[P-CG19] Origin and evolution of materials in space

[PCG19-06] Hot Salty Disks around Massive Protostars: A New Connection from Star-Formation Observation to Meteoritics?

★Invited Papers

*Kei Tanaka^1,2 (1.University of Colorado Boulder, 2.National Astronomical Observatory of Japan)

Keywords:star formation, ALMA observations, refractory species

Massive stars (>10 solar mass, >10,000 solar luminosity) play significant roles in controlling the dynamical and chemical evolution of the interstellar medium in galaxies by intense radiation, stellar winds, and supernovae. Even at the formation stage, the radiation of massive protostars is already powerful, heating the surrounding gas (>1000 au) to over 100 K and producing a variety of chemical species, including complex organic molecules. Such regions/phases of massive protostars, so-called the “hot cores,” have been studied as an important test bed of astrochemistry. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we conduct high-resolution observations toward the massive proto-binary system IRAS 16547-4247, and investigate the innermost structures down to the scale of 100 au. We detect emission lines of sodium chloride (NaCl), silicon compounds (SiO, SiS), and vibrationally-excited water (H₂O v₂=1) associated with the twin protostellar disks (Tanaka et al. 2020, ApJL; see the figure). Gaseous refractory molecules are rarely found in star-forming regions, and this is the second detection of salt in protostellar systems. These newly-detected molecular lines exclusively probe the individual disks at the innermost region of 100 au, while typical hot-core molecules trace the envelope of the 1000 au scale (e.g., complex organic molecules). The presence of the gaseous refractory species, which are products of dust destruction, and the highly-excited water vapor with E_u/k > 3000 K indicates the hot and dynamic nature of massive protostellar disks. The “hot disk” is the new key to understanding massive star formation, and also has excellent potential for future research on metallic elements in star-forming regions. In particular, we expect that the observations of hot-disk lines will provide new insights into the origin of the oldest meteoritic inclusions, i.e., CAIs and chondrules, in the proto-solar nebula.