The 2019 October 22nd multi-chord stellar occultation by (84922) 2003 VS2

Introduction

In the last ten years, stellar occultations by Trans-Neptunian Objects (TNOs) have become one of the best techniques to gather information about the main physical characteristics (size, shape, density and albedo) of these objects, as well as revealing possible atmospheres, satellites or rings [1,2]. 

Due to their large orbital periods and the lack of observations, it is still very challenging to predict and observe positive occultations by TNOs, requiring worldwide campaigns. Here we present the results of the multi-chord stellar occultation produced on 2019 October 22nd by (84922) 2003 VS₂, a plutino object with a double-peaked rotational light-curve and no secondary features discovered so far. A total of twelve positive chords were obtained, reaching the largest number of positive chords by a TNO published thus far [3].

Observations

As part of the systematic search for stellar occultations by TNOs carried out by the Lucky Star project collaboration [4], we predicted, observed and analyzed the occultation of the GAIA source 3449076721168026624 (m_V=14.1 mag) by 2003 VS₂ on 2019 October 22nd. Astrometric updates were performed prior to the occultation with the 1.5-m telescope at Sierra Nevada Observatory in Granada, Spain, and the Liverpool 2-m Telescope in Roque de los Muchachos Observatory (La Palma, Spain). Out of the thirty-nine participating observing sites distributed along the predicted shadow path in Europe, twelve sites, located in Bulgaria (1), Romania (10) and Serbia (1), reported a positive detection (see Figure 1).

Figure 1 .- Shadow path prediction for the 2003 VS₂ occultation on 2019 October 22nd through GAIA source 3449076721168026496, using data from the Liverpool 2-m Telescope in Roque de los Muchachos Observatory (La Palma, Spain). The green line represents the middle of the shadow path. The observing sites involved in the event are also marked: in green are the ones that reported a positive detection; in white, those that reported a negative detection and, in blue, those that could not observe due to technical problems or bad weather.

 

Results

We fitted the extremities of the positive chords to an ellipse to derive the instantaneous limb of 2003 VS_2. We also carried out photometry observations to derive the rotational light-curve amplitude and rotational phase of 2003 VS₂ at the time of the event. Combining this information and assuming a triaxial shape, we derived the three-dimensional shape of 2003 VS_2. The tentative result is not compatible with a homogeneous triaxial body in hydrostatic equilibrium. This is in agreement with previous results [5]. The derived geometric albedo and area-equivalent diameter are compatible with the ones derived from Herschel thermal measurements and Spitzer data [6]. No secondary features were detected, but we give constraints for a putative ring around 2003 VS_2.

Acknowledgements

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). P.S-S. acknowledges financial support by the Spanish grant AYA-RTI2018-098657-J-I00 "LEO-SBNAF" (MCIU/AEI/FEDER, UE). O.V. acknowledges funding provided by the Astronomical Observatory Belgrade(contract 451-03-68/2020-14/200002) through the grants by the Ministry of Education, Science, and Technological Development of the Republic of Serbia. D.I. acknowledges funding provided by the University of Belgrade - Faculty of Mathematics through the grants by the Ministry of Education, Science, and Technological Development of the Republic of Serbia.

 Bibliography

[1] Ortiz, J. L., Sicardy, B., Braga-Ribas, F., et al. 2012, Nature, 491, 566

[2] Braga-Ribas, F., Sicardy, B., Ortiz, J. L., et al. 2013, ApJ, 773, 26

[3] Ortiz, J.L., Santos-Sanz, P., Sicardy, B., et al. 2020a, arXiv e-prints,arXiv:2005.08881

[4] Camargo, J. I. B., Vieira-Martins, R., Assafin, M., et al. 2014, A&A, 561, A37

[5] Benedetti-Rossi, G., Santos-Sanz, P., Ortiz, J. L., et al. 2019, AJ, 158, 159

[6] Lellouch, E., Santos-Sanz, P., Lacerda, P., et al. 2013, A&A, 557, A60