TAOS II: THE ROBOTIC OPERATIONS

In this work, we present the general procedure for the robotic observations of the Transneptunian Automated Occultation Survey (TAOS II). The project aims to detect small TNOs (Transneptunian Objects) by serendipitous stellar occultations. To do so TAOS II will operate three 1.3 m telescopes equipped with CMOS cameras which are able to read about 10,000 stars in multiple subapertures at a 20 Hz cadence. At such rates, it will be possible to identify diffraction features in the lightcurves, helping us to estimate a distance and object size to each occultation event. TAOS II is installed in the Observatorio Astronómico Nacional in San Pedro Mártir, Ensenada, México (OAN-SPM). The site has good observing conditions, typically with around 260 useful nights per year. Here, we describe the different process to be performed in a typical observing night: system start up and shut down, monitoring observing conditions, acquisition of calibration images, field selection, pointing, camera synchronization, determination of aperture sizes and positions, and high speed image acquisition.

Prediction of stellar occultations by distant solar system bodies in the Gaia era

Stellar occultations are a unique technique to access physical characteristics of distant solar system objects from the ground. They allow the measure of the size and the shape at kilometric level, the detection of tenuous atmospheres (few nanobars), and the investigation of close vicinity (satellites, rings) of Transneptunian objects and Centaurs. This technique is made successful thanks to accurate predictions of occultations. Accuracy of the predictions depends on the uncertainty in the position of the occulted star and the object's orbit. The Gaia stellar catalogue (Gaia Collaboration (2017)) now allows to get accurate astrometric stellar positions (to the mas level). The main uncertainty remains on the orbit. In this context, we now take advantage of the NIMA method (Desmars et al.(2015)) for the orbit determination and of the Gaia DR1 catalogue for the astrometry. In this document, we show how the orbit determination is improved by reducing current and some past observations with Gaia DR1. Moreover, we also use more than 45 past positive occultations observed in the 2009-2017 period to derive very accurate astrometric positions only depending on the position of the occulted stars (about few mas with Gaia DR1). We use the case of (10199) Chariklo as an illustration. The main limitation lies in the imprecision of the proper motions which is going to be solved by the Gaia DR2 release.

Water in small bodies of the Solar System

Water in form of ice or vapour is observed in comets, transneptunian objects and icy satellites formed in the outer regions of the Solar System, as well as in objects orbiting in the inner Solar System, such as dwarf planet Ceres. I will present an overview of the water content and properties in these objects and the implications in terms of solar system formation and evolution.