Khagol # 130 - Jan - Jul 2023 - Eng & Hindi

Workshop on the limiting compactness objects: Black holes and Buchdahl stars The workshop on the limiting compactness objects: Black holes and Buchdahl stars was held from 30 October 2023 to 03 November 2023 at IUCAA, Pune. The workshop was organised as a compact discussion/discourse meeting with a threadbare exposition and discussion of the various aspects and the questions arising. It was occasioned by the visit of Professor Håkan Andreasson of the Gothenburg Technical University, Sweden. He has explored the Einstein – Vlasov system with his collaborators for over a decade and a half as a possible matter source for compact objects. This system characterises itself by free particles in motion and interacting only through gravity. For a limiting compactness, this may be themost appropriate state. The main thrust of the workshop was to understand this new object, BS, of limiting compactness without a horizon. It is almost as compact as a BH and yet has no horizon and hence is open for interaction with the outside world. Ever since the proposal of the membrane paradigm envisaging a time-like fiducial surface near the BH horizon, BS offers an excellent possibility of the existence of such a real astrophysical object. It could compete well with BH as a mimicker for various physical and astrophysical phenomena. Thus, it opens up a new vista of study and investigation of all the questions one asks for BH for this new creature, BS. The workshop intended to identify certain interesting questions and those interested in studying them. The workshop has been a huge success as several interesting questions have been identified, a few groups have been formed to undertake different problems, and the work has already started. Nothing more could have one asked from such an exercise. The version containing the summaries of some o f t h e l e c t u r e s c a n b e f o u n d i n Arxiv:2402.15543. The workshop was organised byNareshDadhich, IUCAA, Pune. The Seventh Indo-French Astronomy School (IFAS7) The Indo-French School on Spectroscopy and Spectrographs (IFAS7) was held from November 21-27, 2022 at IUCAA, Pune. The School was the seventh in the series co- organized by the Centre de Recherche Astrophysique de Lyon (CRAL), Lyon, France (LIO, CRAL, CNRS UMR5574, UCBL) and the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, India. The school's venue alternates between Lyon, France, and Pune, India, which has added v a l u e a n d h a s p u t i n t e r n a t i o n a l collaboration at the centre of the project. The twenty participants from different horizons were exposed to high-level specialised lectures on observational astronomy. They carried out an eight-day- long research project in spectroscopy and spectrographs. IFAS7 covered the topics of obse r va t i ona l and da t a- reduc t i on t echn i ques , source de t ec t i on and extraction in integral-field spectroscopy, multi-wavelength photometry and spectral energy distribution modelling. The project- based research was a significant highlight of IFAS7. The format comprised lectures in the morning hours and project work after lunch. The participants primarily included PhD students divided into four groups: A, B, C, and D. Each group presented their research project on the last day, with some spectacular results opening up new perspectives. The characteristics of this IFAS series were: • The high-level lectures given in the morning. • The considerable amount of time devoted to research projects. • The diverse attendance, where Indian and European s tudent s wor ked together. IFAS7 provided the participants full boarding and lodging at the IUCAA guest house. Late-evening sessions (after the dinner) were left to the self-organisation o f t h e s c h o o l p a r t i c i p a n t s , w i t h encouragement to use them to present their thesis work or research activities amongst themselves (no supervision by the professors). Lecturer and Lecture Topics covered duringtheschool • Spectroscopic analysis, spectral c l ass i f i ca t i on and Mu l t i -ob j ec t spectroscopic surveys Jens-Kristian Krogager, CRAL, Lyon, France • Introduction to Spectroscopy and Spectroscopic Instrumentation Ranjan Gupta, IUCAA, Pune, India • Modelling Lyman alpha line and beyond | 07 | KHAG L | No. 130 - JANUARY, APRIL & JULY 2023