.6 m Devasthal Optical Telescope (DOT) at ARIES to find more such gamma-ray emitting NLS1 galaxies at much larger redshifts.

For more details, Dr. Suvendu Rakshit (suvendu[at]aries[dot]res[dot]in) can be contacted.

Publication links:

DOI: https://doi.org/10.1093/mnrasl/slab031
arXiv: https://arxiv.org/abs/2103.16521

The vast majority of Sun like stars are expected to destroy lithium (Li) over the course of their lives. An international team led by Dr. Bharat Kumar Yerra (currently a post-doctoral fellow at NAOC, Beijing) along with Prof. Eswar Reddy (IIA) carried out a large-scale investigation into the Li content of stars in the red clump phase of stellar evolution. They found that all these stars have very high levels of Li for their evolutionary stage, with an increase of a factor of around 40 over the end of the red giant branch phase (the previous stage of their evolution). This suggests that all low-mass stars undergo an Li production phase between the red giant and the red clump stages, when they undergo the helium flash. The new finding is not predicted by the existing theories of stellar evolution, revealing a stark tension between observations and models.

An extreme helium star or EHe is a low-mass supergiant that is almost devoid of hydrogen, the most common chemical element of the universe. There are 21 of them detected so far in our galaxy. The origin and evolution of these Hydrogen deficient objects have been shrouded in mystery. Their severe chemical peculiarities challenge the theory of well-accepted stellar evolution as the observed chemical composition of these stars do not match with that predicted for low mass evolved stars.

A study by the Indian Institute of Astrophysics (IIA) an autonomous institute of Department of Science and Technology which detected the presence of singly ionised fluorine for the first time in the atmospheres of hot Extreme Helium Stars makes a strong case that the main formation of these objects involves a merger of a carbon-oxygen (CO) and a Helium (He) white dwarf.

The research published in the Astrophysical Journal, led by Anirban Bhowmick (Ph.D. student, IIA, Bengaluru), Prof. Gajendra Pandey (IIA) and Prof. David Lambert (University of Texas at Texas-Austin), which showed fluorine abundances determined from singly ionized fluorine (F II) lines suggest a very high enrichment of fluorine, about a factor of 100 to 10000 times higher than normal stars.

Clues to evolution of extreme helium stars require accurate determinations of their chemical composition, and the peculiarities, if any, become very important. Fluorine plays a very crucial role in this regard to determine the actual evolutionary sequence of these hydrogen deficient objects. Severe fluorine enrichment w.r.t normal stars (of the order of 800 − 8000) was observed in the cool EHes along-with the cooler classical hydrogen deficient stars, the RCB variables (R Coronae Borealis Stars) hinting at close evolutionary connection between them. The scientists explored the relationship of hot EHes (EHes having effective temperature ≥ 14000K), with the cooler EHes, based on their fluorine abundance and spotted it in the former, thus establishing an evolutionary connection across a wide range of effective temperature.

High-resolution echelle spectra of 10 hot EHes were obtained from Hanle Echelle Spectrograph (HESP) mounted on the 2-m Himalayan Chandra Telescope at the Indian Astronomical Observatory (IAO) in Hanle, Ladakh, (remotely operated by IIA) including data from McDonald Observatory, USA, and ESO archives.

By comparing the observed fluorine abundances with other abundances of the key elements, the scientists could determine the formation channels responsible for fluorine enrichment. The varied range of observed fluorine abundance across stars having similar atmospheric parameters points out the difference in the individual star’s evolution and the ensuing nucleosynthesis. Particularly, the enrichment of fluorine in the atmospheres of carbon-rich EHes and absence of the same in carbon-poor EHes suggest that fluorine is profusely produced during the merger of a He-CO WD resulting in a carbon-rich EHe, whereas He-He WD merger that results in carbon-poor EHes does not account for fluorine overabundance.

The detection of enhanced fluorine abundances in the atmospheres of hot EHes solves a decade-old mystery about their formation. It firmly places hot EHes in an evolutionary sequence with cool EHes and other hydrogen-deficient stars and zeros in on the evolutionary scenario, which involves the merger of two double degenerate white dwarfs (WDs).

Publication details: The Astrophysical Journal, Volume 891, Issue 1, id.40 https://iopscience.iop.org/article/10.3847/1538-4357/ab6e6d