The outbursts of comet 29P/SW-1 and C/2020 R4 (ATLAS)

<p>We present an analysis of the dynamic dust coma of Centaur 29P/Schewassmann-Wachmann 1 and long-period comet C/2020 R4 (Atlas). Comet P/SW1 has exhibited a considerable level of activity (so-called outbursts) since its discovery in 1925. In 2011, we found the morphology of comet P/SW 1 showed dust features in the form of jets, spirals and shells. This year, we have obtained multi-wavelength observations of 29P/SW 1's dust coma at Lulin observatory and we will present preliminary results including the morphological analysis and the colour (B-V, V-R, and R-I) investigation of the dust coma when comet is at quiet and active period.</p> <p>At least three outbursts found within two weeks from comet Atlas is unusual for long-period comet. However, we didn’t find any new jet features and fragments from the morphology of comet Atlas. Except for the color investigation during the outburst, we will also give the dust/gas production rates in the comparison between pre- and post-outbursts.</p>

MUSE observations of comet 67P/Churyumov-Gerasimenko

Aims. Observations of comet 67P/Churyumov-Gerasimenko were performed with MUSE at large heliocentric distances post-perihelion between 3 and 7 March 2016. These observations are part of a simultaneous ground-based campaign aimed at providing broad-scale information about comet 67P to complement the ESA/Rosetta mission. Methods. We obtained a total of 38 datacubes over five nights. We took advantage of the integral field unit nature of the instrument to carry out a simultaneous study of the spectrum of 67P’s dust and its spatial distribution in the coma. We also looked for evidence of gas emission in the coma. Results. We produced a high-quality spectrum of the dust coma over the optical range that could be used as a reference for future comet observations with this 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 used the Afρ to quantify the dust production and measure values of 65 ± 4 cm, 75 ± 4 cm, and 82 ± 4 cm in the V, R, and I bands, respectively. We detected several jets in the coma as well as the dust trail. Finally, using a novel method combining spectral and spatial information, we detected the forbidden oxygen emission line at 630 nm. Using this line, we derived a water production rate of 1.5 ± 0.6 × 1026 molec. s−1, assuming all oxygen atoms come from the photo-dissociation of water.

Near-Simultaneous Optical + NIR Photometry of Interstellar Comet 2I/Borisov

<p>In August 2019, 2I/Borisov, the second interstellar object and first visibly active interstellar comet, was discovered on a trajectory nearly perpendicular to the ecliptic. Observations of planet forming disks and debris disks serve as probes of the ensemble properties of extrasolar planetesimals, but the passage of an active interstellar comet through our Solar System provides a rare opportunity to individually study these small bodies up close in the same ways in which we investigate objects originating from our own Outer Solar System. Ground-based observations of short period comet <span>67P/Churyumov–Gerasimenko</span> revealed a coma dust composition indistinguishable from what was measured on its nucleus by the orbiting <em>Rosetta</em> spacecraft. Therefore when 2/I Borisov had a dust dominated tail, we attempted to study its composition with near-simultaneous griJ photometry with the Gemini North Telescope. We obtained two epochs of GMOS-N and NIRI observations in November 2019, separated by two weeks. We will report on the inferred optical-near-IR colors of 2I/I Borisov’s dust coma/tail and nucleus. We will compare our measurements to other observations of 2I/Borisov and place the interstellar comet in context with the Col-OSSOS (Colours of the Outer Solar System Survey) sample of small KBOs and interstellar object <span>ʻOumuamua</span> observed in grJ with Gemini North, using the same setup.</p>

Dust tail observation and modeling of the interstellar comet 2I/Borisov

<p class="Sectionheading"><span lang="EN-GB">On 30 August 2019 the amateur Borisov discovered a new comet; after few days it was clear from the characteristics of its orbit (eccentricity > 3 and high hyperbolic excess velocity) that the second interstellar object had been detected and the object received the name of 2I/Borisov. </span></p> <p class="Sectionheading"><span lang="EN-GB">It appears to be very different from 1I/’Oumuamua and can be considered as the first interstellar comet.</span></p> <p class="Sectionheading"><span lang="EN-GB">According to the first observations the comet had a nucleus with a radius of few km and a dust coma and tail due to the activity started in June 2019 (Jewitt et al., 2019).</span></p> <p class="Sectionheading"><span lang="EN-GB">At the beginning of October we submitted the Discretionary Director Time (DDT) proposal to the TNG in order to monitor the comet. Some images have been acquired, in November and December 2019, with the DOLORES instrument in the R filter.</span></p> <p class="Sectionheading"><span lang="EN-GB">We have applied the dust model described in Fulle et al. (2010), that has been tested on the comet 67P/Churyumov-Gerasimenko and validated with the Rosetta measurements.</span></p> <p class="Sectionheading"><span lang="EN-GB">According to the results of our dust model and the activity model (Fulle et al., 2020) we derived a water flux from the nucleus of 8x10<sup>-6 </sup>kg m<sup>-2 </sup>s<sup>-1 </sup>and a dust loss rate of 35 and 30 kg s<sup>-1 </sup>in November and December 2019 respectively (Cremonese et al., 2020). This slight decrease has been observed around the perihelion on 8 December, few months later the comet fragmented.</span></p> <p class="Sectionheading"><span lang="EN-GB">In this work we will describe the dust tail observations and the dust model results, even comparing them with the Jupiter family comet 67P.</span></p> <p class="Sectionheading"><span lang="EN-GB">References</span><span lang="EN-GB">:</span></p> <p class="Abstractsectionheading">G.Cremonese, et al., 2020, ApJL, 893, L12</p> <p class="Abstractsectionheading">M.Fulle et al., 2010, A&A, 522, A63.</p> <p class="Abstractsectionheading">M.Fulle et al., 2020, MNRAS, 493, 4039.</p> <p class="Abstractsectionheading"><span lang="EN-US">Jewitt et al., 2019, ApJ, 886, L29.</span></p>

Long-term activity of Comet C/2007 N3 (Lulin) as monitored by the SLT at the Lulin Observatory

The green comet C/2007 N3 (Lulin) is a new Oort cloud comet that has a retrograde orbit (inclination of $178^{\circ }$). It reached its perihelion on 2009 January 10, and its closest distance to Earth was 0.411 astronomical units (au) on February 24. Soon after its discovery on 2007 July 11, the coma activity of Comet Lulin was monitored closely by an Super Light Telescope 41 cm telescope until 2009 April. After long-term monitoring of Comet Lulin, the dust production rate [A(θ)fρ] was estimated. An unexpected increase in the ${A(0)f\rho}$ near the perigee appears to indicate an opposition effect. By investigating the surface brightness profiles, dust-to-gas ratios, and magnitudes, we ruled out the influences of gas and ion contamination and the outburst phenomenon. We discovered the anti-tail in late December 2008 but were unsure of the composition. We found that this abnormal tail lasted for a considerable time because of the effect of the orbital geometry. We also found that the jet activity coincided with the peak ${A(\theta)f\rho}$ values, and this clue helped us realize what was happening in the dust coma of Comet Lulin.

Interpretation through experimental simulations of phase functions revealed by Rosetta in 67P/Churyumov-Gerasimenko dust coma

Context. The dust-brightness phase curves that have been measured by the OSIRIS cameras on board the Rosetta spacecraft within the coma of comet 67P/Churyumov-Gerasimenko (67P) present a remarkable flattened u-shape. Aims. Our goal is to compare these phase curves with those of tentatively analog dust samples to assess the key dust properties that might induce this shape. Methods. Light-scattering measurements have been made with the PROGRA2 instrument in the laboratory and in microgravity conditions on samples of different physical properties and compositions that are likely to be representative of cometary dust particles. Results. We find that the brightness phase curves of a series of interplanetary dust analogs that have been recently developed (to fit the polarimetric properties of the inner zodiacal cloud and their changes with heliocentric distance) are quite comparable to those of 67P. Key dust properties seem to be related to the composition and the porosity. Conclusions. We conclude that the shape of the brightness phase curves of 67P has to be related to the presence of a significant amount of organic compounds (at least 50% in mass) and of fluffy aggregates (of a size range of 10–200 μm). We also confirm similarities between the dust particles of this Jupiter-family comet and the particles within the inner zodiacal cloud.

VIRTIS-H observations of the dust coma of comet 67P/Churyumov-Gerasimenko: spectral properties and color temperature variability with phase and elevation

We analyze 2–5 μm spectroscopic observations of the dust coma of comet 67P/Churyumov-Gerasimenko obtained with the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-H) instrument on board Rosetta from 3 June to 29 October 2015 at heliocentric distances rh = 1.24–1.55 AU. The 2–2.5 μm color, bolometric albedo, and color temperature were measured using spectral fitting. Data obtained at α = 90° solar phase angle show an increase in bolometric albedo (0.05–0.14) with increasing altitude (0.5–8 km), accompanied by a possible marginal decrease in color and color temperature. Possible explanations include dark particles on ballistic trajectories in the inner coma and radial changes in particle composition. In the phase angle range 50°–120°, phase reddening is significant (0.031%/100 nm deg−1) for a mean color of 2%/100 nm at α = 90°, which might be related to the roughness of the dust particles. Moreover, a decrease in color temperature with decreasing phase angle is also observed at a rate of ~0.3 K deg−1, consistent with the presence of large porous particles, with low thermal inertia, and showing a significant day-to-night temperature contrast. Comparing data acquired at fixed phase angle (α = 90°), a 20% increase in bolometric albedo is observed near perihelion. Heliocentric variations in dust color are not significant in the time period we analyzed. The measured color temperatures vary from 260 to 320 K, and follow a rh−0.6 variation in the rh = 1.24–1.5 AU range, which is close to the expected rh−0.5 value.

First observations of an outbursting comet with the MUSE integral-field spectrograph

We present the first observations of outbursting comet C/2015 ER61 (PANSTARRS) with the Multi-Unit Spectroscopic Explorer (MUSE). The comet was observed on April 9, 2017, only five days after it underwent a significant outburst during which the total brightness increased by a factor of ~7.5. Based on the MUSE observations, we produce simultaneous maps of the CN, C2, NH2 comae, and the dust coma. In turn, we applied image enhancement techniques in order to reveal features in the coma. By comparing the coma morphology for the dust and CN, C2, and NH2, we investigate the release mechanism of those gas species in the coma of comet ER61. We present evidence that NH2 could be released by icy or organic-rich dust grains.