2020AJ....160..222J

We report the discovery of two transiting Neptunes by the HATSouth survey. The planet HATS-37Ab has a mass of 0.099±0.042M_J (31.5 ± 13.4 M_⊕) and a radius of 0.606±0.016R_J, and is on a P=4.3315 day orbit around a V=12.266±0.030 mag, 0.843_–0.012^+0.017M_☉ star with a radius of 0.877_–0.012^+0.019R_☉. We also present evidence that the star HATS-37A has an unresolved stellar companion HATS-37B, with a photometrically estimated mass of 0.654±0.033M_☉. The planet HATS-38b has a mass of 0.074±0.011M_J (23.5 ± 3.5 M_⊕) and a radius of 0.614±0.017R_J, and is on a P=4.3750 day orbit around a V=12.411±0.030 mag, 0.890_–0.012^+0.016M_☉ star with a radius of 1.105±0.016R_☉. Both systems appear to be old, with isochrone-based ages of 11.46_–1.45^+0.79 Gyr, and 11.89±0.60 Gyr, respectively. Both HATS-37Ab and HATS-38b lie in the Neptune desert and are thus examples of a population with a low occurrence rate. They are also among the lowest-mass planets found from ground-based wide-field surveys to date.