Proposal #129

Accretion driven outbursts during the formation of young stars with disks still present are relatively rare events observationally, contrary to theoretical expectations that this may be the main mechanism of the final growth of low-mass stars as they approach the main-sequence with as much as half their final mass being accreted during this phase. Those events that are (serendipitously) caught are not well observed. Hence, we often know little about the duration of these events, the changes in the physical properties of the stars during these events, nor the frequency of the outbursts. One case in point pertains to 2MASS J07092139-1029344, a virtually unstudied star. This star experienced an outburst in early 2015 that lasted less than 150 days. Its lightcurve during the 2015 outburst is comprised of only 7 data points - two during the rapid rise and 5 clustered around peak. A second outburst was "observed" in 2018, with no data points observed during the rise and decline, but with a clustering around peak light (including Gaia). The duration of the second outburst lasted less than 100 days; the breadth of the events are actually defined by observations near quiescence on either side of the peak rather than a time-resolved light curve during outburst. The first outburst was roughly 2.5 mag above quiescence (peak R~16.5 mag) while the second outburst appeared somewhat brighter at R~15.8 mag.

During our late December 2019 run on the WIYN 0.9m at KPNO we obtained new observations of the star clearly showing the star to now be in outburst yet again, at R~14.5 - the brightest outburst yet. We propose to obtain time-resolved imaging in BVRI filters with cadence sufficient to fully characterize the subsequent evolution of the present outburst. We wish to determine what if any color changes occur as the star returns to quiescence, the duration of the outburst and whether it is a smooth transition of undergoing rapid and large variations during the event. We request 4-filter imaging every other day through the next 2 months. The star is observable from both SRO and MJUO over the next many months. If the star has not yet returned to quiescence after the initial 2-month campaign we will request an extention of the ongoing observations. The observations should cycle through IRVB filters with 3x180s exposures in each filter. These observations should be started immediately. My AAVSO observer code is sgua. Please let me know how to notify you if/when the exposure times need to be updated.