APO Time Resolved Color Photometry of Highly-Elongated Interstellar Object 1I/'Oumuamua

Status Report From: e-Print archive
Posted: Wednesday, November 15, 2017

Bryce T. Bolin, Harold A. Weaver, Yanga R. Fernandez, Carey M. Lisse, Daniela Huppenkothen, R. Lynne Jones, Mario Juric, Joachim Moeyens, Charles A. Schambeau, Colin T. Slater, Zeljko Ivezic, Andrew J. Connolly
(Submitted on 14 Nov 2017)

We report on the g, r and i band observations of the Interstellar Object 1I/'Oumuamua taken on 2017 October 29 from 04:28 to 08:40 UTC from the Apache Point Observatory (APO) 3.5m telescope's ARCTIC camera. We use these observations to estimate object colors, and find them to be g−r=0.41±0.24 and r−i=0.23±0.25, consistent with visible spectra (Masiero 2017; Ye et al. 2017; Fitzsimmons et al. 2017) and most comparable to the population of Solar System C/D asteroids, Trojans, or comets, although we find no evidence of any cometary activity, even 1.5 months after 1I/'Oumuamua's close flyby of the Sun. Significant brightness variability was seen in the r observations, with the object becoming notably brighter towards the end of the run. By combining our APO photometric time series data with the Discovery Chanel Telescope (DCT) data of Knight et al. 2017 taken 20 h later on 2017 October 30, we construct an almost complete lightcurve with a most probable lightcurve period of P≃4 h, and reveal the most useful locations during 1I/'Oumuamua's rotation phase for additional data to improve constraints on its lightcurve. This implies a double peaked rotation period of 8.1 ± 0.02 h, with a peak-to-peak amplitude of 1.5 - 2.1 mags. The two values imply that 1I/'Oumuamua has an axial ratio of 4.1 to 6.9 and is rotating below its critical break up limit for most viable values of density and cohesive strength within the range of rotation periods and axial ratios compatible with our data. Our results are compatible with 1I/'Oumuamua having a density > 1.0 g cm−3 or having modest cohesive strength. Astrometry useful for constraining the object's orbit was also obtained and published in Weaver et al. 2017.

Comments:    11 pages, 5 figures, submitted to The Astronomical Journal, data are available at: this https URL
Subjects:    Earth and Planetary Astrophysics (astro-ph.EP)
Cite as:    arXiv:1711.04927 [astro-ph.EP] (or arXiv:1711.04927v1 [astro-ph.EP] for this version)
Submission history
From: Bryce Bolin 
[v1] Tue, 14 Nov 2017 03:23:15 GMT (2663kb,D)

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