Collisional debris around ASASSN-21qj: an update on the dust properties and cloud structure

Jonathan Marshall^1*

¹Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan

* Presenter:Jonathan Marshall, email:jmarshall@asiaa.sinica.edu.tw

ASASSN-21qj is a distant Sun-like star that underwent a prolonged episode of deep dimming events after no prior recorded variability. The observed occultations are consistent with a circumstellar cloud of sub-micron dust grains composed of amorphous pyroxene. The dimming was preceded by a substantial near-infrared excess from NEOWISE 3.4 and 4.6 μm observations, implying temperatures ranging from 1800 to 700 K and a total circumstellar dust mass of around 10^-6 M_Earth. The origin of this extended, opaque cloud has been linked to either the breakup of a large exocometary body around 0.2 au from the star, or a collision between two at a separation of 2 to 16 au from the star. Here we revisit the optical/near-infrared light curve and calculate a time-dependent reddening vector for the obscuration to search for variation in the dust grain properties. We additionally use the denser sampling from LCO and ASASSN observations in conjunction to trace optical depth changes in the cloud to calculate the scale of substructures. Finally, we put these observations into context by comparison with other stars exhibiting comparable dimming events, both with and without infrared excesses.

Keywords: Circumstellar dust, Exoplanets, Debris discs