Brightness and mass accretion rate evolution during the 2022 burst of EX~Lupi

TL;DR

This study analyzed the 2022 outburst of EX Lupi, revealing significant increases in accretion rates, confirming the star's strong accretor nature even in quiescence, and providing insights into its outburst history and future evolution.

Contribution

It presents new measurements of accretion rates during the 2022 burst, showing they are much higher than previously estimated, and offers a detailed analysis of the star's outburst history over 130 years.

Findings

Accretion rate increased by a factor of 7 during the burst.

Mass accreted during the event was 0.8 lunar masses.

EX Lupi could deplete its circumstellar material in less than 160,000 years.

Abstract

EX Lupi is the prototype by which EXor-type outbursts were defined. It has experienced multiple accretion-related bursts and outbursts throughout the last decades, whose study have greatly extended our knowledge about the effects of these types of events. This star experienced a new burst in 2022. We used multi-band photometry to create color-color and color-magnitude diagrams to exclude the possibility that the brightening could be explained by a decrease in extinction. We obtained VLT/X-shooter spectra to determine the Lacc and Macc during the peak of the burst and after its return to quiescence using 2 methods: empirical relationships between line luminosity and Lacc, and a slab model of the whole spectrum. We examined the 130 year light curve of EX Lupi to provide statistics on the number of outbursts experienced during this period of time. Our analysis of the data taken during the 2022 burst confirmed that a change in extinction is not responsible for the brightening. Our two approaches in calculating the Macc were in agreement, and resulted in values that are 2 orders of magnitude above what had previously been estimated, thus suggesting that EX Lupi is a strong accretor even when in quiescence. We determined that in 2022 March the Macc increased by a factor of 7 with respect to the quiescent level. We also found hints that even though the Macc had returned to almost its pre-outburst levels, certain physical properties of the gas had not returned to the quiescent values. We found that the mass accreted during this three month event was 0.8 lunar masses, which is approximately half of what is accreted during a year of quiescence. We calculated that if EX Lupi remains as active as it has been for the past 130 years, during which it has experienced at least 3 outbursts and 10 bursts, then it will deplete the mass of its circumstellar material in less than 160000 yr.