The Transiting Exoplanet Survey Satellite ( TESS ) is NASA ’ s latest space telescope dedicated to the discovery of transiting exoplanets around nearby stars .
Besides the main goal of the mission , asteroseismology is an important secondary goal and very relevant for the high-quality time series that TESS will make during its two year all-sky survey .
Using TESS for asteroseismology introduces strong timing requirements , especially for coherent oscillators .
Although the internal clock on board TESS is precise in its own time , it might have a constant drift and will thus need calibration , or offsets might inadvertently be introduced .
Here we present simultaneously ground- and space-based observations of primary eclipses of several binary systems in the Southern ecliptic hemisphere , used to verify the reliability of the TESS timestamps .
From twelve contemporaneous TESS/ground observations we determined a time offset equal to 5.8 \pm 2.5 sec , in the sense that the Barycentric time measured by TESS is ahead of real time .
The offset is consistent with zero at 2.3 - \sigma level .
In addition , we used 405 individually measured mid-eclipse times of 26 eclipsing binary stars observed solely by TESS to test the existence of a potential drift with a monotonic growth ( or decay ) affecting the observations of all stars .
We find a drift corresponding to \sigma _ { drift } = 0.009 \pm 0.015 sec / day .
We find that the measured offset is of a size that will not become an issue for comparing ground-based and space data for coherent oscillations for most of the targets observed with TESS .