Proper Motions of the Radio Source Orion MR, Formerly Known as Orion n, and New Sources with Large Proper Motions in Orion BN/KL

Abstract

The infrared source known as Orion n was detected in 1980 with observations made with the 3.8-m United Kingdom Infrared Telescope. About two decades later, sensitive observations made with the Very Large Array revealed the presence of a mJy double radio source apparently coincident in position with the infrared source n. The radio source was assumed to be the counterpart of the infrared source. However, over the years it has been concluded that the radio source shows large proper motions to the south while the infrared source n is stationary. Here we reanalyze the proper motions of the radio source adding both older and newer VLA observations than previously used. We confirm the proper motions of the radio source that at present no longer coincides positionally with the infrared source. The solution to this problem is, most probably, that the infrared source n and the radio source are not the same object: the infrared source is a stationary object in the region while the radio counterpart is moving as a result of the explosion that took place in this region some 500 years ago and that expelled large amounts of molecular gas as well as several compact sources. Considering the paper where it was first reported, we refer to this double radio source as Orion MR.In addition, we use these new observations to fully confirm the large proper motions of the sources IRc23 and Zapata 11. Together with sources BN, I, Orion MR, and x, there are at least six compact sources that recede from a point in common in Orion BN/KL. However, IRc23 is peculiar in that its ejection age appears to be only ∼300 years. The relatively large number of sources rules out as a possible mechanism the classic three-body scenario since then only two escaping bodies are expected: a tight binary plus the third star involved in the encounter.

From downtown to the outskirts: a radio survey of the Orion Nebula Cluster

“…The absolute PM of these sources are listed in Table 4 also indicating their equivalent transverse velocities for an adopted distance of 400 pc. The source SW1 (Zapata 11;Zapata et al 2004) was originally reported by Menten & Reid (1995) and its PM have been well constrained on longer timescales using up to 9 VLA epochs ranging from 1985 to 2018 (Dzib et al 2017;Rodríguez et al 2020) reporting PM consistent with our measurements. Additionally, Forbrich et al (2016) reported spectral index measurement for this source with negative value of −0.3±0.09 suggesting nonthermal emission, which has been actually found for YSO jets (see Section 6 in Anglada et al 2018 and reference therein).…”

“…Stars with velocities >10 km s −1 are considered peculiar sources and above 30 km s −1 are already in the runaway regime (Farias et al 2020;Schoettler et al 2020). Stellar proper motions in the ONC are typically 𝜇 𝑡𝑜𝑡 2 mas yr −1 (4 km s −1 ) (Dzib et al 2017;Kim et al 2019) and only a handful number of sources have fast proper motions with 𝜇 𝑡𝑜𝑡 30 mas yr −1 (60 km s −1 ) (Gómez et al 2005(Gómez et al , 2008Rodríguez et al 2020) most of them associated to the ejected stars in the BN/KL region (which will be discussed later in this section).…”

“…1) and astrometric capabilites have been used to constrain the kinematics of the ONC (Gómez et al 2005;Kounkel et al 2014;Dzib et al 2017). The main focus has been on the improvement of proper motion (PM) estimates of the main stellar radio sources in the Orion Becklin-Neugebauer/Kleinmann-Low region (BN/KL) in the inner ONC (Becklin & Neugebauer 1967;Kleinmann & Low 1967;Gómez et al 2008;Zapata et al 2009;Rodríguez et al 2017Rodríguez et al , 2020. The PM of these stars supports the scenario where a multiple stellar system experienced a close dynamical interaction resulting in two massive stars (BN source and source I) and at least one lowmass star being ejected at a few tens of km s −1 triggering a powerful outflow emerging from the OMC1 cloud core prominently seen at near-infrared wavelengths (Bally et al 2015).…”

Evidence for dense gas heated by the explosion in Orion KL

“…This differs from the NIR H 2 emission, part of which is absorbed by massive dust emission associated with the KL nebula (Johnstone & Bally 1999). The CO filaments and H 2 fingers can be traced back to a common origin (Zapata et al 2009;Bally et al 2011Bally et al , 2015Bally et al , 2017) that is consistent with the position to which the proper motions of various radio and NIR emitting young stellar projects can be traced back in space and time (Rodríguez et al 2005;Gómez et al 2005Gómez et al , 2008Luhman et al 2017;Rodríguez et al 2017;Bally et al 2020;Rodríguez et al 2020). Based on their Very Large Array (VLA) proper motion determinations, Rodríguez et al (2017) determine the year 1445 ± 6 as the time when the most prominent radio sources, Source I (in the following Src I) and the Becklin-Neugebauser object (BN), were closest together.…”

“…These findings constitute persuasive evidence the explosion resulted from the merger of young stellar objects, at least one of them massive (Src I), a scenario first discussed by Bally & Zinnecker (2005) in which the 10 48 -10 49 ergs injected into the region represent binding energy released by the orbital decay of components of a multiple system. More detailed observations suggest a more complex picture, a.o., suggesting ejections of sources at later times (Rodríguez et al 2020).…”