Beginning Of Activity In Long-Period Comet C/2015 Er61 (Panstarrs)

Keywords

comets: general; comets: individual (C/2015 ER61); methods: observational

Abstract

We report the beginning of activity for comet C/2015 ER61 (PANSTARRS), the first instance of watching a long-period comet turn on. Pre-discovery observations and observations from the NEOWISE space telescope suggest that the nucleus is large, with a radius of R N ∼ 9 km, assuming an albedo of 0.025. Our photometric data follows the comet from r = 8.9 to 4.8 au as it moved into solar conjunction in 2016 July. Our sublimation model shows that activity began near r = 8.8 au (true anomaly, TA = -139°) in early 2015, driven by CO2 sublimation, which peaked in 2016 April at r = 5.1 au (TA = -127°). Appreciable water sublimation began around r = 5.0 au. Our sublimation model is consistent with an active water sublimation area of 1% of the surface (equivalent to 10.2 km2), and an active surface area for CO2 sublimation of 0.029% (0.3 km2). The CO2 production rate at r = 4.66 au as measured by NEOWISE is (8.4 ± 2) ×1025 s-1. If CO2-ice had been present on the surface, dust dragged from the surface by sublimation would have been observed much farther out - as far as 20 au. Our thermal models suggest that the CO2 ice was present at a depth of 0.4 m. The comet came out of solar conjunction in 2016 December and, unless it brightens significantly, is unlikely to have water production rates much higher than a few ×1028 s-1.

Publication Date

5-1-2017

Publication Title

Astronomical Journal

Volume

153

Issue

5

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.3847/1538-3881/aa63f2

Socpus ID

85019123038 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/85019123038

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