Rapid disappearance of a warm, dusty circumstellar disk

Abstract

Stars form with gaseous and dusty circumstellar envelopes, which rapidly settle into disks that eventually give rise to planetary systems. Understanding the process by which these disks evolve is paramount in developing an accurate theory of planet formation that can account for the variety of planetary systems discovered so far. The formation of Earth-like planets through collisional accumulation of rocky objects within a disk has mainly been explored in theoretical and computational work in which post-collision ejecta evolution typically is ignored, although recent work has considered the fate of such material. Here we report observations of a young, Sun-like star (TYC 8241 2652 1) where infrared flux from post-collisional ejecta has decreased drastically, by a factor of about 30, over a period of less than two years. The star seems to have gone from hosting substantial quantities of dusty ejecta, in a region analogous to where the rocky planets orbit in the Solar System, to retaining at most a meagre amount of cooler dust. Such a phase of rapid ejecta evolution has not been previously predicted or observed, and no currently available physical model satisfactorily explains the observations.

TYC 8241 2652 1 and the case of the disappearing disk: No smoking gun yet

“…Between May 2008 and January 2010 the mid-IR luminosity of TYC 8241 2652 1 dropped by at least a factor of 30, but no changes were observed at shorter wavelengths. The presence of a lithium absorption line proves that the star is young (Melis et al 2012). Its distance of 120.9 ± 5.4 pc (Lindegren et al 2016) and its space motion are consistent with membership in either the Lower Centaurus Crux association (10-20 Myr old) or the TW Hydrae association (TWA; 8 Myr; see supplementary information of Melis et al 2012, and references therein for details).…”

“…The presence of a lithium absorption line proves that the star is young (Melis et al 2012). Its distance of 120.9 ± 5.4 pc (Lindegren et al 2016) and its space motion are consistent with membership in either the Lower Centaurus Crux association (10-20 Myr old) or the TW Hydrae association (TWA; 8 Myr; see supplementary information of Melis et al 2012, and references therein for details). The photospheric Hα line is filled, but is not in emission; this indicates stellar activity but only very weak if any accretion, which is consistent with little or no gas reservoir in the disk.…”

“…So far, no scenario that is consistent with all observational constraints has been able to explain the drop in IR flux. Melis et al (2012) discuss several possibilities that we summarize here (see the supplementary information of their article for more details and references). A change of the disk structure at the inner edge would cast shadows on the outer disk and reduce the mid-IR luminosity, but the energy would still be reradiated, just at shorter wavelengths.…”

“…Based on the age and spectral energy distribution, Melis et al (2012) suggest that this is a debris disk. Alternatively, the object might have hosted a primordial gas-rich disk in an unusual and very short-lived late stage of disk dispersal, where only parts of the inner region of the disk remain to be depleted.…”

“…Only three objects with strong variability in the mid-IR are known, and TYC 8241 2652 1 (Melis et al 2012), the focus of this paper, is the most extreme case; the other two are the two debris disk stars ID8 and HD 23514 (Meng et al 2012). TYC 8241 2652 1 used to show a normal K2 stellar spectrum in the optical and near-IR (out to about 5 µm) and a strong excess over the photospheric spectrum in the mid-IR (8-25 µm), which is indicative of either a primordial or a debris disk.…”