Alma Band 8 Continuum Emission From Orion Source I

Abstract

We have measured continuum flux densities of a high-mass protostar candidate, a radio source I in the Orion KL region (Orion Source I) using the Atacama Large Millimeter/Submillimeter Array (ALMA) at band 8 with an angular resolution of 0.1 ′′ . The continuum emission at 430, 460, and 490 GHz associated with Source I shows an elongated structure along the northwest-southeast direction perpendicular to the so-called low-velocity bipolar outflow. The deconvolved size of the continuum source, 90 au×20 au, is consistent with those reported previously at other millimeter/submillimeter wavelength. The flux density can be well fitted to the optically thick black-body spectral energy distribution (SED), and the brightness temperature is evaluated to be 700-800 K. It is much lower than that in the case of proton-electron or H − free-free radiations. Our data are consistent with the latest ALMA results by Plambeck & Wright (2016), in which the continuum emission have been proposed to arise from the edge-on circumstellar disk via thermal dust emission, unless the continuum source consists of an unresolved structure with the smaller beam filling factor.

Disk-driven rotating bipolar outflow in Orion Source I

“…These are analogous to those of the high excitation lines detected by the recent ALMA observations [19,21]. The PV maps exhibit a signature of a central hole ( Supplementary Figure 1(b)) suggesting that emission from the outer parts of the outflow is dominant, and/or that high opacity continuum emission could obscure the innermost region in the midplane [19,21,22]. The inner and outer radii of the disk, and rotation velocities at these positions are derived from the Si 18 O map, R in (z=0)=24±8 au, R out (z=0)=76±4 au, v φ (z=0,r=R in )=17.9±0.6 km s −1 , and v φ (z=0,r=R out )=7.0±0.4 km s −1 with 1σ errors (Methods section).…”

“…The resultant synthesized beam size were 124 mas×97 mas with the position angle of 73.3 degrees at 484 GHz and 121 mas×104 mas with the position angle of 85.2 degrees at 463 GHz. The maps of the 484 GHz Si 18 O and 463 GHz H 2 O lines were registered with that of the 460 GHz and 490 GHz continuum maps, respectively [22]. The moment maps were created by the CASA task immoments.…”

ALMA Observations of the Archetypal “Hot Core” That Is Not: Orion-KL

“…A discussion on the nature of the strong sources in the field, Orion Source I and BN at submillimeter wavelengths is outside of the scope of the paper, but we refer to the readers to the papers of Beuther et al (2006); Hirota et al (2015Hirota et al ( , 2016; Plambeck & Wright (2016), where a complete discussion is made using ALMA and SMA data.…”

A Face-on Accretion System in High-mass Star Formation: Possible Dusty Infall Streams within 100 AU

“…Almost all of the known circumstellar systems in High-Mass star-formation are in a nearly edgeon orientation (e.g., Patel et al 2005;Torrelles et al 2007;Matthews et al 2010;Carrasco-González et al 2012;Sánchez-Monge et al 2013;Beltrán et al 2014;Cesaroni et al 2014;Hirota et al 2016Hirota et al , 2017Plambeck & Wright 2016). This bias is simply due to their easy identification even with limited angular resolution, based on the velocity gradient of rotating disks and/or envelopes.…”

“…Such a structure suggests a hierarchical fragmentation and accretion process around a High-Mass young stellar object (HMYSO). The innermost compact disks (< 100 au) were resolved in some very high-resolution observations (e.g., Kraus et al 2010;Hirota et al 2014Hirota et al , 2016Hirota et al , 2017Plambeck & Wright 2016).…”