Transit Search for Exoplanets Around Alpha Centauri A and B with ASTERIA

Alpha Centauri is a triple system with two Sun-like stars, α Cen A (V=0.01) and B (V=1.33), and a third fainter star, Proxima Centauri. Current transit missions cannot produce precision photometry of α Cen A and B as they saturate for these very bright stars. The Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA) was a technology demonstration mission with the primary objective of demonstrating key technologies necessary for precision photometry: highly stable thermal control and very precise pointing stability. The payload uses a complementary metal-oxide semiconductor (CMOS) detector that enables monitoring of the brightest stars without saturating. We obtained spatially-unresolved observations of α Cen A and B during opportunistic science campaigns as part of ASTERIA’s extended mission. The resulting photometric precision for the blended α Cen A and B data is 250 ppm (parts per million) per 9s, i.e., less than twice the photon noise limit. We establish limits for transiting exoplanets around both α Cen A and B using transit signal injection and recovery tests. We find that ASTERIA is sensitive to planets with radii as small as 3 R⊕ around α Cen A and 3.7 R⊕ around α Cen B, corresponding to signals of ∼0.5 parts-per-thousand, with periods ranging 0.5 to 6 days, illustrating the effective role of nanosatellites in achieving compelling science output.