Pluto’s Atmosphere in Plateau Phase Since 2015 from a Stellar Occultation at Devasthal

A stellar occultation by Pluto was observed on 2020 June 6 with the 1.3 m and 3.6 m telescopes located at Devasthal, Nainital, India, using imaging systems in the I and H bands, respectively. From this event, we derive a surface pressure for Pluto’s atmosphere of p surf = 12.23 − 0.38 + 0.65 μbar. This shows that Pluto’s atmosphere has been in a plateau phase since mid-2015, a result which is in excellent agreement with the Pluto volatile transport model of Meza et al. This value does not support the pressure decrease reported by independent teams, based on occultations observed in 2018 and 2019 by Young et al. and Arimatsu et al., respectively.

Study of Pluto’s atmosphere based on 2020 stellar occultation light curve results

On 6 June 2020, Pluto’s stellar occultation was successfully observed at a ground-based observatory in Iran, and Pluto’s atmospheric parameters were investigated. We used an atmospheric model of Pluto, assuming a spherical and transparent pure N2 atmosphere. Using ray-tracing code, the stellar occultation light curve was satisfactorily fit to this model. We found that Pluto’s atmospheric pressure at the reference radius of 1215 km was 6.72 ± 0.48 μbar in June 2020. Our estimated pressure shows a continuation of the pressure increase trend observed since 1988 and does not confirm the rapid pressure decrease tentatively reported in 2019. The pressure evolution is consistent with a seasonal transport model. We conclude that the N2 sublimation process from Sputnik Planitia is continuing. This study’s result is shown on the diagram of the annual evolution of atmospheric pressure.

The multi-chord stellar occultation by (19521) Chaos on 2020 November 20

<p>Physical properties of Trans-Neptunian Objects (TNOs) have been of increasing interest in the last two decades, as these objects are considered to be among the least altered through the Solar System evolution, and thus preserve valuable information about its origin [1]. The study of these objects through the ground-based method of stellar occultations has risen in the last years, as this technique allows the determination of physical properties with considerably good accuracies [2,3,4]. </p> <p>Here we present the results of the multi-chord stellar occultation of the GAIA source 3444789965847631104 (m<sub>v</sub>≈16.8) by the TNO (19521) Chaos on 2020 November 20, which was predicted within our systematic programme on stellar occultations by TNOs and outer solar system bodies [5]. The prediction was updated with astrometric observations carried out two days before the event with the 1.23-m telescope at Calar Alto observatory in Almería, Spain, and it was favorable to the South of Europe. The campaign that we organized involved 19 observing sites and resulted in three positive detections, one of them obtained from the 4.2-m WHT telescope at La Palma, 11 negative detections, and 5 sites that could not observe due to bad weather.<em> </em></p> <p>We derived the instantaneous limb of Chaos by fitting the extremities of the positive chords to an ellipse to determine accurate size, shape, and geometric albedo for this object. The preliminary results give a slightly smaller area-equivalent diameter than the one derived from Herschel thermal data [6], but photometric observations of this object are still under analysis to complement and improve the results. <strong><br /><br /></strong><strong>References</strong></p> <p>[1] Morbidelli, A., Levison, H. F., & Gomes, R. 2008, ed. M. A. Barucci, H. Boehnhardt, D. P. Cruikshank, A. Morbidelli, R. Dotson, 275</p> <p>[2] Ortiz, J. L., Sicardy, B., Braga-Ribas, F., et al. 2012, Nature, 491, 566</p> <p>[3] Braga-Ribas, F., Sicardy, B., Ortiz, J. L., et al. 2013, ApJ, 773, 26</p> <p>[4] Ortiz, J.L., Santos-Sanz, P., Sicardy, B., et al. 2017, Nature, 550, 7675, pp. 219-223</p> <p>[5] Camargo, J. I. B., Vieira-Martins, R., Assafin, M., et al. 2014, A&A, 561, A37</p> <p>[6] Vilenius, E., Kiss, C., Mommert, M., Müller, T., et al. 2012, A&A, 541, A94 </p> <p><strong>Acknowledgements</strong><strong> </strong></p> <p>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). 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'' (MCIU/AEI/FEDER, UE). This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). We are grateful to the CAHA and OSN staffs. This research is partially based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by Junta de Andalucía and Consejo Superior de Investigaciones Científicas (IAA-CSIC). This research was also partially based on observation carried out at the Observatorio de Sierra Nevada (OSN) operated by Instituto de Astrofísica de Andalucía (CSIC). Partially based on observations made with the Tx40 telescope at the Observatorio Astrofísico de Javalambre in Teruel, a Spanish Infraestructura Cientifico-Técnica Singular (ICTS) owned, managed and operated by the Centro de Estudios de Física del Cosmos de Aragón (CEFCA). Tx40 is funded with the Fondos de Inversiones de Teruel (FITE).</p>

Automatic prediction, selection and analysis of occultations to characterize asteroid family members

<p>A new 50 cm telescope, the UniversCity telescope, was recently installed at Plateau de Calern, France, to survey stellar occultation by asteroids from collisional families. A stellar occultation occurs when an asteroid passes in front of a distant star blocking its light temporarily. Measuring the time of the occultations provides an accurate astrometric measurement of the asteroid, comparable with the angular size of the asteroid. Thanks to the astrometric catalog from the Gaia mission, astrometry accuracy from occultation reaches a few milliarcseconds.</p><p>The astrometry from the survey is used in turn to improve the orbit of the asteroid, while the duration of the occultation is used to constrain physical characteristics and search for binarity. The orbit improvement aims to detect and measure the drift rate in the orbital elements of asteroids due to the Yarkovsky effect, a non-gravitational force responsible for scattering the orbital elements of collisional family members. Combining the magnitude of the Yarkovsky drift rate from the occultation survey with the accumulated drift since the originating collision, the age determination of the collisional family can be obtained.</p><p>The occultation survey takes advantage of the stellar occultation technique and the Gaia astrometric catalog to systematically derive accurate astrometric measurements for collisional family members.</p><p>The telescope will be operated robotically, dedicating most of its time to the occultation survey, with a small percentage of time to other science cases. The large number of family members and candidates to stellar occultations demands the automation of the occultation prediction, the selection and prioritization of occultation events, telescope scheduling, data reduction, and data analysis.</p><p>The occultation predictions are updated regularly in the light of new astrometric measurements from traditional astrometry and from occultations measurements. The occultations predicted to be visible from the UniversCity site are prioritized based on their chances of detection and contribution to the family age determination. The data acquired each night is automatically reduced to obtain light curves from which detection candidates are analyzed.</p><p>We will present the status of the project and the development and performances of the automatic prediction and processing system.</p>