TRAPPIST monitoring of comet C/2012 F6 (Lemmon)

Abstract

We report the results of the long-term narrowband photometry and imaging monitoring of comet C/2012 F6 (Lemmon) with the robotic TRAPPIST telescope (La Silla Observatory). Observations covered 52 nights pre-and post-perihelion between December 11, 2012, and June 11, 2013 (perihelion: 24 March, 2013. We followed the evolution of the OH, NH, CN, C 3 , and C 2 production rates computed with the Haser model as well as the evolution of the A(θ) f ρ parameter as a proxy for the dust production. All five gas species display similar slopes for the heliocentric dependence. An asymmetry about perihelion is observed, the rate of brightening being steeper than the rate of fading. The chemical composition of the comet's coma changes slightly along the orbit: the relative abundance of C 2 to CN increases with the heliocentric distance (r) below −1.4 au and decreases with r beyond 1.4 au while the C 3 -to-CN ratio is constant during our observations. The behavior of the dust is different from that of the gas, the slope of the heliocentric dependence becoming steeper in early February, correlated to a change in the visual lightcurve slope. However, the dust color does not vary during the observations. The application of several enhancement techniques on the images revealed structures in the CN, C 3 , and C 2 images. These features imply the existence of one or several active zone(s) on the comet nucleus. The shape of the structures is similar in these three filters and changes from a roughly hourglass shape in December and January to a corkscrew shape in February and March. The structures in the continuum filters (sampling the dust) are not correlated to those observed for the gas. During several full nights in February, we observed changes in the CN and C 2 structures that repeated periodically because of the nucleus rotation, our derived rotational period being of 9.52 ± 0.05 h.

TRAPPIST photometry and imaging monitoring of comet C/2013 R1 (Lovejoy): Implications for the origin of daughter species

“…The A(0) f ρ values are at least a factor two higher after perihelion than before at the same heliocentric distance. Asymmetries of the activity about perihelion seem to be a common phenomenon among comets (see, for example, A 'Hearn et al 1995;Schleicher et al 1998;Knight & Schleicher 2013;Opitom et al 2015). It remains difficult to know if such asymmetries happen for all comets or to understand their origin, because large datasets with sufficient temporal coverage and with observations on both sides A121, page 6 of 10 of perihelion are still too scarce.…”

“…The removal of the sky contribution and the photometric calibration of the images followed the procedure described in Opitom et al (2015). After calibration, we derived a median radial profile for each image.…”

Evidence for distributed gas sources of hydrogen halides in the coma of comet 67P/Churyumov–Gerasimenko

“…This is extremely difficult, if not impossible, to do with remote sensing from Earth because of the limitations on angular and hence spatial resolution (see, e.g., Opitom et al 2015, for a recent example). Additionally, remote sensing observations are limited to species with strong transition lines, possibly interfering with the same molecules in the Earth's atmosphere, and give line-of-sight integrated results which have to be inverted using a coma model to obtain spatial density profiles.…”

En Route to Destruction: The Evolution in Composition of Ices in Comet D/2012 S1 (Ison) Between 1.2 and 0.34 Au From the Sun as Revealed at Infrared Wavelengths*

“…Including all 32 measurements resulted in a heliocentric dependence Q(H 2 O) µ - R h 3.28 0.18 ( ) , much steeper than the insolation-limited case. We also performed a fit excluding points associated with periods of enhanced activity, one around November 12-14 Crovisier et al 2013;Opitom et al 2013b;Agúndez et al 2014) and one around November 19 (Opitom et al 2013a); we refer to these periods as "Events 1 and 2" (see Section 4.1.2). Accordingly, we omit the three points from November 15, the point from interval 2and the two points from interval 3 on November 19, and the point from interval 1 on November 22; these seven points are enclosed in rectangular boxes in Figure 4.…”