Candidate stellar occultations by Centaurs and trans-Neptunian objects up to 2014

Abstract

Context. We study trans-Neptunian objects (TNOs) from stellar occultations. Aims. We predict stellar occultations from 2012.5 to the end of 2014 by 5 Centaurs and 34 TNOs. Methods. These predictions were achieved in two ways: first, we built catalogues with precise astrometric positions of the stellar content around the paths on the sky of these targets, as seen by a ground-based observer; second, the observed positions of the targets were determined with the help of these same catalogues so that we could improve their ephemerides and the reliability of the predictions. The reference system is the International Celestial Reference System (ICRS) as realised by the Fourth US Naval Observatory CCD Astrograph Catalog (UCAC4). All the sky paths as well as the selected targets were observed from Oct. 2011 to May 2013 with the ESO/MPG 2.2 m telescope equipped with the Wide Field Imager (WFI). All astrometric results were obtained with the platform for reduction of astronomical images automatically (PRAIA) after correcting the images for overscan, bias, and flatfield. Results. The catalogues with the stellar content around the sky path of each selected target are complete down to magnitude R = 19 and have an average positional accuracy of about 50 milliarcseconds. This same average accuracy also holds for the observed positions of the targets. In the catalogues from the sky paths, stellar proper motions for non-UCAC4 objects were derived from the combination of the current epoch WFI observations with either the 2MASS or the USNO-B1 catalogues. The offsets between the observed and (JPL) ephemeris positions of the targets frequently reach absolute values of some hundreds of milliarcseconds. Conclusions. We present here stellar occultation predictions for the selected 5 Centaurs and 34 TNOs from 2012.5 to the end of 2014. This work is also an extension of two previous prediction works by us, the first one for Pluto, Charon, Nix, and Hydra, and the second for ten other large TNOs. The use of catalogues from the observations of the sky paths in the astrometry of the TNOs and Centaurs enhanced the coherence between their positions and those of the respective occulted candidate stars. New observations of these TNOs and Centaurs are continuously used to redetermine their ephemerides.

Size and Shape of Chariklo from Multi-epoch Stellar Occultations*

“…Stellar occultation predictions by Chariklo for the period 2012.5-2014 were based on local catalogs with astrometric positions of the stars around Chariklo's path on the sky. Moreover, improved ephemerides for Chariklo were obtained from those catalogs with typical uncertainties of 20-30 milliarcsecond (mas) (Camargo et al 2014). A similar approach was used for predictions after 2014 using the Wide Field Imager (WFI) at the MPG 2.2-m telescope (La Silla, Chile) and the IAG 0.6 m telescope at OPD/LNA (Pico dos Dias, Brazil).…”

New orbits of irregular satellites designed for the predictions of stellar occultations up to 2020, based on thousands of new observations

“…2. The search for stellar candidates follows the same procedure as presented by Assafin et al ( , 2012 and Camargo et al (2014). We predicted occultations for the 8 major irregular satellites of Jupiter, Ananke, Carme, Elara, Himalia, Leda, Lysithea, Pasiphae and Sinope, and for Phoebe of Saturn.…”

Orbit determination of trans-Neptunian objects and Centaurs for the prediction of stellar occultations

“…This set of initial predictions must be complete, that is, must contain all possible events of a given TNO that involves stars up to a given magnitude, and must be accurate enough to allow for selecting of those for which observational efforts to refine the initial prediction are worth employing. All initial predictions of stellar occultations to the objects presented in Table 4, with the exception of (2060) Chiron and (60558) Echeclus, are detailed in Assafin et al (2012) and Camargo et al (2014) and are based on observations made at La Silla (Chile) with the ESO 2.2 m telescope that is equipped with the Wide Field Imager (WFI).…”

“…For the initial predictions given by both Assafin et al (2012) and Camargo et al (2014), corrections to ephemerides were done by considering an average offset, which was determined by the position differences in the sense "observation minus ephemeris". As mentioned earlier in the text, this kind of correction (offset) was assumed to be constant until a new one is determined on the basis of newer observations.…”

“…Assafin et al (2012) and Camargo et al (2014) used a constant offset to the ephemeris to refine the predictions. The offset was determined by using a set of observations performed a few weeks to a few months before the predicted occultation.…”