Spatially Resolving Substructures Within the Massive Envelope Around an Intermediate-Mass Protostar: MMS 6/Omc-3

Abstract

With the Submillimeter Array, the brightest (sub)millimeter continuum source in the Orion Molecular Cloud-2/3 region, MMS 6, has been observed in the 850 μm continuum emission with approximately 10 times better angular resolution than previous studies (≈0. 3, ≈120 AU at Orion). The deconvolved size, the mass, and the column density of MMS 6-main are estimated to be 0. 32 × 0. 29 (132 AU × 120 AU), 0.29 M , and 2.1 × 10 25 cm −2 , respectively. The estimated extremely high mean number density, 1.5 × 10 10 cm −3 , suggests that MMS 6-main is likely optically thick at 850 μm. We compare our observational data with three theoretical core models: prestellar core, protostellar core + disk-like structure, and first adiabatic core. These comparisons clearly show that the observational data cannot be modeled as a simple prestellar core with a gas temperature of 20 K. A self-luminous source is necessary to explain the observed flux density in the (sub)millimeter wavelengths. Our recent detection of a very compact and energetic outflow in the CO (3-2) and HCN (4-3) lines supports the presence of a protostar. We suggest that MMS 6 is one of the first cases of an intermediate-mass protostellar core at an extremely young stage. In addition to the MMS 6-main peak, we have also spatially resolved a number of spiky structures and sub-clumps, distributed over the central 1000 AU. The masses of these sub-clumps are estimated to be 0.066-0.073 M , which are on the order of brown dwarf masses. Higher angular resolution and higher sensitivity observations with ALMA and EVLA will reveal the origin and nature of these structures such as whether they are originated from fragmentations, spiral arms, or inhomogeneity within the disk-like structures/envelope.

Accretion disks in luminous young stellar objects

“…For disk studies, the IM stars offer observational advantages as the stars are bright and relatively close-by rendering the disks bright at most wavelengths while subtending a large solid-angle on the sky. Importantly and similar to what has been demonstrated for the solar-type stars, the existence of circumstellar disks in the embedded protostellar phase has been established unambiguously by observations (Zapata et al, 2007;Sánchez-Monge et al, 2010;van Kempen et al, 2012;Takahashi et al, 2012). The properties of these IM star disks are similar to those of their lower-mass counterparts (Beltrán, 2015).…”

Characterizing the Youngest Herschel-Detected Protostars. Ii. Molecular Outflows From the Millimeter and the Far-Infrared*

“…The absence of detected outflow activity in CO (J = 1 → 0) toward the four sources mentioned above cannot be construed as evidence of outflow absence because of our finite resolution and sensitivity. For example, the outflow toward OMC MMS6N (also known as HOPS 87) was only detected when it was observed at the highest resolutions with the SMA (Takahashi et al 2012), due to its very small spatial extent. Thus, the non-detected outflows could be very compact and in the process of breaking out from the envelopes, necessitating higher resolution data.…”

The First Two Thousand Years of Star Formation

“…It is very difficult to observe the protostellar system at a very early stage, because the time spent in it is only a small fraction of the total lifetime. Only a few protostars that have age t ∼ < 100 − 1000 yr are confirmed (e.g., Takahashi & Ho 2012;Takahashi et al 2012), in which the protostellar age (or time scale) was estimated from the protostellar outflow (the outflow length is divided by the outflow speed). On the other hand, it is difficult for a simulation to proceed beyond 1-10 yr after protostar formation (while resolving the protostar) due to the time step limitations.…”