First detection of a disk free of volatile elements around a young A-type star: A possible sign of collisions between rocky planets

Abstract

Aims. We present the first detailed analysis of the astrophysical parameters of the poorly studied Sco-Cen member HD 152384 and its circumstellar environment. Methods. We analyse newly obtained optical-near-IR X-shooter spectra, as well as archival TESS data, of HD 152384. In addition, we use literature photometric data to construct a detailed spectral energy distribution (SED) of the star. Results. The photospheric absorption lines in the spectrum of HD 152384 are characteristic of an A0 V star, for which we derive a stellar mass of 2.1 ± 0.1 M⊙ and a stellar age > 4.5 Myr. Superimposed on the photospheric absorption, the optical spectrum also displays double-peaked emission lines of Ca II, Fe I, Mg I, and Si I, typical of circumstellar disks. Notably, all hydrogen and helium lines appear strictly in absorption. A toy model shows that the observed emission line profiles can be reproduced by emission from a compact (radius < 0.3 au) disk seen at an inclination of ∼24°. Further evidence for the presence of circumstellar material comes from the detection of a moderate IR excess in the SED, similar to those found in extreme debris disk systems. Conclusions. We conclude that HD 152384 is surrounded by a tenuous circumstellar disk that, although rich in refractory elements, is highly depleted of volatile elements. To the best of our knowledge, such a disk is unique among young stars. However, it is reminiscent of the disks seen in some white dwarfs, which have been attributed to the disruption of rocky planets. We suggest that the disk around HD 152384 may have a similar origin and may be due to collisions in a newly formed planetary system.

Identification and spectroscopic characterization of 128 new Herbig stars

“…We now consider the nature of VOS 209 and VOS 668, which have emission lines and IR excess but lack hydrogen emission. van den Ancker et al (2021) found that the intermediate-mass YSO HD 152384 has all hydrogen lines strictly in absorption, but has refractory lines in emission. This led van den Ancker et al (2021) to suggest that HD 152384 is at the late stages of the PMS phase and is surrounded by a tenuous circumstellar disk caused by the collision of rocky planets (see also the extreme debris disks described in Moór et al 2021).…”