Orion SrcI’s Disk Is Salty

Abstract

We report the detection of NaCl, KCl, and their 37 Cl and 41 K isotopologues toward the disk around Orion SrcI. About 60 transitions of these molecules were identified. This is the first detection of these molecules in the interstellar medium not associated with the ejecta of evolved stars. It is also the first ever detection of the vibrationally excited states of these lines in the ISM above v = 1, with firm detections up to v = 6. The salt emission traces the region just above the continuum disk, possibly forming the base of the outflow. The emission from the vibrationally excited transitions is inconsistent with a single temperature, implying the lines are not in LTE. We examine several possible explanations of the observed high excitation lines, concluding that the vibrational states are most likely to be radiatively excited via rovibrational transitions in the 25-35 µm (NaCl) and 35-45 µm (KCl) range. We suggest that the molecules are produced by destruction of dust particles. Because these molecules are so rare, they are potentially unique tools for identifying high-mass protostellar disks and measuring the radiation environment around accreting young stars.

Formation and Evolution of Disks Around Young Stellar Objects

“…The best example is found towards the nearest high-mass YSO Orion Source I, located at only 420 pc ( Fig. 6; Ginsburg et al 2018Ginsburg et al , 2019 and consistent with a central mass of 15 M , slightly higher than the results from previous lower resolution observations: 5-7 M (Kim et al 2008;Hirota et al 2014;Plambeck and Wright 2016).…”

The Orion Protostellar Explosion and Runaway Stars Revisited: Stellar Masses, Disk Retention, and an Outflow from the Becklin–Neugebauer Object

“…A 16-th magnitude star (Vega scale) is visible at the center of the 'disk-shadow' in the K s adaptive optics images (Bally et al 2015). No compact 1.3 to 3 mm source brighter than 0.1 mJy/beam is seen in the 0.03 resolution ALMA continuum images associated with data presented by Ginsburg et al (2018); Ginsburg et al (2019).…”

“…Src I is surrounded by a massive (∼0.1 M ), nearly edge-on, ∼50 AU radius disk whose spin axis is nearly orthogonal to the Src I proper motion vector (Ginsburg et al 2018;Ginsburg et al 2019;Hirota et al 2017). The Src I spin axis is at PA ≈ 53 • .…”

“…The mass measurement was verified using radiative transfer modeling analogous to that used by Plambeck & Wright (2016). Ginsburg et al (2019) show that the two unknown lines are transitions of salt, NaCl, v=2, J=17-16 and v=1, J=18-17, respectively, with upper states 1128 K and 626 K above ground. Farias, & Tan (2018) presented ∼ 10 7 N-body scattering simulations of the stellar dynamical ejection.…”

“…SiO masers and other emission lines tracing the Src I disk show that it has a radial velocity V LSR =5.0 km s −1 (Plambeck & Wright 2016). Ginsburg et al (2018) and Ginsburg et al (2019) found V LSR = 5.5 km s −1 using thermal emission lines. The OMC1 core has a radial velocity V OM C1 = 9.0 to 9.5 km s −1 .…”