HD 152384: A 5 Myr old debris disk system showing a gaseous ring of refractory elements at the dust sublimation radius

Abstract

Context: Circumstellar gas around young stars provides key insights into planet formation and disk evolution. HD 152384, a young (5 Myr) A0 V star in Sco-Cen, shows hybrid-disk traits: a modest infrared excess from small dust grains and atomic emission lines dominated by refractory elements, but its disk structure and origin remain unclear. Aims: We characterise the kinematics and excitation of the circumstellar gas around HD 152384 and constrain the physical properties of its emitting region. Methods: We use new high-resolution optical and near-infrared VLT/UVES and VLT/CRIRES spectra to re-examine the circumstellar environment of HD 152384, previously suggested to host a broad, gas-rich disk. Results: The observations reveal 74 narrow, double-peaked emission lines of Fe, Mg, Si, and Ca, with similar profiles and a 103 km/s peak separation. Keplerian modelling places the gas in a geometrically thin ring at 0.09-0.12 au, close to the dust sublimation radius (0.10-0.14 au for a sublimation temperature of about 1500 K). The Fe I emission is optically thick, whereas the optically thin Mg I lines imply 2.2 x 10^22 kg (3.6 x 10^-3 Earth masses) of magnesium gas in the ring. Conclusions: The dust and gas properties are consistent with a secondary origin involving collisions of rocky planetesimals. We propose that small collision-produced dust grains spiral inward and sublimate near the dust sublimation radius, accumulating atomic gas there. HD 152384 thus represents a young analogue of gas-bearing debris disks such as Beta Pictoris and gaseous debris disks around metal-polluted white dwarfs, offering a new window on the early violent processing of rocky planetesimals.