Satellite shadows through stellar occultations

TL;DR

This paper evaluates how satellite occultations affect astronomical photometry, especially with future high-frequency surveys, and proposes using occultations as a method to study satellite orbits.

Contribution

It introduces the impact of satellite occultations on photometry and suggests high-speed occultation observations as a new way to monitor satellite orbits.

Findings

Occultations cause photometric jitter depending on integration time.

Impact is negligible for current CCD surveys but significant for future high-frequency CMOS surveys.

High-speed occultation observations can be used to determine satellite orbits.

Abstract

The impact of mega-constellations of satellites in low-Earth orbit during nighttime optical observations is assessed. Orbital geometry is used to calculate the impact of stellar occultations by satellites on the photometry of individual stars as well as the effect on the photometric calibration of wide-field observations. Starlink-type satellites will have occultation disks several arcseconds across. Together with occultation crossing times of 0.1-100 msec, this will lead to photometric `jitter' on the flux determination of stars. The level of impact for a given star depends on the ratio of the integration time of the frame over the occultation crossing time. In current-day, CCD-based synoptic surveys this impact is negligible (<<1%), but with future, CMOS-based wide-field surveys obtaining data at frequencies >1Hz, the impact will grow towards complete drop-outs. At integration times similar to the occultation crossing time, the orbit of a satellite can be traced using the occultation method. At even shorter integration times the shape of the occulting satellite can be deduced. Stellar occultations by passing satellites, enabled by high-speed CMOS technology, will be a new method to study orbiting satellites. Large scale monitoring programs will be needed to, independently, determine and update the orbits of satellites.