Disintegration of Long-period Comet C/2019 Y4 (ATLAS). II. Post-Perihelion Remnant Recovery

TL;DR

This study investigates the post-disruption state of comet C/2019 Y4 (ATLAS) using telescopic observations, revealing its remnants are faint or absent and discussing the challenges in confirming comet disruptions.

Contribution

It provides the first post-perihelion observational constraints on C/2019 Y4's remnants and reviews disruption confirmation issues in other long-period comets.

Findings

Remnant brightness constrained to H>20.5, D<0.5 km

No fragments detected in ZTF data at 2.5-2.9 au

Disruption confirmation is often inconclusive in long-period comets

Abstract

We present an investigation into the fate of disrupting near-Sun comet C/2019 Y4 (ATLAS). Imaging observations with the Lowell Discovery Telescope (LDT), obtained 3--5 months after the reported disruption and the last sighting, constrained the primary component C/2019 Y4-B to an absolute magnitude of $H>20.5$ or a diameter of $D<0.5$~km (assuming a geometric albedo of 0.04) at an outbound heliocentric distance of 2.71~au. A search of shallower data obtained from the Zwicky Transient Facility (ZTF) survey, conducted when components A and B receded from 2.5 to 2.9~au from the Sun, yielded no detections, suggesting that the fragments had either ceased to exist or were not substantially active during this period. The uncertain fate of C/2019 Y4 highlights the challenge in understanding the state of presumably disrupted comets. Our review of six other presumably disrupted long-period comets reveals that negative confirmations were not reported for half of them, leaving their disruption presumptions inconclusive.