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Opposition effect on comet 28P/Neujmin 1 observed with Subaru Hyper-Suprime Cam

Presentation #322.22 in the session Comets (Poster)

Published onOct 23, 2023
Opposition effect on comet 28P/Neujmin 1 observed with Subaru Hyper-Suprime Cam

It is highly required to increase the observational data of small solar system bodies (SSSBs) for the essential understanding of the dynamical and collisional evolution of the solar system. Observations with 8-10 m class large telescopes enable us to investigate the detailed properties of small and/or faint SSSBs even if they are far from the Sun. For this purpose, we are working on the project to extract the SSSBs from photometric and imaging data obtained with the Hyper Suprime-Cam (HSC). The HSC is an optical imaging camera installed at the prime focus of the 8.2 m Subaru Telescope. It covers a wide field of view of 1.8 deg2 with 116 CCDs (104 CCDs are used for science imaging). We detected several comets with very weak activity observed at > 10 au from the Sun, beyond Saturn’s orbit, with Subaru/HSC. Among them, an interesting target without coma contamination, comet 28P/Neujmin 1 (hereafter 28P) was observed at near the opposition (α~0.3°-3°) around 10.5 au from the Sun in three filter bands, g-, r-, and y-bands, on three days during February-March 2016. We will show the observational results of comet 28P in this poster. Comet 28P is a short-period comet with an orbital period of 18.2 years and has an aphelion distance of Q = 12.3 au. It is reported that the best estimated period is near 12.75 h. The rotational lightcurve has an asymmetric, double-peaked shape, with a range of 0.45 mag. Comet 28P has a low-activity nucleus, with typically only a very faint tail/coma appearing at perihelion. All the HSC images of 28P appeared point-like without resolved coma. The spectral gradient S’ derived from the HSC data is ~11%/100nm, similar to D-type asteroids, as previous studies suggested. The reduced R magnitude mR(1,1,0.33) derived from our data is ~11.9 mag. The phase curve at α ~ 0.3°-15° based on the HSC data and previous observations indicates that 28P shows an apparent opposition surge with the amplitude of 0.3 mag at α = 0.3°.

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