BINA

The Belgo-Indian Network for Astronomy and astrophysics (BINA) was created to optimize the scientific exploitation of the observations of the solar system, galactic and extragalactic celestial objects gathered with the Indo-Belgian telescopes (DOT: the 3.6-m Devathal Optical Telescope; ILMT: the 4-m International Liquid Mirror Telescope) and the so-called telescopes of interest (those that are accessible for the partner institutes thanks to this collaboration). During this second phase of the project, the focus was shifted from the development of instruments for the DOT to the scientific activities in fields of common interest. Originally, seven science projects were defined: a general one for science with the ILMT and six specific ones for science with the DOT (asteroseismology; gravitational lenses; near-infrared photometry; abundances; high-resolution spectrograph; binaries). Unfortunately, the network activities could only start in 2022 (delay in acceptance of the project in India + COVID-19 pandemic). Moreover, persisting technical issues with the DOT and massive delays in the construction of both the ILMT and the high-resolution spectrograph for the DOT forced us to shift the scientific focus to the use of data from the telescope of interest and/or in publicly available databases. In the course of the project, new collaboration possibilities emerged leading to the definition of two additional science projects (solar system bodies and exoplanetary science; solar physics). Despite these setbacks at the start, BINA-2 turned out to be very productive with more than 60 published joint papers. Now that the term BINA is embedded in the Belgian and Indian astronomical communities, we aim to continue to use it to further stimulate Belgo-Indian collaborations in space sciences.

Overview of completed activities in the 2nd half of the BINA-2 project :
Note that all the network activities took place in the 2 nd half of the BINA-2 project due to a very long delay in the official approval of the BINA-2 on the Indian side that was followed by the COVID-19 pandemic. Therefore, no report was submitted after the 1 st half of the BINA-2 project.

Workshop

1.: 3rd BINA workshop “Scientific impact of the Indo-Belgian telescopes”
The inauguration of the ILMT took place at the Devasthal observatory on 21/03/2023. The telescope was inaugurated jointly by Lt. Ge. (Retd.) Gurmit Singh (Governor of Uttarakhand) and Dr. Jitendra Singh (Minster of State for Science and Technology, Govt. of India) and this facility was opened for the national and international astronomical community. This inauguration event was followed by the 3rd BINA workshop that was organised by ARIES on the campus of the Graphic Era Hill University in Bhimtal (India) on 03/22-24/03/2023. This event was inaugurated by Mr. Didier Vanderhasselt (ambassador of Belgium in India) in the presence of Dr. S. K. Varshney (DST, Govt of India), representatives from BELSPO (Belgium) and other dignitaries from India and Belgium. The BINA-2 funding was used to pay for the participation of 10 members of the Belgian BINA partner institutes to the 3rd BINA workshop (M. De Becker, ULiège; T. Furst, ROB/ULiège; L. Mahy, ROB; T. Merle, ROB/ULB; K. Kolenberg, UAntwerp/KU Leuven; A. Maharana, KU Leuven; T. Baratashvili, KU Leuven; M. Changmai, KU Leuven; K. Singh Dsilva, ULB; B. Arora, ULiège). There were 143 participants from 12 different countries, including a total of 18 from Belgium, reflecting the success of BINA in stimulating collaborations between Belgium and India in space sciences. For the first time, special attention was given to solar physics (separate session) and scientific outreach (general talks for students in local schools and universities and star-viewing activities for the general public), reflecting that the scope and the size of the network are still growing. During these four days, a total of 58 oral and 81 poster presentations were given by participants. In total, 94 research articles were submitted for the proceedings of the 3rd BINA workshop [C7]. They are published in no. 2 of volume 93 (year 2024) of the Bulletin de la Société Royale des Sciences de Liège.

2.: 1-day BINA workshop “Evaluation and future prospects of BINA”
A one-day BINA workshop on “Evaluation and future prospects of BINA” was organized at the ROB (Brussels, Belgium) on 10/10/2023. This meeting was attended by 33 in-person and about 50 online participants from India, Belgium and other countries. The achievements of BINA were evaluated during 13 invited talks, each introducing an ongoing project that was initiated thanks to BINA) and we had an open discussion about possibilities for a long- term continuation of the Indo-Belgian collaboration (search for money for joint workshops, work visits, PhD students, post-docs; creation of BINA website; start series of BINA seminars). It was explicitly acknowledged by Laurent Ghys (BELSPO) that a lot has been achieved with a small amount of money.

Overview of all the accomplished tasks and the final dessimination/outreach activities
In the proposal of the BINA-2 project, seven scientific projects were specified that are of joint interest to the Belgian and Indian partner institutes (A1-A7). In the course of the BINA-2 project, solar system bodies and exoplanetary science (A8) and solar physics (A9) have been added as additional scientific projects. Moreover, special attention has been given to outreach activities.

(A1) Science with the ILMT : During the first years of the BINA-2 project, some preparatory work for the ILMT has been done. A.K. Mandal et al. compiled a catalogue of quasars to be used for the astrometric calibration of the forthcoming ILMT survey. B. Kumar et al. tested the data reduction pipeline while N. Dukiya et al. searched for astrometric and photometric standard candidates for the ILMT survey.
Due to the COVID-19 pandemic, the commissioning of the ILMT was seriously delayed. The ILMT has only seen its first light in April 2022. The inauguration of the 4.0-m ILMT at Devasthal Observatory took place on March 21, 2023. By the end of the BINA-2 project, the third observing run with the ILMT was ongoing:
1.) Observing run 1: October 2022 – November 2022 (9 nights)
2.) Observing run 2: March 2023 – June 2023 (49 nights)
3.) Observing run 3: November 2023 – ongoing
The scientific results based on the first observations obtained with the ILMT have been presented in a separate session of the 3 rd BINA workshop and during the 2 nd International Orbital Debris Conference . P. De Cat et al. Investigated the usefulness of the ILMT data for the study of pulsating stars.

(A2) Asteroseismology:
The Nainital-Cape survey is a dedicated ground-based project that was originally initiated between astronomers of India and South Africa to study the variability and search for pulsations in chemically peculiar Ap and Am/Fm stars. Thanks to the BINA project, Belgian investigators got involved in this survey too. We studied the ground-based high-resolution spectra and the space-based photometry for the Kepler/K2 mission of five Am stars in the region of the open cluster M44 . Three of them were previously reported as non-variables but are now classified as a variable: HD73045 and HD76310 have characteristics compatible with non-stationary and short-lived sports or cloud-like co-rotating structures while HD73619 exhibits electrocardiogram-like features that are typical for so- called “heartbeat stars” (close, eccentric binaries showing brightening episodes near periastron). There is no evidence for pulsations in these systems. For HD73618 and HD73574, the existing datasets are not adequate to classify their variability nature. These results were presented in a poster presentation during the Sub-Saharan Africa Astronomy Summer School Galaxies, Extrasolar Planets, and Stellar Physics: Gazing into the Deep Space, searching for New Worlds, and Insights into Stellar Interior Physics in Entebbe (Uganda) by O. Trust .

S. Joshi (ARIES, India) and P. De Cat (ROB, Belgium) initiated a project with O. Trust & E. Jurua (Mbarara, Uganda) to investigate the atmospheric, chemical, and pulsational properties of A- and Am/Fm-type stars. Special attention is given to the so-called “hump and spike” (HNS) stars whose frequency spectrum from Kepler data shows a hump of unresolved frequencies (interpreted as Rossby modes) with a sharp peak at the high-frequency end (believed to give an approximate value for the rotational frequency of the star) . High-resolution spectra with the HERMES spectrograph (1.2-Mercator@RMO; La Palma, Spain) have been gathered for a sample of these stars to derive various stellar parameters such as effective temperatures, surface gravities, projected rotational velocities, micro-turbulent velocities, radial velocities and individual chemical abundances. For HD180347, no pulsations were found in the data obtained during three sectors of the TESS space mission. From a detailed analysis of its HERMES spectrum, we could classify this star as an Am star (kA1hA8mA8) and conclude that the inclusion of non-local thermodynamic equilibrium (NLTE) in the derivation of the aboundances of 13 chemical elements improved the results [R27]. On 01/04/2022, O. Trust successfully defended his PhD thesis entitled Evaluating the origin of chemical anomalies in Am stars with “hump and spike” features in their frequency Spectra (supervisors: E. Jurua, S. Joshi, and P. De Cat).

J. Adassuriya (Colombo, Sri Lanka) finished his PhD entitled Mode identification of oscillations of Delta Scuti stars using multicolour photometry and high-resolution spectroscopy in 2022 (supervisors: Ch. Jayaratne, S. Ganesh). On 17/09/2020, P. De Cat (ROB, Belgium) observed one high-resolution spectrum with HERMES (1.2- Mercator@RMO; La Palma, Spain) on his request for SZ Lyn, which is a binary system containing a δ Scuti-type pulsating star. It was analysed in combination with 561 low-resolution spectra gathered with LISA (0.5-m@MIRO; Rajasthan, India) obtained in 2016. The equivalent widths of the Balmer lines Hα, Hβ, and Hγ were measured over the pulsation cycle of SZ Lyn to derive the temperature profile of SZ Lyn using the curve of growth analysis.

Furthermore, the stellar parameters were determined by comparing the observed spectral lines in high resolution with synthetic ones in a best-fit analysis.

(A3) Graviational lenses:
Gravitational lensing occurs when the light of a distant object is deflected by a massive compact foreground object. Microlensing is a powerful tool for probing the inner structure of distant quasars. D. Hutsemékers et al. studied two images of the broad absorption line (BAL) quasar SDSS J081830.46+060138.0 and concluded that it is a gravitationally lensed quasar (instead of a binary quasar) having two spatially separated continuum sources (a microlensed compact one and a non-microlensed extended one).

Belgian and Indian partners are active members of the Gaia Gravitational Lenses working group (GraL) in which the data of the Gaia space mission are combined with ground-based follow-up observations to identify and study candidate lensed quasars. D. Stern et al. found 12 quadruply imaged quasars by combining, increasing the total number of this kind of object by about 20%. T. Connor et al. investigated nine of the lensed quasars identified by GraL and found that three of them are of particular interest: one showing evidence for flux variability, the most closely separated individual lensed sources resolved by XMM-Newton, and one of the brightest quasars in X-rays at a redshift larger than 3. D. Dobie et al. analysed new radio observations in combination with existing optical measurements for a sample of 24 confirmed and candidate strongly lensed quasars. They discovered radio emission from 20 lensed systems but the spatial resolution of their observations is not sufficient to resolve the individual lensed images. The two BAL quasars in their sample show evidence for extended emission. The technique that is being used for a spectroscopic identification of multiply imaged quasars has been explained during a contributed talk at the 3 rd BINA workshop.

Belgian and Indian partners contributed to a review describing the observational hints for deviations from the cosmological principle saying that the universe is spatially isotropic and homogeneous on large scales and another one that describes the search for strong gravitational lenses covering various sources, lenses, datasets, and wavelengths.

(A4) Near-Infrared photometry:
TANSPEC is one of the instruments that is attached to the 3.6-m DOT. It allows to perform observations in the near-infrared (NIR) bands (RIYJHK; 0.55 - 2.54 μm). Observations in the K-band were gathered for a few objects of the project Optical characterization and radial velocity monitoring with Belgian and Indian telescopes (ORBIT) that is lead by Y.C. Joshi (ARIES, India) and P. De Cat (ROB, Belgium). However, the lightcurves were either too short or of insufficient quality to be included in papers so far.

(A5) Abundances:
D. Karinkuzhi (CoU, India) and S. Van Eck (ULB, Belgium) are collaborating to understand the nucleosynthetic origin of peculiar abundance patterns in low-mass stars, which are crucially needed to better understand the underlying stellar physics. Their group developed a coherent research strategy in the field of stellar physics that involves observational studies (chemical composition of low-mass stars, their binary properties, and tomography of stellar atmospheres) that use the large ESO telescopes and HERMES at the 1.2-m Mercator@RMO telescope (La Palma, Spain) 1.2-m that is operated by the KU Leuven (Belgium). This collaboration has been very successful, which is reflected in the number of refereed papers and presentations at international conferences.

(A6) High-resolution Spectrograph (HRS) for the 3.6-m DOT:
Astronomers and technicians from both countries have interacted with each other for the development of a high- resolution spectrograph (HRS) for the 3.6-m DOT. The spectrograph is being built by Australian Astronomical Optics (AAO), Australia. The preliminary design review (PDR) took place on 09/12/2022 and the final design review was done in August 2023. The procurement of various elements of the instruments and their assembly in parallel is in progress. The HRS should only become available at the end of 2024 or the beginning of 2025. Hence, no scientific results could be obtained for this project yet.

(A7) Binaries:
We started the project ORBIT to study candidate exoplanet hosts and low-mass eclipsing binary stars involving spectroscopic observations gathered with HERMES (1.2-m Mercator@RMO; La Palma, Spain) and HESP (2.01-m HCT@IAO; Hanle, India) and photometric observations obtained with the ground-based (1.3-m@ARIES, 1.04- m@ARIES, 3.6-m DOT@ARIES) telescopes. These studies also benefit from space-based observations from satellite missions like Kepler/K2 and TESS. A sample of five W Ursae Majoris eclipsing binaries was studied and a change in the observed orbital period was found for two systems that is likely due to a loss of angular momentum via magnetic braking. For EPIC211982753 and EPIC211915147, the analysis of the observed times of minimum brightness did not reveal any orbital period changes but there is evidence of dark spots in the case of EPIC211915147 . HERMES and HESP spectroscopy were combined with Kepler photometry to derive accurate orbital solutions from radial velocities and time delays for four systems with A/F-type (candidate) hybrid pulsators .

The research groups of M. De Becker (ULiège, Belgium), J.C. Pandey (ARIES, India), and A. Tej (IIST, India) are involved in the study of massive, early-type stars whose thermal winds radiate free-free continuum. They are frequently found in multiple systems. Binary systems with a colliding-wind region, additionally show non-thermal emission. Most of the radio observations are done for frequencies larger than 1GHz. Benaglia et al. used the GMRT@NCRA-TIFR telescope to study emission with frequencies between 325 and 610 MHz for all known Wolf- Rayet and O-type stars in a region of about 15 sq degrees in the Cygnus region and could detect 11 of them in this frequency range. They also report on the first detection of a colliding-wind binary system at frequencies as low as 150 MHz. Arora et al. performed a long-term study of the colliding-wind binary WR125 both in the infrared and X-rays. They found long-term changes in its X-ray emission state that seem to be linked to the orbital phase and compatible with the recurrence time of episodic dust production. Hence, the study of the dust production of massive stars is suggested as an indirect technique to detect and characterise massive, early-type binaries with colliding winds. The long-term variations of the thermal and non-thermal X-ray emission of the massive O-type star HD93250 were studied for an independent detection and confirmation of the orbit known from astrometric observations and the X-ray spectrum of this object was used to derive the plasma temperature. They concluded that the X-ray emission from HD93250 is dominated by the colliding-wind region. The results of this collaboration have been presented on several occasions.

Magnetic cataclysmic variables (MCVs) are interacting semi-detached binaries with a magnetic white dwarf (WD) and a Roche-filling star as primary and secondary components, respectively. Based on the strengths of the magnetic field of the WD, a difference is made between intermediate polar and polar. N. Rawat (ULiège, Belgium), J.C. Pandey (ARIES, India), A. Joshi (IIA, India), and their collaborators performed a detailed investigation of archival and new data of two candidate MCVs (1RXS J174320.1−042953 and YY Sex) from which they conclude that they belong to the polar subclass. Preliminary results obtained for the confirmed intermediate polar UU Col and the candidate intermediate polar Swift J0939.7-3224 were presented during a contributed talk at the 3rd BINA workshop.

(A8) Solar System Bodies and Exoplanetary Science:
Comets are small icy objects orbiting the Sun that are of common interest in the research groups of E. Jehin(ULiège) and S. Ganesh (PRL, India). In 2018, the comet 46P/Wirtanen had an exceptionally close approach to Earth, making it possible to start gathering low-resolution spectra with LISA (0.5-m@MIRO; Rajasthan, India) to monitor the activity of this comet and to derive the relative abundances in the coma as a function of the distance to the Sun. They concluded that this comet has a typical coma composition, the abundance ratios with respect to CN remained nearly constant during the observations, and that the production rates of NH2 emission are nearly symmetric across perihelion but that the dust production shows clear asymmetries. Spectroscopic observations of the bright long-period comet C/2022 E3 (ZTF) have also been obtained. The derived production rates and the values of the Afρ dust proxy are in agreement with the determinations available in the literature.

An exoplanet is a planet orbiting a star other than the Sun. Belgian and Indian partners are involved in the validation of candidate exoplanets discovered in the lightcurves of data of the TESS space mission. They have contributed to the confirmation and characterisation of eight potential super-earths. There is also an involvement of Indian and Belgian partners in the development of the Santa Cruz Array of Lanslets for Exoplanet Spectroscopy (SCALES), which is a new 2.5-micron coronographic integral field spectrograph to be attached to the 10-m Keck telescope. It is designed to gather low- and medium-resolution spectroscopy for the detection and characterisation of cold exoplanets.

(A9) Solar physics:
As both the Belgian and Indian partner institutes of BINA are involved in studies of different aspects of the Sun, we have introduced solar physics as an additional topic for BINA during the 3 rd BINA workshop to further stimulate long-term collaborations on space science.

The middle corona is the region at distances between 1.5 and 6 solar radii around the Sun and is situated between the corona and heliosphere. West et al. devoted an extended review paper to the definition of this region and a full description of its physical characteristics and ongoing processes.

Several studies are related to the magnetic field of the Sun. A coronal mass ejection (CME) is a violent event in which magnetic field and plasma from the Sun are ejected from the corona into the heliosphere. On 26/03/3022, the Solar Orbiter spacecraft detected one at high northern latitudes. The available observations at extreme-ultraviolet wavelengths were used for a 3D construction resulting in a full characterisation of the event. It is not yet fully understood which mechanism(s) is (are) responsible for the heating of the corona, D. Lim et al. studied the role of high-frequency transverse oscillations in small-scale coronal loops. They concluded from modelling of the velocity power spectrum of propagating transverse waves detected with the Coronal Multi-channel Polarimeter (CoMP) with a power law that these high-frequency transverse oscillations could provide a dominant contribution to the total coronal heating generated by decayless transverse oscillations. A.K. Shrivastav et al. used high-resolution observations from the Extreme Ultraviolet Imager of the Solar Orbiter space mission to derive the properties of decayless oscillations in small-scale loops embedded in the quiet corona and coronal holes. These authors conclude that it is not likely that they can produce enough energy to heat the quiet Sun and accelerate the solar wind in coronal holes. T. Van Doorselaere et al. investigated how low-frequency waves propagate in a coronal loop assuming that it is built up from strands each having a different temperature with a Gaussian temperature distribution. They found that the multithermal apparent damping is more important for shorter-period slow waves .

Belgian and Indian partners have contributed to a white paper with a science case for Firefly, a concept for a future space mission that has been accepted for study by NASA. The mission consists of two pairs of spacecrafts orbiting the Sun (one pair at a fixed angular distance of ±90 to ±120° from the Earth; one pair out of the ecliptic at a solar latitude of about 70°) to explore the heliosphere from the solar interior up to the solar wind. As the launches are scheduled early to mid-2030s, it opens possibilities for a long-term collaboration.