| Authors : | Koshvendra Singh, Joe P. Ninan, Marina M. Romanova, David A. H. Buckley, Devendra K. Ojha, Arpan Ghosh, Andrew Monson, Malte Schramm, Saurabh Sharma, Daniel E. Reichart, Joanna Mikolajewska, Juan Carlos Beamin, J. Borissova, Valentin D. Ivanov, Vladimir V. Kouprianov, Franz-Josef Hambsch and Andrew Pearce |
| Authors Affiliation: | Koshvendra Singh, Joe P Ninan, Devendra K Ojha Affiliation (Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Mumbai, 400005, India)
Marina M. Romanova Affiliation (Department of Astronomy, Cornell University, Ithaca, NY 14853, USA)
David A. H. Buckley Affiliation (South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape Town, South Africa)
David A. H. Buckley Affiliation (Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa)
David A. H. Buckley Affiliation (Department of Physics, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa)
Arpan Ghosh, Saurabh Sharma Affiliation (Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263001, India)
Andrew Monson Affiliation (Steward Observatory and Department of Astronomy, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721, USA)
Malte Schramm Affiliation (Universit\"at Potsdam, Karl-Liebknecht-Str. 24/25, D-14476 Potsdam, Germany)
Daniel E. Reichart, Vladimir V. Kouprianov Affiliation (Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Campus Box 3255, Chapel Hill, NC 27599-3255, USA)
Joanna Mikolajewska Affiliation (Nicolaus Copernicus Astronomical Centre, Polish Academy of Sciences, Bartycka 18, PL-00716 Warsaw, Poland)
Juan Carlos Beamin Affiliation (Fundaci\'on Chilena de Astronom\'ia, El Vergel 2252, Santiago, Chile)
J. Borissova Affiliation (Instituto de F\'isica y Astronom\'ia, Facultad de Ciencias, Universidad de Valpara\'iso, ave. Gran Breta\~na, 1111, Casilla 5030, Valpara\'iso, Chile)
J. Borissova Affiliation (Millennium Institute of Astrophysics (MAS), Nuncio Monse\~nor Sotero Sanz 100, Of. 104, Providencia, Santiago, Chile)
Valentin D. Ivanov Affiliation (European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany)
Franz-Josef Hambsch, Andrew Pearce Affiliation (American Association of Variable Star Observers, 185 Alewife Brook Parkway, Cambridge, MA 02138, MA, USA)
Franz-Josef Hambsch Affiliation (Vereniging Voor Sterrenkunde, Oostmeers 122 C, Bruges, 8000 Brugge, Belgium)
Franz-Josef Hambsch Affiliation (Bundesdeutsche Arbeitsgemeinschaft f\"ur Ver\"anderliche Sterne e. V., Munsterdamm 90, Berlin, D-12169, Germany)
Franz-Josef Hambsch Affiliation (Groupe Europ\'een d'Observations Stellaires (GEOS), 23 Parc de Levesville, 28300 Bailleau l\'Ev\^eque, France}
\author{Andrew Pearce
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| Abstract : | In this talk, I will present our first discovery of migration of the magnetic accretion funnel footprint during a period of enhanced accretion onto a young stellar object (YSO), EX Lupi. This phenomenon was predicted by dipolar magnetic field MHD simulations more than a decade ago. EX Lupi is the prototype of a class of young stellar objects (YSOs), EXors, that undergo repetitive outbursts (brightness increase by a few to a hundred) on the time scales of a few months to years. Though EX Lupi has a long history of recorded and well-studied outbursts since the 1940s, the most recent 2022’s outburst could be observed by us as well as other astronomers around the globe at an unprecedented cadence. We observed spectroscopically with HRS on 10-m SALT, SA and photometrically with LCRO, TMMT and CTIO. This data, along with the other publicly available data from ASAS-SN, TESS and AAVSO, enables accurate modelling of the accretion funnel footprint. I shall present how our analysis shows that the hotspot, the footprint of disk-mediated accretion onto the star, moved azimuthally ahead on the stellar surface by ∼ 112◦± 5◦, along the star’s rotation during the March 2022 outburst. The hotspot also moved down to a lower latitude by ∼ 10◦. Our 3-dimensional MHD simulations support the hotspot’s movement over the stellar surface during the state of high accretion rate. The hotspot held on to its new location even after the completion of the outburst, leading us to hypothesise a heated and thickened inner disk during the outburst. Our further analysis showed the pre-outburst azimuthally concentrated hotspot gains a temperature gradient during the outburst and gets azimuthally spread. These results also have broader implications on the other compact accreting sources. |
