SB2

The discovery of trans-Neptunian objects (TNOs) marked an important milestone in the understanding of the outer Solar System. Due to their environmental conditions, these objects could preserve the most pristine materials that were present on the protoplanetary disk. Studies focused on understanding TNOs physical and dynamical properties can be used to probe planetary formation processes and the subsequent solar system dynamical evolution that followed the formation era.

Nowadays, above 3,000 TNOs have been detected, including four large ones that receive the official designation of dwarf-planets. Analysis of TNOs revealed a compositionally and dynamically diverse population. However, despite all the progress in the last decades, much is still unknown about the composition of the TNOs.

The recently launched James Webb Space Telescope (launched on December 25, 2021) will provide a powerful tool to investigate the TNOs surface composition, where all prior instrumentation has fallen short. The NIRSpec instrument onboard JWST will provide high-quality data that will surpass the quality of the data available by orders of magnitude. DiSCo-TNOs, lead by the Florida Space Institute, is the only large program approved by JWST for the study of the Solar System. With it, we aim to assess the relative ratio of water ice, complex organics, silicates, and volatiles on the surface of a large sample of TNOs. This information is vital to improving models of the formation of our Solar System and other planetary systems. In this talk we present the scope of the DiSCo program, and the tools that are being developed to extract the maximal information from the data. We pay special attention to the compositional modeling technique that uses an implementation of a nested sampling algorithm for Bayesian inference of the abundances and grain sizes distribution of the materials present on TNOs surfaces.

How to cite: De Pra, M., Pinilla-Alonso, N., Souza Feliciano, A. C., Schambeau, C., Harvison, B., Emery, J., Cruikshank, D., Pendleton, Y., Holler, B., Stansberry, J., Lorenzi, V., Muller, T., Guilbert-Lepoutre, A., Peixinho, N., Bannister, M., and Brunetto, R.: Discovering the Surface Composition of TNOs (DiSCo-TNOs) with the James Webb Space Telescope, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1196, https://doi.org/10.5194/epsc2022-1196, 2022.

The stellar occultation technique is a very powerful tool to obtain the size and shape of Solar System bodies with high accuracy [6]. Size determination allows to obtain geometric albedos and, in the case of binary/multiple objects, even the mass density can be derived [3]. Satellites, atmospheres, and rings can also be detected and characterized [1,2,3]. The observation of stellar occultations produced by Kuiper Belt Objects (KBOs) and Centaurs with the James Webb Space Telescope (JWST) offers a unique possibility to extend our knowledge of these bodies [4] by providing key information on the body's ability to retain volatiles, surface thermal properties, roughness, porosity, etc.

We will present our Target of Opportunity (ToO) program [5] accepted within Heidi Hammel's JWST Guaranteed Time Observations (GTO), dedicated to observing stellar occultations by trans-Neptunian objects (TNO) and distant dwarf planets or particularly interesting centaurs (such as the ringed centaurs Chariklo [1] or Chiron [2]). Predictions of such events visible from JWST are challenging due to the chaotic motion of the space telescope around the Lagrange 2 (L2) point. Statistically, we expect there to be approximately a 50% chance of such an occultation of a star brighter than K=19 by a numbered TNO observable from JWST in Cycle 1. We will discuss the possible candidates for Cycle 1 occultations that we have identified so far. As JWST station-keeping maneuvers are executed, the list of possible occultations and their uncertainties will be revised. Very accurate relative astrometry will be performed using the latest releases of the Gaia catalog for particularly promising occultation events through established ground-based programs. Suppose a stellar occultation event is confirmed through such an astrometric revision to have a predicted impact parameter less than 3 times the estimated target radius and to have a 1 sigma uncertainty in prediction less than 2 times the target radius. In that case, the ToO observation will be triggered. JWST station-keeping and trajectory-prediction operations have been studied in the context of stellar occultations by solar system bodies [4]. The accuracy of the trajectory predictions is adequate to support this triggering mechanism up to roughly 30 days before an occultation event: the ToO response time is set to 14 days, the minimum value for a non-disruptive ToO.

The observations will be made with NIRCam and the F070W and F277W filters. These filters were chosen to maximize the flux from the star while minimizing the reflected flux from the TNO or Centaur. This filter combination could change based on the properties of the occulted star and the occulting TNO/Centaur. Other technical aspects and updates on this project will be provided during the presentation.

Acknowledgments. We acknowledge financial support from the Spanish grant AYA-RTI2018-098657-J-I00 “LEO-SBNAF” (MCIU/AEI/FEDER, UE) and from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). Funding from Spanish projects PID2020-112789GB-I00 from AEI and Proyecto de Excelencia de la Junta de Andalucía PY20-01309 is also acknowledged. Part of this work has received funding from the European Research Council under the European Community’s H2020 (2014-2020/ERC Grant Agreement no. 669416 “LUCKY STAR”). M.V-L. acknowledges funding from Spanish project AYA2017-89637-R (FEDER/MICINN).

References

[1] Braga-Ribas et al., Nature 508, 72 (2014)

[2] Ortiz et al., A&A 576, id.A18 (2015)

[3] Ortiz, Santos-Sanz et al., Nature 550, 219 (2017)

[4] Santos-Sanz et al., PASP 128, 959 (2016)

[5] Santos-Sanz, JWST Proposal. Cycle 1, ID. #1271

[6] Sicardy et al., Nature 439, 52 (2006)

How to cite: Santos-Sanz, P., Pinilla-Alonso, N., Stansberry, J., Holler, B. J., Gomes Junior, A. R., Morgado, B. E., Ortiz, J. L., Sicardy, B., Morales, N., Vara-Lubiano, M., Fernández-Valenzuela, E., Desmars, J., Kretlow, M., Souami, D., Braga-Ribas, F., Camargo, J., Benedetti-Rossi, G., Rommel, F. L., Duffard, R., and Assafin, M.: Unveiling the Kuiper belt from the JWST through stellar occultations, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-362, https://doi.org/10.5194/epsc2022-362, 2022.

Earlier reviews of trans-Neptunian light curves reported mean rotation periods of P = 7-8 h (Duffard et al., 2009), and it was also found that the binary trans-Neptunian population rotates slower (Thirouin & Sheppard, 2014), and objects in the cold classical population have larger variability and rotate slower than the non-cold classical TNOs (Benecchi et al., 2013,Thirouin & Sheppard, 2019). While ground-based observations have obvious limitations in detecting long-period light curves the K2 mission of the Kepler Space Telescope allowed long (up to ~80 days), uninterrupted observations of many Solar system objects, including main belt asteroids, Hildas, Jovian trojans, and also the irregular satellites of giant planets. Light curves were also published for a few, selected trans-Neptunian objects based on K2 observations (see Kiss et al., 2020, for a summary). A common outcome of the studies of larger samples, across all dynamical classes, was the identification of an increased number of targets with long rotation periods compared to previous ground-based studies. A similar trend is observed among the data of nearly 10 000 main belt asteroids obtained by the TESS Space Telescope (Pál et al., 2020), and asteroids with long rotation periods were identified in other surveys like the Asteroid Terrestrial-impact Last Alert System (ATLAS), the Zwicky Transient Facility (Erasmus et al., 2021) and the All-Sky Automated Survey for Supernovae (Hanus et al., 2021). 

We have collected the K2 trans-Neptunian object observations between Campaigns C03 (November 2014 -- February 2015) to C19 (August -- September, 2018), which includes 67 targets. Due to the faintness of our targets the detectability rate of a light curve period is ~57 %, notably lower than in the case of other small body populations, like Hildas or Jovian trojans. We managed to obtain light curve periods with an acceptable confidence for 36 targets; the majority of these cases are new identifications. We were able to give light curve amplitude upper limits for the other 31 targets. Several of the newly detected light curve periods are longer than ~24 h, in many cases close to ~100 h, i.e., slow rotators.

There is a very significant difference between the rotation rates of the LCDB and K2 TNO samples (Figs. 1 and 2). The mean LCD spin frequency is 2.71 c/d (8.8 h), while it is 0.87 c/d (27.6 h) in the K2 sample which is more similar to the K2 Hilda and Jovian Trojan spin frequency distrbutions. Thirouin & Sheppard (2019) obtained 9.48±1.53 h and  8.45±0.58 h mean rotation periods for the cold classical and the non-cold classical TNOs. Our mean values for the same dynamical groups (but using different targets) are notably longer: 1.21^+1.58_-0.63 c/d (19.83 h) and 0.83^+1.81_-0.23 c/d (P=28.91 h), respectively. The K2 mean frequency is higher than that of the K2 Jovian Trojans and Hildas, but we could not detect the very long period targets that were observed in these other K2 samples.  

Figure 1: frequency distribution of asteroids. The cyan, magenta, green and blue colours represent the TNOs in the LCDB and Jovian trojans, Hildas and TNOs from K2, respectively.

Figure 2: Frequency as a function of absolute magnitude. Big circles with error bars mark the median values standard deviations for the different samples. The horizontal dashed lines mark the spin frequencies of fast, slow, and very slow rotators (Pravec et al., 2002).  

While there are only three objects with D>500 km in our sample, there are a number of objects -- both with and without detected light curve periods -- that fall in the 300≤D≤500 km transitional zone where asphericity -- hence light curve amplitude -- is expected to drop assuming a single rotating body, assuming main belt composition. Main belt asteroids are already almost extinct in this size range, and so are Centaurs -- for these bodies irregular shapes are expected in most cases. 

While the general trend is that larger objects have smaller light curve amplitudes among TNOs -- a trend followed both by our sample and the LCDB TNOs -- there are a considerable number of TNOs with high asphericity in the 300≤D≤500 km size range. This contradiction could be resolved if TNOs had higher-than-expected compressive strength and become spherical for sizes larger than their main belt counterparts, and remain 'irregular' in the 300≤D≤500 km range. However, their general low density and high porosity point against this scenario. A notable fraction of contact or semi-contact binary systems in which the members themselves are in hydrostatical equlibrium could produce a population of high-amplitude light curves in this size range (Lacerda et al., 2006, 2014). As some authors pointed out, contact binaries may be very frequent, especially in the plutino population (Thirouin & Sheppard, 2018,2019). The long term stability of such systems against their tidal evolution, however, should be investigated to answer the reliability of this assumption. Finally, spherical (rotationally flattened) bodies with large albedo variegations could also explain the observed amplitudes. While the general expectation in most TNO light curve studies was a double peak light curve, in our sample most light curves were found to be single-peak, after comparing the single-peak and double-peak solutions.

Fgiure 3: Light curve amplitude versus the estimated size of the targets in our sample. The region between the vertical dashed lines mark the irregular-to-spherical transition size range in the main belt. Blue and red symbols mark the K2 targets and K2 upper limits, small grey symbols correspond to main belt asteroids. Large gray symbols represent the theoretical maximum light curve amplitudes the of large main belt objects if it was solely caused by the elongated shape of a body with homogeneous albedo.

How to cite: Kecskeméthy, V., Kiss, C., Szakáts, R., Pál, A., Szabó, G. M., Molnár, L., Sárneczky, K., Vinkó, J., Szabó, R., Marton, G., Farkas-Takács, A., Kalup, C., and Kiss, L. L.: Rotational properties of Kuiper belt objects as seen by the K2 mission, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-677, https://doi.org/10.5194/epsc2022-677, 2022.

Beyond the orbit of Neptune lies a sea of small icy bodies known as the Kuiper belt. The surfaces of these Kuiper Belt Objects (KBOs) have remained relatively unprocessed since their formation as a consequence of their distance from the Sun. This means that we can investigate their formation conditions in the early Solar System by studying their surfaces today. Generally, the small and most numerous KBOs are quite dim (r mag > 22), and so it is difficult to study their surfaces spectroscopically. Instead, we can use broadband photometry to take effectively very low-resolution spectra of their surfaces.

When studied spectroscopically, the surfaces of smaller KBOs have generally shown very flat and featureless spectra within certain wavelength ranges. This means that broadband photometry (within those wavelength ranges) can reveal enough information to characterise the optical and near-infrared spectral slopes of these planetesimals. The Colours of the Outer Solar System Origins Survey (Col-OSSOS) has obtained optical and near-infrared broadband photometry of a sample of 92 KBOs, at unprecedented precision (~ ±0.03 mag in optical wavelengths). These broadband surface colours allow small, dynamically excited KBOs to be characterised into a bimodal colour distribution (as with previous colour surveys), along with the identification of potentially outlying surface colours.

As a side effect of Col-OSSOS’s observing technique we have a sample of objects with repeated optical colours, and some repeated near-infrared colours. We also have taken additional optical photometry of a small sample of KBOs with outlying surface colours. This allows us to investigate the possibility of photometric variation across multiple epochs for this sample of objects. Col-OSSOS observed sequential broadband filters on timescales less than the typical periods of small KBOs. Therefore, we can simultaneously fit a linear lightcurve and photometric colours to our photometry and potentially rule out lightcurve effects causing photometric variations. This means that differing colours across multiple epochs implies either differing surface composition, or that our approximation of linear brightness variability across the observing sequence is invalidated. We will present this sample and discuss implications for the spectrovariable population within the Kuiper belt.

How to cite: Buchanan, L., Schwamb, M., Fraser, W., Bannister, M., Marsset, M., Pike, R., Kavelaars, J., Benecchi, S., Lehner, M., Wang, S.-Y., Peixinho, N., Volk, K., Alexandersen, M., Chen, Y.-T., Gladman, B., Gwyn, S., and Petit, J.-M.: Exploring Variability within the Col-OSSOS Sample, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-936, https://doi.org/10.5194/epsc2022-936, 2022.

We report a multi-opposition discovery of 17 Trans-Neptunian Objects (TNOs) with the Chilean node of the Korea Microlensing Telescope Network (KMTNet-CTIO) which has a 1.6 m wide-field optical telescope covering 2x2 square degree field of view. The first survey observations were made with 4 fields around (RA,DEC = 197.6°, -7.9°) every other day from April 5 to April 15, 2019, and recovery observations were carried out every year since then. More than half of the 17 objects were not initially observed in 2019 but were discovered in later years. The observed R magnitudes of discovered TNOs are from ~22 to ~24 and their H magnitudes are estimated to be from 6.6 to 8.5. Of the 17 TNOs, two objects, 2021 GU122 and 2022 GV6, have been found to be detached objects with perihelion distance greater than 40 AU. 2022 GV6 has an estimated semi-major axis of 110 AU and is currently passing near its perihelion. Most objects have current heliocentric distance around 40 AU but one object, 2022 FA7, is at ~ 50 AU. In addition to the 17 multi-opposition objects, 7 more single-opposition objects received their provisional designations by Minor Planet Center. This marked the first TNO discovery in South Korea although the telescope itself is located overseas.

How to cite: JeongAhn, Y., Moon, H.-K., Kim, M.-J., and Choi, Y.-J.: Trans-Neptunian Object discoveries at KMTNet-CTIO, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-338, https://doi.org/10.5194/epsc2022-338, 2022.

We have carried out a long term photometric analysis of time series images of the trans-Neptunian object (TNO) 2008 OG₁₉ with which we have refined its physical properties from its long-term variability.

Photometric Analysis

The first detailed analysis of 2008 OG₁₉ was carried out by [1] using rotational light-curves from 2014 and 2016 from which a volume-equivalent diameter, a rotation period (P), a triaxial ellispoidal shape model, and a density were estimated.

We have used 1,314 images covering a time-span of six years (2014-2021), obtained with the Sierra Nevada 1.5-m telescope and the Calar Alto 1.2-m telescope, both in Spain, in order to build yearly rotational light-curves for 2008 OG₁₉. To refine the rotation period estimation of 2008 OG₁₉, we have combined the whole set of data and applyed the lomb periodogram [2] and the Phase Dispersion Minimization techniques [3] resulting in P = 8.72565 +/- 0.0008 hr. The resulting rotational light-curve can be seen in Figure 1.

Long-term variability

By folding the light-curves with the refined period, we have been able to see an increase of the amplitude of the rotational light-curve. This increase is due to a change in the aspect angle, that allows to estimate the orientation of 2008 OG₁₉ rotational axis as seen in Figure 2. Using the largest rotational light-curve amplitude and assuming hydrostatic equilibrium we have updated its triaxial ellispoid model and its density.

Figure 1: 2008 OG₁₉ rotational light-curves folded to P = 8.72565 h. Observational data are represented by color points with each color indicating a different observational night. The black dashed line represent the Fourier series fit.

Figure 2: Model of the amplitude given by the fit to the observational data using b/a = 0.643 in blue (best fit). Other pole solutions are possible with different values of the b/a such as the red model. The gray line represents 2008 OG₁₉ aspect angle given by the best fit. The magenta points with error bars are the observational data from this work.

References
[1] E. d. M. Fernández-Valenzuela, Physical properties of transneptunian objects and centaurs; Ph.D. thesis, University of Granada, Spain, 2017.
[2] N. R. Lomb, Least-squares frequency analysis of unequally spaced data, Astrophysics and Space Science 39 (1976) 447–462. doi:10.1007/BF00648343.
[3] R. F. Stellingwerf, Period determination using phase dispersion minimization, ApJ 224 (1978) 953–960. doi:10.1086/156444.2

How to cite: Costa-Sitjà, M., Fernández-Valenzuela, E., Ortiz, J. L., Morales, N., Santos-Sanz, P., and Vara-Lubiano, M.: Long-term photometric analysis of the trans-Neptunian object 2008 OG19, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-610, https://doi.org/10.5194/epsc2022-610, 2022.

Hi’iaka is the largest satellite of the dwarf planet Haumea, with an estimated area-equivalent diameter of 300 km (Fernández-Valenzuela et al., 2021). It is the best studied satellite in the trans-Neptunian region. Its rotational light-curve was observed with Hubble, for which an approximate rotation period of 9.8 h was obtained (Hastings et al. 2016). The system is very peculiar because it stands out from all other TNO-binary systems. While all other known satellites are thought to be synchronous, Hi’iaka’s rotation period is fast compared to the 49 days that takes to complete an orbit around Haumea. Therefore, the study of Haumea-Hi’iaka system yields important information about the formation processes of the whole Haumea’s system, which includes another moon (Brown et al. 2006), a ring (Ortiz et al. 2017) and a family of objects (Brown et al. 2007).

Our group has been observing Haumea since its discovery, compiling a large database of images since around 20 years ago. Using this set of images we have obtained high accuracy astrometric measurements of the photocenter of the Haumea-Hi’iaka system. We have applied a similar procedure as in Ortiz et al. (2017) to disentangle the position of Haumea from the contribution of Hi'iaka, but for a much larger time span as mentioned above. Therefore, we have been able to determine more accurate orbits for Haumea and Hi'iaka.

Additionally, we have carried out two specific observational runs of several days in order to obtain the rotational phase of Hi’iaka at that moment of the two stellar occultations that occurred last year (in April 2021). We used the 1.23-m telescope at Calar Alto Observatory, the Artemis telescope at Teide Observatory and the 1.5-m telescope at Sierra Nevada Observatory to acquire images of the unresolved system. The resulting photometry of these images give rise two rotational light-curves of Haumea in 2021 and 2022. We fitted a fourth-order Fourier function, which represents Haumea’s body-shape contribution to the rotational light-curves. From this fit, we took the residuals of the observational data and searched for periodicities within them. We obtained a rotation period in agreement with the estimations in Hastings et al. (2016), but much more accurate. These residuals, when folded to the resulting period, provide Hi’iaka’s rotational light-curve. The amplitude obtained for Hi’iaka’s rotational light-curve is 0.015 mag, which agrees with the expected signal induced in Haumea’s rotational light-curve when accounting for a variable source as that produced by Hi’iaka, i.e., considering the rotational light-curve obtained in Hastings et al. (2016). We have not detected a change in the amplitude of Hi’iaka’s rotational light-curve when comparing our data, taken in 2021 and 2022, with those from Hastings et al. (2016), taken in 2010. This means that the obliquity of Hi’iaka must be close to 90º in its orbit around Haumea.

Brown et al. (2006), The Astrophysical Journal, Volume 639, Issue 1, pp. L43-L46.

Brown et al. (2007), Nature, Volume 446, Issue 7133, pp. 294-296.

Fernández-Valenzuela et al. (2021), AAS Division of Planetary Science meeting #53, id. 503.05. Bulletin of the American Astronomical Society, Vol. 53, No. 7 e-id 2021n7i503p05.

Hastings et al. (2016), The Astronomical Journal, Volume 152, Issue 6, article id. 195, 12 pp.

Ortiz et al. (2017), Nature, Volume 550, Issue 7675, pp. 219-223.

How to cite: Fernández-Valenzuela, E., Ortiz, J. L., Morales, N., Jehin, E., Burdanov, A., de Wit, J., Ferrais, M., Vara-Lubiano, M., Morales, R., Kretlow, M., Santos-Sanz, P., Alvarez-Candal, A., Duffard, R., Pál, A., Kiss, C., and Szakáts, R.: Hi’iaka’s physical and dynamical properties using long-term photometric data, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-406, https://doi.org/10.5194/epsc2022-406, 2022.

Centaurs and trans-Neptunian objects (TNOs) are considered to be among the most pristine members of our solar system and carry plenty of information on the physical and dynamical processes that shaped our solar system.

Here we report the occultation observation of the star Gaia EDR3 133768513079427328 (G: 11.7 mag, R: 11.3 mag) by the TNO (119951) 2002 TC302 on November 11, 2021. The shadow path was predicted to cross central Europe and USA. We received a total of 57 observations reports, with at least 19 positive detections and 25 miss reports (no event detected).

2002 TC302 is a high-inclination (i ~ 35°) TNO in a 2:5 resonance with Neptune, orbiting the Sun in an average distance of about 55 au. The radiometric diameter from Herschel and Spitzer thermal observations is 584.1 (+106.5, -88.0) km [1], while the analysis of a multi-chord stellar occultation observed on 28 January 2018, combined with light curve data, revealed an area-equivalent diameter of 499.6 ± 10.2 km [2]. From our preliminary elliptical profile fit of the 11 November 2021 occultation observations we derived a projected area-equivalent diameter of 500.3 ± 2.5 km, which is consistent with the above mentioned value from the previous stellar occultation in 2018. The 2018 and 2021 occultation diameters are significant (about 84 km) smaller than the radiometric diameter, which might be even larger (D ~ 643 km) after a reanalysis of the Herschel data [3]. This discrepancy might indicate the existence of an unresolved satellite, but other possibilities are being considered as well [see also 2,3].

Acknowledgments: We acknowledge financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). Funding from Spanish projects PID2020-112789GB-I00 from AEI and Proyecto de Excelencia de la Junta de Andalucía PY20-01309 is acknowledged. Part of the research leading to these results has received funding from the European Research Council under the European Community’s H2020 (2014-2020/ERC Grant Agreement no. 669416 “LUCKY STAR”). M.V-L. acknowledges funding from Spanish project AYA2017-89637-R (FEDER/MICINN). P.S-S. acknowledges financial support by the Spanish grant AYA-RTI2018-098657-J-I00 “LEO-SBNAF”.

References
[1] S. Fornasier, E. Lellouch, T. Müller, et al., A&A, 555 (2013) A15.
[2] J. L. Ortiz, P. Santos-Sanz, B. Sicardy, et al., A&A, 639 (2020) A134.
[3] J. L. Ortiz, and the 20-coauthor team, EPSC2020-686, https://doi.org/10.5194/epsc2020-686, 2020.

How to cite: Kretlow, M., Ortiz, J. L., Sicardy, B., Braga-Ribas, F., Desmars, J., Fernández-Valenzuela, E., Morales, N., Santos-Sanz, P., Kilic, Y., Morgado, B., Benedetti-Rossi, G., Camargo, J., Rommel, F. L., Vara-Lubiano, M., Duffard, R., Assafin, M., Ramos Gomes Júnior, A., Souami, D., Vieira-Martins, R., and Álvarez-Candal, Á. and the 2002 TC302 occultation team: The 11 November 2021 multi-chord stellar occultation by trans-Neptunian object (119951) 2002 TC302, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-172, https://doi.org/10.5194/epsc2022-172, 2022.

The discovery of long period comet C/2014 UN271 (Bernardinelli-Bernstein) announced in June 2021 quickly suggested an inactive nucleus with an absolute magnitude of H_V = 7.8 mag [1], which implied a diameter between 130 and 260 km assuming geometric albedos between 2% and 8%. Immediate follow-up observations with our Las Cumbres Observatory (LCO) Outbursting Objects Key project (LOOK) [2] as well as with SkyGems Namibia [3] revealed that the comet was active at 20.18 au. Evidence was quickly found that C/2014 UN271 had been active since 2018 and possibly even active at the time it was first observed in 2014 (at 29 au) [4,5]. After the discovery announcement, follow-up observations with ALMA and HST determined that Bernardinelli-Bernstein has a cometary albedo (0.033 ± 0.009) and an effective diameter of 137 ± 17 km, distinguishing it as the largest observed Oort-cloud comet [6,7].

Prior to the observations of C/2014 UN271, the most distant comet discoveries were C/2010 U3 and C/2017 K2, which were made between 15 and 20 au, but for which pre-discovery images indicate activity beyond 20 au [8,9]. C/2014 UN271 was significantly brighter than those comets at the same distance, which provided an exceptional opportunity to characterize its very distant comet activity close to 20 au. In this presentation we will report the results of our observing program with FORS2 on ESO’s 8-meter VLT in July and August 2021. The VLT/FORS data are interpreted in combination with targeted observations with the 4.1-m SOAR and the long-term monitoring campaign with 1-m facilities within the LOOK Project [10,11]. 

The multi-facility long-term photometric monitoring of C/2014 UN271 enabled our team to identify three outbursts between June and September 2021, indicating that the comet's optical brightness was dominated by cometary outbursts during the VLT observing run. Our VLT/FORS2 multi-band imaging and spectroscopic observations allowed us therefore to characterize the comet’s outburst in terms of spectral slope and coma morphology, including arc-like features. We will also present our efforts to characterize the comet’s short-term variability and rotation period.  

References: [1] https://minorplanetcenter.net/mpec/K21/K21M53.html [2] Kokotanekova, R., et al. (2021), ATel, 14733 [3] https://minorplanetcenter.net/mpec/K21/K21M83.html [4] https://minorplanetcenter.net/mpec/K21/K21M83.html [5] Farnham, T. (2021), ATel, 14759 [6] Lellouch, E. et al. (2022) A&,659, L1, 8 [7] Hui, M.-T., et al. (2022) ApJL, 929, 1, L12, 7 [8] Hui, M.-T., et al. (2019) AJ 157 [9] Jewitt, D. et al. (2021) AJ 161, 188 [10] Lister et al., submitted [11] Kelley et al., submitted.

How to cite: Kokotanekova, R., Kelley, M. S. P., Holt, C. E., Opitom, C., Protopapa, S., Knight, M. M., Lister, T., Bannister, M. T., Snodgrass, C., and Fitzsimmons, A.: Observations during a 20-au outburst of the largest observed Oort-cloud comet C/2014 UN271 (Bernardinelli-Bernstein), Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-989, https://doi.org/10.5194/epsc2022-989, 2022.

Introduction

Comets are the leftovers from the formation of the Solar System. Understanding their composition allow us to investigate the physical and chemical processes occurring at the early stages of its formation. In this contribution we analyze high resolution spectra of comet C/2020 F3 (NEOWISE) obtained with the High Accuracy Radial Velocity Planet Searcher (HARPS-N) echelle spectrograph at the 3.6 m Telescopio Nazionale Galileo (TNG). C/2020 F3 was discovered on 27 March 2020 as a long-period comet, the brightest one observed in the northern hemisphere since the Hale-Bopp in 1997. Its remarkable brightness offered a unique opportunity to investigate its composition through high-resolution spectroscopy, which is otherwise challenging on these targets due to their usual faintness. Our observations already allowed the identification of 4488 cometary emission lines belonging to C2, C3, CN, CH, NH2, Na I and [OI] [1]. We here follow up the molecular identifications by characterizing the gaseous environment of C2020/F3 through the analysis of the molecules’ production rates.

Dataset and Methods

We analyze one HARPS-N spectra of C/2020 F3 obtained on 26 July, at a heliocentric distance of 0.72 AU, covering the wavelengths between 383-693 nm at a spectral resolving power of 115000. We reduced the spectrum by performing absolute calibration, sky subtraction and dust-continuum normalization using IRAF routines and observations of the spectrophotometric standard HR5501 and the solar analog Land 107-684. The calibrated spectra were used in combination with the identified line identification [1] to measure the fluxes of given bands of molecules CN (388.3 nm band), C₂ (516.5 nm band), C₃ (405.0 nm band), NH₂ (577.4 nm band) and OI (630.0 nm line). For each emission line or band, the flux was measured in IRAF through a fit of multiple gaussian profiles, centered at the catalog wavelengths. Cometary production rates are then estimated using a Haser model [2] which parameters were derived from literature studies (e.g., [3])

Results

We estimate production rates of Q[CN]=2.2*10²⁶ , Q[C₂]=2.28*10²⁶ , Q[C₃]=2.15*10²⁷ and finally Q[NH₂]=1.08*10²⁷ . We estimate a H₂O production rate of Q[H₂O]=2.89*10²⁹ , using the OI emission line at 630 nm, therefore assuming that all the flux of this line comes from dissociation of water. Our estimate is in agreement with independent estimates from the SOHO/SWAN instrument[4]. A detailed analysis of the production rate and their comparison with other comets will be presented at the conference.

References

[1] P.Cambianica, et al., 2021, A&A, 656, A160.

[2] Haser, L. 1957Bull. Soc. R. Sci. Liege, 43 (1957), pp. 740-750

[3] Langland-Shula, L., Smith, G. H.,2011, Icarus, Volume 213, Issue 1, 2011, 280-322, 0019-1035

[4] M. R. Combi et al 2021 ApJL 907 L38

How to cite: Munaretto, G., Cambianica, P., Cremonese, G., Fulle, M., Boschin, W., Di Fabrizio, L., Harutyunyan, A., Podio, L., and Codella, C.: Production rates of comet C2020/F3 (NEOWISE) from high resolution spectroscopy, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-360, https://doi.org/10.5194/epsc2022-360, 2022.

Comet NEOWISE (C/2020 F3) displayed a highly structured dust tail, exhibiting the most prominent dust tail features visible from Earth since Comet McNaught (C/2006 P1) in the Southern Hemisphere and Comet Hale-Bopp (C/1995 O1) in the Northern Hemisphere. Using images taken by the amateur astronomer community, this dust tail is analysed using the Finson-Probstein model. The comet’s position in the sky in amateur images is calculated using an open source algorithm [1], the position and exact time then calculated, and the dust tail is simulated. This modelled dust tail structure is then projected and overlaid onto the comet image to directly compare and identify similarities and discrepancies between the model and the image. Using the novel analysis method of mapping the image to a plot of dust grain beta against ejection time[2], tail structures can be more easily identified, analysed and tracked over time (where beta is the ratio of force due to solar radiation pressure and that due to the sun’s gravity).

Dust tail structures such as syndynic bands and striae (near-parallel linear features) have been identified and characterised in terms of dust ejection time and dust beta values. These structures are tracked over time, and compared to the analysis of similar structures seen in C/2006 P1 (McNaught) [2]. There are some clear differences between the two comets, particularly in the alignment and arrangement of their striae, most likely due to different heliospheric conditions during each comet’s perihelion passage.   

These results, all based on amateur observations, provide a thorough description of Comet NEOWISE’s dust tail to contribute to the collection of cometary dust tail profiles currently available. This will enable convenient comparison between comets in the future, and will eventually enable population studies on cometary dust tails and their features. Due to the comet’s very high activity, it also exhibited a rarely seen tail of neutral sodium atoms. This sodium tail has also been parameterised in this work, with an estimated ionization lifetime of the sodium atoms of 17 hours ± 2 hours.

[1] Lang, Dustin, David W. Hogg, Keir Mierle, Michael Blanton, and Sam Roweis. 2010.”Astrometry.net: Blind Astrometric Calibration of Arbitrary Astronomical Images”. The Astronomical Journal 139 (5): 1782-1800. doi:10.1088/0004-6256/139/5/1782.

[2] Price, Oliver, Geraint H. Jones, Jeff Morrill, Mathew Owens, Karl Battams, Huw Morgan, Miloslav Drückmuller, and Sebastian Deiries. 2019. "Fine-Scale Structure In Cometary Dust Tails I: Analysis Of Striae In Comet C/2006 P1 (Mcnaught) Through Temporal Mapping". Icarus 319: 540-557. doi:10.1016/j.icarus.2018.09.013.

How to cite: Afghan, Q., H. Jones, G., Price, O., and J. Coates, A.: Structural analysis of the dust tail of Comet NEOWISE (C/2020 F3), Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-895, https://doi.org/10.5194/epsc2022-895, 2022.

We will present our observations of the bright comet C/2021 A1 (Leonard) with the newly upgraded CRIRES+ high resolution IR spectrometer mounted on the ESO VLT in Paranal, Chile. C/2021 A1 is a long period comet that reached perihelion on January 3, 2022, at 0.62 AU from the Sun. It is one of the brightest comet of recent years, reaching a visual magnitude of 3 close to perihelion (Seiichi Yoshida's webpage).

Originating from the cold Oort Cloud were it spent most of its dynamical lifetime, C/2021 A1 has presumably experienced little transformation or activity, keeping a pristine memory of the chemistry of the protoplanetary disk at the place where it formed. The sublimation of the nucleus volatile ices during its close approach to the Sun was an unique opportunity to have a glimpse at C/2021 A1 composition through the fluorescence of the species in its coma. We observed the comet with CRIRES+ for three nights close to its perihelion at 0.62 AU between December 28, 2021, and January 3, 2022, and derived the production rates of several parent volatiles including H₂O, CH₄, C₂H₆, H₂CO and CH₃OH. During the period of observation, the proximity to the Sun triggered a series of outbursts in C/2021 A1 (Jehin et al, 2022), enhancing the release of material in the coma and ultimately leading to the disintegration of the comet. The observations were made nodding on sky to subtract telluric features in the spectra, and the spectra were later corrected for atmospheric absorption (dominant in the NIR region) and wavelength calibrated by an atmospheric transmittance model computed with the ESO MOLECFIT software (Smette 2015). A flux reference star was also observed to calibrate the target's flux. The chemical composition of the comet will be compared to other comets from the same and other dynamical groups. The ongoing effort to build a chemical taxonomy of comets (A’Hearn et al., 1995; Dello Russo et al., 2016; Lippi et al., 2021) and compare it to the established dynamical classification underlies the need to better constrain the chemical composition of an increasing number individual comets. 

The high resolution IR spectrometer CRIRES+ is an upgrade of the CRIRES spectrometer into a cross-dispersed spectrograph, increasing the simultaneously covered wavelength by a factor 10 (Dorn et al, 2020). It has been available at the VLT since October 2021, offering a resolving power up to 100000 with a 0.2'' slit between 1 and 5 µm. This first observation of a comet with CRIRES+ will also serve to demonstrate its capabilities to target such objects in the IR.

How to cite: Vander Donckt, M., Lippi, M., Faggi, S., and Jehin, E.: The NIR chemical composition of C/2021 A1(Leonard) at perihelion from CRIRES+ at the VLT, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-685, https://doi.org/10.5194/epsc2022-685, 2022.

As the solar wind encounters a comet, ionized gas released from the nucleus propagates away from the Sun with the wind, forming the ion tail of the comet that can stretch for multiple astronomical units. The transport of cometary material antisunward of the comet provides opportunities to measure the cometary composition and plasma interactions at a significant distance from a comet’s nucleus. Serendipitous crossings by spacecraft of comets’ ion tails is a surprisingly commonplace occurrence, but can go unnoticed, as any measured plasma fluctuations can be small.

Using the measured flow of the solar wind at the spacecraft, we can estimate the motion of the solar plasma upstream of the spacecraft, and compare this trajectory with the locations of known comets. This method can uncover previously unnoticed ion tail encounters and predict future encounters.

In December 2021, while comet C/2021 A1 (Leonard) traversed the ecliptic plane, sunward of the spacecraft Solar Orbiter, the spacecraft was immersed in the comet’s ion tail. This encounter was predicted using a range of estimated solar wind velocities to estimate the motion of solar wind plasma to the spacecraft. A wealth of data was collected during the encounter, including results from multiple instruments that support the prediction. We present data returned from the SWA and magnetometer instruments, providing information on the structure of the induced magnetotail. Additionally, images of comet Leonard’s ion tail from other spacecraft during the encounter provide a uniquely complete picture of the tail crossing.

Fig: Orbital configuration of comet Leonard and Solar Orbiter on 18th December 2021, during which Solar Orbiter was immersed in the ion tail of comet Leonard. 

How to cite: Grant, S., Jones, G., Owen, C., and Matteini, L.: The Prediction of, and Results from Solar Orbiter's encounter with Comet C/2021 A1 (Leonard)., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1106, https://doi.org/10.5194/epsc2022-1106, 2022.

1. Introduction

C/2016 R2 (PanSTARRS) was a surprising comet. Detected on September 7, 2016 by Pan-STARRS it showed an unusual composition when it became a bright comet at the end of 2017 and the beginning of 2018. It developed a coma at large (~6 au) heliocentric distance and observations showed that it had a highly unusual composition: no water molecules (or OH radical) could be detected, and the abundances of the usual radicals (CN, C₂, C₃) were unusually low, with a surprising coma composition dominated by CO, CO₂ and N₂ molecules with bright CO⁺ and N₂⁺ emission lines in the visible range. A high CO production rate of about 10²⁹ molecules s^-1 was measured (Biver et al. 2018; Wierzchos & Womack 2018) as well as a high CO₂ production rate (CO₂/CO=1.1 from Opitom et al. 2019), and a high ratio N₂/CO varying between 0.06 and 0.09 (Biver et al. 2018; Cochran & McKay 2018a,b; Opitom et al. 2019; Venkataramani et al. 2020).

The detection of such bright N₂⁺ emission lines in this comet highlighted the necessity of a good modeling of the N₂⁺ fluorescence spectrum in comets. The high-quality spectra published by Opitom et al. (2019) provided a good opportunity to test such a model. This model also permits to compute the fluorescence spectrum of the ¹⁴N¹⁵N⁺ species, leading to the possibility of future measurements of the ¹⁴N/¹⁵N isotopic ratio in the N₂ molecules, one of the main constituant of the solar nebula.

2. Observations

The spectra used for this work have been obtained with the UVES spectrograph mounted on the ESO 8.2 m UT2 telescope of the VLT. Three different observing nights have been used, corresponding to February 11, 13 and 14, 2018. One single exposure of 4800 s of integration time was obtained during each night and we used a 0.44” wide slit, providing a resolving power R~80,000. The slit length was 8” corresponding to about 14,500 km at the distance of the comet (geocentric distance of 2.4 au). The average heliocentric distance was 2.76 au. Opitom et al. (2019) describe in more details the data processing.

From the 2D spectra having a spatial extension of 30 rows, each of them corresponding to a different cometocentric distance, we extracted different 1D spectra for each night. These spectra were then averaged for similar cometocentric distances allowing a detailed comparison of these spectra at different cometocentric distances, the furthest one corresponding to 2x4 rows at the two extremities of the slit (i.e. at a cometocentric distance varying between 4800 and 6600 km).

3. Modeling the N₂⁺ fluorescence spectrum

We developed a new fluorescence model for modeling our observational spectra. The transition involved in this spectrum is the first negative group, i.e. the B²Σ_u⁺ → X²⁺Σ_g⁺ electronic transition with the (0,0) bandhead appearing near 3914 Å. We considered the first three vibrational levels (v = 0; 1; 2) for both X²⁺Σ_g⁺ and B²Σ_u⁺ state, each of them with all the rotational levels from N = 0 to 40.

N₂⁺ having no permanent dipole moment, the pure rotational and vibrational transitions are forbidden (or have a very low probability, through quadrupolar transitions, not taken into account in our model). For that reason it takes a long time for this species to reach its fluorescence equilibrium because it needs a few tens of absorption / emission cycles between the X²⁺Σ_g⁺ and B²Σ_u⁺ states to reach this equilibrium. A comparison of the spectrum obtained on the nucleus with the one obtained at the edges of the slit revealed clear differences due to different rotational relative populations. For that reason we decided to model the N₂⁺ fluorescence spectrum with a Monte-Carlo simulation. Such a computational method allows to compute a spectrum at different times from an initial relative population distribution. Our model starts with a Boltzmann relative population distribution of 80 K (representing an estimate of the kinetic temperature in the inner coma) and uses 10,000 s of evolution time.

We managed to explain satisfactorily the observed N₂⁺ emission spectrum. Fig. 1 presents a close up view around the (0,0) bandhead. This work, presented in more details in Rousselot et al. (2022) also allowed to compute accurate fluorescence efficiencies.

Figure 1: Comparison of the observed VLT UVES spectrum of comet C/2016 R2 (blue) obtained at the ends of the slit with our N₂⁺ model (red).

4. ¹⁴N¹⁵N⁺ fluorescence spectrum

Our modeling of the N₂⁺ fluorescence spectrum can be used to compute the ¹⁴N¹⁵N⁺ fluorescence spectrum, leading to the possibility of measuring the ¹⁴N/¹⁵N isotopic ratio in N₂ molecules. We will present such a spectrum as well as a search for this isotopologue in the C/2016 R2 spectra. Such comets are rare but future observations will reveal other comets similar in composition to C/2016 R2. With future observing facilities now under construction (such as the ESO ELT) ¹⁴N/¹⁵N measurements for N₂ molecules will probably become possible, leading to new constraints on this isotopic ratio.

References

Biver N., et al., 2018, A&A 619, A127

Cochran A. L. & McKay, A. J. 2018a, ApJ, 856, L10

Cochran A. L. & McKay A. J., 2018b, ApJ, 854, L20

Opitom C., et al. 2019, A&A, 624, A64

Rousselot P., et al., 2022, A&A, in press

Venkataramani K., et al., 2020, MNRAS, 495, 3559

Wierzchos K. & Womack M. 2018, AJ, 156, 134

How to cite: Rousselot, P., Anderson, S., Alijah, A., Noyelles, B., Jehin, E., Hutsemékers, D., Opitom, C., and Manfroid, J.: Modeling of N2+ and 14N15N+ fluorescence spectrum in comets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-596, https://doi.org/10.5194/epsc2022-596, 2022.

Introduction: Radio observations of long-period comet C/2016 R2 (PanSTARRS) revealed that it was remarkably depleted in water (Biver et al. 2018). The spectrum was instead dominated by bands of CO⁺ and N₂⁺, rarely seen in such abundance in comets before (Cochran & Mckay 2018). Understanding the nature of this comet would allow us to investigate key features in the timeline of planetesimal formation.

By measuring the observed emission fluxes of the observed N₂⁺ in C/2016 R2's spectrum, ionic ratios of N₂⁺/CO⁺ in the coma were estimated to be between 0.06 (Cochran & Mckay. 2018), Opitom et al. 2019) and 0.08 (Biver et al. 2018). This would be the same ratio for N₂/CO since ionization efficiencies of N₂ and CO are similar at 1 au for quiet Sun (Huebner et al. 1992).

C/2016 R2 provides a unique opportunity to set a baseline for identifying N₂ in cometary spectra. By using the Ultraviolet-Visual Echelle Spectrograph (UVES) mounted on the 8.2 m UT2 telescope of the European Southern Observatory Very Large Telescope (ESO VLT) observations, we can constrain the properties of N2 in the cometary coma and establish new Haser scalelengths in order to determine the N2 production rate, which we present here.

Observations: The observations of C/2016 R2 used in our work were collected on 2018 February 11, 13, and 14 with UVES. All observations were made when the comet was near its perihelion distance of 2.6 au, at 2.76 and 2.75 au. A full description of the observations and data reduction can be found in Opitom et al. (2019).

Methods: We aim to fit the observed flux with a Haser profile (Haser (1957)), providing an analytical solution to the column density of parent- and daughter-species in the coma along the line of sight. N₂⁺ being an ion, the Haser model will be restricted to an area near the coma. The UVES slit covers ~6500 km on either side of the nucleus, a narrow region in which ions should be undisturbed by the solar wind.

CN scalelengths and Production Rate: We first fit a Haser profile on the CN emissions to ensure scalelengths can properly be determined from our data. We created a synthetic CN model evaluated by interpolation from a spectrum calculated by Zucconi (1985). This model is then convolved by the response of our instrument, with an FWHM of 0.06 Å. For each night of 11, 13, and 14 Feb, the CN lines are identified and summed along the spectroscopic slit. The total flux measured for CN over the entire spectrograph and averaged over the three nights of observation was 2.1x10^-15 erg/s/cm2. The flux intensities are then averaged again over their cometocentric distances so as to allow for a proper fit of the Haser model.

By using a X² test, we estimate the best fit of the Haser model to the observed intensity profile and determine the scalelengths of both the parent- (HCN) and daughter- (CN) species in the coma of C/2016 R2. We found l_p = 1.3 x 10⁴ km and l_d = 2.8 x 10⁵ km (scaled to 1 au using an rh2 law) as shown on Fig. 1. With g = 3.52 x 10^-2 photons/s/molecule at 1 au (Schleicher et al. 2010), we estimate a production rate of Q(CN) = (9.8±0.5) x 10²⁴ mol/s.

N2+ scalelengths and Production Rate: The production rate was estimated via relative ratios with g =7 x 10^-2 photons/ion/s from Lutz et al. (1993) by Wierzchos (2018) as Q(N2) = (2.8 ±0.4) x 10²⁷ mol/s and by McKay (2019) as Q(N2) = (4.8 ± 1.1)x10²⁷ mol/s. It can be inferred from Biver et al. (2018) to be ~8.5 x 10²⁷ mol/s for a Q(CO) = 1.1 x 10²⁹ mol/s. These results are first re-calculated with the most recent g factor from Rousselot et al. 2022. With g =4.90 x 10^-3 photons/mol/s at 1 au, prior measurements of the N₂⁺ production rates become Q(N₂) = 4.6x10²⁷ mol/s (Wierzchos & M. Womack 2018), =8.0x10²⁷ mol/s (McKay et al. 2019), and 1.4x10²⁸  mol/s (Biver et al. 2018).

We limit the identification process to the 3885.5 Å to 3915.0 Å interval to further avoid contamination by the CN emission lines. We explore this interval with the X² test and find new scalelengths of l_p = 2.8 x 10⁶ km and l_d = 3.8 x 10⁶ km scaled to 1 au (see Fig. 1). These values are within the expected range estimated from the rate coefficients. However, at this scale, multiple pairs of scalelengths could be selected for N2+ with an equally good fit. We thus have a large uncertainty on the production rate.

Using g = 5.41 x 10^-3 photons/mol/s (at r_h) for the (0,0) band between 3885.5-3915.0 Å and FTOT = 1.0 x 10^-14 erg/s/cm², we find Q(N₂)=(8 ±1) x 10²⁷. With Q(CO) ~ 1.1 × 10²⁹ molecules.s^-1, N2/CO = 0.07, consistent with observed intensity ratios.

Figure 1: The best fit of the Haser model for CN (top, purple, compared to other fits using scalelengths from literature) and N2+ (bottom, blue).

References

A’Hearn et al., 1995) ICARUS 118, 223A

Biver N., et al., 2018, A&A 619, A127

Cochran A. L. & McKay, A. J. 2018a, ApJ, 856, L20

Cochran A. L. & McKay A. J., 2018b, ApJ, 854, L10

Haser L., 1957, BSRSL 43 740H

Huebner W.F., Keady J.J., & Lyon S.P., 1992, ApSS 195 1H

Lutz B.  et al., 1993, ApJ 03 402-411

McKay A. J., et al., 2019, AJ, 158, 128

Opitom C., et al. 2019, A&A, 624, A64

Raghuram S. et al. 2020, MNRAS 501 3 4035-4052

Rousselot P., et al., 2022, A&A, in press

Schliecher D.G., 2010, AJ 140 973S,

Venkataramani K., et al., 2020, MNRAS, 495, 3559

Wierzchos K. & Womack M. 2018, AJ, 156, 134

Wyckoff S. &  Wehinger P. A. 1976, ApJ 204 604W

Zucchoni J.M. & Festou M.C. 1985, AA 150 180Z

How to cite: Anderson, S., Rousselot, P., Noyelles, B., Opitom, C., Jehin, E., Hutsemékers, D., and Manfroid, J.: The N2 Production Rate in C/2016 R2 (PanSTARRS), Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-538, https://doi.org/10.5194/epsc2022-538, 2022.

I - Introduction

Main Belt Comets (MBCs) display comet-like dust-release while occupying asteroid-like orbits in the Main Asteroid Belt (2AU<a<2.5AU). Asteroids and comets have long been perceived as two very distinct populations, initially formed within and beyond the snowline respectively, then split into separate reservoirs. However, the recent discovery of icy objects in the Main Belt, as well as of other active asteroids and inactive comets, blurs the physical, dynamical and observational boundaries between comets andasteroids and indicates it is rather a continuum.

So far no direct detection of gas has been made due to the low gas production rates in MBCs, but dust features of various strengths have been observed. Several mechanisms unrelated to outgassing can lead to apparent activity in asteroids, such as impacts or rotational instability. Therefore, to be recognised as an MBC, an active asteroid must display recurring activity (a tail and/or coma) during multiple passages at perihelion.

Sonnett et al. (2011) previously estimated the MBC to asteroid ratio to be <1:400 in the Main Belt. So far 8 objects have shown recurring activity, and sublimation is a possible driver of activity for a few more candidates (approximately 20 objects in total) (Jewitt & Hsieh 2022). Hence it is challenging to study and characterize such a small population.

Focusing on the Outer Main Belt (a>2.82AU) where most MBCs are found, Kim et al. (2018) showed that the longitudes of perihelion ϖ of MBCs and MBC candidates known at the time were clustered around that of Jupiter (ϖ_J»15°). They concluded that, if this is a real feature of MBCs, these comets would more likely be discoverable in the northern fall night sky.

II - Methods

Using this hypothesis as a criterion, we conducted an imaging survey to search for new active asteroids and MBCs. We selected a sample of 530 Outer Main Belt asteroids with longitudes of perihelion 0°<ϖ<30, and the activity of which would likely be observable if they were MBCs (apparent magnitude, closeness to perihelion, etc.). These objects were observed between 2018 and 2020 using the Wide Field Camera on the Isaac Newton Telescope (La Palma, Spain) and a Sloan-r filter.

We developed an automated pipeline to reduce and analyse our data using tail and coma detection methods adapted from those developed by Sonnett et al. (2011). The tail detection method aims to detect an excess of brightness in one direction around the asteroid. An example is given in Figure 1. The coma detection method builds a frame-specific Point Spread Function (PSF) using neighbouring stars and an artificial coma-profile, then compares them to the asteroid to look for fuzziness. An example is given in Figure 2.

III – Results and perspectives

We reproduced the statistical study of Kim et al. (2018) taking into account more recent discoveries of active asteroids and MBCs (as summarised by Jewitt & Hsieh, 2022) and report that the clustering of longitudes of perihelion persists, which supports our approach a posteriori.

Out of our 549 observations (some asteroids having been observed multiple times), the pipeline was successfully applied to 291 asteroids that did not have any close neighbouring star biasing the analysis. For the remaining objects the pipeline performed the data reduction and produced deep images of the asteroids that we manually reviewed.

Among our targeted sample of objects, we report no detection of activity from the pipeline, nor from visual inspection of the remaining frames. For comparison, we applied the same procedure to random stars and random asteroids on our frames, and saw no difference in the distributions of activity detection levels. We will present our results and statistical conclusions on the MBC population. In the future, our research group intends to implement a similar pipeline to apply these methods to other data, in particular those from the Vera C. Rubin observatory.

Figures

Figure 1 - a: Asteroid 105073 observed on 10/11/2018. b: Illustration of the tail detection method developed by Sonnett et al. (2011). We compare the median brightness of each red segment to the local background flux (median in the cyan annulus). The top-right diagram represents the relative brightness of the segments. Here, the brightest segment is in the South-West direction. We then perform the same study on neighbouring stars to evaluate whether such brightness levels seem atypical given the quality of the frame. In this example, the asteroid happens to be crossing a background star. The star appears trailed as we stacked multiple exposures, giving it the aspect of a tail.

Figure 2 - Example of the coma detection method adapted from Sonnett et al. (2011), applied to asteroid 105073 observed on 10/11/2018. a: Thumbnail of the asteroid. b: PSF constructed from 12 neighbouring stars. c: Simulated coma profile built by convolving a 1/r profile with the PSF. We then fit a linear mix of the PSF and the coma profile to the image of the asteroid. In this case the best fit had a proportion of coma <10^-4. d: Residue of the fit (image a subtracted to the best fit result).

Acknowledgements

We acknowledge contributions from Alan Fitzsimmons (Queen’s University, Belfast, UK) and Henry Hsieh (Planetary Science Institute, Honolulu, US), as well as observers Richard Smith (Queen’s University, Belfast, UK), Daniel Gardener (Institute for Astronomy, Edinburgh, UK) and Hissa Medeiros (Instituto de Astrofísica de Canarias, Tenerife, Spain).

References

David Jewitt and Henry H. Hsieh. The Asteroid-Comet Continuum. arXiv e-prints, arXiv:2203.01397, March 2022.

Yoonyoung Kim, Youngmin JeongAhn, and Henry H. Hsieh. Orbital Alignment of Main-belt Comets. 50:201.04D, October 2018.

Sarah Sonnett, Jan Kleyna, Robert Jedicke, and Joseph Masiero. Limits on the size and orbit distribution of main belt comets. Icarus, 215:534–546, October 2011.

How to cite: Ferellec, L., Snodgrass, C., and Opitom, C.: A targeted search for Main Belt Comets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-925, https://doi.org/10.5194/epsc2022-925, 2022.

Main-belt comets are objects orbiting in the main belt, they have near-surface ice, supposed to be water ice, and it is surprising, because water ice is unstable against sublimation at the surface temperatures of asteroids at the distance of the main belt. This water content is important to better understand the thermal and compositional history of our Solar System, to place constraints on protosolar disk models, and to probe a potential primordial source of terrestrial water.

The main-belt asteroid 324P/La Sagra has been confirmed as main-belt comet by showing repeated dust emission activity during at least two subsequent perihelion passages. The nature of the dust emission in MBCs suggests that it is most likely driven by the sublimation of water ice.

We present photometric analysis of archival data of the main-belt comet 324P/La Sagra from different telescopes: Canada-France-Hawaii Telescope (CFHT), Very Large Telescope (VLT), Gemini North Telescope, Hubble Space Telescope (HST), New Technology Telescope (NTT), Discovery Channel Telescope (DCT).

We find the absolute R-band total magnitude and the estimated total dust mass of the object to be consistent with published results. We also confirm that the activity during the 2015 perihelion passage has significantly decreased compared to the previous perihelion passage in 2010 (Fig. 1). We analysed data in the period December 2011 - April 2019. We also study the recent activity of the main-belt comet 324P/La Sagra at the 2021 perihelion passage, to search for more changes that should provide insight into the evolution of MBC activity over time. Additionally, we measure the dust trail brightness profile of the main-belt comet 324P/La Sagra. From the debris trail brightness profile, we constrain the size of the largest particles that gas drag is able to lift, which is diagnostic of the sublimation rate. Understanding the ice content of outer main-belt asteroids is crucial to constrain the distribution of volatiles in the early solar system and the formation and subsequent evolution of planetesimals.

Figure 1: Absolute magnitudes measured in the central aperture of 324P as a function of orbital position. Circles refer to our analysis of archival data, while triangles are from the literature. After perihelion, the magnitude stabilises around a constant value (18.4 mag in R-band) near a true anomaly of 120°, indicating that dust production has ceased and that dust has left the immediate environment of the nucleus due to solar radiation pressure. An absolute magnitude of 19 measured at true anomaly of -150° indicates that the nucleus could be strongly elongated and be correspondingly faint during part of its rotational lightcurve.

How to cite: Mastropietro, M., Hsieh, H., Kim, Y., and Agarwal, J.: Activity of the Main-Belt Comet 324P/La Sagra, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1211, https://doi.org/10.5194/epsc2022-1211, 2022.

How to cite: Kim, Y., Jewitt, D., Agarwal, J., Mutchler, M., Li, J., and Weaver, H.: Active Asteroid P/2020 O1: Constraining the Ice Line in the Main Asteroid Belt, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-28, https://doi.org/10.5194/epsc2022-28, 2022.

The binary main-belt comet 288P is peculiar both because of its comet-like activity and because of its unusual system properties, combining near-equal component sizes with a wide separation of about 100 times the primary radius. The system likely formed by rotational disruption after YORP spin-up and subsequently widened, possibly by radiative or outgassing torques.
We present Hubble Space Telescope data obtained in 2021 while 288P re-approached perihelion and activity re-kindled. The data show a developing dust tail. We constrain the time of activity onset and investigate whether one or both components were active, which is key to understanding whether the splitting was the cause of the activity.

How to cite: Agarwal, J., Kim, Y., Jewitt, D., Mutchler, M., Weaver, H., and Larson, S.: Re-activation of main-belt comet 288P in 2021, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-379, https://doi.org/10.5194/epsc2022-379, 2022.

1. INTRODUCTION

Active asteroids are small solar system bodies, having at the same time the orbital characteristics of asteroids but showing the physical characteristics of comets, including coma and tail-like appearance. A subpopulation of active asteroids that have sublimation as the main source of activity is known as main-belt comets (MBCs, [6]). The MBCs could be a key to tracing the origin and evolution of volatile materials in the asteroid belt and could help our understanding of the protoplanetary disk process and planetary formation. The number of known MBCs is, however, still relatively small. For this reason, the characterisation of new objects is of considerable importance.

This work analyses active asteroid (248370) 2005QN173, (aka 433P). Its activity was recently discovered by Fitzsimmons et al. [4] in the images collected by the Asteroid-Terrestrial-Impact Last Alert System (ATLAS;[11]). Based on the recurrent activity, Chandler et al. [3] suggested that activity is sublimation-driven, making asteroid 248370 a main-belt comet. Aiming to constrain possible activity mechanisms further, we performed photometric observations of 248370. Our primary goals are to quantify the activity level variation and determine the rotation period. The activity changes could help better understand what is driving the activity. Similarly, the rotation period provides a clue on a possible mass shedding due to rotational instabilities. Furthermore, we also analysed its dynamical stability in order to get insights into the past orbit evolution. Finally, we investigated its possible association with asteroid families.

2. OBSERVATIONS

Observations of the 248370 were collected on 2021 October 5/6 from the Astronomical station Vidojevica (C89), using a 1.4 m Milanković telescope. All images were made in standard Johnson-Cousin R-filter.