Oral Presentation
The Unusual Dimming of Main-sequence Stars from Kepler to ASAS-SN
Presenter: Ciska Kemper (Institut de Ciències de l'Espai (ICE-CSIC) / ICREA / IEEC)
The unusual dimming of main-sequence stars from Kepler to ASAS-SN
The search for transiting exoplanets using surveys such as the one done by Kepler has turned up the existence of stars showing exceptionally long and deep dimming events. The first main sequence star reported to show this behavior was KIC 8462852 (Boyajian et al. 2015), an object affectionally known as "Tabby's star" or "Boyajian's star". Among the more exotic initial explanations of this unusual obscuration event was the presence of a partial Dyson sphere built by an alien civilization (Wright et al. 2015). Paul Ho brought this to our attention, and together we set off on a quest to find a more natural explanation involving circumstellar dust. We observed KIC 8462852 with JCMT and SMA, were able to constrain the amount of cold dust present in the system (Thompson et al. 2016). Combining this with other observational constraints, we concluded that the dust resulting from the destruction of a cloud of comets provides the most likely explanation.
To date, the number of objects showing deep and long lasting dimming events inconsistent with planetary transits has grown to about a few dozen. The most extreme dimming is reported for an object discovered by the All-Sky Automated Survey for Supernovae in December 2021. The stellar flux of this object, ASASSN-21qj, was almost completely extinguished during the two deepest dips in the light curve. We have performed ground-based follow-up observations in order to extend the ASASSN lightcurve, using the time between the two deepest dips as an indication of an orbital period (Marshall et al. 2023). We complemented this with a lightcurve from NEOWISE, showing a near-infrared brightening in advance of the dimming event. We have used these observations to constrain the mass and temperature of dust in the circumstellar environment and conclude that the source of this dust could be the catastrophic breakup of one or more exocomets. Recently, an alternative explanation was provided by Kenworthy et al. (2023), who suggest a collision between two ice giants further out in the planetary system as the source of the dust. We will compare the two scenarios.
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