Free Astronomy Magazine March-April 2022

R epresentation of a violent flare erupting from the red dwarf Proxima Centauri. [NRAO/S. Dagnello] T he Bright Stars Survey Telescope (BSST) from Zhongshan Station, Antarctica. [Chinese Center of Antarctic Astronomy] which the real database was sub- jected had a sensitivity useful for detecting transits with a depth of five thousandths of a magnitude, a value just sufficient to show Prox- ima b. However, from this minimum value up, no periodic event similar to a transit was highlighted. Also in 2019, a work by James Jenk- ins (Department of Astronomy, Uni- versidad de Chile) and colleagues was published that was based on data from the Spitzer Infrared Space Telescope. Observations at the 4.5 micron wavelength over 48 hours did not reveal any transit on sched- ule, despite the benefit of the re- peated stellar flares of Proxima Centauri appearing less prominent in the infrared. Spitzer’s sensitivity would certainly have shown the transit of a planet with a minimum diameter of no less than 40% the Earth’s. By considering the minimum mass estimated for Proxima b, it is practically impossible that it could be so small: even a diameter for a planet of just under 0.9 earth diam- eters would require that that planet be entirely composed of iron! To dispel residual doubts that Prox- ima b does not pass in front of its star, a team led by Emily Gilbert (University of Chicago, Department of Astronomy and Astrophysics) col- lected and analyzed photometric observations of Proxima Centauri made by the Transiting Exoplanet Survey Satellite (TESS) in the periods of April-June 2019 and April-May 2021, for a total of almost 80 days 2006-2017. Despite the amount and variety of data, the team failed to pinpoint any transit candidates, while they easily confirmed the star’s considerable and unpre- dictable photometric variability. A selection of the highest quality light curves already reworked by Blank and colleagues became, in 2019, the database on which a dif- ferent team led by Dax Feliz (Van- derbilt University, Nashville, TN) worked. These researchers focused their analysis on orbital periods in the 1-to-30-day range. To better evaluate the sensitivity threshold of their investigation methods, they in- cluded in the database some series of “synthetic” signals with different properties, easily recognizable if de- tected in the photometric noise. The team was thus able to establish that the mathematical procedures to