scholarly journals Pluto’s ephemeris from ground-based stellar occultations (1988–2016)

2019 ◽  
Vol 625 ◽  
pp. A43 ◽  
Author(s):  
J. Desmars ◽  
E. Meza ◽  
B. Sicardy ◽  
M. Assafin ◽  
J. I. B. Camargo ◽  
...  

Context. From 1988 to 2016, several stellar occultations have been observed to characterise Pluto’s atmosphere and its evolution. From each stellar occultation, an accurate astrometric position of Pluto at the observation epoch is derived. These positions mainly depend on the position of the occulted star and the precision of the timing. Aims. We present 19 Pluto’s astrometric positions derived from occultations from 1988 to 2016. Using Gaia DR2 for the positions of the occulted stars, the accuracy of these positions is estimated at 2−10 mas, depending on the observation circumstances. From these astrometric positions, we derive an updated ephemeris of Pluto’s system barycentre using the NIMA code. Methods. The astrometric positions were derived by fitting the light curves of the occultation by a model of Pluto’s atmosphere. The fits provide the observed position of the centre for a reference star position. In most cases other publications provided the circumstances of the occultation such as the coordinates of the stations, timing, and impact parameter, i.e. the closest distance between the station and centre of the shadow. From these parameters, we used a procedure based on the Bessel method to derive an astrometric position. Results. We derive accurate Pluto’s astrometric positions from 1988 to 2016. These positions are used to refine the orbit of Pluto’system barycentre providing an ephemeris, accurate to the milliarcsecond level, over the period 2000−2020, allowing for better predictions for future stellar occultations.

2019 ◽  
Vol 492 (1) ◽  
pp. 770-781
Author(s):  
A R Gomes-Júnior ◽  
M Assafin ◽  
F Braga-Ribas ◽  
G Benedetti-Rossi ◽  
B E Morgado ◽  
...  

ABSTRACT We report six stellar occultations by Phoebe (Saturn IX), an irregular satellite of Saturn, obtained between mid-2017 and mid-2019. The 2017 July 6 event was the first stellar occultation by an irregular satellite ever observed. The occultation chords were compared to a 3D shape model of the satellite obtained from Cassini observations. The rotation period available in the literature led to a sub-observer point at the moment of the observed occultations where the chords could not fit the 3D model. A procedure was developed to identify the correct sub-observer longitude. It allowed us to obtain the rotation period with improved precision compared to the currently known value from literature. We show that the difference between the observed and the predicted sub-observer longitude suggests two possible solutions for the rotation period. By comparing these values with recently observed rotational light curves and single-chord stellar occultations, we can identify the best solution for Phoebe’s rotational period as 9.27365 ± 0.00002 h. From the stellar occultations, we also obtained six geocentric astrometric positions in the ICRS as realized by the Gaia DR2 with uncertainties at the 1-mas level.


Icarus ◽  
2011 ◽  
Vol 214 (2) ◽  
pp. 685-700 ◽  
Author(s):  
Angela M. Zalucha ◽  
Xun Zhu ◽  
Amanda A.S. Gulbis ◽  
Darrell F. Strobel ◽  
J.L. Elliot

2017 ◽  
Vol 12 (S330) ◽  
pp. 397-398
Author(s):  
J. I. B. Camargo ◽  
M. V. Banda-Huarca ◽  
R. L. Ogando ◽  
J. Desmars ◽  
F. Braga-Ribas ◽  
...  

AbstractThe stellar occultation technique is a powerful tool to study distant small solar system bodies. Currently, around 2 500 trans-neptunian objects (TNOs) and Centaurs are known. With the astrometry from Gaia and large surveys like the Large Synoptic Survey Telescope (LSST), accurate predictions of occultation events will be available to tens of thousands of TNOs and Centaurs and boost the knowledge of the outer solar system.


2021 ◽  
Author(s):  
Mónica Vara-Lubiano ◽  
Nicolás Morales ◽  
Flavia Rommel ◽  
José Luis Ortiz ◽  
Bruno Sicardy ◽  
...  

<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>


2021 ◽  
Author(s):  
Estela Fernández-Valenzuela ◽  
Jose Luis Ortiz ◽  
Bryan Holler ◽  
Monica Vara-Lubiano ◽  
Nicolas Morales ◽  
...  

<p>Two stellar occultations by the largest satellite of the dwarf planet Haumea, Hi'iaka, were predicted to happen on April, 6th and 16th, 2021. Additional high accuracy astrometric analysis was carried out in order to refine the prediction for April 6th, using several telescopes in the 1.2-m to 2-m range, with the final shadow path crossing North Africa. We successfully detected the first event from TRAPPIST-North telescope at Oukaïmeden Observatory (Morocco). Although it was recorded from only one site, this first detection allowed us to improve the prediction for the second that crossed North America from East to West. We had a good success recording six positive detections and several negative detections that constrain the shape and size of the body. The light curves obtained from the different observatories provide the time at which the star disappears and reappears, which are translated into chords (the projected lines on the sky-plane as observed from each location). Additionally, we carried out a campaign to study Hi'iaka's rotational light-curve, studying the residuals of Haumea's rotational light-curve to a four-order Fourier fit. We obtained the rotational phases at the times of the occultations, which is critical for the analysis of the occultations, given that Hi’iaka is clearly non-spherical. Our preliminary results show that Hi'iaka indeed has a triaxial shape with a larger effective diameter than what has been published so far. The preliminary results and their implications will be discussed in this talk. </p>


2006 ◽  
Vol 2 (S236) ◽  
pp. 65-68 ◽  
Author(s):  
W.P. Chen ◽  
C. Alcock ◽  
T. Axelrod ◽  
F.B. Bianco ◽  
Y.I. Byun ◽  
...  

AbstractThe Taiwan-America Occultation Survey (TAOS) aims to determine the number of small icy bodies in the outer reach of the Solar System by means of stellar occultation. An array of 4 robotic small (D=0.5 m), wide-field (f/1.9) telescopes have been installed at Lulin Observatory in Taiwan to simultaneously monitor some thousand of stars for such rare occultation events. Because a typical occultation event by a TNO a few km across will last for only a fraction of a second, fast photometry is necessary. A special CCD readout scheme has been devised to allow for stellar photometry taken a few times per second. Effective analysis pipelines have been developed to process stellar light curves and to correlate any possible flux changes among all telescopes. A few billion photometric measurements have been collected since the routine survey began in early 2005. Our preliminary result of a very low detection rate suggests a deficit of small TNOs down to a few km size, consistent with the extrapolation of some recent studies of larger (30–100 km) TNOs.


2019 ◽  
Vol 492 (1) ◽  
pp. L17-L21 ◽  
Author(s):  
Gy M Szabó ◽  
T Pribulla ◽  
A Pál ◽  
A Bódi ◽  
L L Kiss ◽  
...  

ABSTRACT Kepler-13Ab (KOI-13) is an exoplanet orbiting a rapidly rotating A-type star. The system shows a significant spin–orbit misalignment and a changing transit duration most probably caused by the precession of the orbit. Here, we present a self-consistent analysis of the system combining Kepler and Transiting Exoplanet Survey Satellite (TESS) observations. We model the light curves assuming a planet transits a rotating oblate star that has a strong surface temperature gradient due to rotation-induced gravity darkening. The transit chord moves slowly as an emergent feature of orbital precession excited by the oblate star with a decline rate in the impact parameter of db/dt = −0.011 yr−1, and with an actual value of b = 0.19 for the latest TESS measurements. The changing transit duration that was measured from Kepler Q2 and Q17 quarters and the TESS measurements indicates a linear drift of the impact parameter. The solutions for the stellar spin axis suggest a nearly orthogonal aspect, with inclination around 100°.


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