The early rise of a new outburst of EX Lup
ATel #15271; Lihang Zhou, Gregory J. Herczeg (KIAA and Department of Astronomy, Peking University)
on 12 Mar 2022; 04:36 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Gregory Herczeg (gherczeg1@gmail.com)
Subjects: Optical, Request for Observations, Star, Young Stellar Object, Pre-Main-Sequence Star
We report a brightening of the young stellar object EX Lup over the past month, as seen in g-band photometry obtained by ASAS-SN (Shappee et al. 2014, Kochanek et al. 2017). In four observations on 2022-03-09 to 2022-03-10, the average brightness was g=11.67, about 1.6 mag brighter than the previous baseline. A linear fit to the rise, starting on 2022-02-15, yields m=13.20 - 0.064 * (d - 9625), where d is days in MJD-50000. EX Lup is getting steadily brighter by about 0.064 mag/day.
EX Lup is the namesake of its class of young stellar outbursts. Brightening events are interpreted as increases in the accretion rate from the circumstellar disk onto the star. Outbursts of EX Lup in 1955 and 2008 reached 5 mag above quiescence and lasted for about half a year (Aspin et al. 2010). A few sporadic, smaller bursts of EX Lup in the 1990s peaked at about the current brightness and were much shorter than the 1955 and 2008 bursts (Herbig et al. 2007). The ASAS-SN lightcurve of EX Lup was stable in 2018-2019 with an average brightness of g=13.54 in 2018-2019, had some small bursts of ~0.8 mag in 2020, and then was stable at g=13.34 in 2021.
The next weeks offer a unique opportunity to study the rise of an EX Lup outburst. Such studies were not possible for the 2008 outburst because the rise occurred when EX Lup was behind the sun. If this burst reaches 5 mag above the quiescent level, we should have 1-2 more months to follow the changes in the system during the rise. We encourage spectroscopic and photometric monitoring across the electromagnetic spectrum to understand the causes and consequences of what will likely be the 2022 outburst of EX Lup.
EX Lup is located at 16:03:05.49 -40:18:25.43. The ASAS-SN lightcurve of EX Lup can be obtained from their public sky-patrol website at https://asas-sn.osu.edu/sky-patrol/coordinate/3d39b4df-7547-4940-8c35-e492aa9be6b9
Aspin, C., Reipurth, B., Herczeg, G. J., & Capak, P. 2010, ApJL, 719, L50
Herbig, G.H., 2007, AJ, 133, 2679
Kochanek, C. S., Shappee, B. J., Stanek, K. Z., et al. 2017, PASP, 129, 104502
Shappee, B. J., Prieto, J. L., Grupe, D., et al. 2014, ApJ, 788, 48
