Observations of Disintegrating Long-period Comet C/2019 Y4 (ATLAS): A Sibling of C/1844 Y1 (Great Comet)
Abstract
We present a study of C/2019 Y4 (ATLAS) using Sloan gri observations from 2020 mid-January to early April. During this time span, the comet brightened with a growth in the effective cross-section of $\left(2.0\pm 0.1\right)\times {10}^{2}$ m2 s-1 from the beginning to ∼70 days preperihelion in late 2020 March, followed by a brightness fade and the comet gradually losing the central condensation. Meanwhile, the comet became progressively bluer, and was even bluer than the Sun (g - r ≈ 0.2) when the brightness peaked, likely due to activation of subterranean fresh volatiles exposed to sunlight. With the tailward bias-corrected astrometry we found an enormous radial nongravitational parameter, ${A}_{1}=\left(+2.25\pm 0.13\right)\times {10}^{-7}$ au day-2 in the heliocentric motion of the comet. Taking all of these findings into consideration, we conclude that the comet has disintegrated since 2020 mid-March. By no means was the split new to the comet, as we quantified that the comet had undergone another split event around last perihelion ∼5 kyr ago, during which its sibling C/1844 Y1 (Great Comet) was produced, with the in-plane component of the separation velocity ≳1 m s-1. We constrained that the nucleus of C/2019 Y4 before disintegration was ≳60 m in radius, and has been protractedly ejecting dust grains of ∼10-40 μm (assuming a dust bulk density of 0.5 g cm-3) with an ejection speed of ∼30 m s-1 in early 2020 March and increased to ∼80 m s-1 toward the end of the month for grains of ∼10 μm.
- Publication:
-
The Astronomical Journal
- Pub Date:
- August 2020
- DOI:
- 10.3847/1538-3881/ab9d81
- arXiv:
- arXiv:2004.10990
- Bibcode:
- 2020AJ....160...91H
- Keywords:
-
- Long period comets;
- Comets;
- Small solar system bodies;
- 933;
- 280;
- 1469;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- Accepted to Astronomical Journal