ASASSN-13db 2014-2017 Eruption as an Intermediate Luminosity Optical Transient

TL;DR

The paper analyzes a 2014-2017 outburst of the young star ASASSN-13db, comparing it to Intermediate Luminosity Optical Transients, and suggests it was caused by proto-planet accretion or disk instability, with the least energetic ILOT recorded.

Contribution

It presents a detailed analysis of the outburst, proposing a novel origin involving proto-planet accretion and comparing it to known ILOTs, expanding understanding of low-energy stellar eruptions.

Findings

Light curve decline similar to V838 Mon, a Luminous Red Nova.

Outburst powered by accretion of a shredded proto-planet.

Estimated energy of the outburst is approximately 10^42 erg.

Abstract

The low mass star ASASSN-13db experienced an EXor outburst in 2013, which identified it as a Young Stellar Object (YSO). Then, from 2014 to 2017 it had another outburst, longer and more luminous than the earlier. We analyze the observations of the second outburst, and compare it to eruptions of Intermediate Luminosity Optical Transients (ILOTs). We show that the decline of the light curve is almost identical to that of the V838 Mon, a prototype of a type of ILOT known as Luminous Red Nova (LRN). This similarity becomes conspicuous when oscillations that are associated with rotation are filtered out from the light curve of ASASSN-13db. We suggest that the eruption was the result of accretion of a proto-planet of a few Earth masses. The proto-planet was shredded by tidal forces before it was accreted onto the YSO, releasing gravitational energy that powered the outburst for $\approx 800$ days, and ended in a $\approx 55$ days decline phase. When the accretion material started depleting the accretion rate lowered and the eruption light curve declined for almost two months. Then it exhausted completely, creating a sharp break in the light curve. Another possibility is that the mass was a result of an instability in the proto-planetary disk that lead to a large episode of accretion from an inner viscous disk. We find that the variation of the temperature of the outburst is consistent with the surface temperature expected from a depleted viscous accretion disk. The 2014-2017 outburst of ASASSN-13db may be the least energetic ILOT to have been discovered to date, with an energy budget of only $\approx 10^{42}$ erg.