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

We report the results of the narrow band photometry and imaging monitoring of comet C/2013 R1 (Lovejoy) with the robotic telescope TRAPPIST (La Silla observatory). We gathered around 400 images over 8 months pre- and post-perihelion between September 12, 2013 and July 6, 2014. We followed the evolution of the OH, NH, CN, C3 , and C2 production rates computed with the Haser model as well as the evolution of the dust production. All five gas species display an asymmetry about perihelion, the rate of brightening being steeper than the rate of fading. The study of the coma morphology reveals gas and dust jets which indicate one or several active zone(s) on the nucleus. The dust, C2 , and C3 morphologies present some similarities while the CN morphology is different. OH and NH are enhanced in the tail direction. The study of the evolution of the comet activity shows that the OH, NH, and C2 production rates evolution with the heliocentric distance is correlated to the dust evolution. The CN and, to a lesser extent, the C3 do not display such a correlation with the dust. These evidences and the comparison with parent species production rates indicate that C2 and C3 on one side and OH and NH on the other side could be -at least partially- released from organic-rich grains and icy grains. On the contrary, all evidences point to HCN being the main parent of CN in this comet.Comment: Accepted for publication in Astronomy & Astrophysics, 10 page

Ground-based monitoring of comet 67P/Churyumov-Gerasimenko gas activity throughout the <i>Rosetta</i> mission

Simultaneously to the ESA Rosetta mission, a world-wide ground-based campaign provided measurements of the large scale activity of comet 67P/Churyumov-Gerasimenko through measurement of optically active gas species and imaging of the overall dust coma. We present more than two years of observations performed with the FORS2 low resolution spectrograph at the VLT, TRAPPIST, and ACAM at the WHT. We focus on the evolution of the CN production, as a tracer of the comet activity. We find that it is asymmetric with respect to perihelion and different from that of the dust. The CN emission is detected for the first time at 1.34 au pre-perihelion and production rates then increase steeply to peak about two weeks after perihelion at (1.00±0.10) ×1025 molecules s−1, while the post-perihelion decrease is more shallow. The evolution of the comet activity is strongly influenced by seasonal effects, with enhanced CN production when the Southern hemisphere is illuminated

A Monitoring Campaign for Luhman 16AB. I. Detection of Resolved Near-Infrared Spectroscopic Variability

[abbreviated] We report resolved near-infrared spectroscopic monitoring of the nearby L dwarf/T dwarf binary WISE J104915.57-531906.1AB (Luhman 16AB), as part of a broader campaign to characterize the spectral energy distribution and temporal variability of this system. A continuous 45-minute sequence of low-resolution IRTF/SpeX data spanning 0.8-2.4 micron were obtained, concurrent with combined-light optical photometry with ESO/TRAPPIST. Our spectral observations confirm the flux reversal of this binary, and we detect a wavelength-dependent decline in the relative spectral fluxes of the two components coincident with a decline in the combined-light optical brightness of the system over the course of the observation. These data are successfully modeled as a combination of brightness and color variability in the T0.5 Luhman 16B, consistent cloud variations; and no significant variability in L7.5 Luhman 16A. We estimate a peak-to-peak amplitude of 13.5% at 1.25 micron over the full lightcurve. Using a two-spot brightness temperature model, we infer an average cloud covering fraction of ~30-55% for Luhman 16B, varying by 15-30% over a rotation period. A Rhines scale interpretation for the size of the variable features explains an apparent correlation between period and amplitude for three highly variable T dwarfs, and predicts relatively fast winds (1-3 km/s) for Luhman 16B consistent with lightcurve evolution on an advective time scale (1-3 rotation periods). Our observations support the model of a patchy disruption of the mineral cloud layer as a universal feature of the L dwarf/T dwarf transition.Comment: 11 pages, 7 figures; accepted for publication in Astrophysical Journa

MUSE observations of comet 67P/Churyumov-Gerasimenko:A reference for future comet observations with MUSE

Observations of comet 67P/Churyumov-Gerasimenko were performed with MUSE at large heliocentric distances post-perihelion, between March 3 and 7, 2016. Those observations were part of a simultaneous ground-based campaign aimed at providing large-scale information about comet 67P that complement the ESA/Rosetta mission. We obtained a total of 38 datacubes over 5 nights. We take advantage of the integral field unit (IFU) nature of the instrument to study simultaneously the spectrum of 67P's dust and its spatial distribution in the coma. We also look for evidence of gas emission in the coma. We produce a high quality spectrum of the dust coma over the optical range that could be used as a reference for future comet observations with the instrument. The slope of the dust reflectivity is of 10%$/100$ nm over the 480-900 nm interval, with a shallower slope towards redder wavelengths. We use the $\mathrm{Af\rho}$ to quantify the dust production and measure values of 65$\pm$4 cm, 75$\pm$4 cm, and 82$\pm$4 cm in the V, R, and I bands respectively. We detect several jets in the coma, as well as the dust trail. Finally, using a novel method combining spectral and spatial information, we detect the forbidden oxygen emission line at 630 nm. Using this line we derive a water production rate of $1.5\pm0.6 \times 10^{26} \mathrm{molec./s}$, assuming all oxygen atoms come from the photo-dissociation of water.Comment: Accepted for publication in Astronomy and Astrophysic

FeI and NiI in cometary atmospheres. Connections between the NiI/FeI abundance ratio and chemical characteristics of Jupiter-family and Oort-cloud comets

FeI and NiI emission lines have recently been found in the spectra of 17 Solar System comets observed at heliocentric distances between 0.68 and 3.25 au and in the interstellar comet 2I/Borisov. The blackbody equilibrium temperature at the nucleus surface is too low to vaporize the refractory dust grains that contain metals, making the presence of iron and nickel atoms in cometary atmospheres a puzzling observation. Moreover, the measured NiI/FeI abundance ratio is on average one order of magnitude larger than the solar photosphere value. We report new measurements of FeI and NiI production rates and abundance ratios for the Jupiter-family comet (JFC) 46P/Wirtanen in its 2018 apparition and from archival data of the Oort-cloud comet (OCC) C/1996 B2 (Hyakutake). The comets were at geocentric distances of 0.09 au and 0.11 au, respectively. The emission line surface brightness was found to be inversely proportional to the projected distance to the nucleus, confirming that FeI and NiI atoms are ejected from the surface of the nucleus or originate from a short-lived parent. Considering the full sample of 20 comets, we find that the range of NiI/FeI abundance ratios is significantly larger in JFCs than in OCCs. We also unveil significant correlations between NiI/FeI and C$_2$/CN, C$_2$H$_6$/H$_2$O, and NH/CN. Carbon-chain- and NH-depleted comets show the highest NiI/FeI ratios. The existence of such relations suggests that the diversity of NiI/FeI abundance ratios in comets could be related to the cometary formation rather than to subsequent processes~in~the~coma.Comment: Accepted for publication in A&A Letter

The dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS and VLT observations in the 4.5 to 2.9 au heliocentric distance range inbound

Context. The ESA Rosetta spacecraft, currently orbiting around cornet 67P/Churyumov-Gerasimenko, has already provided in situ measurements of the dust grain properties from several instruments, particularly OSIRIS and GIADA. We propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution. Aims. To constrain the dust grain properties, we take Rosetta OSIRIS and GIADA results into account, and combine OSIRIS data during the approach phase (from late April to early June 2014) with a large data set of ground-based images that were acquired with the ESO Very Large Telescope (VLT) from February to November 2014. Methods. A Monte Carlo dust tail code, which has already been used to characterise the dust environments of several comets and active asteroids, has been applied to retrieve the dust parameters. Key properties of the grains (density, velocity, and size distribution) were obtained from. Rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. In this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately. Results. The dust parameters derived from the inner coma measurements by OSIRIS and GIADA and from distant imaging using VLT data are consistent, except for the power index of the size-distribution function, which is alpha = -3, instead of alpha = -2, for grains smaller than 1 mm. This is possibly linked to the presence of fluffy aggregates in the coma. The onset of cometary activity occurs at approximately 4.3 AU, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 AU. This implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the MIRO experiment