SORA: Stellar occultation reduction and analysis

Abstract

The stellar occultation technique provides competitive accuracy in determining the sizes, shapes, astrometry, etc., of the occulting body, comparable to in-situ observations by spacecraft. With the increase in the number of known Solar System objects expected from the LSST, the highly precise astrometric catalogues, such as Gaia, and the improvement of ephemerides, occultations observations will become more common with a higher number of chords in each observation. In the context of the Big Data era, we developed sora, an open-source python library to reduce and analyse stellar occultation data efficiently. It includes routines from predicting such events up to the determination of Solar System bodies’ sizes, shapes, and positions.

A dense ring of the trans-Neptunian object Quaoar outside its Roche limit

“…Abrupt opaque edges models, including the effects of diffraction, finite band width, exposure time and the Gaia DR2 stellar diameter, were fitted to the star dis-and re-appearances behind Quaoar's main body using the procedures within the Stellar Occultation Reduction and Analysis (sora) package 36 . For the ring events, an additional parameter is the apparent ring opacity p ′ that measures the fractional drop of stellar flux.…”

“…where r i is the observed distance of the i th data point to the ring center, r ′ i is the corresponding distance of the model (the ellipse) and σ i is the uncertainty on the distance associated with the timing uncertainty of the i th data point. Finally, the σ model parameter accounts for extra uncertainties associated with our model 11,36 , stemming in particular from the unknown shape of Quaoar itself, resulting in model bias on its center position. Considering we have a single chord event that we fit an area equivalent circle of radius 555 km, but Quaoar's shape may be a Maclaurin spheroid 4 with an equatorial radius of 569 km and an oblateness of 0.087, this would cause a bias in the central position typically of ∼27 km, the value we choose for the σ model .…”

The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package*

“…The widespread usage of astroquery is apparent from the range of keywords represented in the journal articles that cite the astroquery paper ; everything from asteroids to galaxies is represented. Additionally, astroquery functionality has been built into several special-purpose Python packages, such as LightKurve (Lightkurve Collaboration et al 2018) and SORA (Gomes-Júnior et al 2022). More than 4,000 repositories on GitHub make use of astroquery in some way, and astroquery features in a large number of tutorials on various facets of astronomical analysis.…”

A stellar occultation by the transneptunian object (50000) Quaoar observed by CHEOPS

“…As only one chord was recorded, we fitted the centre of the figure ( f 0 , g 0 ), allowing the shape to vary within the Maclaurin spheroid solution proposed by Braga-Ribas et al (2013), with an equatorial radius of 581 +12 −8 km, apparent oblateness varying between 0 and 0.114, and a pole position angle between 0 and 180 degrees. This fit was done using sora, with a method that is fully described in Gomes-Júnior et al (2022). The negative chord was used to eliminate solutions that would result in a positive detection of the occultation by J. Broughton.…”