Characterization of the Nucleus, Morphology, and Activity of Interstellar Comet 2I/Borisov by Optical and Near-infrared GROWTH, Apache Point, IRTF, ZTF, and Keck Observations

Bryce T. Bolin , Carey M. Lisse , Mansi M. Kasliwal , Robert Quimby , Hanjie Tan , Chris M. Copperwheat , Zhong-Yi Lin , Alessandro Morbidelli (1) , Lyu Abe (1) , Philippe Bendjoya (1) , James Bauer , Kevin B. Burdge , Michael Coughlin , Christoffer Fremling , Ryosuke Itoh , Michael Koss , Frank J. Masci , Syota Maeno , Eric E. Mamajek , Federico Marocco , Katsuhiro Murata , Jean-Pierre Rivet (1) , Michael L. Sitko , Daniel Stern , David Vernet (2) , Richard Walters , Lin Yan , Igor Andreoni , Varun Bhalerao , Dennis Bodewits , Kishalay De , Kunal P. Deshmukh , Eric C. Bellm , Nadejda Blagorodnova , Derek Buzasi , S. Bradley Cenko , Chan-Kao Chang , Drew Chojnowski , Richard Dekany , Dmitry A. Duev , Matthew Graham , Mario Jurić , Emily A. Kramer , Shrinivas R. Kulkarni , Thomas Kupfer , Ashish Mahabal , James D. Neill , Chow-Choong Ngeow , Bryan Penprase , Reed Riddle , Hector Rodriguez , Philippe Rosnet (3) , Roger M. Smith , Jesper Sollerman , Maayane T. Soumagnac

1 LAGRANGE - Joseph Louis LAGRANGE
2 OCA - Observatoire de la Côte d'Azur
3 LPC - Laboratoire de Physique de Clermont

We present visible and near-infrared (NIR) photometric and spectroscopic observations of interstellar object (ISO) 2I/Borisov taken from 2019 September 10 to 2019 December 20 using the GROWTH, the Apache Point Observatory Astrophysical Research Consortium 3.5 m, and the NASA Infrared Telescope Facility 3.0 m combined with pre- and postdiscovery observations of 2I obtained by the Zwicky Transient Facility from 2019 March 17 to 2019 May 5. Comparison with imaging of distant solar system comets shows an object very similar to mildly active solar system comets with an outgassing rate of ∼1027 mol s−1. The photometry, taken in filters spanning the visible and NIR range, shows a gradual brightening trend of ∼0.03 mag day−1 since 2019 September 10 UTC for a reddish object becoming neutral in the NIR. The light curve from recent and prediscovery data reveals a brightness trend suggesting the recent onset of significant H2O sublimation with the comet being active with super volatiles such as CO at heliocentric distances >6 au consistent with its extended morphology. Using the advanced capability to significantly reduce the scattered light from the coma enabled by high-resolution NIR images from Keck adaptive optics taken on 2019 October 4, we estimate a diameter for 2I’s nucleus of ≲1.4 km. We use the size estimates of 1I/’Oumuamua and 2I/Borisov to roughly estimate the slope of the ISO size distribution, resulting in a slope of ∼3.4 ± 1.2, similar to solar system comets and bodies produced from collisional equilibrium.

Domaines: Physique [physics]

Bryce T. Bolin, Carey M. Lisse, Mansi M. Kasliwal, Robert Quimby, Hanjie Tan, et al.. Characterization of the Nucleus, Morphology, and Activity of Interstellar Comet 2I/Borisov by Optical and Near-infrared GROWTH, Apache Point, IRTF, ZTF, and Keck Observations. Astron.J., 2020, 160 (1), pp.26. ⟨10.3847/1538-3881/ab9305⟩. ⟨hal-02879519⟩