Nobeyama 45 m mapping observations toward Orion A. III. Multi-line observations toward an outflow-shocked region, Orion Molecular Cloud 2 FIR 4

Abstract

We present the results of mapping observations toward an outflow-shocked region, OMC-2 FIR 4 using the Nobeyama 45-m telescope. We observed the area in 13We detected a dense molecular clump that contains FIR 4/5. We also detected in 13 CO blueshifted and redshifted components driven presumably by protostellar outflows in this region. The axes of the FIR 3 and VLA 13 outflows, projected on the plane of the sky, appear to point toward the FIR 4 clump, suggesting that the clump may be compressed by protostellar outflows from Class I sources, FIR 3 and VLA 13. Applying the hyperfine fit of N 2 H + lines, we estimated the excitation temperature to be ∼ 20 K. The high excitation temperature is consistent with the fact that the clump contains protostars. The CCS emission was detected in this region for the first time. Its abundance is estimated to be a few ×10 −12 , indicating that the region is chemically evolved at ∼ 10 5 years, which is comparable to the typical lifetime of the Class I protostars. This timescale is consistent with the scenario that star formation in FIR 4 is triggered by dynamical compression of the protostellar outflows. The [HNC]/[HCN] ratio is evaluated to be ∼ 0.5 in the dense clump and the outflow lobes, whereas it is somewhat larger in the envelope of the dense clump. The small [HNC]/[HCN] ratio indicates that the HNC formation was prevented due to high temperatures. Such high temperatures seem to be consistent with the scenario that either protostellar radiation or outflow compression, or both, affected the thermal properties of this region.

Isotopic fractionation study towards massive star-forming regions across the Galaxy

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“…requires from the environment 1.01 eV to be spontaneous. Then, since 1 eV corresponds to 11.6×10 4 K, at the typical temperature of the ISM (10-100 K) this reaction is not spontaneous.…”

“…1.1), characterised by higher accretion rates and non-spherical geometry. However, this scenario presents some problems as the theory assumes the existence of turbulent massive cores 4 that have prevented fragmentation during their formation. Radiative feedback from the star or magnetic fields are thought to inhibit fragmentation (e.g.…”

“…The dashed blue curves represents the probability of a close encounter with a distance less than 400 au (to produce Sedna), but no encounters at a distance < 225 au in order to preserve the planetary orbits. The dotted orange curve is the probability to have an external FUV with G0 ≤10 4 . Finally, the red solid line is the joint probability distribution with <N > = 4300±2800.…”

“…For a high-mass star the tKH ∼10 4 yr is shorter than the tacc ∼10 5 yr. when the star arrives on the ZAMS, and the hydrogen starts to burn, the accretion from the surrounding gas continues. Then, a necessary condition to form a massive star (with mass M * ), is that the acceleration of a unit mass, dm, at a radius r, due to gravity, GM * r 2 must exceed the outward-directed radiative acceleration of the accreting gas, κL 4πr 2 c .…”